Morphological divergence rate tests for natural selection: uncertainty of parameter estimation and robustness of results

Abstract

In this study, we used a combination of geometric morphometric and evolutionary genetics methods for the inference of possible mechanisms of evolutionary divergence. A sensitivity analysis for the constant-heritability rate test results regarding variation in genetic and demographic parameters was performed, in order to assess the relative influence of uncertainty of parameter estimation on the robustness of test results. As an application, we present a study on body shape variation among populations of the poeciliine fish Poecilia vivipara inhabiting lagoons of the quaternary plains in northern Rio de Janeiro State, Brazil. The sensitivity analysis showed that, in general, the most important parameters are heritability, effective population size and number of generations since divergence. For this specific example, using a conservatively wide range of parameters, the neutral model of genetic drift could not be accepted as a sole cause for the observed magnitude of morphological divergence among populations. A mechanism of directional selection is suggested as the main cause of variation among populations in different habitats and lagoons. The implications of parameter estimation and biological assumptions and consequences are discussed.

The pace of morphological change: historical transformation of skull shape in St Bernard dogs

“…The rate of change computed from the regression of shape on time yields a change of approximately 0.084 units of Procrustes distance over the 120 years of the study period. This is comparable to the distances in average body shapes among fish populations separated by periods up to 4000 years (Monteiro & Gomes-Jr. 2005) or between tooth shape divergence of mammal taxa separated by thousands to millions of years (Polly 2001). Episodes of particularly strong selection can achieve even faster divergence, as suggested by selection experiments on wing shape in Drosophila (Houle et al 2003) or observations on bill size and shape in Darwin's finches (Grant & Grant 2002.…”

Morphological divergence patterns among populations of Poecilia vivipara (Teleostei Poeciliidae): test of an ecomorphological paradigm

“…Divergence rate tests applied to morphological differences among population means with known maximum times of separation indicated directional selection as the most probable process influencing shape diversification among P. vivipara populations (Monteiro & Gomes, 2005). Although suggestive of natural selection, these previous results lack the determination of possible agents of selection to explain the body shape divergence observed.…”

“…This paradigm provides a framework for the interpretation of body shape divergence patterns and a functional hypothesis for predation as an agent of selection. This interpretation, along with quantitative genetics theory of genetic drift as a null model (Lande, 1979;Ackermann & Cheverud, 2002;Monteiro & Gomes, 2005), allows for robust assessments of evolutionary processes acting on interpopulational phenotypic divergence patterns, even for species not yet exhaustively studied.…”

Growth pattern and survival in populations of Poecilia vivipara (Teleostei; Poeciliidae) inhabiting an environmental gradient: a common garden study

“…The growth of the delta formed a large number of river arms that after closing formed inland lagoons, entrapping populations of P. vivipara that inhabited the paleoestuary in freshwater environments with a different fish community than the one found in the brackish water of the estuary and the brackish water lagoons closer to the ocean (Bizerril and Primo 2001). The phenotypic variation among P. vivipara populations and evolutionary processes in this gradient have been well described by (Neves and Monteiro 2003;Monteiro and Gomes Jr. 2005;Gomes Jr. and Monteiro 2007;Gomes Jr. and Monteiro 2008). These authors found a direct association of mean body size with the salinity gradient, as well as other adult size correlates, such as fecundity and offspring size.…”