This study investigates the genetics underlying character variation among individuals within a population, and how the genetic structure of species evolves. Because characters are affected by many genes, and because genes affect many characters, variation in different characters (e.g., arm length and leg length) are not independent of each other. The genetic variance-covariance matrix (G-matrix) summarizes these interdependencies. This study will estimate the G-matrix for eight species of Anolis lizards. Because species of these lizards on different islands have adapted to the same environment, this study will allow the comparison of distantly related species that have experienced the same natural selection pressures, as well as closely related species that live on the same island, but have experienced different selective pressures. These comparisons will permit evaluation of the factors that affect how the G-matrix evolves.
The G-matrix is of fundamental importance in describing evolutionary change by translating natural selection in one generation into phenotypic change in the next. Nonetheless, scientists still do not have a good understanding of what factors affect evolution of the G-matrix. By examining many species, this study will be the most extensive study to date and will thus greatly expand understanding of the genetics underlying evolutionary change. This project will support the training of a postdoctoral scholar, a graduate student, and several undergraduates, including students from traditionally underrepresented groups. Anolis lizards have become one of the major models for studying evolutionary diversification and relaying that understanding to a broad audience. Accounts of Anolis evolution have appeared in countless textbooks, television programs and popular publications. This project will continue those efforts.
This study investigates the genetics underlying character variation among individuals within a population, and how the genetic structure of species evolves. Because characters are affected by many genes, and because genes affect many characters, variation in different characters (e.g., arm length and leg length) is not independent of each other. The goal of this study was to investigate how different characters are correlated within a species, and how these correlations vary from one species to another. Understanding the importance of genetic correlations is of fundamental importance in describing evolutionary change because it dictates how natural selection in one generation will lead to evolutionary change in the next. Nonetheless, scientists still do not have a good understanding of what factors affect the evolution of genetic correlations. By examining many species, this study will be the most extensive study to date and will thus greatly expand understanding of the genetics underlying evolutionary change. Lizards in the genus Anolis on islands in the Caribbean are a particularly good group of species to study such questions. On each of the islands of the Greater Antilles, anole species have evolved for the most part independently, yet the same set of habitat specialists has evolved on each island. Thus, for example, species specialized to use narrow surfaces (termed "twig anoles") have evolved on all four islands. As a result, species are more closely related evolutionarily to species on their own island, but are more similar in the body proportions to species on other islands that are similarly adapted to use the same part of the environment. Taking advantage of this natural evolutionary experiment, we set out to test whether the pattern of genetic trait correlations was more similar among closely related species that differ in their habitat specialization, or among more distantly related species that are similar in their adaptations. We captured eight lizard species from three island radiations and brought them into the laboratory to breed them. By examining the similarity between parents and offspring, we can estimate the genetic basis for trait variation. In total, we produced 3245 juveniles from 540 unique sets of parents. Complete target samples sizes for breeding pairs (adults) are in hand for four species and the fifth and sixth are nearing completion. The final two species, which were mostly collected in 2009, are continuing to breed and produce juveniles. All parents and offspring have been x-rayed. An undergraduate undertook a longitudinal study of the effects of X-ray and chilling on bone development and growth to test whether repeated X-ray exposure would influence anatomical development. Preliminary analyses show no effect of repeated X-ray exposure. All individuals are being X-rayed at least 3 times during juvenile stages (1 month, 3 months, 6 months) to generate a growth chart for each individual. These data will allow comparison of growth trajectories as well as comparisons of genetic trait correlations. So far, we have found that the pattern of genetic correlations is remarkably similar across the four species in which we have measured it. This includes two species that are distantly-related, but similar in habitat adaptations, as well as three adaptively differently species that are closely-related. These data suggest that both shared evolutionary history and convergent selection have been important in shaping the evolution of the genetic system. A more complete analysis of data for awaits the completion of breeding for the remaining species. This grant led to training of researchers at many stages of career development, including three postdoctoral fellows, four graduate students and 12undergraduates. In addition, more than 70 undergraduates were exposed to the research process as they helped in lizard husbandry and local school groups regularly toured the breeding facilities.
