Identification of mechanisms that promote variation in life history traits is critical to understand the evolution of divergent reproductive strategies. Here we compiled a large life-history dataset (674 lizard populations, representing 297 species from 263 sites globally) to test a number of hypotheses regarding the evolution of life history traits in lizards. We found significant phylogenetic signal in most life history traits, although phylogenetic signal was not particularly high. Climatic variables influenced the evolution of many traits, with clutch frequency being positively related to precipitation and clutches of tropical lizards being smaller than those of temperate species. This result supports the hypothesis that in tropical and less seasonal climates, many lizards tend to reproduce repeatedly through the season producing smaller clutches during each reproductive episode. Our analysis also supported the hypothesis that viviparity has evolved in lizards as a response to cooler climates. Finally, we also found that variation in trait values explained by clade membership is unevenly distributed among lizard clades with basal clades and a few younger clades showing most variation. Our global analyses are largely consistent with life history theory and previous results based on smaller and scattered datasets, suggesting that these patterns are remarkably consistent across geographic and taxonomic scales.
Life history data of lizards of the world
Life is defined by a capacity for reproduction, yet the ways in which animals reproduce vary tremendously among species. Reproductive life histories are complex phenomena influenced by a variety of factors, such as physical condition of individuals, food supply, bauplan, and phylogenetic history, which are often correlated. Understanding life histories is crucial in evolutionary ecology because they represent different strategies that evolved to maximize individual fitness. Variation in life history can be attributed to both historical (= phylogenetic) and non-historical (= environmental) causes. We compiled a large dataset on lizard life history variables. Our dataset consists of life history data for 737 lizard populations, representing 337 species in 33 families from 280 study sites globally. About 64% of these data were collected directly by the authors. Regarding data collected by authors, we sexed lizards by dissection and direct examination of gonads. Females were considered reproductive if vitellogenic follicles or oviductal eggs were present. We regarded the simultaneous presence of enlarged vitellogenic follicles and either oviductal eggs or corpora lutea as evidence for the sequential production of more than one clutch of eggs per year. We considered clutch size as the number of vitellogenic follicles or oviductal eggs in mature females. For each population, we recorded the following variables, if available: adult female mass (g), adult female SVL (mm), female SVL at maturity (based on SVL of smallest reproductive female), offspring SVL (based on hatchling size or smallest individual in population), clutch or litter size (number of offspring per clutch or litter for all reproductive females in the population), total number of clutches or litters per year, clutch frequency (single- or multiple-brooded), relative clutch or litter mass [total volume of eggs or embryos (cc) divided by adult female mass (g)], reproductive mode (oviparous or viviparous), foraging mode (sit-and-wait or active), distribution (tropical or temperate), and preferred habitat type (aquatic, arboreal, bromelicolous, fossorial, psammophilous, saxicolous, semi-arboreal, or terrestrial). These data are valuable to test various life history hypotheses, including phylogenetic design constraints and effects of ecology and climate on reproductive tactics.
Data (revised).txt