Morphological correlates of life-history variation: Is lizard clutch size related to the number of germinal beds in the ovary?

Clutch size varies widely in reptiles, both intraspecifically and interspecifically. The mechanisms that generate this variation have attracted detailed study, focusing primarily on ecological factors (e.g. food availability), trade-offs with other traits (e.g. offspring size), and physical constraints (e.g. maternal body shape). Does ovarian morphology, specifically the number of germinal beds from which ova are produced, also correlate with clutch size? Our review of published data on 58 lizard species reveals that clutch size is correlated with the number of germinal beds per ovary (more fecund species have more germinal beds), and that phylogenetic changes in germinal beds have been consistently associated with concurrent phylogenetic changes in fecundity. These correlations imply a causal connection: either clutch size is constrained by ovarian morphology, and/or ovarian morphology evolves to allow adaptive shifts in clutch size. The latter hypothesis is more consistent with available data.