Reproduction of two species of freshwater turtle, Chelodina rugosa and Elseya dentata, from the wet-dry tropics of northern Australia

Chelodina rugosa is a fast-growing, carnivorous turtle that occupies season ally ephemeral habitats, whereas Elseya dentata is relatively slow-growing, largely herbivorous and confined to permanent water. Ovarian cycles follow ed an annual cycle of enlargement beginning in December (E. dentata) and Ja nuary (C. rugosa), followed by ovulation and then follicular regression. Ne sting season was determined from presence of gravid females, and for C. rug osa spans some 8 months from the late wet season until mid dry season, duri ng which the turtle lays multiple clutches of eggs in underwater nests. Nes ting may continue for longer when waterholes dry later following prolonged wet season rains. Nesting by E. dentata also begins in the late wet season but is complete by May and only one clutch is laid. Females of both species reproduce each year and clutch size and mass are related to female size. A nnual spermatogenic cycles are similar in timing to those reported for temp erate-zone chelids but would be classified as pre-nuptial because spermatog enesis begins before breeding. Genial proliferation begins at the start of the wet season and spermiation coincides with the onset of ovulation. Matin g was not observed but in C. rugosa probably occurs during December and Jan uary soon after turtles emerge from aestivation. Post-mating storage of spe rm in the epididymes did not occur in E. denatata but did appear to occur i n some C. rugosa. The high reproductive output and extended nesting season of C. rugosa reflects its occupation of highly productive but unpredictable habitats and a reproductive strategy which ensures that some hatchlings me et optimal conditions for emergence. In contrast, the comparatively low fec undity and short nesting season of E. dentata, despite year-round warm temp eratures and access to permanent water, suggests that its reproductive outp ut may be energetically limited by a largely herbivorous protein-poor diet.