The evolution of oviparity in squamate reptiles: An adaptationist perspective

摘要: Phylogenetically based analyses can suggest directions of evolutionary transitions, on parsimony, but never provide unambiguous answers. To clarify the relative frequency phylogenetic shifts from oviparity to viviparity versus reverse, we need additional sources evidence. Adaptationist thinking (i.e., consideration selective forces) has revealed a great deal about transition viviparity, rarely been employed consider reverse transition. An evaluation costs and benefits identifies major obstacles re-evolution oviparity. For example, even modest decrease in degree embryogenesis completed utero shift back toward "normal" oviparity) requires mother find suitable nest-site (often, risky endeavor), minor duration uterine retention eggs may not substantially reduce maternal (because many those are minimized by behavioral adaptations pregnancy). In climates, small would allow female produce second clutch within same season; thus, fecundity disadvantage viviparity. Life-history theory thus suggests an asymmetry fitness consequences intermediate stages between That facilitates "forward" (based thermally driven offspring viability) opposes "reverse" lower heavily burdened females that seek nest-sites). These factors should constrain specific conditions (e.g., where abundant nest-sites available female's usual home range, rather than requiring extensive migration).