Search

During terrestrial nesting forays, north-temperate freshwater turtles may experience a range of environmental temperatures that could cause overheating or constrain movement if temperatures are too high or low. Yet, we have very little understanding of how body temperature (Tb) varies in freshwater turtles during various nesting foray activities. We studied Tb variation in Chrysemys picta marginata from a small marsh in northern Michigan, 2003-2004. Three individuals left the marsh, nested, and returned to the marsh in a single day; whereas, 5 others remained on land for up to 3 days, mostly immobile under leaf litter. While on land, Tb of turtles and air temperature (Ta) showed parallel, diel oscillations. Mean Tb of mobile turtles exceeded prevailing Ta values but was similar to Tb recorded for those same individuals while aquatic 1 week before and after the nesting foray. Therefore, active nesting turtles on forays may have maintained suitable Tb values by use of sun or shade. During the nesting process, Tb decreased from 23.5°C to 20.0°C. Turtles that entered terrestrial refugia after evening nesting had Tb values similar to those while mobile, often at times when the evening sky illuminated the nesting areas. Therefore, low light levels, which could limit navigation, and Tb values, which could impede movements, did not directly cause turtles to seek terrestrial refugia after nesting. Instead, we suggest that impending low environmental temperatures, waning light levels that would eventually impair navigation abilities, and, ultimately, the risk of predation while returning to the marsh caused turtles to seek terrestrial refugia. [ABSTRACT FROM AUTHOR]

Reproductive characteristics and the age-body size relationship of female Chrysemys picta marginata were studied at Miller's Marsh on Beaver Island, Michigan. Environmental influences on reproduction were evident in that turtles nested relatively early when the previous spring (April and May) temperatures were relatively warm. Clutch wet mass (CWM), clutch size (CS), and egg wet mass (EWM) were all correlated with maternal carapace length (CL). Over six activity seasons, significant annual variations in EWM and CS occurred, but these variations were not related to temperature or precipitation patterns of the current or previous year. Therefore, it seems unlikely that annual variation in EWM represents proximate variation or adaptive phenotypic plasticity where offspring size might be adjusted to meet predictable temporal changes in offspring growing and survival conditions. Annual variation in CS was mainly caused by slight variations in mean maternal CL. When compared to previously published studies on C. p. marg/nata populations from southern Michigan, Miller's Marsh turtles were larger in CL, produced large EWM and small CS relative to maternal body size, and apparently delayed sexual maturation, which would have resulted in relatively large maternal CL (and therefore EWM and CS) at primiparity and thereafter. [ABSTRACT FROM AUTHOR]