Ecological and evolutionary physiology最新文献

AbstractEvolved increases in hemoglobin (Hb)-O₂ affinity are common across high-altitude mammals and birds, but the downstream physiological effects of such increases remain poorly understood. In deer mice (Peromyscus maniculatus), the genetic variants of α- and β-globin in high-altitude populations are also associated with evolved changes in breathing pattern and the hypoxic ventilatory response, raising the question of whether chronic increases in Hb-O₂ affinity affect breathing and gas exchange in this species. We tested this possibility in lab-raised deer mice from low-altitude populations by pharmacologically increasing Hb-O₂ affinity over 4 wk using cyanate. Treatments were conducted during adulthood and early postnatal development in normoxia to examine whether the influence of Hb-O₂ affinity is life stage specific. Breathing, arterial O₂ saturation, and aerobic metabolism (O₂ consumption rate) were then measured in normoxia, hypoxia (10% O₂), and hypoxic hypercarbia (10% O₂, 3% CO₂). Cyanate-treated mice experienced pronounced decreases in O₂ pressure at 50% Hb saturation compared to saline-treated controls and exhibited corresponding increases in arterial O₂ saturation in hypoxic conditions in both adults and juveniles. Total ventilation increased and metabolism decreased in hypoxia and hypoxic hypercarbia, but cyanate had little to modest effects on these responses. Effects of cyanate on breathing frequency, tidal volume, and the relationship between total ventilation and tidal volume (an indicator of breathing pattern) were also modest and inconsistent between adults and juveniles. The results suggest that chronic increases in Hb-O₂ affinity have no clear and consistent effects on breathing pattern or the hypoxic ventilatory response.

AbstractThe cuticle of arthropods provides the first line of defense against predators, pathogens, and parasites. While most studies focus on the role of cuticular defense against microbial pathogens, few have examined whether the cuticle protects against parasites. Here, we investigate the relative importance of cuticular sclerotization and behavioral defenses in Drosophila nigrospiracula against an ectoparasite (Macrocheles subbadius). We first tested whether newly eclosed (NE; i.e., teneral) flies are more susceptible to parasitism than fully sclerotized (FS) flies. In a separate experiment, we severed the wings to test whether the differential susceptibility between NE and FS flies was explained by wing-mediated defenses. We also performed endurance (negative geotaxis) assays to determine whether reduced physical endurance among NE flies contributed to higher vulnerability to parasitism. We found that regardless of whether wings were intact or removed, the prevalence and intensity of infection was significantly higher among NE flies than among FS flies. The negative geotaxis assay also showed that NE flies had lower endurance than FS flies. Moreover, differences in the probability and severity of parasitism between NE and FS flies were magnified when the wings were removed. These results suggest that while cuticular sclerotization serves as the primary first line of defense, wing-mediated behaviors likely allow flies to avoid or minimize mite attacks, and the effectiveness of these behaviors is likely limited by physical endurance. Differences in morphology and behavior between immature adults (not FS) and mature organisms (FS) may drive variation in parasitism risk across developmental stages.

AbstractPopulation-level differences in the ability to maintain immunity can lead to contrasting survival outcomes between groups and determine how future outbreaks will spread. Pathology and infectiousness during subsequent infections can be influenced by immunity and an increase in resistance or tolerance of individuals. However, determining the longevity and effectiveness of immunity in a wildlife population is challenging because of the lack of infrastructure for long-term monitoring of populations and individuals and for host-pathogen-specific tests. Furthermore, predicting wildlife disease dynamics requires an understanding of individual-level heterogeneity in pathology and behavior, as well as a knowledge of how populations with differing partial immunity will transmit disease, which is currently limited. Using an avian host-pathogen system, we ran two experiments to determine whether previously exposed birds had immunity to Mycoplasma gallisepticum (MG) after 3 yr and whether MG transmission differed between first- and second-infection index birds. Birds retained partial immunity to MG for 3 yr after their original infection and showed signs of being resistant to infection. The transmission experiment revealed that although first- and second-infection index birds experienced pathology and pathogen growth, only first-infection birds transmitted MG. Here, 3 yr could represent lifetime protection for individuals who survive their first infection and a reduction in risk for other members of their flock. Our research has important implications for understanding MG epidemics in wild populations of birds and disease in wildlife more broadly.

AbstractTheory predicts that signals of strength should reliably reflect an individual's fighting ability, with the costs of producing and/or displaying high-quality signals maintaining their reliability. Crustaceans offer a unique system to explore these costs because signal (chela) size and reliability (strength relative to size) can be decoupled-chela muscles are concealed beneath an exoskeleton, allowing some individuals to display large but weak chelae. In this study, we quantified the locomotor costs associated with weapon size and reliability in males and females of the crayfish Cherax destructor using both correlative analyses and experimental manipulations. We measured chela size, strength, and swimming performance of crayfish when intact, after an initial chela removal treatment (control, one, or two), and again after removal of the remaining chela/chelae. We predicted that larger chelae would reduce swimming performance because of added mass and drag and that relatively stronger individuals (greater reliability) would swim slower because of energetic investment in muscle. We found that males and females with larger chelae swam more slowly and that speed increased following the removal of one (11.6%) and two (14.6%) chelae. Individuals with relatively larger chelae showed a greater increase in speed after both chelae were removed. Crayfish with relatively stronger chelae swam more slowly, but this pattern did not hold after chela removal. Our study is the first to demonstrate the independent costs of both signal size and their reliability. While individuals must bear the costs of signaling large weapons, the costs of their reliability may also incentivize the use of unreliable weapons.

AbstractTelomere dynamics have been linked to differences in reproductive effort across vertebrates. In the Cocos booby (Sula brewsteri), we predicted that parents' telomeres would shorten according to their breeding effort during incubation. During mid-incubation, we blood-sampled 24 adults to estimate telomere length by a quantitative polymerase chain reaction and recorded their body mass, clutch size, and hatching success. At the end of incubation, a second body mass measurement and blood sample were collected. Unexpectedly, parents' telomere length increased throughout incubation. Individuals with two-egg clutches, higher hatching success, and increased body mass exhibited greater telomere elongation. Thus, telomere dynamics did not reflect costs of reproductive effort. The results suggest that telomeres elongate, probably depending on individual quality differences, as proposed by the excess resources elongation hypothesis. Future studies should investigate whether the observed short-term telomere elongation is widespread in breeding animals, as it may be part of a potential mechanism for resilience to predictable stressful events like reproduction.

AbstractClutch size variation may be adaptive in bird populations if parents lay a clutch size that maximizes offspring recruitment. Brood size manipulation experiments allow for testing the optimization of clutch size by studying the effect on nestling body condition and fitness-related physiological traits. If the clutch size is optimized, parents rearing an enlarged brood size are expected to produce low-quality nestlings. Here, we tested this prediction in a population of blue tits (Cyanistes caeruleus), inhabiting two nearby oak forests (differing mainly in humidity) in which blue tits differ in clutch size. We manipulated the brood size (producing reduced, control, and enlarged broods) within each habitat and evaluated the immune system, oxidative status, telomere dynamics, and morphological parameters of the largest and smallest nestlings within broods. We also recorded parental feeding effort and nestling diet composition. Clutch size was higher in the more humid forest, and parents from the two habitats successfully raised the extra nestlings. However, the nestling body mass diminished in enlarged broods compared to control and reduced broods, while the structural size, telomere dynamics, immune system, and oxidative status did not vary with the manipulation treatments. In each forest, parents did not increase their feeding effort in enlarged broods, despite initial between-forest differences in clutch size. Our findings suggest that although blue tits were able to raise extra offspring, clutch size is optimized at the fine scale. Hence, blue tits seem to lay, in every habitat, the clutch size that guarantees the maximal production of high-quality fledglings.

AbstractEndothermic homeothermy, a key adaptation in mammals and birds, enables survival across diverse environments, albeit at significant energetic costs. Some mammals mitigate these costs through flexible thermoregulation, alternating homeothermy with daily heterothermy or hibernation in response to environmental variability. We hypothesize that flexible thermoregulators have evolved adaptive molecular changes in thermoregulatory genes to enhance responsiveness to environmental change. To test this, we analyzed 54 thermoregulation-associated genes in 21 rodent species, traditionally classified as homeothermic, daily heterothermic, or hibernating. Signals of positive selection were identified in 35 genes, many of which were shared among thermoregulatory strategies. Daily heterotherms exhibited stronger selection signals in metabolic and stress-response genes, while hibernators showed selection in homeostasis-related genes. Protein modeling and structural docking analyses revealed that amino acid substitutions in Ucp1 marginally altered predicted folding, likely enhancing thermal stability and acclimation to fluctuating temperatures in daily heterotherms. Hibernators showed increased connectivity in thermoregulatory protein networks, suggesting greater molecular complexity and flexibility. The overlap of positively selected genes in multiple species suggests that thermoregulatory strategies form a continuum rather than discrete categories. Our findings highlight how gene evolution and network connectivity underpin the emergence of thermoregulatory flexibility in mammals, enabling adaptative responses to environmental challenges.

AbstractGiven the usually dark colors that melanin pigments confer to the plumage of birds, local depigmentation creates conspicuous plumage patterns with white feathers that are commonly termed "partial leucism." Such color aberrations have been adduced to urbanization in some species of birds, tentatively assigning the potential of pollutants to induce oxidative stress as a causative agent. White feathers, however, can be produced by a lack of melanocytes in feather follicles without the course of oxidative stress. In contrast, the appearance of white feathers with age is caused by the oxidative stress-induced impairment and death of melanocytes. Both mechanisms are often confounded because the oxidative status of birds with white feather anomalies has not been investigated. Here we compare the cellular oxidative status of wild partially leucistic cinereous vultures (Aegypius monachus) with that of normally pigmented vultures using levels of malondialdehyde (MDA) in plasma, a product of lipid peroxidation. Leucistic vultures exhibited significantly lower MDA levels than normally pigmented birds, arguing against a causative role of oxidative stress in bird leucism, at least in raptors. As similar positive effects of leucism on the systemic oxidative status have previously been found in mammals and fish, these findings suggest that partial depigmentation may benefit animals and stress the importance of identifying the depigmentation mechanism to interpret the context in which color aberrations occur.

AbstractAnthropogenic climate change is driving an increase in climate extremes, including concurrent drought and heat wave events. To understand the ecological consequences of these events, research is needed to identify their separate and compound effects on organisms across life stages. Oviparous species are particularly vulnerable to environmental stress at the embryonic stage, as embryos are relatively unprotected from hydric and thermal extremes. The embryonic environment can substantially shape offspring physiology and fitness. However, the developmental impacts of extreme climate events, including downstream effects on offspring survival in the field, are not well described. In this study, we investigated the independent and interactive effects of flash drought and heat waves during embryonic development in an oviparous vertebrate model, the painted turtle (Chrysemys picta). In a fully factorial experiment, we imposed simulated flash drought and heat wave events and examined the effects on egg mass, incubation time, and offspring body size. After turtles overwintered in the laboratory, we conducted a release experiment in the field to measure early-life survival in an ecologically relevant context. We found that flash drought and heat wave events interactively influenced egg mass during late embryonic development and independently reduced incubation time and postoverwintering body mass. In addition, smaller individuals had a lower probability of survival in the field. Our results suggest that oviparous species will face negative impacts on embryonic development and early-life traits as compound drought and heat wave events become more frequent and severe.

AbstractLong-distance endurance flight in migratory birds requires numerous physiological adaptations. Maintaining the necessary physiological machinery may require increased energy expenditure, which could manifest as an elevated basal metabolic rate (BMR). Comparing the BMR of long-distance migrants and residents using global BMR datasets is complicated by the fact that data for migrants typically come from higher latitudes and colder regions than those for nonmigrants. Separating the effects of ambient temperature (T_a) and migratory tendency on BMR is challenging because of the well-documented high phenotypic plasticity of avian BMR, which is reflected in the negative relationship between BMR and T_a. We hypothesized that tropical migrants would have a higher BMR than residents because of the cost of maintaining a more enduring and/or flexible physiology. Additionally, according to the climatic variability hypothesis (CVH), BMR plasticity should be greater in regions with more variable climates. To test these hypotheses, we measured BMR in 130 sedentary species and 25 migratory species from two remote areas in Vietnam that differ in climate. As expected, we found that in both sites, migrants on their wintering grounds maintained a higher mass-independent BMR compared with tropical residents. Moreover, the BMR of wintering migrants was not lower than their BMR on their breeding grounds. Sedentary species inhabiting a milder and more stable climate had lower BMR than those in colder and more variable environments. The individual long-term repeatability of BMR in the milder climate was higher than that in the area with a more variable climate, which is consistent with the CVH.