Maternal factors have the potential to influence the morphometrics of offspring; however, the magnitude and persistence of those influences are not well known. I investigated the extent to which maternal factors influenced offspring phenotype at the individual and population level for captive white-tailed deer (Odocoileus virginianus) originating from three distinct physiographic regions of Mississippi, USA. First, I tested whether male white-tailed deer displayed improvements in weaponry and body size after two generations of being released from nutritional restrictions. I found that improved nutrition positively influenced all morphometrics; however, we observed variation in magnitude of improvement. Antler size was most responsive to improved nutrition while body mass and skeletal structures were less responsive; potentially indicating an adaptive strategy allowing males to increase yearly reproductive success without jeopardizing lifetime reproductive success. Second, we assessed whether maternal characteristics, early life characteristics or a combination of both persistently influenced morphometrics throughout maturity. I found that late birth date positively influenced offspring body mass through three-years of age; indicating that late-born fawns over-compensated for a late start to life. I also identified an indirect silver-spoon effect as early-, heavy-born fawns were heavy juveniles. In turn, heavy juveniles were also heavy adults. Therefore, male white-tailed deer may gain reproductive opportunities by displaying one of two strategies to increase body mass. Lastly, I estimated heritability for six antler characteristics and quantified the influence of maternal factors such as parturition date and litter size on the predictability of antler size. All antler characteristics were highly heritable. Yearling antler size was a moderate predictor of antler size later in life, but accounting for maternal factors greatly improved predictability. The influence of maternal factors decreased with increasing male age suggesting that compensation for the negative influence of maternal factors may occur after an individual’s first year of life. My results suggest that although antler characteristics are highly heritable, the large influence of maternal factors on predictability indicates that use of yearling antler size as selective harvest criteria may not achieve all management goals.

Phenotypic plasticity is hypothesized to facilitate colonization by enabling rapid adaptive responses to novel environments. The colonization of land exposed ancestrally aquatic animals to new ecological and physiological challenges, including toxic waste disposal in dry environments. The repeated evolution of terrestrial breeding in frogs creates opportunities to study developmental adaptations that may facilitate aquatic-to-terrestrial transitions. My dissertation examines the regulation of nitrogen excretion by early life stages in three anuran lineages that independently evolved terrestrial development. First, to assess developmental and environmentally cued changes, I measured N-waste accumulation over development in wet and dry environments in four species, then determined ammonia LC50 values to assess their risk of toxicity on land and the adaptive role of urea excretion. Ammonia accumulates developmentally in clutches or nests of all species and I found urea from both parental and embryonic larval sources. Embryonic larval urea excretion increased in response to dry conditions, and with ammonia accumulation, in the two species with longer terrestrial periods, and their urea excretion appears adaptive, preventing exposure to potentially lethal levels of ammonia. Where early life stages did not risk ammonia toxicity, they excreted no urea. Next, I examined biochemical mechanisms of ammonia detoxification. Urea excretion involves early onset of activity of two ornithine-urea cycle enzymes, arginase and carbamoyl phosphate synthetase, with regulatory plasticity in response to ammonia level during prolonged terrestriality and experimentally high aquatic ammonia. Glutamine synthetase activity provides another mechanism to detoxify ammonia during terrestrial development. Finally, I examined effects of prolonged terrestriality and the larval foam-making activity that supports it on larval physiology, development, and metamorphosis in Leptodactylus fragilis. Even young larvae effectively produced multiple foam nests. I found high ammonia concentrations in new larval nests, high urea excretion by developmentally arrested older larvae, and faster growth of larvae in water than while constructing nests. Larval foam-making extended terrestriality affected the aquatic larval period and age at metamorphosis, while metamorph size decreased with aquatic larval period, but increased with sibship size. Overall, my results suggest that, along with high ammonia tolerance, urea synthesis facilitates terrestrial development but carries physiological costs that may favor plasticity. Dehydration and ammonia accumulation are common, linked risks of terrestrial development. Along with parental adaptations, the evolved traits and plastic responses of early life stages are critical for transitions from aquatic to terrestrial breeding.

Leaf morphology of Quercus (oak) species is highly variable and complicated confounded with phenotypic plasticity and fluctuating asymmetry (FA). However, the study of variation is mostly limited to leaf morphology. This study was extended to plasticity and FA variations in Q. alba (white oak), Q. palustris (pin oak), and Q. velutina (black oak). It was hypothesized that light exposure, individual trees, leaf position, and other leaf traits will influence variation in these species. Leaves were sampled from trees of these species and their morphological traits were measured. Absolute asymmetry of leaf width and area were determined and plasticity of each species was calculated. The data were analyzed using nested ANOVA with General Linear Model. Leaf morphology, plasticity and FA varied across the species and light exposure was the main source of variation. Individual trees and several leaf covariate traits also influenced leaf morphological and FA variations in all species.

Poikilothermic organisms experience trade-offs associated with life at different temperatures caused by incompatible physiological and biochemical demands caused by temperature extremes. As the result many such organisms exhibit acclamatory effects, adjusting their metabolism and physiology to recently experiences temperatures. One such acclamatory effect is the metabolic compensation that allows an organism to withstand increases in temperature by decelerating biological rates below Arrhenius expectations, presumably reducing energetic demand and reducing stress. Daphnia magna is resilient across a wide temperature range, and if acclimated to mildly stressful temperatures first, exhibits longer survival in lethal temperatures. Certain genotypes of Daphnia also exhibit higher acute thermal tolerance than others, indicating the presence of genetic variation and local adaptation in heat tolerance. This study examined the effect of ambient temperature (5°C-37°C) and acclimation history (2 generations at 10°C or 25°C) on the oxygen consumption rates of 8 genotypes of Daphnia (4 with high acute temperature tolerance, and 4 low). There are nonlinear decelerations of Daphnia respiratory rates across a temperature gradient when acclimated to 25°C or following short 8-hour acclimation to measurement temperatures. Furthermore, Daphnia exposed to a near-lethal temperature (35°C) with a subsequent 24-hour recovery period at their native 25°C-acclimation temperature shows no indication of respiratory damage. Genotype showed no difference in metabolic compensation, indicating the process is genetically constrained. Regulation of mitochondrial and membrane function are promising areas to further characterize the mechanism of metabolic compensation found in this study.

Poikilothermic organisms experience trade-offs by differential physiological demands generated by temperature extremes. Many such organisms exhibit acclimatory effects, adjusting their metabolism and physiology to recently experienced temperatures. One such acclimatory effect is metabolic compensation, the deceleration of biological rates below Arrhenius expectations. Daphnia magna is eurythermal, and if acclimated to mildly stressful temperatures first, survives longer in lethal temperatures. This study examined the effect of ambient temperature (5°C-37°C) and acclimation history (lifetime at 10°C or 25°C) on the oxygen consumption rates of 8 genotypes of Daphnia with high or low acute temperature tolerance. There were decelerations of respiratory rates across a temperature gradient when acclimated to 25°C or following short 8- hour acclimation to measurement temperatures. Daphnia exposed to a near-lethal temperature (35°C) with a 24-hour recovery period at 25°C-acclimation temperature showed no difference in respiratory control compared to unexposed 25°C-acclimated Daphnia. Genotypes showed no difference in potential compensatory ability.

Phenotypic plasticity is the ability of the genotype to express alternative phenotypes in response to different environmental conditions and this is considered to be an adaptation in which a species can survive and persist in a rapidly changing environment. Some grasshoppers and locusts are capable of expressing an extreme form of density-dependent phenotypic plasticity, known as locust phase polyphenism. At low population density, the individuals typically have a cryptic coloration as nymphs, are less active, and only seek out conspecifics for reproductive purposes. At high density, however, they develop a drastically different phenotype in which they have a conspicuous coloration, are much more active, and tend to stay together in large groups. The American Birdwing grasshopper, Schistocerca americana, is a non-swarming species related to the desert locust, S. gregaria, which shows density-dependent phenotypic plasticity in behavior, color, and morphology. In this thesis, I have identified the duration of crowding necessary for a 6th instar S. americana reared in the isolated condition to express the typical crowded behavior. The behavior changed after just one hour of crowding and the effect of crowding diminished after 48 hours to near-complete isolated behavior. In reverse, the crowded condition was isolated, but behavior did not significantly change over time. Gene expression of the following three genes suspected of having a role in behavior change were investigated based on studies of S. gregaria: protein kinase A (PKA), L-Tryptophan-5-monooxygenase (T-5), and Aromatic L-amino acid decarboxylase (Decarb). T-5 was up-regulated in the long-term isolated condition compared to the long-term crowded condition. T-5 and Decarb were up-regulated in isolated individuals that were crowded for 10 hours compared to the long-term isolated condition. This study represents a novel contribution in the study of phenotypic plasticity as it establishes the time course of behavioral and molecular plasticity in a non-swarming grasshopper for the first time.

No description available.

High altitude is one of the most extreme environments experienced by terrestrial mammals due to both low ambient temperatures and oxygen availability. Deer mice native to high altitude have a greater thermogenic capacity in hypoxia compared to a lowland population, likely as a consequence of both genetic adaptations and phenotypic plasticity. To understand the adaptive variation in phenotypic plasticity, F1 generation lab-reared mice were acclimated to chronic warm-hypoxia, cold-normoxia, and cold-hypoxia. Acclimation led to equal increases in thermogenic capacity in hypoxia for all stressors in high altitude deer mice. Low altitude mice also increased their thermogenic capacity after acclimation, with a distinct increase after acclimation to cold-hypoxia. The thermogenic capabilities of the high and low altitude mice tested in hypoxia were equal, suggesting that both populations of mice had reached a “metabolic ceiling”. Basal metabolic rate increased after acclimation to cold and cold-hypoxia. Nonshivering thermogenesis was not affected by acclimation or altitude ancestry. Shivering thermogenesis contributed 70 to 80 % of total heat produced during VO2summit across all acclimations, and in both populations. VO2summit in hypoxia was supported by lipids in deer mice even though carbohydrates would provide an oxygen saving advantage. Also, rates of lipid oxidation increased after acclimation to cold, and cold combined with hypoxia in the high altitude population. Together these findings suggest that the increased thermogenic capacity of the high altitude wild mice is based both on differences in phenotypic plasticity, and on differences in genotype from the low altitude mice. Adult phenotypic plasticity is pivotal in the thermogenic capabilities of both populations, and it is likely that developmental plasticity also plays an important role. / Thesis / Master of Science (MSc)

Phenotypic plasticity and local adaptation via genetic change are two major mechanisms of response to dynamic environmental conditions. These mechanisms are not mutually exclusive, since genetic change can establish similar phenotypes to plasticity. This connection between both mechanisms raises the question of how much of the variation observed between species or populations is plastic and how much of it is genetic. In this study, we used a structured population of fire salamanders (Salamandra salamandra), in which two subpopulations differ in terms of physiology, genetics, mate-, and habitat preferences. Our goal was to identify candidate genes for differential habitat adaptation in this system, and to explore the degree of plasticity compared to local adaptation. We therefore performed a reciprocal transfer experiment of stream- and pond-originated salamander larvae and analyzed changes in morphology and transcriptomic profile (using species-specific microarrays). We observed that stream- and pond-originated individuals diverge in morphology and gene expression. For instance, pond-originated larvae have larger gills, likely to cope with oxygen-poor ponds. When transferred to streams, pond-originated larvae showed a high degree of plasticity, resembling the morphology and gene expression of stream-originated larvae (reversion); however the same was not found for stream-originated larvae when transferred to ponds, where the expression of genes related to reduction-oxidation processes was increased, possibly to cope with environmental stress. The lack of symmetrical responses between transplanted animals highlights the fact that the adaptations are not fully plastic and that some level of local adaptation has already occurred in this population. This study illuminates the process by which phenotypic plasticity allows local adaptation to new environments and its potential role in the pathway of incipient speciation.

No description available.