Reproductive Effort in Anoline Lizards

Abstract

Lizards in the large neotropical genus Anolis exhibit an unusual mode of reproduction; all species lay a clutch of a single egg. In contrast, the more typical pattern for lizards is a multi—egg clutch in which the number of eggs increases with female size both inter— and intra—specifically. In Anolis low clutch number is associated with a potential for frequent ovipositions. Field rates for several tropical forest species are one egg every 1—2 wk. Thus, high rates of egg production coupled with a generation time of about 4 mo gives these species very high reproductive potentials. The evolution of low clutch number in relatively small tropical lizards has several non—exclusive explanations. One, which is specific to arboreal lizards (Anolis, geckonids, and some scincids), involves their adhesive toe pads, which facilitate climbing. Because pad area increases by the square of linear dimensions while body weight increases by the cube, pad area may put a limit both on lizard size and the weight of reproductive materials carried at any one time. A second and more general explanation involves the association between clutch size and climatic regime. Lizards in temperate and seasonal tropical habitats have a larger clutch number than do lizards of relatively equable tropical habitats. In these latter habitats short—term fluctuations in rainfall (associated with reproductive success) favor genotypes that are opportunistic reproducers, and relatively high predation intensity favors r—selected life history patterns. Anoline lizards are “extreme” examples of species living under such selective regimes.