Matheson, Elinor J.

Female painted turtles may increase their fitness either by increasing the success of their offspring within a single reproductive season, or by increasing the number of reproductive seasons in which they can participate. Painted turtle nest-sites can be described in relation to specific microhabitat characteristics that, because of their effect on soil microclimate, may influence hatching success and/or over-winter success of hatchlings. Female painted turtles selected nest-sites based on canopy cover, understory vegetation, slope angle and aspect. Increased hatching success was associated with decreased organic content, which may serve as a surrogate for little or no vegetation cover and canopy. Turtle-selected nests had slightly higher hatching success than randomly located nests, suggesting that turtles choose nest-sites that increase offspring survival. No relationship was found between over-winter success and micro habitat, possibly due to the buffering effects of deep snow cover. The two methods of increasing fitness may not be mutually exclusive.

Sex ratio theory suggests that the strength of intersexual selection will increase as a population more male-biased; reflecting increased selectivity in mate choice. Populations of pond turtle have varying adult sex ratios, in painted turtles (Chrysemys picta), reported sex ratios range from female biased (1:3) to male biased (3:1). I investigated the effect of sex ratio on male reproductive success (quantified as “fertilization success”) in painted turtles. I examined the mating system of painted turtles in a female-biased population using microsatellite paternity analysis, relating variation in male fertilization success to male phenotype and offspring survival, employed ex situ behavioural observation to clarify the mechanism behind the variation in male fertilization success and used agentbased modeling to simulate the effects of changing sex ratio, population density and proportions of male phenotype on male fertilization success. Small males contributed sperm to a greater number of clutches than did larger males, but were not more likely to reproduce in a season than larger males. There was no offspring fitness advantage related to male body size and no relationship between male claw length and fertilization success. Large male painted turtles courted at a higher frequency than small males. I found no relationship between male courtship behavior and claw length. Females showed no preference for males of any phenotype. Agent-based simulations were based on the distribution of best fit from the observed data; an amalgam of two Poisson distributions, each with its own probability of success and proportional representation in the final distribution. Increased female sex ratio bias, increased population density and increased proportions of “more successful” males all increased the mean and variance of male fertilization success, based on increased encounter rate among turtles. Small and large male painted turtles enjoy different fertilization success. It is uncertain whether this difference is based on active female choice, cryptic female choice, sperm competition or a combination of factors. Sex ratio simulations predict the opposite result as that predicted by sex ratio theory. These contrary results should be compared to simulations manipulating choosiness and field data from painted turtle populations to clarify mechanisms influencing male reproductive success.

We tested the hypothesis that female midland painted turtles (Chrysemys picta marginata Agassiz, 1857) provide significant parental care to their offspring through their choice of nest site. Painted turtle nest sites can be described in relation to specific microhabitat characteristics that, because of their effects on soil microclimate, may influence survival to hatch. We created models of the relationships between nest-site microhabitat and nest-site selection and between nest-site microhabitat and survival to hatch, and judged the fit of the models using Akaike’s information criterion corrected for small sample sizes. Female painted turtles selected nest sites with little canopy cover, little understory vegetation, and a southwestern slope aspect. Increased survival to hatch was associated with decreased organic content, which may serve as a surrogate for little or no vegetation or canopy cover. Nests in sites selected by turtles had slightly higher survival to hatch rates than nests in randomly chosen sites, suggesting that turtles may choose nest sites which increase offspring survival. Selection of nest sites may constitute significant parental investment and should be considered in studies of turtle life history. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that handling turtle eggs decreases embryo survival in a well-studied population of midland painted turtle (Chrysemys picta marginata) by comparing embryo survival in handled and nonhandled natural nests during 3 nesting seasons. All nests were protected from mammalian predators. Upon excavation of the nests in the following spring, we found no differences in survival between the 2 treatments, suggesting that the benefits in knowledge gained from nest excavation far outweigh the possibility of a small increase in mortality that could arise from handling the eggs. [ABSTRACT FROM AUTHOR]