Journal of experimental zoology. Part A, Ecological and integrative physiology最新文献

Many animals undergo irreversible ontogenetic color changes (OCCs), yet these changes are often overlooked despite their potential ethological relevance. The problem is compounded when OCCs involve wavelengths invisible to humans. Wall lizards can perceive ultraviolet (UV) light, and their conspicuous ventral and ventrolateral coloration—including UV-reflecting patched—likely serves social communication. Here, we describe OCCs in the ventral (throat and belly) and ventrolateral (outer ventral scales, OVS) coloration of juvenile common wall lizards (Podarcis muralis) as perceived by conspecifics. We measured reflectance in hatchling and yearling lizards raised under semi-natural conditions and used visual modeling to estimate chromatic distances within individuals and across life stages (i.e., hatchlings, yearlings, and adults). Hatchlings typically exhibit UV-enhanced white (UV⁺white) on their ventral surfaces (throat, belly, and OVS), a color that is likely discriminable to conspecifics from the most frequent adult colors in the throat (i.e. orange, yellow, and UV-reduced white; UV⁻white) and OVS (i.e., UV-blue). The prevalence of UV⁺white decreases with age, with the decline being less pronounced in female bellies. OCCs to UV-blue in the OVS are more apparent in males than in females and appear delayed relative to changes in the throat and belly. While throat colors in yearlings are indistinguishable to conspecifics from adult throat colors, yearling UV-blue patches remain chromatically distinct from those of adults. This delay may reflect variations in the mechanisms of color production or distinct selective pressures acting on these patches. Overall, our results show that OCCs in P. muralis fulfill a key requirement for social signals by being perceptible to conspecifics. This supports the hypothesis that OCCs may play a role mediating interactions between juveniles and adults, as well as delaying the onset of colors involved in social communication.

Assessments of the interplay between physiology and whole-organism performance are fundamental to understand how individuals function in different ecological contexts. Here, we investigated the relationship between locomotor performance, androgen levels, and metabolic capacity of muscle tissues in the lizard Tropidurus catalanensis. We hypothesized that faster individuals would exhibit higher circulating androgen concentrations and greater metabolic capacity in skeletal and cardiac muscles, regardless of body size. We measured morphological variables, maximum sprint speed (v), plasma testosterone concentration, and the maximum activity of the enzymes lactate dehydrogenase (LDH) and citrate synthase (CS) in the gastrocnemius, iliofibularis, and cardiac muscles of adult males. We found that intraspecific variations in v were not explained by body size, plasma testosterone concentration, nor by the activity of LDH or CS in skeletal muscles. The absence of an effect of testosterone on locomotion suggests that androgen concentrations may change in response to other factors, such as environmental stressors or reproductive state. Our results indicated that the fastest lizards also had the highest CS activity in the heart. This relationship suggests that cardiac oxidative capacity plays an important role in clearing metabolites in the postexercise recovery phase. We also found a positive relationship between CS and LDH in all tissues, suggesting a functional complementarity between glycolytic and aerobic pathways that should be relevant in situations that require rapid alternation between bursts of speed and endurance, such as predator evasion or thermoregulation. Ultimately, our results highlight the importance of integrating performance and physiological traits to understand interactions between animals and their environment.

Rapidly increasing anthropogenic CO₂ can impose physiological challenges for fish species that are thought to be tolerant. We tested the hypothesis that elevated pCO₂ will affect the routine activity and escape response by affecting energy metabolism and/or the muscle physiology of coastal fish. We exposed threespine stickleback (Gasterosteus aculeatus) to pCO₂ of ~ 700 µatm (pH 7.9 representing current levels), ~ 1400 µatm (pH 7.6 representing upwelling events) and ~ 3500 µatm (pH 7.3 representing a future predicted scenario for coastal areas) for 2 weeks. Baseline activity was significantly higher in fish exposed to 1400 µatm compared to the control at both sampling points, while the escape response was lower (p < 0.05). Metabolic rate was not different (p > 0.05), but lactate dehydrogenase activity was significantly higher at 3500 µatm compared to control fish after the first week (p < 0.05), while no difference was found in muscle histology between treatments or time points. Our study demonstrates that the baseline activity and escape responses of adult marine coastal fish were temporarily affected by the current level of ocean acidification, but this was not due to changes in metabolism or muscle function, but potentially neuronal effects of high pCO₂. Our study shows that ocean acidification might affect predator-prey interactions during current upwelling events and in the future.

Peroxisome proliferator-activated receptors (PPAR) are master transcriptional regulators that maintain metabolic homeostasis in vertebrates. Amphibians are often exposed to endocrine disrupting compounds (EDCs) that could dysregulate lipid metabolism. Larvae of the African clawed frog (Xenopus laevis) are routinely used as a model to study aquatic EDC exposures, but PPAR expression has not been characterized across larval development or metamorphosis in this species. We conducted two experiments to elucidate (a) the expression in late metamorphosis for xPPARα/β/γ subtypes, and (b) the effect of pharmaceutical PPAR agonists (pirinixic acid, bezafibrate, and ciprofibrate) on the expression of xPPARα/β/γ target genes. Additionally, we considered apical endpoints (body mass, body condition [scaled mass index, SMI], and relative liver mass). We hypothesized pharmaceuticals would agonize hepatic xPPARα/β/γ, upregulating expression of downstream target genes and reducing apical endpoints with variation reflective of developmental patterns of nuclear receptor expression. We observed upregulation of xPPARα during late premetamorphosis (NF 51), prometamorphosis (NF 56–57), and metamorphic climax (NF 58–66), which also held for xPPARγ with exception for peak of metamorphic climax (NF 62). For xPPARβ, we only observed upregulation at conclusion of metamorphic climax (NF 66). Agonists did not cause changes in gene expression for xPPARα/β/γ targets, but pirinixic acid exposure decreased female body condition. The dynamic hepatic expression of xPPARα/β/γ during late metamorphosis is presumably necessary to coordinate energy flux and highlights a potential period of susceptibility to PPAR agonism. However, pharmaceuticals identified to interact with xPPARα/β/γ did not elicit a response concordant with PPAR agonism at high doses. These results suggest that X. laevis may not be a sensitive model for studies testing PPAR-mediated effects of xenobiotics.

Developmental stressors may result in adaptive adjustments in physiology, increasing fitness later in life in otherwise damaging environments. Environmental conditions during development can permanently alter the responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis, which may allow organisms to avoid cellular damage in stressful conditions. We hypothesized that zebra finches (Taeniopygia guttata castanotis) thermally conditioned during development will have lower baseline plasma corticosterone (cort) and baseline erythrocyte DNA damage as adults, as well as lower post-stressor cort and DNA damage, and higher survival rates following a thermal stressor in adulthood compared to juvenile controls. To test this, we exposed juvenile male and female zebra finches to a mild heat (38°C) or control (22°C) temperature every other day for 28 days. As adults, these finches were then subjected to either a high heat stressor (42°C) or control (22°C) temperature for 3 consecutive days. We measured plasma cort levels and erythrocyte genomic DNA damage before and at the end of each treatment period. As adults, the heat-conditioned juvenile finches had higher baseline DNA damage levels, persistently higher body masses, and lower cort levels 4 h following the adult high heat stress treatment compared to juvenile controls. Moreover, this cort phenotype was associated with reduced body mass loss and increased survival rates. However, females had reduced survival if they were not also exposed to the high heat treatment as adults. Our results demonstrate adaptive developmental plasticity in cort levels; however, this phenotype may be detrimental when there is an environmental mismatch.