Evolutionary theory predicts that when phenotypic variation arises during development that differently influences the fitness of each sex, selection should favor the maternal ability to match offspring phenotype to the sex that incurs a fitness benefit from that phenotype. In reptiles with temperature-dependent sex determination, the temperatures experienced during incubation can influence numerous phenotypic parameters, including sex. To mimic more naturalistic conditions, this experiment examined how variation in temperature fluctuations affects offspring sex as well as a suite of phenotypic parameters having putative fitness consequences in the Northern Painted Turtle ( Chrysemys picta (Schneider, 1783)). We also characterized variation in natural nest temperatures, including the daily temperature range, related to the vegetation cover surrounding the nest. We found that temperature fluctuations did not affect hatchling morphology, immune response, or behavior, but did significantly affect offspring sex ratios. Thermal profiles of natural nests were related to the amount of surrounding vegetation. Results suggest that nest-site choice by females could influence the sex of their offspring, but we found no evidence that variation in temperature fluctuations adaptively matches offspring sex and phenotype.
Phenotypic variation is a fundamental component of the process of evolution and understanding the factors that create this variation is critical to investigations of this process. We test the hypothesis that phenotypic variation created under natural incubation conditions will differ from that created under constant laboratory conditions in a reptile species with temperature-dependent sex determination (TSD), the red-eared slider turtle (Trachemys scripta). Using a split clutch design, we demonstrate that offspring morphology, behavior, and sex differed between hatchlings incubated in the field and those from the laboratory, but immune response did not. The interactions between different phenotypic parameters will ultimately determine how natural selection acts upon offspring, and consequently our data suggest that offspring developing under these differing conditions should have different fitnesses. The relationship between offspring sex and phenotype serves as the theoretical foundation on which most investigations into the evolution of TSD are built. Thus, it may be necessary to use natural incubation conditions to accurately examine how offspring sex relates to other phenotypic parameters if we are to understand the evolution of this sex determining mechanism.
How and when turtles first acquire gut microflora is largely speculative. In this study, the eggshell and hatching process were evaluated for their role in the initial acquisition of Salmonella, by red-eared slider turtles (Trachemys scripta elegans). First, we examined whether the eggshell is a viable substrate for bacterial persistence during incubation, and if internal egg components (i.e., albumen, yolk, and embryo) have detectable bacterial loads. Second, we experimentally manipulated Salmonella by treating eggs with combinations of Salmonella and gentamicin, an effective Gram-negative antibiotic. We found that the eggshell is a viable substrate for maintaining bacteria, as well as an effective barrier to Salmonella transmission as internal egg components were largely bacteria-free. Water samples collected 18 days post-hatch from individuals that were experimentally inoculated with a topical application of Salmonella as eggs had a higher prevalence of Salmonella than those from eggs inoculated with Salmonella but topically treated with gentamicin prior to hatching, control eggs, and eggs only treated with gentamicin, but by day 35 post-hatch there were no detectable differences among the treatment groups. Though it can also act as a barrier that prevents the bacteria from infecting the embryo prior to hatching these findings suggest that the eggshell is a likely source of Salmonella infection in turtle hatchlings.
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