Why are clutch sizes more variable in some species than in others?

Abstract

In lizards, virtually invariant clutch sizes have evolved independently in at least 23 lineages in seven families. Reduced variance in clutch size may arise either as an adaptation (because females with less variable clutch sizes have higher fitness) or as an indirect by-product of selection on other life-history characteristics. Comparative data on Australian scincid lizards indicate that variance in clutch sizes is lowest among species with low mean clutch sizes, small body sizes and a low variance in body sizes of adult females. Phylogenetic analysis shows that evolutionary decreases in the variance of clutch size have accompanied decreases in mean clutch sizes and decreases in the variance of adult female body sizes. Tropical lizards may also exhibit lower variance in clutch size. These characteristics may be allometrically tied to small body size. Exceptions to the general patterns (especially, lizard species with invariant clutch sizes but large body sizes) may be due to loss of genetic variance for clutch sizes in lineages that have passed through a "bottleneck' of small body sizes and hence, low variance in clutch sizes. -from Authors