Diversity of limno-terrestrial tardigrades of the Americas in relation to the Great American Biotic Interchange hypothesis (GABI)

Zoogeographical studies on Tardigrada are limited by the extent of our knowledge on tardigrade taxonomy and faunistics. In this paper we analyse the relationships between the tardigrade fauna of North, Central and South America (Nearctic and Neotropical regions) and provide the first test of whether the tardigrade fauna of the Americas has undergone the great American interchange. Our analyses were based on 384 tardigrade species records obtained for 1702 localities in North, South and Central America. We found that (1) some tardigrade species are distributed, as predicted by the Great American Biotic Interchange (GABI) hypothesis, on both sides of the Panama Isthmus; (2) the Central American tardigrade fauna is specific and different from both the South and the North American faunas, although it is closer to the tropical areas of South America; (3) either the tardigrade fauna of South and North America appear to be more similar to each other than to that of Central America, or there is a Nearctic–Neotropic division of the faunas; and (4) endemism in Central America suggests a more complex biogeographical process than predicted by the connection of two continents.