The Herpetological Journal

pp. 346-360

Authors: J. Jaime Zúñiga-Vega, Jesualdo A. Fuentes-G., J. Gastón Zamora-Abrego, Uri O. García-
Vázquez, Adrián Nieto-Montes de Oca & Emília P. Martins

Abstract: Life histories are directly related to fitness and, hence, are the focus of strong selective pressures. However, different life-history
traits may evolve at different paces and may respond differentially to particular selective pressures. We examined patterns
of evolutionary change in the following life-history traits of xenosaurid lizards: size at maturity, average size of adult females,
litter size, neonate size, and relative litter mass. We used a phylogenetic hypothesis of the genus Xenosaurus and different
phylogenetic comparative methods to search for evolutionary relationships between traits as well as to estimate ancestral
states, rates of evolution, and the amount of phylogenetic signal on each trait. In addition, we searched for differences in
these life-history traits among the different environments where these lizards inhabit (cloud forest, tropical forest, oak-pine
forest, and xeric scrub). We found an evolutionary relationship between size at maturity and average adult size, with larger
species maturing at larger sizes. We also found an evolutionary trade-off between litter size and neonate size. Ancestral state
reconstructions revealed differences among traits in the relative timing of diversification. Litter size and neonate size began
diversification early in the history of the genus. In contrast, size at maturity and relative litter mass remained phenotypically
invariant for a long time period before diverging into distinct phenotypic values. Litter size exhibited significant phylogenetic
signal because the diversification history of this trait has tracked the phylogeny closely. The observed variation among species
in neonate size also showed some trace of the phylogenetic relationships. The remaining three traits diverged throughout time
without a clear phylogenetic pattern. In addition, litter size and relative litter mass exhibited the highest evolutionary rates
whereas average adult size and neonate size exhibited the lowest rates. Litter size was the only trait that differed significantly
among environments, with largest litters in cloud forests. We discuss potential hypotheses to explain the observed differences
among life-history traits in the tempo and mode of evolution.

Keywords: ancestral state reconstructions, evolutionary rates, life histories, phylogenetic signal, trade-offs, xenosaurid lizards