Costs of reproduction in conspecific oviparous and viviparous lizards, Lerista bougainvillii

For iteroparous organisms, life history theory predicts a trade-off between current reproductive expenditure and probable future reproductive output. A high current investment in reproduction may entail 'costs', by decreasing an organism's chances of surviving to reproduce again and/or decreasing its future fecundity. Both of these 'costs of reproduction' may be present in squamate reptiles, and because viviparous animals carry their offspring for longer, they may experience greater costs than do similar oviparous taxa. We examined the costs of reproduction in both oviparous and viviparous forms of the lizard, Lerista bougainvillii, to address three questions: (1) Are any costs of reproduction incurred by reproducing female L. bougainvillii? (2) If so, what 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 the intuitively predicted costs, but many showed different, and sometimes surprising, patterns. For example, despite being burdened with their offspring, gravid females (both egg-layers and live-bearers) had faster running speeds than their non-reproductive counterparts. This counter-intuitive result may be due to a shift in escape strategy, to less frequent stopping and turning, by reproductive lizards. Contrary to prediction, the costs of reproduction do not appear to be significantly greater for viviparous L. bougainvillii than for their oviparous conspecifics. Live-bearers have larger body sizes, which may offset the predicted 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 taxa, behavioral shifts by reproductive individuals, and seasonal shifts in behavior or performance can all make it difficult to determine what 'costs' are present in different groups of organisms. Given this complexity, attempts to model the costs of reproduction on the basis of any single index (other than lifetime reproductive success) will likely be applicable only to small groups of ecologically similar taxa.