COSTS OF REPRODUCTION IN CONSPECIFIC OVIPAROUS AND VIVIPAROUS LIZARDS, LERISTA-BOUGAINVILLII

For iteroparous organisms, life history theory predicts a trade-off be tween current reproductive expenditure and probable future reproductiv e output. A high current investment in reproduction may entail ''costs '', by decreasing an organism's chances of surviving to reproduce agai n and/or decreasing its future fecundity. Both of these ''costs of rep roduction'' may be present in squamate reptiles, and because viviparou s animals carry their offspring for longer, they may experience greate r costs than do similar oviparous taxa. We examined the costs of repro duction in both oviparous and viviparous forms of the lizard, Lerista bougainvillii, to address three questions: (1) Are any costs of reprod uction incurred by reproducing female L. bougainvillii? (2) If so, wha t is the nature of these costs? and (3) Are the costs greater for live -bearers than for egg-layers? Some of the variables measured showed th e intuitively predicted costs, but many showed different, and sometime s surprising, patterns. For example, despite being burdened with their offspring, gravid females (both egg-layers and live-bearers) had fast er running speeds than their non-reproductive counterparts. This count er-intuitive result may be due to a shift in escape strategy, to less frequent stopping and turning, by reproductive lizards. Contrary to pr ediction, the costs of reproduction do not appear to be significantly greater for viviparous L, bougainvillii than for their oviparous consp ecifics. Live-bearers have larger body sizes, which may offset the pre dicted increase in costs associated with the evolution of viviparity. Thus, while straightforward in theory, actually measuring the costs of reproduction is a very complex task. Ecological differences between t axa, behavioral shifts by reproductive individuals, and seasonal shift s in behavior or performance can all make it difficult to determine wh at ''costs'' are present in different groups of organisms. Given this complexity, attempts to model the costs of reproduction on the basis o f any single index (other than lifetime reproductive success) will lik ely be applicable only to small groups of ecologically similar taxa.