Abstracts (first author)

Talk 

Quantitative genetic variation, selection and secular change of skull shape in humans

Author(s): Klingenberg C, Martínez-Abadías N, Esparza M, Sjøvold T, Hernández M

Summary:

The combined use of geometric morphometrics and quantitative genetics provides a set of powerful tools for obtaining quantitative information that is crucial for many important questions concerning the evolution of shape. In particular, the demographic information that is available for human populations make humans a unique study system for studying the mechanisms of evolutionary change in morphological traits. We investigate skull shape in the population of Hallstatt (Austria), where a collection of human skulls with associated records offer a unique opportunity for such studies. We use an individual-based statistical model to estimate the genetic covariance matrix, and characterize selection using fitness estimates from demographic data. We find clear evidence for directional selection, but not for nonlinear selection (stabilizing or disruptive selection). The predicted response to this selection, computed with genetic parameters from the population, does not match the estimate of secular change over the 150-year range of the data. We discuss possible reasons for the mismatch.



Abstracts (coauthor)

Summary:

Quantitative multidimensional traits, such as shape, have been used in phylogeography and phylogenetics in recent years. However, there is no consensus about the reliability of the phylogenies built using these traits. Empirical studies have yielded different results in this regard, but no study has systematically studied it. Here, we simulate the evolution of four taxa under a Brownian motion model in a multidimensional space with varying dimensionality and different sets of branch lengths. In addition, two more sets of simulations with different degrees of integration among variables are tested using modified Brownian motion models. The percentage of correct phylogenetic reconstructions is used as a measure of phylogenetic accuracy. The results suggest that with low dimensionality, the phylogenetic accuracy is poor and problems of long-branch attraction appear. When few variables are used to describe the taxa, the reliability is poor and convergence appears even when two far-related groups of taxa are used, if one taxon within each group has evolved much. The accuracy is better when many variables are used. However, a high number of variables does not prevent from convergence when the variables used have the same pattern of dependency. Integration among variables has a strong negative effect. Reducing its effect implies knowing the pattern of interdependence among variables during the evolutionary process, which is difficult or impossible and requires large sample sizes. There are just very few favourable and restricted situations in which quantitative multidimensional data can be used to build phylogenies with accurate results. The effect of integration, really widespread, makes this technique not to be advisable.

Summary:

Studying integration and modularity is essential to understand the evolution of shape because the coherence of recognizable parts of most organisms is dependent on their developmental origin and structure. Drosophila wing morphology has been used extensively as an important model trait in evolutionary biology, since its genetics and development are well known. The aim of the present study is to address questions related to the evolution and developmental process of the wing shape architecture. Specifically, the questions are: 1- Are the Drosophila wings a single integrated morphological unit consistently in all the species groups across the whole genus? 2- Does morphological integration evolve across the genus? 3- Is there any evolutionary integration in the Drosophila wing? To study these morphological changes we used geometric morphometrics as a tool for analyzing shape variation and its covariation between the anterior and posterior (A/P) compartments of the wing and to compare the different covariance matrices between species. Moreover, we also used comparative methods for mapping the shape data onto the phylogeny. The analyses show, on the one hand, strong differences between the species of this genus. Indeed, the modularity test for the A/P wing compartments showed that they are not independent in all the species studied, confirming previous results for D. melanogaster at large scale. On the other hand, mapping the variation of covariance matrices onto the phylogeny shows the pattern of evolution of integration in the genus. This study has helped to answer questions related to the evolutionary process of the Drosophila wing shape and to show that the A/P wing compartments are not separate modules of variation. We have also found a clear evolutionary integration into all the different traits of wing shape. We can conclude that the wing shape shows strong internal covariation, and also that the integration process has evolved in the genus.

Summary:

Plants usually have a modular body plan, which consists of a number of building blocks (or modules). As sessile organisms, they are often confronted with spatially heterogeneous environmental conditions. Plastic responses may thus contribute to variation on several hierarchically organized levels: among parts within a module, among modules within an individual, among individuals within populations or species, and among populations or species. Flowers are particularly interesting, since most of them are composite modules consisting of several, repeated subunits, and within-flower variation can manifest itself as asymmetry. To assess the plastic component in flower shape variation, we examine whether directional environmental influences such as sun radiation and gravity produce a directional plastic response in morphometric traits. We compare several species of Heliosperma with 5-merous, radially symmetric flowers. Plants were grown in common garden, representative photographs of several flowers per individual were taken together with orientation and inclination data of each flower, and flat preparations of petals were made. Geometric morphometrics was used to characterize shape variation and asymmetry. Correlations of asymmetry with orientation and inclination of single flowers were evaluated and related to possible ecological functions and selective advantages. Furthermore, we quantified the amounts of variation associated with different levels – among and within species, among flowers within individuals, and between petals of one single flower. We discuss the role of plasticity for floral asymmetry, subindividual and higher-level variation.

Contacts

Chairman: Octávio S. Paulo
Tel: 00 351 217500614 direct
Tel: 00 351 217500000 ext22359
Fax: 00 351 217500028
email: mail@eseb2013.com

Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

Website

Computational Biology & Population Genomics Group 
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