Reproductive Strategies of Sympatric Freshwater Emydid Turtles in Northern Peninsular Florida

Abstract

Florida has the highest species diversity of emydid turtles in the New World. Four relatively large, closely related species (Pseudemys floridana, P. nelson, Trachemys scripta, and Deirochelys reticularia) occur sympatrically in lentic habitats in northern peninsular Florida, although two (P. nelsoni and T. scripta) are essentially parapatric. Fossils of Pleistocene age or older document a lengthy period of coexistence for these species in Florida. The basic reproductive strategy of all four species involves four features: (1) multiple, large clutches; (2) relatively small eggs; (3) delayed maturity; and (4) extended longevity. This same basic strategy is found in most smaller, previously studied temperate turtles. In Florida, however, the long growing season not only permits more clutches (four to six) per year but also allows for larger body sizes and consequently larger clutches than are characteristic of most temperate species. For each of the two largest species, (Pseudemys floridana and P. nelsoni) clutch size is more highly correlated with body mass or volume than with plastral length. Major temporal differences in reproduction exist among the species. Pseudemys nelsoni and Trachemys scripta nest during spring and/or summer. In contrast, P. floridana and Deirochelys reticularia begin nesting in September or October and continue through March (D. reticularia) or June (P. floridana). The two patterns are contrasted as "summer" and "winter"- nesting patterns. Field temperatures permit immediate and continuous development of eggs of summer-nesting species following oviposition. Eggs of winter-nesting species, on the other hand, become dormant below 20°C and initiate or resume development when soil temperatures exceed this in the spring. Laboratory incubation experiments suggest that innate developmental differences may exist between eggs representing each of the two nesting patterns. Hatchlings of all four Florida species, unlike most northern species, apparently do not overwinter in the nests but instead emerge during the summer rainy season. Summer-nesting is viewed as the conservative retention of a reproductive pattern typical of most north temperate reptiles. Large-bodied, fecund summer-nesting species may benefit from predator satiation. Hypothetical advantages of winter-nesting include rapid hatchling growth, reduced nest predation, and interspecific competitive advantage.