Ecological and evolutionary physiology最新文献

AbstractFor terrestrial animals, evaporative water loss (EWL) is a crucial component of osmotic balance and thermoregulation. At high ambient temperatures, augmented EWL for thermoregulation is well recognized, but there is growing evidence that insensible EWL at temperatures within and below thermoneutrality is also regulated and does not just passively conform to Fick's Law. We investigated the capacity of the arid-habitat mulga parrot (Psephotellus varius) to physiologically regulate its insensible EWL within or below thermoneutrality (15°C-30°C) using open-flow respirometry and manipulating two physical parameters, the water vapor pressure deficit (by varying atmospheric relative humidity) and the water diffusion coefficient (using a helox atmosphere). Both experimental approaches provided evidence for physiological control of EWL. There was no significant effect of relative humidity on EWL despite the reduced water vapor pressure deficit at high relative humidity, and EWL did not increase in response to a higher vapor diffusion coefficient in helox despite expected increases in thermal conductance, metabolic rate, and ventilatory parameters. Adjustments of both respiratory and cutaneous EWL contributed to the control of EWL, achieved by modifying a combination of ventilatory parameters, expired air temperature, skin resistance, and, to a lesser extent, skin temperature. These results are important for understanding how animals function in, and respond to, their environment.

AbstractThe diet of an organism can influence various biological processes, including digestion. By examining how dietary changes can shift gut physiology in an herbivorous fish, we can gain insight into what that species can tolerate in terms of dietary shifts. Thus, we investigated how gut mass, digestive enzyme activity, hindgut microbial diversity, levels of gastrointestinal fermentation, and hindgut and liver transcriptomics respond to dietary perturbations in the marine herbivorous fish Cebidichthys violaceus. Contrary to our expectations, fish fed an omnivore diet (45% protein) in the laboratory exhibited the most similarity to wild-caught herbivorous fish, sharing a high abundance of taxa in the Bacteroidota and Bacillota phyla (families Ruminococcaceae and Rikenellaceae) and the highest concentrations of short-chain fatty acids. Fish in these groups shared similarities in gene expression patterns too. Fish fed herbivore (~23% protein) or carnivore (~69% protein) diets in the laboratory had a high abundance of taxa from the Pseudomonadota phylum (families Burkholderiaceae and Oxalobacteraceae) and lower short-chain fatty acid concentrations. The hindgut had 519 differentially expressed genes, with wild-caught fish exhibiting a high expression of genes associated with ion transport, lipid metabolism, and glucose metabolism. The liver had 4,650 differentially expressed genes, and wild-caught fish had a high expression of genes related to fatty acid synthesis and proteolysis. Hindgut digestive enzyme activities also varied with diet and microbial diversity. Our integrative study furthers our understanding of the physiology of an herbivorous fish and how it responds to shifting dietary resources, particularly with an eye toward herbivorous fish aquaculture.

AbstractEthanol is a naturally occurring molecule produced via fermentation of sugar-rich foods by yeast. Ethanol catabolism is followed by production of secondary metabolites such as ethyl glucuronide (EtG), which can be measured to provide a retrospective view of dietary exposure. To date, occurrence of this molecule has not been studied in vertebrates other than humans and several other mammalian taxa. Here, we describe a method of testing for the presence of EtG in bird feathers and livers using mass spectrometry. Birds that regularly consume fruit and nectar may accordingly be ingesting ethanol on a chronic basis. We predicted that avian species with diets rich in fermentable sugars consume physiologically significant amounts of ethanol and therefore accumulate detectable levels of EtG. The suitability of EtG assays was tested across 17 avian species representing a diversity of diets. Assays of avian feathers yielded positive results for 10 of 17 avian species; EtG was also present at substantial levels in the livers of two of five study species. We found that EtG was present in nectarivorous hummingbirds but also in species in other trophic niches (three granivores, one omnivore, three invertivores, and one vertivore). Dietary exposure to ethanol may thus be much more widespread than has previously been recognized, and diverse features of avian nutritional ecology (e.g., secondary consumption via ingestion of prey items) may contribute to its accumulation in tissues.

AbstractHuman activities frequently alter environmental conditions and affect the use of sexually selected traits like color in animals. However, the effects of environmental stressors are unlikely to be uniform across populations that experience different environments or between sexes. We aimed to understand the underlying genetic, environmental, and gene-by-environment contributions to color expression in males and females of a sexually dimorphic fish. Pseudocrenilabrus multicolor is a haplochromine cichlid found in environments that vary dramatically, particularly with respect to oxygen and turbidity levels. We reared fish from one swamp (hypoxic, clear) and one river (normoxic, turbid) population in a split-brood design (hypoxic/normoxic × clear/turbid) and then quantified color and carotenoid concentrations. As expected in this sexually dimorphic species, females were far less colorful than males. In males, hypoxia and turbidity were drivers of traits associated with color, suggesting that color was modified under energetically or visually unfavorable conditions. Males in the hypoxic treatment from both populations were not as bright as males reared under normoxic conditions, which corresponds to results observed in wild fish. Males reared in turbid conditions were also marginally less bright along the ventral surface than males reared in clear water. Rearing under turbid conditions reduced carotenoid concentrations in male skin, but carotenoids were not correlated with spectral characteristics of male color. We did not find effects of population on color traits, suggesting that differences in color between wild populations are due to plastic rather than fixed genetic effects. Overall, we provide evidence that hypoxia and turbidity affect signaling traits, although the consequences for mating success remain to be determined.

AbstractIn many species, reproduction and lifespan are maximized at different dietary protein-to-carbohydrate (p∶c) ratios. Protein-biased diets tend to favor higher reproduction, while carbohydrate-biased diets tend to favor longer lifespans, but the mechanisms responsible for the apparent survival costs of reproduction remain unclear. Prior studies of this topic for females have primarily measured egg production, which could be an inadequate measure of fitness, and have not assessed the rate and timing of reproduction across lifespan, which can provide insights into fitness costs and benefits. To test how variation in dietary p∶c ratio effects are integrated across whole lifespans, we reared migratory locusts (Locusta migratoria) from fifth instar through adulthood on one of three artificial isocaloric diets varying in p∶c ratios (14p∶28c, 21p∶21c, 35p∶7c). We then put pairs of locusts in cages and each week measured male and female survival, the number of eggs and egg pods laid, and hatchlings per reproductive pair throughout the lifespan. Carbohydrate-biased diets increased female lifespans, but macronutrient content had no effect on male lifespans. Locusts eating a carbohydrate-biased diet incurred the cost of a 1-wk delay in the onset of egg laying; however, macronutrient balance did not affect the total number of hatchlings produced over their entire lifespans. Locusts consuming protein-biased diets laid more eggs per pod but fewer total egg pods, and their eggs were lighter than eggs laid by locusts on other diets. Earlier reproduction did not appear to fully explain the reduced longevity of locusts on high-protein diets, as locusts feeding on a balanced diet had similar reproductive schedules but had longer lifespans. In summary, our data show that reproductively active females are more susceptible to the negative effects of high protein on longevity than males and that macronutrient balance affects some nuances of egg production but does not affect overall hatchling success in lab populations. Macronutrient balance may have a greater impact on reproductive success in field populations, depending on predation pressures (reproducing earlier may be paramount), food availability (hatchlings from larger eggs may be more robust to starvation), or other factors.

AbstractBecause of their extended fasting period on land during breeding, male king penguins have been extensively studied in order to unravel the physiological adaptations that enable them to fast while having to find a partner, defend their territory, or brood their offspring. While the different phases of fasting and the nature of the metabolic fuels used are well characterized in male king penguins, few studies have focused on the efficiency of the conversion of the metabolic resources into energy at a cellular level through mitochondrial respiration. Furthermore, little information is available on females in general while they experience fasting periods. Here, we measured mitochondrial respiration rates of red blood cells (RBCs) at the beginning (3 d) and end (10 d) of a natural egg-incubation fast in male and female king penguins. We tested whether RBC mitochondrial metabolism and its efficiency are modulated by fasting duration in free-living king penguins but also assessed whether this modulation is sex specific. In response to fasting, the respiration allocated to ATP synthesis in RBCs decreased in both sexes. Interestingly, RBC mitochondrial metabolic rates were higher in females at any stage of fasting. Furthermore, RBC mitochondrial metabolism efficiency decreased in males after 10 d of fasting but remained constant in females. Our results demonstrate that RBC mitochondrial metabolism is context and state dependent, differing between sexes and changing with fasting. They underline the importance of taking both sexes into account in physiological studies, where females remain underrepresented.

AbstractSmall birds in temperate regions are faced with a large range of environmental conditions throughout the year, including fluctuating temperatures. During cold winters, birds often exhibit an increase in metabolic rates, body mass, and pectoralis muscle mass because of the heightened energetic needs of thermoregulation. However, climate change is altering weather patterns, and in addition to widespread winter warming, temperature variability and the frequency of extreme temperatures are also expected to increase, including more winter cold snaps. In the present study, our goal was to determine whether an increase in temperature variability in a cold environment will impact the metabolic rates, organ masses, and body mass of winter-phenotype house sparrows (Passer domesticus). After exposing birds to stable warm, stable cold, or fluctuating cold temperatures, we found no significant differences in masses or metabolic rates between the stable and fluctuating cold groups. Compared to the warm treatment, both cold treatments had higher basal, but not summit (i.e., maximum, cold induced), metabolic rates. These results suggest that increasing temperature variability may not influence the maintenance costs or the thermoregulatory capacity of winter-phenotype house sparrows.

AbstractChanges of deleterious traits in mitochondria within hybrids of two different species are likely to be reflected across whole-animal phenotypes. Two processes linked to mitochondrial fitness are oxidative stress and inflammation. Here, plasma oxidative stress (lipid oxidative damage, total antioxidant capacity, and activities of catalase, glutathione peroxidase, and superoxide dismutase concentration) and cytokine concentrations (IL-1β, IL-6, and TNF-α) from wolf-dog hybrids of low to mid wolf content are presented and then compared with previously published values for similar-sized dogs and gray wolves. Results indicate that lipid oxidative damage and catalase activity were not significantly different across species and hybrids. Total antioxidant capacity and glutathione peroxidase were significantly lower in wolf-dog hybrids than in domestic dogs and wolves (although total antioxidant capacity significantly increased with wolf content), but superoxide dismutase concentration was higher in hybrids. Thus, it seems that a low percentage of wolf content decreases several aspects of antioxidants but without any accumulating lipid oxidative damage. Additionally, wolf-dog hybrids had higher IL-1β and IL-6 concentrations but lower TNF-α concentrations than domestic dogs. And there was a significantly positive correlation between percentage of wolf content and IL-1β. These data imply either a mitonuclear incompatibility or a nuclear-nuclear incompatibility within wolf-dog hybrids, a case that does not support heterosis.

AbstractReduced oxygen availability can become an environmental stressor that imposes constraints on the energy and/or time budget of aquatic animals. This also seems to be the case for bimodal breathers, since it was previously reported that the amount of oxygen in the water interacts with feeding and egg-laying activities. The great pond snail (Lymnaea stagnalis) is a typical bimodal breather and a simultaneous hermaphrodite for which both male and female mating behaviors have been studied in detail. The aim of this study was to test whether hypoxic conditions affect mating behavior in this bimodal breather and to investigate whether mating motivation and the choice of sexual role is influenced by this environmental condition. Our results show that when oxygen cannot be acquired via cutaneous respiration or aerial respiration, mating and locomotion are inhibited. When oxygen is available only via air, the occurrence of unilateral insemination, reciprocal insemination, and biting behavior is reduced and courtship duration is decreased compared to when oxygen is also available in the water. Our results indicate that depending on the oxygen availability in the environment, water, and air, this bimodal breather has to weigh its motivation to mate against its need for cutaneous and/or aerial respiration. These findings contribute to our understanding of how animals optimize their behavioral investment decisions under changing environmental circumstances.

AbstractRegions worldwide over the next few decades are projected to experience higher rates of drought, and animals will be faced with increasingly arid conditions. Understanding physiological effects of low water availability, such as impacts on metabolism and water loss, can further understanding of how animals will cope with aridification. Common degus (Octodon degus) are social rodents native to central Chile, an area that has been experiencing drought since 2010. Using a laboratory population of female degus, we subjected individuals to either (1) control conditions in which water was provided ad lib. or (2) a water-restriction regimen in which water allotments were decreased by 25% each week for 3 wk. Basal metabolic rate and evaporative water loss were estimated using flow-through respirometry before experimental manipulation and at the end of each week. We also collected urine samples, quantified daily food consumption, and weighed animals weekly. We found that body mass decreased significantly in water-restricted animals compared to in controls and that their capacity to concentrate urine increased significantly after 1 wk of water restriction. However, the rate of evaporative water loss did not decrease until the third week of water restriction. Thus, under conditions of low water availability in the absence of heat stress, female degus primarily limit urinary water loss and later decrease evaporative water loss, a strategy that may also be used by similar-sized mammals.