Reproductive Ecology of the Painted Turtle (Chrysemys picta) in the Nebraska Sandhills and across Its Range

Abstract

Female painted turtles in western Nebraska matured after 5-6 activity seasons at 160-165 mm carapace length. Annual adult survivorship was at least 91.5%, and some females apparently survive beyond 30 yr of age. Nesting was recorded from 19 May to 17 July, and its onset was inversely related to March-May temperatures. Internesting interval averaged 16.4 days and decreased through the nesting season. Females usually produced two clutches per season, but many produced three clutches, and two may have produced four clutches. Average annual clutch frequency was estimated at 2.78 per female. Egg size was correlated with female size. When standardized for body size, egg size was negatively correlated with body size and clutch size and varied across estimated clutch number (early season clutches having larger, more elongate eggs than later ones) but not among years. Egg size was not constrained by pelvic canal width. Clutch size averaged 13.9, was positively correlated with body size, and varied across estimated clutch number (later clutches being smaller than earlier clutches) as well as across years. Clutch mass increased with body size but remained constant as a proportion of spent female body mass (=RCM). RCM varied across clutch number within years (higher in earlier clutches) and across years (with a trend for higher RCM in years following a warmer Oct.). Actual annual clutch output in triple-nesting females averaged 42 eggs or 30.9% of spent female body mass. Across populations of painted turtles, body size is positively correlated with latitude and elevation and negatively correlated with average frost-free days and mean annual temperature. Clutch frequency remains one of the most elusive traits but seems to be inversely related to latitude and age at maturity and positively related to frost-free days. Both egg size and clutch size tend to vary with body size within and among populations, with clutch size varying the most. Presumably because of its correlation with body size, clutch size also varied with latitude, elevation, the inverse of frost-free days, and the inverse of mean annual temperature. Populations of small turtles (at lower latitudes and/or warmer climates) apparently produce the largest eggs possible within the constraints of their pelvic canal diameter, whereas no such constraint exists for larger-bodied populations at high latitudes. Selection is probably more intense on egg size than clutch size, and clutch size seems to have a much greater environmental component.