Testing multiple hypotheses about the history of neotropical rainforests with a complete phylogeny of spiny orb-weavers (Micrathena)

MAGALHAES, IVAN L. F.; MARTINS, PEDRO H; FALEIRO, BÁRBARA T; CARVALHO, LEONARDO S; ADALBERTO J. SANTOS

Montevideo

Congreso; 22nd International Congress of Arachnology; 2023

The Neotropical region is the most diverse on the planet, largely due to its mosaic of tropical rainforests. Multiple tectonic and climatic processes have been hypothesized to play a role in generating this diversity. We use the spiny spider genus Micrathena (Araneidae) as a model to study the biogeographic history of Neotropical rainforests. Its ~120 species are distributed from Mexico to Argentina, including the Antilles. We estimated a complete, dated phylogeny using morphological data for all species and molecular data for 79 species. This resulted in a mainly robust phylogeny largely supporting previous taxonomic proposals, although with uncertainty in the phylogenetic position of some species. The genus began to diversify about 25 million years ago. We estimated ancestral distributions and the timing and direction of dispersal events, as well as identified areas where diversity was generated, while accounting for phylogenetic and biogeographic uncertainty. Andean cloud forests generated the most species, but Amazonia was the major source of species for adjacent areas. The dry diagonal received species from other areas but generated very little diversity. There was intense species exchange between Central and South America, with 20 dispersal events beginning at least 20 million years ago, indicating that Micrathena dispersed between these continents before closure of the Isthmus of Panama. Sampling all species of the genus was fundamental to some of the conclusions, especially in identifying the Andes as the area that generates the most species. This study highlights the importance of a solid and complete taxonomic sampling in biogeographic studies.