Ecological and evolutionary physiology最新文献

AbstractAt certain intensities and durations, environmental stressors during development can result in changes in physiology that prepare organisms for future stressful conditions. Such plasticity can allow organisms to maintain good condition when confronted with a poor environment, potentially conferring an advantage in fitness. However, the physiological changes underlying these adaptive phenotypic adjustments are understudied. Using captive male zebra finches (Taeniopygia castanotis), we tested whether exposure to a prolonged mild stressor during development would adaptively modify their antioxidant enzyme expression, reducing oxidative damage when exposed to a high-intensity stressor in adulthood and allowing the maintenance of a secondary sexual trait. To do this, we exposed juvenile finches to either a prolonged mild heat stressor treatment (38°C) or a control temperature treatment (22°C). As adults, these finches were then exposed to either an acute high-intensity heat stressor treatment (42°C) or control temperature treatment (22°C). The beak color of males-a sexually selected trait-was quantified, as were oxidative stress parameters in the testes and liver tissues. We saw that the mild-heat-conditioned males had beaks with higher saturation and lower brightness at baseline in adulthood but that the changes in beak color in response to the high heat stressor varied. After exposure to the high heat stressor as adults, finches had higher levels of superoxide dismutase 1 and 2 in the testes and lower levels of lipid damage in the liver if they were also exposed to the mild heat conditioning as juveniles, indicating an adaptive phenotypic change.

AbstractHormones can induce trait development in one species yet have no effect on the same trait in a closely related species, but the mechanisms underlying these differences are unclear. Here, we compare two closely related lizard species to explore the cellular mechanisms associated with the evolutionary loss of hormonally mediated ventral coloration. The eastern fence lizard (Sceloporus undulatus) has sexually dimorphic blue and black ventral coloration that develops when maturational increases in androgens induce melanin synthesis in males. The closely related striped plateau lizard (Sceloporus virgatus) has sexually monomorphic white ventral skin that does not produce melanin in response to the same signal. We used immunohistochemistry to localize the androgen receptor (AR) in the skin of both species and to test whether the loss of ventral coloration in S. virgatus corresponds to the loss of AR in the skin. We found that the ventral skin of S. virgatus displays little or no AR staining in the pigment cell layer, potentially explaining the loss of androgen sensitivity in this tissue, relative to the robust AR staining in the same layer of S. undulatus. Based on the location of three markers for melanophores (microphthalmia-associated transcription factor, dopachrome tautomerase, and tyrosinase), AR appears to be present in melanophores in S. undulatus. However, we could not detect these melanophore markers in the skin of S. virgatus. Therefore, the evolutionary loss of ventral coloration may have occurred via the loss of the AR-producing melanophore in mature ventral skin, preventing the development of a male-typical trait and sexual dimorphism in this tissue.

AbstractUnderstanding the relationship between the environment parents experience during reproduction and the environment embryos experience in the nest is essential for determining the intergenerational responses of populations to novel environmental conditions. Thermal stress has become commonplace for organisms inhabiting areas affected by rising temperatures. Exposure to body temperatures that approach, but do not exceed, upper thermal limits often induces adverse effects in organisms, but the propensity for these temperatures to have intergenerational consequences has not been explored in depth. Here, we quantified the effects of thermal stress on the reproductive physiology and development of brown anoles (Anolis sagrei) when thermal stress is experienced by mothers and by eggs during incubation. Mothers exposed to thermal stress produced smaller eggs and smaller offspring with reduced growth rates, while egg stress reduced developmental time and offspring mass. Hatchling survival and growth were negatively affected by thermal stress experienced by mothers but not by thermal stress experienced as eggs. We found mixed evidence for an additive effect of thermal stress on offspring; rather, thermal stress had specific (and most often negative) effects on different components of offspring phenotypes and fitness proxies when experienced either by mothers or by eggs. Stressful body temperatures therefore can function in a similar manner to other types of maternal effects in reptiles; however, this maternal effect has predominantly negative consequences on offspring.

AbstractMammalian herbivory represents a complex adaptation requiring evolutionary changes across all levels of biological organization, from molecules to morphology to behavior. Explaining the evolution of such complex traits represents a major challenge in biology, as it is simultaneously muddled and enlightened by a growing awareness of the crucial role of symbiotic associations in shaping organismal adaptations. The concept of hologenomic evolution includes the partnered unit of the holobiont, the host with its microbiome, as a selection unit that may undergo adaptation. Here, we test some of the assumptions underlying the concept of hologenomic evolution using a unique experimental evolution model: lines of the bank vole (Myodes [=Clethrionomys] glareolus) selected for increased ability to cope with a low-quality herbivorous diet and unselected control lines. Results from a complex nature-nurture design, in which we combined cross-fostering between the selected and control lines with dietary treatment, showed that the herbivorous voles harbored a cecal microbiome with altered membership and structure and changed abundances of several phyla and genera regardless of the origin of their foster mothers. Although the differences were small, they were statistically significant and partially robust to changes in diet and housing conditions. Microbial characteristics also correlated with selection-related traits at the level of individual variation. Thus, the results support the hypothesis that selection on a host performance trait leads to genetic changes in the host that promote the maintenance of a beneficial microbiome. Such a result is consistent with some of the assumptions underlying the concept of hologenomic evolution.

AbstractIsland vertebrates that are small on the mainland tend to be larger and exhibit tamer behavior than their mainland conspecifics-a combined set of characteristics known as "island syndrome." Such island-specific traits are often attributed to lower predation pressure on islands than on the mainland. While the morphology and behavior of island vertebrates has received significant attention, relatively few studies have compared physiological traits between island and mainland populations. Given that hormones such as glucocorticoids are involved in responding to predation, it is reasonable to test whether island populations that have demonstrated characteristics of island syndrome also have different glucocorticoid levels than their mainland conspecifics. Here, we used a long-term museum collection of deer mice (Peromyscus maniculatus) obtained from two archipelagos and two mainland regions to test the hypothesis that island syndrome includes changes in time-averaged corticosterone levels, as measured in hair. As predicted by island syndrome, deer mice from islands were structurally larger and heavier for their given structural size than their mainland conspecifics. When we compared size-matched individuals (i.e., holding size constant), hair corticosterone levels did not differ between island and mainland mice. However, corticosterone levels scaled positively with body mass and condition across our sample population. This led to a relative increase in corticosterone levels among median-sized mice from islands relative to median-sized mice from mainland populations. We conclude that island syndrome does include effects on deer mouse stress physiology but only indirectly through the evolution of larger body size in island populations.

AbstractThe social environment can drive female birds to alter their investment in reproduction in the form of greater incubation behavior, more parental care, and greater allocation of physiological mediators to yolks. However, less is known about how social variables impact the speed at which females grow ovarian follicles in preparation for ovulation. We hypothesized that the social environment would influence how long ovarian follicles remain in rapid yolk deposition before reaching the size necessary for ovulation. For 8 d, we tested the effects of three types of social interactions: no social engagement (control), engagement with the same four females (social group 1), or engagement with the same four females plus six randomly selected roosters (social group 2). Starting on day 5 of engagement, we collected eggs and measured egg and yolk masses and yolk diameters. Then we stained the yolks with potassium dichromate to quantify the number of days the ovarian follicle spent accumulating yolk. We compared the results of the treatment groups with those of the control hens that were kept in individual laying cages throughout the study. The number of eggs laid, the yolk mass, and the yolk diameter did not differ among any of the three groups, but hens exposed to both females and males produced yolks with significantly more rings than hens in the other groups. Thus, the presence of males appeared to lengthen the time it took for ovarian follicles to reach the size needed for ovulation but did not result in larger or heavier yolks.