Phylogenetic niche conservatism in Sicarius spiders associated to Neotropical arid environments: a matter of scale?

IVAN LUIZ FIORINI DE MAGALHÃES; FABRÍCIO R SANTOS; TEOFÂNIA H D A VIDIGAL; ANTONIO D. BRESCOVIT; ADALBERTO J. SANTOS

Guarujá, São Paulo

Congreso; Evolution 2015; 2015

SSE/ASN/SSB

Phylogenetic niche conservatism is thought to be an important biological pattern that helps understanding the distribution of organisms. This is especially true regarding taxa that occur in habitats with peculiar environmental conditions, such as arid lands. In the Neotropical region, arid lands are represented by deserts and dry tropical forests, both of which have disjunct distributions. Our aim is to investigate the evolution of organisms associated with these environments, particularly regarding two points: 1) what is the timing of diversification of organisms associated with these disjunct environments? 2) Do their distributions show a strong pattern of phylogenetic niche conservatism? To answer these questions, we studied the spider genus Sicarius, which is restricted to deserts and dry forests in Southern Africa and South and Central Americas, and thus is a good model for addressing these questions. We inferred a complete phylogeny of the twenty species of Neotropical Sicarius through Bayesian analysis of morphological data and five molecular markers, resulting in a highly resolved, well-supported phylogenetic hypothesis. Divergence times were estimated using fossils and mutation rates as calibrations. Neotropical Sicarius are an old, monophyletic group that began to diversify around 37 million years ago (mya). Most species diverged from their sister taxa between 10 and 20 mya, indicating that they have been evolving in isolation for a long time, and that events in the Miocene led to the currently disjunct distribution pattern of the genus. A principal component analysis of climatic variables indicates that Sicarius species can be divided into two groups associated to habitats with distinct climatic characteristics, corresponding to deserts and dry forests. Phylogenetic relationships indicate that species associated to each of those environments do not form monophyletic groups: there is evidence of at least 3?4 events of colonization of dry forests by desert-inhabiting ancestors. In addition, at least two species occupy both types of habitat. This suggests that Sicarius spiders have been able to shift between distinct types of dry habitats during their history with relative ease. Thus, it seems that on a large scale Sicarius exhibit phylogenetic niche conservatism and are restricted to disjunct arid environments scattered throughout the Neotropical region. However, on a smaller scale they have successfully colonized distinct types of dry habitats multiple times.