Fredrik Andreasson, Arne Hegemann, Andreas Nord, and Jan-Ake Nilsson

The capacity to get rid of excess heat produced during hard work is a possible constraint on parental effort during reproduction [heat dissipation limit (HDL) theory]. We released hard-working blue tits (Cyanistes caeruleus) from this constraint by experimentally removing ventral plumage. We then assessed whether this changed their reproductive effort (feeding rate and nestling size) and levels of self-maintenance (change in body mass and innate immune function). Feather-clipped females reduced the number of feeding visits and increased levels of constitutive innate immunity compared with unclipped females but did not fledge smaller nestlings. Thus, they increased self-maintenance without compromising current reproductive output. In contrast, feather clipping did not affect the number of feeding visits or innate immune function in males, despite increased heat loss rate. Our results show that analyses of physiological parameters, such as constitutive innate immune function, can be important when trying to understand sources of variation in investment in self-maintenance versus reproductive effort and that risk of overheating can influence innate immune function during reproduction.

Andreas Nord, Arne Hegemann, and Lars P. Folkow

Animals in seasonal environments must prudently manage energy expenditure to survive the winter. This may be achieved through reductions in the allocation of energy for various purposes (e.g. thermoregulation, locomotion, etc.). We studied whether such trade-offs also include suppression of the innate immune response, by subjecting captive male Svalbard ptarmigan (Lagopus muta hyperborea) to bacterial lipopolysaccharide (LPS) during exposure to either mild temperature (0°C) or cold snaps (acute exposure to –20°C), in constant winter darkness when birds were in energy-conserving mode, and in constant daylight in spring. The innate immune response was mostly unaffected by temperature. However, energy expenditure was below baseline when birds were immune challenged in winter, but significantly above baseline in spring. This suggests that the energetic component of the innate immune response was reduced in winter, possibly contributing to energy conservation. Immunological parameters decreased (agglutination, lysis, bacteriostatic capacity) or did not change (haptoglobin/PIT54) after the challenge, and behavioural modifications (anorexia, mass loss) were lengthy (9 days). While we did not study the mechanisms explaining these weak, or slow, responses, it is tempting to speculate they may reflect the consequences of having evolved in an environment where pathogen transmission rate is presumably low for most of the year. This is an important consideration if climate change and increased exploitation of the Arctic would alter pathogen communities at a pace outwith counter-adaption in wildlife.

Ana Gabriela Jimenez, Emily Cornelius Ruhs, Kailey J. Tobin, Katie N. Anderson, Audrey Le Pogam, Lyette Regimbald, and Francois Vezina

Seasonal changes in maximal thermogenic capacity (M_sum) in wild black-capped chickadees suggests that adjustments in metabolic performance are slow and begin to take place before winter peaks. However, when mean minimal ambient temperature (T_a) reaches –10°C, the chickadee phenotype appears to provide enough spare capacity to endure days with colder T_a, down to –20°C or below. This suggests that birds could also maintain a higher antioxidant capacity as part of their cold-acclimated phenotype to deal with sudden decreases in temperature. Here, we tested how environmental mismatch affected oxidative stress by comparing cold-acclimated (–5°C) and transition (20°C) phenotypes in chickadees exposed to an acute 15°C drop in temperature with that of control individuals. We measured superoxide dismutase, catalase and glutathione peroxidase activities, as well as lipid peroxidation damage and antioxidant scavenging capacity in pectoralis muscle, brain, intestine and liver. We generally found differences between seasonal phenotypes and across tissues, but no differences with respect to an acute cold drop treatment. Our data suggest oxidative stress is closely matched to whole-animal physiology in cold-acclimated birds compared with transition birds, implying that changes to the oxidative stress system happen slowly.

Erin Gorrell, Ashley Shemery, Jesse Kowalski, Miranda Bodziony, Nhlalala Mavundza, Amber R. Titus, Mark Yoder, Sarah Mull, Lydia A. Heemstra, Jacob G. Wagner, Megan Gibson, Olivia Carey, Diamond Daniel, Nicholas Harvey, Meredith Zendlo, Megan Rich, Scott Everett, Chaitanya K. Gavini, Tariq I. Almundarij, Diane Lorton, and Colleen M. Novak

Non-shivering thermogenesis can promote negative energy balance and weight loss. In this study, we identified a contextual stimulus that induces rapid and robust thermogenesis in skeletal muscle. Rats exposed to the odor of a natural predator (ferret) showed elevated skeletal muscle temperatures detectable as quickly as 2 min after exposure, reaching maximum thermogenesis of >1.5°C at 10–15 min. Mice exhibited a similar thermogenic response to the same odor. Ferret odor induced a significantly larger and qualitatively different response from that of novel or aversive odors, fox odor or moderate restraint stress. Exposure to predator odor increased energy expenditure, and both the thermogenic and energetic effects persisted when physical activity levels were controlled. Predator odor-induced muscle thermogenesis is subject to associative learning as exposure to a conditioned stimulus provoked a rise in muscle temperature in the absence of the odor. The ability of predator odor to induce thermogenesis is predominantly controlled by sympathetic nervous system activation of β-adrenergic receptors, as unilateral sympathetic lumbar denervation and a peripherally acting β-adrenergic antagonist significantly inhibited predator odor-induced muscle thermogenesis. The potential survival value of predator odor-induced changes in muscle physiology is reflected in an enhanced resistance to running fatigue. Lastly, predator odor-induced muscle thermogenesis imparts a meaningful impact on energy expenditure as daily predator odor exposure significantly enhanced weight loss with mild calorie restriction. This evidence signifies contextually provoked, centrally mediated muscle thermogenesis that meaningfully impacts energy balance.

Peter J. Edmunds and Scott C. Burgess

Experiments with coral fragments (i.e. nubbins) have shown that net calcification is depressed by elevated P_CO2. Evaluating the implications of this finding requires scaling of results from nubbins to colonies, yet the experiments to codify this process have not been carried out. Building from our previous research demonstrating that net calcification of Pocillopora verrucosa (2–13 cm diameter) was unaffected by P_CO2 (400 and 1000 µatm) and temperature (26.5 and 29.7°C), we sought generality to this outcome by testing how colony size modulates P_CO2 and temperature sensitivity in a branching acroporid. Together, these taxa represent two of the dominant lineages of branching corals on Indo-Pacific coral reefs. Two trials conducted over 2 years tested the hypothesis that the seasonal range in seawater temperature (26.5 and 29.2°C) and a future P_CO2 (1062 µatm versus an ambient level of 461 µatm) affect net calcification of an ecologically relevant size range (5–20 cm diameter) of colonies of Acropora hyacinthus. As for P. verrucosa, the effects of temperature and P_CO2 on net calcification (mg day^–1) of A. verrucosa were not statistically detectable. These results support the generality of a null outcome on net calcification of exposing intact colonies of branching corals to environmental conditions contrasting seasonal variation in temperature and predicted future variation in P_CO2. While there is a need to expand beyond an experimental culture relying on coral nubbins as tractable replicates, rigorously responding to this need poses substantial ethical and logistical challenges.

Surendra Singh Patel, Sanyami Zunjarrao, and Beena Pillai

Eisenia fetida, the common vermicomposting earthworm, shows robust regeneration of posterior segments removed by amputation. During the period of regeneration, the newly formed tissue initially contains only undifferentiated cells but subsequently differentiates into a variety of cell types including muscle, nerve and vasculature. Transcriptomics analysis, reported previously, provided a number of candidate non-coding RNAs that were induced during regeneration. We found that one such long non-coding RNA (lncRNA) is expressed in the skin, only at the base of newly formed chaetae. The spatial organization and precise arrangement of the regenerating chaetae and the cells expressing the lncRNA on the ventral side clearly support a model wherein the regenerating tissue contains a zone of growth and cell division at the tip and a zone of differentiation at the site of amputation. The temporal expression pattern of the lncRNA, named Neev, closely resembled the pattern of chitin synthase genes, implicated in chaetae formation. We found that the lncRNA has 49 sites for binding a set of four microRNAs (miRNAs) while the chitin synthase 8 mRNA has 478 sites. The over-representation of shared miRNA sites suggests that lncRNA Neev may act as a miRNA sponge to transiently de-repress chitin synthase 8 during formation of new chaetae in the regenerating segments of Eisenia fetida.

Fredrik Christiansen, Kate R. Sprogis, Jasmin Gross, Juliana Castrillon, Hunter A. Warick, Eva Leunissen, and Susan Bengtson Nash

An animal's body condition provides valuable information for ecophysiological studies, and is an important measure of fitness in population monitoring and conservation. While both the external body shape of an animal and its internal tissues (i.e. fat content) can be used as a measure of body condition, the relationship between the two is not always linear. We compared the morphological body condition (external metric obtained through aerial photogrammetry) of migrating humpback whales (Megaptera novaeangliae) with their outer blubber lipid concentration (internal metric obtained through blubber biopsy sampling) off the coast of south-west Australia early and late in the breeding season (spanning ~4.5 months). The external body condition index of juvenile and adult humpback whales decreased by 26.9 (from 18.8% to –8.1%) and 12.0 percentage points (from 8.6% to –3.4%), respectively, between the early and late phase. In contrast, we found no intra-seasonal change in blubber lipid concentration, and no difference between reproductive classes (juveniles, adults and lactating females); however, the small sample size prevented us from effectively testing these effects. Importantly, however, in the 33 animals for which paired metrics were obtained, we found no correlation between the morphometric body condition index and the blubber lipid concentration of individual whales. The lack of a linear relationship suggests that changes in outer blubber lipid concentration do not reflect external changes in body shape, thus limiting the utility of outer blubber lipid reserves for individual body condition evaluation. The wider spectrum of change in body morphometry captured with aerial photogrammetry supports the use of body morphometry as a reliable and well-tested method.

Ayelen M. Blanco, Juan I. Bertucci, Jose L. Soengas, and Suraj Unniappan

This research assessed the direct effects of insulin on nutrient-sensing mechanisms in the brain of rainbow trout (Oncorhynchus mykiss) using an in vitro approach. Cultured hypothalamus and hindbrain were exposed to 1 µmol l^–1 insulin for 3 h, and signals involved in appetite regulation and nutrient-sensing mechanisms were measured. Additionally, the involvement of the phosphatidylinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway in the actions of insulin was studied by using the inhibitor wortmannin. Treatment with insulin alone did not elicit many changes in the appetite regulators and nutrient-sensing-related genes and enzymes tested in the hypothalamus and hindbrain. However, we found that, when insulin and nutrients were added together, insulin reversed most of the effects exerted by nutrients alone, suggesting that insulin changes responsiveness to nutrients at the central level. Effects reversed by insulin included expression levels of genes related to the sensing of both glucose (slc2a2, slc5a1, gck, pck1, pklr, g6pcb, gys1, tas1r3 and nr1h3 in the hindbrain, and slc2a2, pklr and pck1 in the hypothalamus) and fatty acid (cd36 in the hindbrain, and cd36 and acly in the hypothalamus). Nutrient-induced changes in the activity of Acly and Cpt-1 in the hindbrain and of Pepck, Acly, Fas and Hoad in the hypothalamus were also reversed by insulin. Most of the insulin effects disappeared in the presence of wortmannin, suggesting the PI3K/Akt pathway is a mediator of the effects of insulin reported here. This study adds new information to our knowledge of the mechanisms regulating nutrient sensing in fish.

Yves Bötsch, Zulima Tablado, Bettina Almasi, and Lukas Jenni

Outdoor recreational activities are booming and most animals perceive humans as predators, which triggers behavioural and/or physiological reactions [e.g. heart rate increase, activation of the hypothalamic–pituitary–adrenal (HPA) axis]. Physiological stress reactions have been shown to affect the immune system of an animal and therefore may also affect the amount of maternal antibodies a female transmits to her offspring. A few studies have revealed that the presence of predators affects the amount of maternal antibodies deposited into eggs of birds. In this study, using Eurasian blue and great tit offspring (Cyanistes caeruleus and Parus major) as model species, we experimentally tested whether human recreation induces changes in the amount of circulating antibodies in young nestlings and whether this effect is modulated by habitat and competition. Moreover, we investigated whether these variations in antibody titre in turn have an impact on hatching success and offspring growth. Nestlings of great tit females that had been disturbed by experimental human recreation during egg laying had lower antibody titres compared with control nestlings. Antibody titre of nestling blue tits showed a negative correlation with the presence of great tits, rather than with human disturbance. The hatching success was positively correlated with the average amount of antibodies in great tit nestlings, independent of the treatment. Antibody titre in the first days of life in both species was positively correlated with body mass, but this relationship disappeared at fledging and was independent of treatment. We suggest that human recreation may have caused a stress-driven activation of the HPA axis in breeding females, chronically increasing their circulating corticosterone, which is known to have an immunosuppressive function. Either, lower amounts of antibodies are transmitted to nestlings or impaired transfer mechanisms lead to lower amounts of immunoglobulins in the eggs. Human disturbance could, therefore, have negative effects on nestling survival at early life-stages, when nestlings are heavily reliant on maternal antibodies, and in turn lead to lower breeding success and parental fitness. This is a so far overlooked effect of disturbance on early life in birds.

Daniel P. Small, Piero Calosi, Samuel P. S. Rastrick, Lucy M. Turner, Stephen Widdicombe, and John I. Spicer

Regulation of extracellular acid–base balance, while maintaining energy metabolism, is recognised as an important aspect when defining an organism's sensitivity to environmental changes. This study investigated the haemolymph buffering capacity and energy metabolism (oxygen consumption, haemolymph [l-lactate] and [protein]) in early benthic juveniles (carapace length <40 mm) of the European lobster, Homarus gammarus, exposed to elevated temperature and P_CO2. At 13°C, H. gammarus juveniles were able to fully compensate for acid–base disturbances caused by the exposure to elevated seawater P_CO2 at levels associated with ocean acidification and carbon dioxide capture and storage (CCS) leakage scenarios, via haemolymph [HCO₃^–] regulation. However, metabolic rate remained constant and food consumption decreased under elevated P_CO2, indicating reduced energy availability. Juveniles at 17°C showed no ability to actively compensate haemolymph pH, resulting in decreased haemolymph pH particularly under CCS conditions. Early benthic juvenile lobsters at 17°C were not able to increase energy intake to offset increased energy demand and therefore appear to be unable to respond to acid–base disturbances due to increased P_CO2 at elevated temperature. Analysis of haemolymph metabolites suggests that, even under control conditions, juveniles were energetically limited. They exhibited high haemolymph [l-lactate], indicating recourse to anaerobic metabolism. Low haemolymph [protein] was linked to minimal non-bicarbonate buffering and reduced oxygen transport capacity. We discuss these results in the context of potential impacts of ongoing ocean change and CCS leakage scenarios on the development of juvenile H. gammarus and future lobster populations and stocks.

Zhi-Jun Zhao, Davina Derous, Abby Gerrard, Jing Wen, Xue Liu, Song Tan, Catherine Hambly, and John R. Speakman

Lactating mice increase food intake 4- to 5-fold, reaching an asymptote in late lactation. A key question is whether this asymptote reflects a physiological constraint, or a maternal investment strategy (a ‘restraint’). We exposed lactating mice to periods of food restriction, hypothesizing that if the limit reflected restraint, they would compensate by breaching the asymptote when refeeding. In contrast, if it was a constraint, they would by definition be unable to increase their intake on refeeding days. Using isotope methods, we found that during food restriction, the females shut down milk production, impacting offspring growth. During refeeding, food intake and milk production rose again, but not significantly above unrestricted controls. These data provide strong evidence that asymptotic intake in lactation reflects a physiological/physical constraint, rather than restraint. Because hypothalamic neuropeptide Y (Npy) was upregulated under both states of restriction, this suggests the constraint is not imposed by limits in the capacity to upregulate hunger signalling (the saturated neural capacity hypothesis). Understanding the genetic basis of the constraint will be a key future goal and will provide us additional information on the nature of the constraining factors on reproductive output, and their potential links to life history strategies.

Karen L. Carleton, Daniel Escobar-Camacho, Sara M. Stieb, Fabio Cortesi, and N. Justin Marshall

Among vertebrates, teleost eye diversity exceeds that found in all other groups. Their spectral sensitivities range from ultraviolet to red, and the number of visual pigments varies from 1 to over 40. This variation is correlated with the different ecologies and life histories of fish species, including their variable aquatic habitats: murky lakes, clear oceans, deep seas and turbulent rivers. These ecotopes often change with the season, but fish may also migrate between ecotopes diurnally, seasonally or ontogenetically. To survive in these variable light habitats, fish visual systems have evolved a suite of mechanisms that modulate spectral sensitivities on a range of timescales. These mechanisms include: (1) optical media that filter light, (2) variations in photoreceptor type and size to vary absorbance and sensitivity, and (3) changes in photoreceptor visual pigments to optimize peak sensitivity. The visual pigment changes can result from changes in chromophore or changes to the opsin. Opsin variation results from changes in opsin sequence, opsin expression or co-expression, and opsin gene duplications and losses. Here, we review visual diversity in a number of teleost groups where the structural and molecular mechanisms underlying their spectral sensitivities have been relatively well determined. Although we document considerable variability, this alone does not imply functional difference per se. We therefore highlight the need for more studies that examine species with known sensitivity differences, emphasizing behavioral experiments to test whether such differences actually matter in the execution of visual tasks that are relevant to the fish.

Samantha M. Logan, Kama E. Szereszewski, Nigel C. Bennett, Daniel W. Hart, Barry van Jaarsveld, Matthew E. Pamenter, and Kenneth B. Storey

Mole-rats are champions of self-preservation, with increased longevity compared to other rodents their size, strong antioxidant capabilities, and specialized defenses against endogenous oxidative stress. However, how the brains of these subterranean mammals handle acute in vivo hypoxia is poorly understood. This study is the first to examine the molecular response to low oxygen in six different species of hypoxia-tolerant mole-rats from sub-Saharan Africa. Protein carbonylation, a known marker of DNA damage (hydroxy-2’-deoxyguanosine), and antioxidant capacity did not change following hypoxia but HIF-1 protein levels increased significantly in the brains of two species. Nearly 30 miRNAs known to play roles in hypoxia-tolerance were differentially regulated in a species-specific manner. The miRNAs exhibiting the strongest response to low oxygen stress inhibit apoptosis and regulate neuroinflammation, likely providing neuroprotection. A principal component analysis using a subset of the molecular targets assessed herein revealed differences between control and hypoxic groups for two solitary species (Georychus capensis and Bathyergus suillus), which are ecologically adapted to a normoxic environment, suggesting a heightened sensitivity to hypoxia relative to species that may experience hypoxia more regularly in nature. By contrast, all molecular data were included in the PCA to detect a difference between control and hypoxic populations of eusocial Heterocephalus glaber, indicating they may require many lower-fold changes in signaling pathways to adapt to low oxygen settings. Finally, none of the Cryptomys hottentotus subspecies showed a statistical difference between control and hypoxic groups, presumably due to hypoxia-tolerance derived from environmental pressures associated with a subterranean and social lifestyle.

Juha Nuutila, Anna E. Honkanen, Kyösti Heimonen, and Matti Weckström

Using tethered American cockroaches walking on a trackball in a spherical virtual reality environment, we tested optomotor responses to horizontally moving black-and-white gratings of different vertical extent under six different light intensities. We found that shortening the vertical extent of the wide-field stimulus grating within a light level weakened response strength, reduced average velocity, and decreased angular walking distance. Optomotor responses with the vertically shortened stimuli persisted down to light intensity levels of 0.05 lx. Response latency seems to be independent of both the height of the stimulus and light intensity. The optomotor response started saturating at the light intensity of 5 lx, where the shortest behaviourally significant stimulus was 1°. This indicates that the number of vertical ommatidial rows needed to elicit an optomotor response at 5 lx and above is in the single digits, maybe even just one. Our behavioural results encourage further inquiry into the interplay of light intensity and stimulus size in insect dim-light vision.

Krishnamoorthy Krishnan, Asif Shahriar Nafi, Roi Gurka, and Roi Holzman

Fish larvae are the smallest self-sustaining vertebrates. As such, they face multiple challenges that stem from their minute size, and from the hydrodynamic regime in which they dwell. This regime, of intermediate Reynolds numbers, was shown to affect the swimming of larval fish and impede their ability to capture prey. Prey capture is impeded because smaller larvae produce weaker suction flows, exerting weaker forces on the prey. Previous observations on feeding larvae also showed prey exiting the mouth after initially entering it (hereafter "in-and-out"), although the mechanism causing such failures had been unclear. In this study, we used numerical simulations to investigate the hydrodynamic mechanisms responsible for the failure to feed caused by this in-and-out prey movement. Detailed kinematics of the expanding mouth during prey capture by larval Sparus aurata were used to parameterize age-specific numerical models of the flows inside the mouth. These models revealed that for small larvae which expand their mouth slowly, fluid entering the mouth cavity is expelled through the mouth before it is closed, resulting in flow reversal at the orifice. This relative efflux of water through the mouth was >8% of the influx through the mouth for younger ages. However similar effluxes were found when we simulated slow strikes by larger fish. The simulations can explain the observations of larval fish failing to fish due to the in-and-out movement of the prey. These results further highlight the importance of transporting the prey from the gape deeper into the mouth cavity in determining suction-feeding success.

Rohini Singh and Timothy A. Linksvayer

Wolbachia is a widespread group of maternally-transmitted endosymbiotic bacteria that often manipulates the reproductive strategy and life history of its hosts to favor its own transmission. Wolbachia mediated phenotypic effects are well characterized in solitary hosts, but effects in social hosts are unclear. The invasive pharaoh ant, Monomorium pharaonis, shows natural variation in Wolbachia infection between colonies and can be readily bred under laboratory conditions. We previously showed that Wolbachia-infected pharaoh ant colonies had more queen-biased sex ratios than uninfected colonies, which is expected to favor the spread of maternally-transmitted Wolbachia. Here, we further characterize the effects of Wolbachia on the short- and longer-term reproductive and life history traits of pharaoh ant colonies. First, we characterized the reproductive differences between naturally infected and uninfected colonies at three discrete time points and found that infected colonies had higher reproductive investment (i.e. infected colonies produced more new queens), particularly when existing colony queens were three months old. Next, we compared the long-term growth and reproduction dynamics of infected and uninfected colonies across their whole life cycle. Infected colonies had increased colony-level growth and early colony reproduction, resulting in a shorter colony life cycle, when compared to uninfected colonies.

Brian K. McNab and Kerry A. Weston

The thermal physiology of the endangered New Zealand rockwren (Xenicus gilviventris) is examined. It is a member of the Acanthisittidae, a family unique to New Zealand. This family, derived from Gondwana, is thought to be the sister taxon to all other passerines. Rockwrens permanently reside above the climatic timberline at altitudes from 1,000 to 2,900 meters in the mountains of South Island. They feed on invertebrates and in winter face ambient temperatures far below freezing and deep deposits of snow. Their body temperature and rate of metabolism are highly variable. Rockwrens regulate body temperature at ca. 36.4°C, which in one individual decreased to 33.1°C at an ambient temperature of 9.4°C. Its rate of metabolism decreased by 30%; body temperature spontaneously returned to 36°C. The rate of metabolism in a second individual twice decreased by 35%, nearly to the basal rate expected from mass without a decrease in body temperature. The New Zealand rockwren's food habits, entrance into torpor, and continuous residence in a thermally demanding environment suggest that it may hibernate. For that conclusion to be accepted, evidence of its use of torpor for extended periods is required. Those data are not presently available. Acanthisittids are distinguished from other passerines by the combination of their permanent temperate distribution, thermal flexibility, and a propensity to evolve a flightless condition. These characteristics may principally reflect their geographical isolation in a temperate environment isolated from Gondwana for 82 million years in the absence of mammalian predators.

Yi Huang, Jazmin Osorio Mendoza, Catherine Hambly, Baoguo Li, Zengguang Jin, Li Li, Moshen Madizi, Sumei Hu, and John R. Speakman

The heat dissipation limit theory predicts lactating female mice consuming diets with lower specific dynamic action (SDA) should have enhanced lactation performance. Dietary fat has lower SDA than other macronutrients. Here we tested the effects of graded dietary fat levels on lactating Swiss mice. We fed females five diets varying in fat content from 8.3 to 66.6%. Offspring of mothers fed diets of 41.7% fat and above were heavier and fatter at weaning compared to those of 8.3% and 25% fat diets. Mice on dietary fat contents of 41.7% and above had greater metabolizable energy intake at peak lactation (8.3%: 229.4±39.6, 25%: 278.8±25.8, 41.7%: 359.6±51.5, 58.3%: 353.7±43.6, 66.6%: 346±44.7 kJ day^–1), lower daily energy expenditure (8.3%: 128.5±16, 25%: 131.6±8.4, 41.7%: 124.4±10.8, 58.3%: 115.1±10.5, 66.6%: 111.2±11.5 kJ day^–1) and thus delivered more milk energy to their offspring (8.3%: 100.8±27.3, 25%: 147.2±25.1, 41.7%: 225.1±49.6, 58.3%: 238.6±40.1, 66.6%: 234.8±41.1 kJ day^–1). Milk fat content (%) was unrelated to dietary fat content, indicating females on higher fat diets (> 41.7%) produced more rather than richer milk. Mothers consuming diets with 41.7% fat or above enhanced their lactation performance compared to those on 25% or less, probably by diverting dietary fat directly into the milk, thereby avoiding the costs of lipogenesis. At dietary fat contents above 41.7% they were either unable to transfer more dietary fat to the milk, or they chose not to do so, potentially because of a lack of benefit to the offspring that were increasingly fatter as maternal dietary fat increased.

Lewis C. Naisbett-Jones, Nathan F. Putman, Michelle M. Scanlan, David L. G. Noakes, and Kenneth J. Lohmann

A variety of animals sense Earth's magnetic field and use it to guide movements over a wide range of spatial scales. Little is known, however, about the mechanisms that underlie magnetic field detection. Among teleost fish, growing evidence suggests that crystals of the mineral magnetite provide the physical basis of the magnetic sense. In this study, juvenile Chinook salmon (Oncorhynchus tshawytscha) were exposed to a brief but strong magnetic pulse capable of altering the magnetic dipole moment of biogenic magnetite. Orientation behaviour of pulsed fish and untreated control fish was then compared in a magnetic coil system under two conditions: (1) the local magnetic field; and (2) a magnetic field that exists near the southern boundary of the natural oceanic range of Chinook salmon. In the local field, no significant difference existed between the orientation of the control and pulsed groups. By contrast, orientation of the two groups was significantly different in the magnetic field from the distant site. These results demonstrate that a magnetic pulse can alter the magnetic orientation behaviour of a fish and are consistent with the hypothesis that salmon have magnetite-based magnetoreception.

Lakshman Abhilash, Arshad Kalliyil, and Vasu Sheeba

Even though the rhythm in adult emergence and rhythm in locomotor activity are two different rhythmic phenomena that occur at distinct life-stages of the fly life cycle, previous studies have hinted at similarities in certain aspects of the organisation of the circadian clock driving these two rhythms. For instance, the period gene plays an important regulatory role in both rhythms. In an earlier study, we have shown that selection on timing of adult emergence behaviour in populations of Drosophila melanogaster leads to the co-evolution of temperature sensitivity of circadian clocks driving eclosion. In this study, we were interested in asking if temperature sensitivity of the locomotor activity rhythm has evolved in our populations with divergent timing of adult emergence rhythm, with the goal of understanding the extent of similarity (or lack of it) in circadian organisation between the two rhythms. We found that in response to simulated jetlag with temperature cycles, late chronotypes (populations selected for predominant emergence during dusk) indeed re-entrain faster than early chronotypes (populations selected for predominant emergence during dawn) to 6-h phase-delays, thereby indicating enhanced sensitivity of the activity/rest clock to temperature cues in these stocks (entrainment is the synchronisation of internal rhythms to cyclic environmental time-cues). Additionally, we found that late chronotypes show higher plasticity of phases across regimes, day-to-day stability in phases and amplitude of entrainment, all indicative of enhanced temperature sensitive activity/rest rhythms. Our results highlight remarkably similar organisation principles between emergence and activity/rest rhythms.

Daniel J. Tobiansky, Meredith C. Miles, Franz Goller, and Matthew J. Fuxjager

Performance trade-offs can dramatically alter an organism's evolutionary trajectory by making certain phenotypic outcomes unattainable. Understanding how these trade-offs arise from an animal's design is therefore an important goal of biology. To explore this topic, we study how androgenic hormones, which regulate skeletal muscle function, influence performance trade-offs relevant to different components of complex reproductive behaviour. We conduct this work in golden-collared manakins (Manacus vitellinus), a Neotropical bird in which males court females by rapidly snapping their wings together above their back. Androgens help mediate the snap displays by radically increasing the twitch speed of a dorsal wing muscle [scapulohumeralis caudalis (SH)], which actuates the bird's wing-snap. Through hormone manipulations and in situ muscle recordings, we test how these positive effects on SH speed influence trade-offs with endurance. Indeed, this trait impacts the display by shaping signal length. We find that androgen-dependent increases in SH speed incur a cost to endurance, particularly when this muscle performs at its functional limits. Moreover, when behavioural data are overlaid on our muscle recordings, displaying animals appear to balance display speed with fatigue-induced muscle fusion (physiological tetanus) to generate the fastest possible signal while maintaining an appropriate signal duration. Our results point to androgenic hormone action as a functional trigger of trade-offs in sexual performance—they enhance one element of a courtship display, but in doing so, impede another.

S. Ghods, S. Waddell, E. Weller, C. Renteria, H.-Y. Jiang, J. M. Janak, S. S. Mao, T. J. Linley, and D. Arola

Fish scales serve as a dermal armor that provides protection from physical injury. Due to a number of outstanding properties, fish scales are inspiring new concepts for layered engineered materials and next-generation flexible armors. While past efforts have primarily focused on the structure and mechanical behavior of ontogenetic scales, the structure-property relationships of regenerated scales have received limited attention. In the present study, common carp (Cyprinus carpio) acquired from the wild were held live in an aquatic laboratory at 10° and 20°C. Ontogenetic scales were extracted from the fish for analysis, as well as regenerated scales after approximately 1 year of development and growth. Their microstructure was characterized using microscopy and Raman spectroscopy, and the mechanical properties were evaluated in uniaxial tension to failure under hydrated conditions. The strength, strain to fracture and toughness of the regenerated scales were significantly lower than those of ontogenetic scales from the same fish, regardless of the water temperature. Scales that regenerated at 20°C exhibited significantly higher strength, strain to fracture and toughness than those regenerated at 10°C. The regenerated scales exhibited a highly mineralized outer layer, but no distinct limiting layer or external elasmodine; they also possessed a significantly lower number of plies in the basal layer than in the ontogenetic scales. The results suggest that a mineralized layer develops preferentially during scale regeneration with the topology needed for protection, prior to the development of other qualities.

Simon Tapper, Joseph J. Nocera, and Gary Burness

Climatic warming is predicted to increase the frequency of extreme weather events, which may reduce an individual's capacity for sustained activity due to thermal limits. We tested whether the risk of overheating may limit parental provisioning of an aerial insectivorous bird in population decline. For many seasonally breeding birds, parents are thought to operate close to an energetic ceiling during the 2-3 week chick-rearing period. The factors determining the ceiling remain unknown, although it may be set by an individual's capacity to dissipate body heat (the heat dissipation limitation hypothesis). Over two breeding seasons we experimentally trimmed the ventral feathers of female tree swallows (Tachycineta bicolor, Vieillot, 1808) to provide a thermal window. We then monitored maternal and paternal provisioning rates, nestling growth rates, and fledging success. We found the effect of our experimental treatment was context-dependent. Females with an enhanced capacity to dissipate heat fed their nestlings at higher rates than controls when conditions were hot, but the reverse was true under cool conditions. Control females and their mates both reduced foraging under hot conditions. In contrast, male partners of trimmed females maintained a constant feeding rate across temperatures, suggesting attempts to match the feeding rate of their partners. On average, nestlings of trimmed females were heavier than controls, but did not have a higher probability of fledging. We suggest that removal of a thermal constraint allowed females to increase provisioning rates, but additionally provided nestlings with a thermal advantage via increased heat transfer during maternal brooding. Our data provide support for the heat dissipation limitation hypothesis and suggest that depending on temperature, heat dissipation capacity can influence reproductive success in aerial insectivores.

Thomas J. Lisney, Shaun P. Collin, and Jennifer L. Kelley

Ecological factors such as spatial habitat complexity and diet can explain variation in visual morphology, but few studies have sought to determine whether visual specialisation can occur among populations of the same species. We used a small Australian freshwater fish (the western rainbowfish, Melanotaenia australis) to determine whether populations showed variation in eye size and eye position, and whether this variation could be explained by environmental (light availability, turbidity) and ecological (predation risk, habitat complexity, invertebrate abundance) variables. We investigated three aspects of eye morphology, (1) eye size relative to body size, (2) pupil size relative to eye size, and (3) eye position in the head, for fish collected from 14 sites in a major river catchment in northwest Western Australia. We found significant variation among populations in all three measures of eye morphology, but no effect of sex on eye size or eye position. Variation in eye diameter and eye position was best explained by the level of habitat complexity. Specifically, fish occurring in habitats with low complexity (i.e. open water) tended to have smaller, more dorsally-located eyes, than those occurring in more complex habitats (i.e. vegetation present). The size of the pupil relative to the size of the eye was most influenced by the presence of surrounding rock formations; fish living in gorge habitats had significantly smaller pupils (relative to eye size) than those occupying semi-gorge sites or open habitats. Our findings reveal that different ecological and environmental factors contribute to habitat-specific visual specialisations within a species.

C. M. Lind, J. Agugliaro, and T. M. Farrell

Mounting an immune response may be energetically costly and require the diversion of resources away from other physiological processes. Yet, both the metabolic cost of immune responses and the factors that impact investment priorities remain poorly described in many vertebrate groups. For example, although viviparity has evolved many times in vertebrates, the relationship between immune function and pregnancy has been disproportionately studied in placental mammals. To examine the energetic costs of immune activation and the modulation of immune function during pregnancy in a non-mammalian vertebrate, we elicited an immune response in pregnant and non-pregnant pygmy rattlesnakes, Sistrurus miliarius, using lipopolysaccharide (LPS). Resting metabolic rate (RMR) was measured using flow-through respirometry. Immune function was examined using bactericidal assays and leukocyte counts. The RMR of pygmy rattlesnakes increased significantly in response to LPS injection. There was no statistically significant difference in the metabolic response of non-reproductive and pregnant snakes to LPS. Mean metabolic increments for pregnant females, non-reproductive females, and males were 13%, 18%, and 26%, respectively. The ratio of heterophils to lymphocytes was elevated in response to LPS across reproductive categories; however, LPS did not impact plasma bactericidal ability in non-reproductive snakes. Although pregnant females had significantly higher plasma bactericidal ability compared to non-reproductive snakes prior to manipulation, their bactericidal ability declined in response to LPS. LPS administration also significantly reduced several litter characteristics, particularly when administrated relatively early in pregnancy. Our results indicate that immune performance is energetically costly, altered during pregnancy, and that immune activation during pregnancy may result in tradeoffs that affect offspring in a viviparous reptile.

Jing Wen, Tingbei Bo, Xueying Zhang, Zuoxin Wang, and Dehua Wang

Ambient temperature and food composition can affect energy metabolism of the host. Thermal transient receptor potential (thermo-TRPs) ion channels can detect temperature signals and are involved in the regulation of thermogenesis and energy homeostasis. Further, the gut microbiota has also been implicated in thermogenesis and obesity. In the present study, we tested the hypothesis that thermo-TRPs and gut microbiota are involved in reducing diet-induced obesity (DIO) during low temperature exposure. C57BL/6J mice in obese (body mass gain >45%), lean (body mass gain <15%), and control (body mass gain<1%) groups were exposed to high (23±1°C) or low (4±1°C) ambient temperature for 28 days. Our data showed that low temperature exposure attenuated DIO, but enhanced brown adipose tissue (BAT) thermogenesis. Low temperature exposure also resulted in increased norepinephrine (NE) concentrations in the hypothalamus, decreased TRP melastatin 8 (TRPM8) expression in the small intestine, and altered composition and diversity of gut microbiota. In DIO mice, there was a decrease in overall energy intake along with a reduction in TRP ankyrin 1 (TRPA1) expression and an increase in NE concentration in the small intestine. DIO mice also showed increases in Oscillospira, [Ruminococcus], Lactococcus, and Christensenella and decreases in Prevotella, Odoribacter, and Lactobacillus at the genus level in fecal samples. Together, our data suggest that thermos-TRPs and gut microbiota are involved in thermogenesis and energy metabolism during low temperature exposure in DIO mice.

Kelsey L. Jones, Rahmatollah Rajabzadeh, Guncha Ishangulyyeva, Nadir Erbilgin, and Maya L. Evenden

Flight polyphenisms naturally occur as discrete or continuous traits in insects. Discrete flight polyphenisms include winged and wingless morphs, whereas continuous flight polyphenisms can take the form of short- or long-distance fliers. The mountain pine beetle (Dendroctonus ponderosae) exhibits polyphenic variation in flight distance but the consequences of this flight variation on life history strategies of beetles is unknown. This study assessed the effect of flight on two particular aspects of beetle biology: (1) an energetic trade-off between flight distance and host colonisation capacity; and (2) the relationship between flight distance and pheromone production. A 23-h flight treatment was applied to a subset of beetles using computer. After flight treatment, both flown and unflown (control) beetles were given the opportunity to colonise bolts of host trees, and beetles that entered hosts were aerated to collect pheromone. A trade-off occurred between initiation of host colonisation and percent body weight lost during flight, which indicates energy-use during flight affects host acceptance in female mountain pine beetles. Furthermore, production of the aggregation pheromone trans-verbenol by female beetles was influenced by both percent weight lost during flight and flight distance. Male production of exo-brevicomin was affected by beetle condition following flight but not by the energy used during flight. These novel results give new insight into the polyphenic flight behaviour of mountain pine beetles. Flight variation is adaptive by acting to maintain population levels through safe and risky host colonisation strategies. These findings suggest mechanisms that facilitate the extremities of the continuous flight polyphenism spectrum. These opposing mechanisms appear to maintain the high variation in flight exhibited by this species.

Myriam Franzke, Christian Kraus, David Dreyer, Keram Pfeiffer, M. Jerome Beetz, Anna L. Stöckl, James J. Foster, Eric J. Warrant, and Basil el Jundi

Monarch butterflies (Danaus plexippus) are prominent for their annual long-distance migration from North America to their overwintering area in Central Mexico. To find their way on this long journey, they use a sun compass as their main orientation reference but will also adjust their migratory direction with respect to mountain ranges. This indicates that the migratory butterflies also attend to the panorama to guide their travels. While the compass has been studied in detail in migrating butterflies, little is known about the orientation abilities of non-migrating butterflies. Here we studied if non-migrating butterflies - that stay in a more restricted area to feed and breed - also use a similar compass system to guide their flights. Performing behavioral experiments on tethered flying butterflies in an indoor LED flight simulator, we found that the monarchs fly along straight tracks with respect to a simulated sun. When a panoramic skyline was presented as the only orientation cue, the butterflies maintained their flight direction only during short sequences suggesting that they potentially use it for flight stabilization. We further found that when we presented the two cues together, the butterflies incorporate both cues in their compass. Taken together, we here show that non-migrating monarch butterflies can combine multiple visual cues for robust orientation, an ability that may also aid them during their migration.

Emily J. Lombardi, Candice L. Bywater, and Craig R. White

The Oxygen and Capacity-Limited Thermal Tolerance (OCLTT) hypothesis proposes that the thermal tolerance of an animal is shaped by its capacity to deliver oxygen in relation to oxygen demand. Studies testing this hypothesis have largely focused on measuring short-term performance responses in animals under acute exposure to critical thermal maximums. The OCLTT hypothesis, however, emphasises the importance of sustained animal performance over acute tolerance. The present study tested the effect of chronic hypoxia and hyperoxia during development on medium to long-term performance indicators at temperatures spanning the optimal temperature for growth in the speckled cockroach, Nauphoeta cinerea. In contrast to the predictions of the OCLTT hypothesis, development under hypoxia did not significantly reduce growth rate or running performance, and development under hyperoxia did not significantly increase growth rate or running performance. The effect of developmental temperature and oxygen on tracheal morphology and metabolic rate were also not consistent with OCLTT predictions, suggesting that oxygen delivery capacity is not the primary driver shaping thermal tolerance in this species. Collectively, these findings suggest that the OCLTT hypothesis does not explain moderate-to-long-term thermal performance in Nauphoeta cinerea, which raises further questions about the generality of the hypothesis.

David J. Pritchard and Mario Vallejo-Marin

Vibrations play an important role in insect behaviour. In bees, vibrations are used in a variety of contexts including communication, as a warning signal to deter predators and during pollen foraging. However, little is known about how the biomechanical properties of bee vibrations vary across multiple behaviours within a species. In this study, we compared the properties of vibrations produced by Bombus terrestris audax (Hymenoptera: Apidae) workers in three contexts: during flight, during defensive buzzing, and in floral vibrations produced during pollen foraging on two buzz-pollinated plants (Solanum, Solanaceae). Using laser vibrometry, we were able to obtain contactless measures of both the frequency and amplitude of the thoracic vibrations of bees across the three behaviours. Despite all three types of vibrations being produced by the same power flight muscles, we found clear differences in the mechanical properties of the vibrations produced in different contexts. Both floral and defensive buzzes had higher frequency and amplitude velocity, acceleration, and displacement than the vibrations produced during flight. Floral vibrations had the highest frequency, amplitude velocity and acceleration of all the behaviours studied. Vibration amplitude, and in particular acceleration, of floral vibrations has been suggested as the key property for removing pollen from buzz-pollinated anthers. By increasing frequency and amplitude velocity and acceleration of their vibrations during vibratory pollen collection, foraging bees may be able to maximise pollen removal from flowers, although their foraging decisions are likely to be influenced by the presumably high cost of producing floral vibrations.

Nadia Vicenzi, Alejandro Laspiur, Paola L. Sassi, Ruben Massarelli, John Krenz, and Nora R. Ibargüengoytia

In ectotherms, temperature exerts a strong influence on the performance of physiological and ecological traits. One approach to understand the impact of rising temperatures on animals and their ability to cope with climate change is to quantify variation in thermal-sensitive traits. Here, we examined the thermal biology, the temperature dependence and the thermal plasticity of bite force (endurance and magnitude) in Diplolaemus leopardinus, an aggressive and territorial lizard, endemic to Mendoza province, Argentina. Our results indicated that this lizard behaves like a moderate thermoregulator which uses the rocks of its environment as the main heat source. Bite endurance was not influenced by head morphometry and body temperature, whereas bite force was influenced by head length and jaw length, and exhibited thermal dependence. Before thermal acclimation treatments, the maximum bite force for D. leopardinus occured at the lowest body temperature and fell sharply with increasing body temperature. After acclimation treatments, lizards acclimated at higher temperatures exhibited greater bite force. Bite force showed phenotypic plasticity, which reveals that leopard iguanas are able to maintain (and even improve) their bite force under a rising-temperature scenario.

Jorge de Costa, Gustavo Barja, and Pedro F. Almaida-Pagan

Lipid composition of cell membranes is linked to metabolic rate and lifespan in mammals and birds but very little information is available for fishes. In this study, three fish species of the short-lived annual genus Nothobranchius with different maximum lifespan potentials (MLSP) and the longer-lived outgroup species Aphyosemion australe were studied to test whether they conform to the predictions of the longevity-homeoviscous adaptation (LHA) theory of aging. Lipid analyses were performed in whole fish samples and peroxidation indexes (PIn) for every PL class and for the whole membrane, were calculated. Total PL content was significantly lower in A. australe and N. korthausae, the two species with the highest MLSP, and a negative correlation between membrane total PIn and fish MLSP was found, this meaning that the longer-lived fish species have more saturated membranes and therefore, a lower susceptibility to oxidative damage, as the LHA theory posits.

Scarlet J. Park and William W. Ja

Factors that mediate ethanol preference in Drosophila melanogaster are not well understood. A major confound has been the use of diverse methods to estimate ethanol consumption. We measured fly consumptive ethanol preference on base diets varying in nutrients, taste, and ethanol concentration. Both sexes showed ethanol preference that was abolished on high nutrient concentration diets. Additionally, manipulating total food intake without altering the nutritive value of the base diet or the ethanol concentration was sufficient to evoke or eliminate ethanol preference. Absolute ethanol intake and food volume consumed were stronger predictors of ethanol preference than caloric intake or the dietary caloric content. Our findings suggest that the effect of the base diet on ethanol preference is largely mediated by total consumption associated with the delivery medium, which ultimately determines the level of ethanol intake. We speculate that a physiologically relevant threshold for ethanol intake is essential for preferential ethanol consumption.

David E. Cade, J. Jacob Levenson, Robert Cooper, Rafael de la Parra, D. Harry Webb, and Alistair D. M. Dove

Whale sharks (Rhincodon typus Smith 1828) – the largest extant fish species – reside in tropical environments, making them an exception to the general rule that animal size increases with latitude. How this largest fish thrives in tropical environments that promote high metabolism but support less robust zooplankton communities has not been sufficiently explained. We used open-source inertial measurement units (IMU) to log 397 hours of whale shark behavior in Yucatan, Mexico, at a site of both active feeding and intense wildlife tourism. Here we show that the strategies employed by whale sharks to compensate for the increased drag of an open mouth are similar to ram-feeders five orders of magnitude smaller and one order of magnitude larger. Presumed feeding constituted 20% of the total time budget of four sharks, with individual feeding bouts lasting up to 11 consecutive hrs. Compared to normal, sub-surface swimming, three sharks increased their stroke rate and amplitude while surface feeding, while one shark that fed at depth did not demonstrate a greatly increased energetic cost. Additionally, based on time-depth budgets, we estimate that aerial surveys of shark populations should consider including a correction factor of 3 to account for the proportion of daylight hours that sharks are not visible at the surface. With foraging bouts generally lasting several hours, interruptions to foraging during critical feeding periods may represent substantial energetic costs to these endangered species, and this study presents baseline data from which management decisions affecting tourist interactions with whale sharks may be made.

Jack Nguyen and Meir M. Barak

Cortical bone remodeling is an ongoing process triggered by microdamage, where osteoclasts resorb existing bone and osteoblasts deposit new bone in the form of secondary osteons (Haversian systems). Previous studies revealed regional variance in Haversian systems structure and possibly material, between opposite cortices of the same bone. As bone mechanical properties depend on tissue structure and material, it is predicted that bone mechanical properties will vary in accordance with structural and material regional heterogeneity. To test this hypothesis, we analyzed the structure, mineral content and compressive stiffness of secondary bone from the cranial and caudal cortices of the white-tailed deer proximal humerus. We found significantly larger Haversian systems and canals in the cranial cortex but no significant difference in mineral content between the two cortices. Accordingly, we found no difference in compressive stiffness between the two cortices and thus our working hypothesis was rejected. Seeing that the deer humerus is curved and thus likely subjected to bending during habitual locomotion, we expect that similar to other curved long bones, the cranial cortex of the deer humerus is likely subjected primarily to tensile strains and the caudal cortex is likely subject primarily to compressive strains. Consequently, our results suggest that strain magnitude (larger in compression) and sign (compression vs. tension) affect differently the osteoclasts and osteoblasts in the BMU. Our results further suggest that osteoclasts are inhibited in regions of high compressive strains (creating smaller Haversian systems) while osteoblasts’ osteoid deposition and mineralization is not affected by strain magnitude and sign.

Shih-Jung Hsu and Bo Cheng

In the presence of wind or background image motion, flies are able to maintain a constant retinal slip velocity via regulating flight speed to the extent permitted by their locomotor capacity. Here we investigated the retinal slip compensation of tethered blue-bottle flies (Calliphora vomitoria) flying semi-freely along an annular corridor in a magnetically levitated flight mill enclosed by two motorized cylindrical walls. We perturbed the flies’ retinal slip via spinning the cylindrical walls, generating bilaterally averaged retinal slip perturbations from -0.3 to 0.3 m·s^–1 (or -116.4 to 116.4 deg.·s^–1) When the perturbation was less than ~0.1 m·s^–1 (38.4 deg.·s^–1), the flies successfully compensated the perturbations and maintained a retinal slip velocity by adjusting their airspeed up to 20%. However, with greater retinal slip perturbation, the flies’ compensation became saturated, as the flies’ airspeed plateaued, indicating that they were unable to further maintain a constant retinal slip velocity. The compensation gain, i.e., the ratio of airspeed compensation and retinal slip perturbation, depended on the spatial frequency of the grating patterns, being the largest at 12 m^–1 (0.04 deg.^–1).

Annette E. Allen, Joshua W. Mouland, Jessica Rodgers, Beatriz Bano-Otalora, Ronald H. Douglas, Glen Jeffery, Anthony A. Vugler, Timothy M. Brown, and Robert J. Lucas

An animal's temporal niche – the time of day at which it is active – is known to drive a variety of adaptations in the visual system. This includes variations in the topography, spectral sensitivity and density of retinal photoreceptors, and changes in the eye's gross anatomy and spectral transmission characteristics. We have characterised visual spectral sensitivity in the murid rodent Rhabdomys pumilio (‘the four-striped grass mouse’), which is the same family as (nocturnal) mice and rats, but exhibits a strong diurnal niche. As is common in diurnal species, the Rhabdomys lens acts as a long-pass spectral filter, providing limited transmission of light <400nm. Conversely, we found strong sequence homologies with the Rhabdomys SWS and MWS opsins and those of related nocturnal species (mice and rats) whose SWS opsins are maximally sensitive in the near UV. We continued to assess in vivo spectral sensitivity of cone vision using electroretinography and multi-channel recordings from the visual thalamus. These revealed that responses across the human visible range could be adequately described by those of a single pigment (assumed to be MWS opsin) maximally sensitive ~500nm, but that sensitivity in the near UV required inclusion of a second pigment whose peak sensitivity lay well into the UV range (_max <400nm, likely ~360nm). We therefore conclude that, despite the UV-filtering effects of the lens, the Rhabdomys retains an SWS pigment with a UV-A _max. In effect, this somewhat paradoxical combination of long-pass lens and UV-A _max results in narrow-band sensitivity for SWS cone pathways in the UV-A range.

Brad A. Seibel and Curtis Deutsch

The capacity to extract oxygen from the environment and transport it to respiring tissues in support of metabolic demand reportedly has implications for species’ thermal tolerance, body-size, diversity and biogeography. Here we derive a quantifiable linkage between maximum and basal metabolic rate and their oxygen, temperature and size dependencies. We show that, regardless of size or temperature, the physiological capacity for oxygen supply precisely matches the maximum evolved demand at the highest persistently available oxygen pressure and this is the critical PO₂ for the maximum metabolic rate. For most terrestrial and shallow-living marine species, this "P_crit-max" is the current atmospheric pressure, 21 kPa. Any reduction in oxygen partial pressure from current values will result in a calculable decrement in maximum metabolic performance. However, oxygen supply capacity has evolved to match demand across temperatures and body sizes and so does not constrain thermal tolerance or cause the well-known reduction in mass-specific metabolic rate with increasing body mass. The critical oxygen pressure for resting metabolic rate, typically viewed as an indicator of hypoxia tolerance, is, instead, simply a rate-specific reflection of the oxygen supply capacity. A compensatory reduction in maintenance metabolic costs in warm-adapted species constrains factorial aerobic scope and the critical PO₂ to a similar range, between ~2 and 6, across each species’ natural temperature range. The simple new relationship described here redefines many important physiological concepts and alters their ecological interpretation.

Maria Stager, Nathan R. Senner, Bret W. Tobalske, and Zachary A. Cheviron

Flexibility in heat generation and dissipation mechanisms provides endotherms the ability to match their thermoregulatory strategy with external demands. However, the degree to which these two mechanisms account for seasonal changes in body temperature regulation is little explored. Here we present novel data on the regulation of avian body temperature to investigate how birds alter mechanisms of heat production and heat conservation to deal with variation in ambient conditions. We subjected Dark-eyed Juncos (Junco hyemalis) to chronic cold acclimations of varying duration and subsequently quantified their metabolic rates, thermal conductance, and ability to maintain normothermia. Cold-acclimated birds adjusted traits related to both heat generation (increased summit metabolic rate) and heat conservation (decreased conductance) to improve their body temperature regulation. Increases in summit metabolic rate occurred rapidly, but plateaued after one week of cold exposure. In contrast, changes to conductance occurred only after nine weeks of cold exposure. Thus, the ability to maintain body temperature continued to improve throughout the experiment, but the mechanisms underlying this improvement changed through time. Our results demonstrate the ability of birds to adjust thermoregulatory strategies in response to thermal cues and reveal that birds may combine multiple responses to meet the specific demands of their environments.

Jessica M. Judson, Dawn M. Reding, and Anne M. Bronikowski

Immunosenescence is a well-known phenomenon in mammal systems, but its relevance in other long-lived vertebrates is less understood. Further, the influence of age and reproductive effort on immune function in long-lived species can be challenging to assess, as long-term data are scarce and it is often difficult to sample the oldest age classes. We used the painted turtle (Chrysemys picta) to test hypotheses of immunosenescence and a trade-off between reproductive output and immune function in a population of a long-lived vertebrate that has been monitored for over 30 years. These long-term data are utilized to employ a unique approach of aging turtles with mark-recapture data and population-specific growth modeling to obtain more accurate estimates of age. We analyzed natural antibodies, lysis ability, and bactericidal competence in 126 individuals from 1 to 33 years of age captured during May and June in 2011. Older turtles exhibited greater natural antibody levels than young individuals across sexes. Young females with large clutches exhibited greater lysis ability, while older females with large clutches had decreased lysis ability, suggesting a trade-off between reproductive output and immune function conditional upon age. However, bactericidal competence increased later in the nesting season for older females. Our study rejects the hypothesis of immunosenescence in a long-lived turtle, despite evidence of actuarial and reproductive senescence in this population. Additionally, we detected mixed evidence for a trade-off between reproduction and immune health.

Christine Elizabeth Cooper, Laura Leilani Hurley, Pierre Deviche, and Simon Charles Griffith

Desert birds inhabit hot, dry environments that are becoming hotter and drier as a consequence of climate change. Extreme weather such as heatwaves can cause mass-mortality events that may significantly impact populations and species. There are currently insufficient data concerning physiological plasticity to inform models of species’ response to extreme events and develop mitigation strategies. Consequently, we examine here the physiological plasticity of a small desert bird in response to hot (mean maximum ambient temperature=42.7°C) and cooler (mean maximum ambient temperature=31.4°C) periods during a single Austral summer. We measured body mass, metabolic rate, evaporative water loss, and body temperature, along with blood parameters (corticosterone, glucose, and uric acid) of wild zebra finches (Taeniopygia guttata; Gould 1837) to assess their physiological state and determine the mechanisms by which they respond to heatwaves. Hot days were not significant stressors; they did not result in modification of baseline blood parameters or an inability to maintain body mass, provided drinking water was available. During heatwaves, finches shifted their thermoneutral zone to higher temperatures. They reduced metabolic heat production, evaporative water loss and wet thermal conductance, and increased hyperthermia, especially when exposed to high ambient temperature. A consideration of the significant physiological plasticity that we have demonstrated to achieve more favourable heat and water balance is essential for effectively modelling and planning for the impacts of climate change on biodiversity.

Background

Canagliflozin reduced renal and cardiovascular events in people with type 2 diabetes in the CREDENCE trial. We assessed efficacy and safety of canagliflozin by initial estimated glomerular filtration rate (eGFR).

Background

Experimental and observational studies have raised concerns that giving intravenous (IV) iron to patients, such as individuals receiving maintenance hemodialysis, might increase the risk of infections. The Proactive IV Iron Therapy in Haemodialysis Patients (PIVOTAL) trial randomized 2141 patients undergoing maintenance hemodialysis for ESKD to a high-dose or a low-dose IV iron regimen, with a primary composite outcome of all-cause death, heart attack, stroke, or hospitalization for heart failure. Comparison of infection rates between the two groups was a prespecified secondary analysis.

Background

Clinically significant CKD following surgery for kidney cancer is associated with increased morbidity and mortality, but identifying patients at increased CKD risk remains difficult. Simple methods to stratify risk of clinically significant CKD after nephrectomy are needed.

Background

Fluid overload in patients undergoing hemodialysis contributes to cardiovascular morbidity and mortality. There is a global trend to lower dialysate sodium with the goal of reducing fluid overload.

Background

After accounting for known risk factors for CKD progression in children, clinical outcomes among children with CKD still vary substantially. Biomarkers of tubular injury (such as KIM-1), repair (such as YKL-40), or inflammation (such as MCP-1, suPAR, TNF receptor-1 [TNFR-1], and TNFR-2) may identify children with CKD at risk for GFR decline.

Background

The inactivation of the ciliary proteins polycystin 1 or polycystin 2 leads to autosomal dominant polycystic kidney disease (ADPKD). Although signaling by primary cilia and interstitial inflammation both play a critical role in the disease, the reciprocal interactions between immune and tubular cells are not well characterized. The transcription factor STAT3, a component of the cilia proteome that is involved in crosstalk between immune and nonimmune cells in various tissues, has been suggested as a factor fueling ADPKD progression.

Background

Studies have linked mutations in genes encoding the eight-protein exocyst protein complex to kidney disease, but the underlying mechanism is unclear. Because Drosophila nephrocytes share molecular and structural features with mammalian podocytes, they provide an efficient model for studying this issue.

Background

Water and solute transport across epithelia can occur via the transcellular or paracellular pathways. Tight junctions play a key role in mediating paracellular ion reabsorption in the kidney. In the renal collecting duct, which is a typical absorptive tight epithelium, coordination between transcellular sodium reabsorption and paracellular permeability may prevent the backflow of reabsorbed sodium to the tubular lumen along a steep electrochemical gradient.