THE EFFECTS OF REPRODUCTIVE MODE AND CLIMATE ON REPRODUCTIVE SUCCESS IN THE AUSTRALIAN LIZARD, LERISTA-BOUGAINVILLII

The most widely accepted hypothesis invokes cold climates as the selec tive force responsible for the evolution of viviparity in reptiles. Th e ''cold climate'' hypothesis proposes that viviparity is adaptive in cold climates because developing embryos experience warmer temperature s in utero (through maternal thermoregulation) than they would in a ne st. Most authors have assumed that these warmer incubation temperature s provide an advantage by protecting embryos from lethally low tempera tures or by allowing them to hatch before the onset of winter. Thus, t he ''cold climate'' hypothesis (at least in its traditional form) purp orts that viviparity evolves in cold climates because females that ret ain their developing offspring in utero will have greater reproductive success than females that lay their eggs in a nest. To test this hypo thesis, I conducted a reciprocal transplant experiment using the repro ductively bimodal Australian lizard, Lerista bougainvillii. Gravid ovi parous and viviparous females were transplanted into field enclosures in both a ''hot'' and a ''cold'' climate, to monitor the effects of cl imate on their reproductive success. The live-bearers had higher repro ductive success than the egg-layers in both climates, but reproductive success did not differ between the hot and cold climates within eithe r reproductive mode. The viviparous lizards were more successful at pr oducing offspring, regardless of climatic conditions. Thus, viviparity provided an advantage (in terms of embryo and/or neonate survival) un der the conditions of the experiment, but this advantage was not restr icted to cold environments.