The origin of the buthid scorpion fauna of the Caribbean islands

The Caribbean islands have a large scorpion population where many species are endemic for this area. But how did this unique fauna originate? There have been three theories of the origins of the flora and fauna diversity seen in The Caribbean: 1. Connections via land bridges, 2. Vicariance events, 3. Overwater dispersal from continents and among islands.

Lauren Esposito and Lorenzo Prendini have now published a study investigating the biogeographical diversification of the New World buthid scorpion subfamily Centruroidinae Kraus, 1955 and trying to understand the origin of the Caribbean populations of these taxa.

The results of this study show that the centruroidine scorpions colonized the Caribbean islands on two independent occasions (35 mya ago from South America and the Greater Antilles and 20 mya ago North America, probably via Cuba). Interestingly, the results also point to a case of "reverse-colonization" event for the genus Heteroctenus Pocock, 1893. This genus seems to have a Caribbean ancestor, which subsequently colonized Central America and North America, and eventually re-colonized the Greater Antilles.

Abstract:
Scorpions are an excellent system for understanding biogeographical patterns. Most major scorpion lineages predate modern landforms, making them suitable for testing hypotheses of vicariance and dispersal. The Caribbean islands are endowed with a rich and largely endemic scorpion fauna, the origins of which have not been previously investigated with modern biogeographical methods. Three sets of hypotheses have been proposed to explain present patterns of diversity in the Caribbean: (1) connections via land bridges, (2) vicariance events, and (3) overwater dispersal from continents and among islands. The present study investigates the biogeographical diversification of the New World buthid scorpion subfamily Centruroidinae Kraus, 1955, a clade of seven genera and more than 110 species; infers the ancestral distributions of these scorpions; and tests the relative roles of vicariance and dispersal in the formation of their present distributions. A fossil calibrated molecular phylogeny was estimated with a Bayesian criterion to infer the dates of diversification events from which ancestral distributions were reconstructed, and the relative likelihood of models of vicariance vs. dispersal, calculated. Although both the timing of diversification and the ancestral distributions were congruent with the GAARlandia land-bridge hypothesis, there was no significant difference between distance-dependent models with or without the land-bridge. Heteroctenus Pocock, 1893, the Caribbean-endemic sister taxon of Centruroides Marx, 1890 provides evidence for a Caribbean ancestor, which subsequently colonized Central America and North America, and eventually re-colonized the Greater Antilles. This ‘reverse colonization’ event of a continent from an island demonstrates the importance of islands as a potential source of biodiversity.

Reference:
Esposito LA, Prendini L. Island Ancestors and New World Biogeography: A Case Study from the Scorpions (Buthidae: Centruroidinae). Sci Rep. 2019;9(1):3500. [Open Access]