Abstract
We compared adult survivorships in two populations of the lizard Anolis mariarum with different mean and asymptotic body sizes to examine one prediction of age-specific mortality theory; that populations that experience higher adult mortality should exhibit earlier maturation and smaller adult body sizes. We used a maximum likelihood approach to evaluate different survivorship models and model-averaging to estimate survivorship and capture probabilities for each site and sex. Relative tail length did not affect survivorship rates of adults in these two populations, but body size was related to survivorship, with the largest individuals at the time of first capture having lower survivorship rates, so body size was included as a covariate in some of the models examined. Analyses revealed that males at both sites had higher survivorships than females, but there were no differences among the sites in survivorship rates or capture probabilities for either sex. The differences in body sizes documented for these sites still could represent life history adaptations to differences among the sites in mortality rates in the egg or juvenile stages of the life cycle, or may represent a case of phenotypic plasticity to differing environmental conditions, but they appear not to be related to differences in adult survivorships. The estimates of annual survivorships (11.7% to 21.2%) were high for a small, mainland Anolis, and this is the first report of survivorships of male anoles exceeding those of females.
Highlights
There is growing evidence that multilocus quantitative phenotypic traits show greater inter-populational divergence than do neutral molecular markers (Merilä & Crnokrak, 2001; Reed & Frankham, 2001), implying that natural selection on phenotypic traits in natural populations is pervasive, and that it is directional, leading each population to adapt to its own local conditions (i.e., Baker, 1992; Waldmann & Andersson, 1998)
Their study found that all traits differed significantly among the sites in both sexes, but attempts to correlate these differences with two environmental variables indicated that only body size was related to precipitation levels at each site, implying that body size had been the target of past natural selection (Bock, et al, 2009)
We report here estimates of survivorships obtained from maximum likelihood analyses of the capture-mark-recapture data sets for each site
Summary
There is growing evidence that multilocus quantitative phenotypic traits show greater inter-populational divergence than do neutral molecular markers (Merilä & Crnokrak, 2001; Reed & Frankham, 2001), implying that natural selection on phenotypic traits in natural populations is pervasive, and that it is directional (vs. stabilizing), leading each population to adapt to its own local conditions (i.e., Baker, 1992; Waldmann & Andersson, 1998). Sites that receive less rainfall might provide better thermoregulation opportunities to these high-elevation ectotherms, thereby improving their foraging and digestive efficiencies (Avery, 1994; Chen, et al, 2003; Du, et al, 2000; Ji, et al, 1996; Van Damme, et al, 1991; Zhang & Ji, 2004) and growth rates (Autumn & deNardo, 1995; Avery, 1984; Niewiarowski, 2001; Niewiarowski & Roosenburg, 1993) To inspect for this possibility, Bock et al, (2009) conducted a capture-mark-recapture study of individually-marked lizards from their two most extreme sites (in terms of precipitation and body sizes), and reared a small number of adult males from both sites in a common garden study in the laboratory. Both groups attained the same asymptotic sizes in the laboratory as were documented for their populations in the field, reinforcing the conclusion that body size differences at these sites represent fixed, genetically-based local adaptations
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