Modularity and morphological diversification in mammals

Abstract

Modularity in Biology refers to the pattern of connections among elements: genes, proteins, morphological traits. This pattern emerges whenever a high connectivity between some elements in the system exists, forming modules, and at the same time those same elements are more loosely connected to others elements that compose other modules. Many types of modules have been recognized in Biology, such as: a) functional, composed of characters that work together to perform a function, b) development, which correspond to parts of an embryo that are relatively autonomous with respect to the developing pattern and differentiation, or an independent signaling cascade, c) variation modules, composed of characters that vary together and are relatively independent of other sets of characters (Wagner et al. 2007). One way to study the modularity of organisms is to investigate the pattern of genetic covariances and correlations between their characters, because traits with common function or development tend to form relatively independent groups of variation among themselves, or modules. If modular organization exists in an organism, the expectation would be a pattern of high correlations between traits within the modules and low correlations between traits in different modules (Olson & Miller, 1958; Cheverud 1982 and 1984). Studying the modularity, or the morphological integration of organisms, is fundamental to understanding the evolution of complex features, as the modular structure influences the multivariate evolution: the relationship between the inherited patterns of modular covariation and patterns of selection may, for example, restrict or facilitate certain evolutionary paths for a population (Marroig & Cheverud 2001, 2004 e 2005, Schluter 1996, Magwene 2001, Marroig et al. 2004, Marroig & Cheverud 2005, Pavlicev et al., 2008). In this project, we aim to analyze the patterns of modularity in mammals in a comparative way, explicitly incorporating the phylogeny of the groups. Those Phylogenies will be obtained in the literature for some groups, and others will be produced within the scope of the project itself. (AU)