Magalhaes, I. L. F. | Search bioRxiv

bioRxiv2023

Complete phylogeny of Micrathena spiders suggests multiple dispersal events among Neotropical rainforests, islands, and landmasses, and indicates Andean orogeny promotes speciation

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; these include Andean orogeny, closure of the Panama Isthmus, the hypothesized GAARlandia land bridge, and putative historical connections among currently isolated forests. Micrathena spiny spiders (Araneidae) include [~]120 species distributed mostly in forests from Mexico to Argentina, including the Antilles. Here, we use it as a model to study the biogeographic history of Neotropical rainforests by estimating a complete, dated phylogeny using morphological data for all species and molecular data for a subsample of 79 species. This resulted in a phylogeny that is mostly robust and supports most of the previously recognized species groups, although with uncertainty in the phylogenetic position of some species, especially those lacking sequences. The genus began diversifying about 25 million years ago. We use an event-based approach and biogeographic stochastic mapping to estimate ancestral distributions and the timing and direction of dispersal events, and to identify areas where diversity was generated, while accounting for phylogenetic uncertainty. Andean cloud forests generated the majority of species through in-situ speciation, but the Amazon was the major source of species for adjacent areas through dispersal; on the other extreme, the Dry Diagonal received species from other areas but generated very little diversity. Species exchange between Central and South America was intense, with [~]23 dispersal events beginning at least 20 million years ago, indicating that Micrathena dispersed between these continents before closure of the Isthmus of Panama. We also inferred [~]4 over-water dispersal events from Central and North America to the Antilles, which happened in the last 20 million years, and thus much after the proposed age of the GAARlandia land bridge. We identified an important species exchange route between the Amazon and the Atlantic forests. Sampling all species of the genus was fundamental to some of the conclusions above, especially in identifying the Andes as the area that generated the majority of species. This study highlights the importance of a solid and complete taxonomic sampling in biogeographic studies.

evolutionary biology↗

bioRxiv2021

Incorporating topological and age uncertainty into event-based biogeography supports paleo-islands in Galapagos and ancient connections among Neotropical dry forests

Event-based biogeographic methods, such as dispersal-extinction-cladogenesis, have become increasingly popular for attempting to reconstruct the biogeographic history of organisms. Such methods employ distributional data of sampled species and a dated phylogenetic tree to estimate ancestral distribution ranges. Because the input tree is often a single consensus tree, uncertainty in topology and age estimates are seldom taken into account, even when they may affect the outcome of biogeographic estimates. Even when such uncertainties are taken into account for estimates of ancestral ranges, they are usually ignored when researchers compare competing biogeographic hypotheses. We explore the effect of incorporating this uncertainty in a biogeographic analysis of the 21 species of sand spiders (Sicariidae: Sicarius) from Neotropical xeric biomes, based on a total-evidence phylogeny including a complete sampling of the genus. By using a custom R script made available here, we account for uncertainty in ages and topology by estimating ancestral ranges over a sample of trees from the posterior distribution of a Bayesian analysis, and for uncertainty in biogeographic estimates by using stochastic maps. This approach allows for counting biogeographic events such as dispersal among areas, counting lineages through time per area, and testing biogeographic hypotheses, while not overestimating the confidence in a single topology. Including uncertainty in ages indicates that Sicarius dispersed to the Galapagos Islands when the archipelago was formed by paleo-islands that are now drowned; model comparison strongly favors a scenario where dispersal took place before the current islands emerged. We also investigated past connections among currently disjunct Neotropical dry forests; failing to account for topological uncertainty underestimates possible connections among the Caatinga and Andean dry forests in favor of connections among Caatinga and Caribbean+Mesoamerican dry forests. Additionally, we find that biogeographic models including a founder-event speciation parameter ("+J") are more prone to suffer from the overconfidence effects of estimating ancestral ranges using a single topology. This effect is alleviated by incorporating topological and age uncertainty while estimating stochastic maps, increasing the similarity in the inference of biogeographic events between models with or without a founder-event speciation parameter. We argue that incorporating phylogenetic uncertainty in biogeographic hypothesis-testing is valuable and should be a commonplace approach in the presence of rogue taxa or wide confidence intervals in age estimates, and especially when using models including founder-event speciation.

evolutionary biology↗