Reproductive variation of the lizard Xenosaurus platyceps: comparing two populations of contrasting environments

We studied litter size, size at birth, and relative litter mass (RLM) in two populations of the crevice-dwelling lizard Xenosaurus platyceps: one located in a low-altitude tropical forest; and the other in a high-altitude temperate oak forest. We found a significant relationship between female size and litter size. Females from the temperate site produced significantly larger litters in comparison with those from the tropical site after adjusting for female size. Neither a relationship between female size and offspring size nor a difference between populations in offspring size was detected, which suggests that this trait could be either constrained or optimized. RLM showed the same pattern as litter size: Larger females exhibited greater RLM, and this trait showed significantly larger values in the temperate locality. This pattern is explained by evidence that females in the temperate population are producing more young of similar size than those produced by their tropical counterparts. We did not find significant interannual variation in any of the reproductive traits studied. We suggest reciprocal transplant or common garden experiments to determine the genetic and proximal causes of the observed intraspecific variation