social structure and behavior

Although turtles typically do not display pair bonds or family group affiliations, social organizations exist in some species. For example, dominance hierarchies have been described in gopher tortoises (Gopherus agassizii; McCrae et al. 1981), and individuals of this species as well as snapping turtles (Chelydra serpentina) also defend home ranges that may be important in mate access or control (Galbraith et al. 1987, 1993; McCrae et al. 1981). Home ranges may not be exclusively guarded, but males occupying overlapping areas often establish dominance through fights (Galbraith et al. 1987; McCrae et al. 1981).

In wood turtles (Clemmys insculpta), male dominance hierarchies also exist, and male rank has been shown to affect reproductive success. Males who consistently win fights against other (usually smaller) males enjoy a higher dominance rank and greater access to extended copulations with females (Kaufmann 1992). Based on DNA paternity data, high-ranking males were found to father a significantly greater number of offspring than those of lower rank (Galbraith 1991).

Movement and dispersal are other important behaviors that influence a species' mating system in a given population. In some freshwater turtles, gender differences exist in dispersal tendencies or in total distance traveled per year (Morreale et al. 1984). In addition, the two sexes may differ in seasonal activity levels, with females more active in the nesting seasons of late spring or early summer (in north temperate regions), and males more active in the fall (Gibbons 1968; MacCulloch and Secoy 1983; Pearse 1923). These movements have been interpreted as corresponding to peaks in female nesting and male mate-searching activities, respectively (MacCulloch and Secoy 1983).

Marine turtles present an entirely different life history, with intervals of several years between breeding events, and long distances traveled between communal feeding and nesting grounds (Kuchling 1999; Limpus et al. 1994). Little is known about the behaviors of marine turtles at sea, but both male and female green turtles (Chelonia mydas) have been observed mating more than once over a several-day period, immediately prior to the nesting season (Booth and Peters 1972). Such multiple mating raises questions about mate choice, sperm competition, and genetic paternity of the offspring. Thus, as has also been found for some lizards (Bull et al. 1998), social aspects of turtle biology may prove more important than previously thought for mating system patterns