more about turtles

Unlike many birds and mammals, turtles are not known to form pair bonds or cohesive social groups, and neither sex provides parental care beyond nesting (Shine 1988; but see Iverson 1990). A male's contribution to his offspring is therefore limited to fertilization and indirect genetic effects. With respect to a female's choice of mate, any trade-off between social status or territory quality on the one hand, and male genetic quality on the other, is presumably much reduced. Thus instead of asking under what circumstances a female may seek extrapair copulations (as has been done in many bird species; e.g., Double and Cockburn 2000; Kempenaers et al. 1992), questions about turtle mating systems revolve around the number or quality of a female's mates, the timing of her remating decisions, her capacity for sperm storage (Galbraith et al. 1993; Kaufmann 1992), and the fitness ramifications of a long reproductive life (Gibbons 1987). Female turtles are unlikely to receive many of the proposed direct benefits of multiple mating (e.g., parental care, nuptial gifts), so indirect benefits (e.g., genetic contributions) presumably play a more singular role in mate choice and paternity distributions in turtles than has been found in most bird, fish, and mammal species studied (Andersson 1994; Birkhead 1995).

The aims of this review are to discuss aspects of turtle biology relevant to field-based studies of sperm storage and reproduction; review the available literature on the genetic mating systems of turtles; consider hypotheses for the evolutionary benefits of multiple mating and sperm storage in this taxon; and highlight future research directions that might take advantage of the unique opportunities afforded by the reproductive biology of turtles. This is not intended to be a comprehensive review of sperm storage and competition, but a focused treatment on the special features of turtles relevant to paternity analysis and mating system studies. For a more comprehensive treatment of sperm competition in reptiles, see Olsson and Madsen (1998).