COMPARATIVE ANALYSES OF PHYLOGENETIC EFFECTS IN THE LIFE-HISTORY PATTERNS OF IGUANID REPTILES

Numerous theoretical and empirical studies have attempted to evaluate the degree to which life-history traits represent adaptations to contemporary external selective pressures. Because life-history traits are likely to be correlated with a species' phylogenetic history, unequivocal evidence for adaptation to local environmental conditions may be recognized only after the variation in a trait attributable to phylogeny is removed. In this study, we employed three statistical methods for analyzing variation in a trait related to phylogeny. First, life-history traits were analyzed by nested ANCOVAs to evaluate the taxonomic level at which most of the variation was associated. We subsequently calculated an intraclass correlation coefficient, a measure of the differences among descendent taxa at a given taxonomic level. Finally, we employed a network autocorrelation method that maps the species' life-history attributes onto their evolutionary relationships and hence yields patterns of variation that are explained by phylogenetic interrelationships. This latter analysis explicitly tests whether life-history attributes of species within the lizard family Iguanidae are a consequence of phylogenetic effects. Significant phylogenetic autocorrelations were demonstrated for female body size, age at first reproduction, and neonate size. Because the latter two-life history traits are strongly correlated with body size, we recalculated the autocorrelations using residuals from a linear regression model that removed size-related effects from the life-history traits. With the exception of clutch size, the results show that the phylogenetic effect on the life-history traits is largely attributable to correlation with body size. Thus, residual variation in the remaining traits may in part represent species-specific responses to unique ecological selective regimes.