Reproductive allometry and the size-number trade-off for lizards

Fundamental to life-history theory is the assumed inverse proportionality between the number of offspring and the resource allocation per offspring. Lizards have been model organisms for empirical tests of this theory for decades; however, the expected negative relationship between clutch size and offspring size is often not detected. Here we use the approach developed by Charnov and Ernest to demonstrate that this often concealed trade-off can be made apparent in an interspecific comparison by correcting for size-dependent resource allocation. Our data set also shows a tight allometry for annual production that is consistent with life-history models for indeterminate growers. To account for nonindependence of species data we also compare the fit of nonphylogenetic and phylogenetic regression models to test for phylogenetic signal in these allometry and trade-off patterns. When combined, these results demonstrate that the offspring size/clutch size trade-off is not isolated to a single clutch but is shaped by the resource investment made over an entire year. We conclude that, across diverse lizard species, there is strong evidence for the predicted trade-off between offspring size and the annual number of eggs produced.