Search for: All records

Abstract Populations during early stages of establishment are sensitive to forms of demographic regulation coinciding with rapid growth, which may also coincide with specific patterns of natural selection due to demographic variation. Understanding how selection varies during the establishment of new populations, however, is complicated by the constraint of knowing the precise age of a population as it grows over time. To address this, we established six brown anole (Anolis sagrei) populations on spoil islands in Florida and manipulated initial sex ratios to understand how natural selection is influenced by the demographic composition of founding populations. We found that initial sex ratios of founding populations led to age-specific patterns of natural selection. Juveniles experienced stronger selection in populations that began with a female-biased sex ratio, and the strength of natural selection on juvenile size strengthened with increasing population density. We also found substantial variation in selection, suggesting that the relationship between phenotypes and fitness across early generations of a population is not consistent over time. As a result, variation in natural selection driven by demographic aspects within populations may provide opportunities for rapid population growth and novel evolutionary trajectories during the earliest stages of establishment. 

Abstract Theory predicts that thermal developmental plasticity evolves in response to thermal heterogeneity, suggesting that plasticity may be an important trait for establishment in novel climates. However, few studies use multispecies comparisons to examine how plasticity evolves, meaning that there is little empirical basis with which to examine key theoretical predictions. We estimate patterns of thermal developmental plasticity in morphological and performance traits for 7 Anolis lizard species inhabiting South Florida, USA. We found interspecific differences as well as intraspecific variation in reaction norms across species. Neither temperature heterogeneity in present-day invasive ranges in Florida nor historical temperature heterogeneity from the contemporary native ranges predicted reaction norm variation. Phylogeny and species identity typically predicted around 90%–95% of reaction norm variation. Overall, these results suggest that thermal developmental plasticity in these traits exhibits variation that could be inconsistent with patterns expected under adaptive evolution to macroclimate. Examining the role of maternal nesting behavior and sampling of additional species can help to distinguish between neutral variation and selection toward multiple adaptive peaks. Our comparative study of thermal developmental plasticity in lizards provides new insights about macroevolutionary dynamics behind the evolution of developmental plasticity and the conditions under which adaptive plasticity is expected to evolve.