Deep mtDNA Sequence Divergences and Possible Species Radiation of Whip Spiders (Arachnida, Amblypygi, Phrynidae, Phrynus/Paraphrynus) among Caribbean Oceanic and Cave Islands

Abstract

Islands—whether classic oceanic islands or habitat islands such as isolated thermal vents, mountain tops, or caves—often promote the diversification of lineages that colonize them. We examined CO1 mtDNA sequence divergences within the tailless whip spider genus Phrynus Lamarck, 1809 (Amblypygi: Phrynidae) among oceanic islands and among cave ’islands´ distributed across the Caribbean archipelago and on the continental mainland. The significance of this study lies in the extensive taxon sampling of a supposedly depauperate lineage (considering its age), over a large proportion of its geographical range, and the discovery of deep mtDNA sequence divergences. We sampled thousands of specimens—and sequenced 544, including six outgroup species—across 173 localities on 17 islands (135 localities) and five countries on the North to South American mainland (38 localities), including a total of 63 caves. Classical taxonomy identified ten named Phrynus and two Paraphrynus Moreno, 1940 species. Paraphrynus seems to be paraphyletic and nested in Phrynus. Uncorrected genetic distances within named species and among morphological species ranged up to 15% and 19%, respectively. Geographic distances explained a significant portion of genetic distances on islands (19%, among both subterranean and epigean specimens), and for epigean specimens on the mainland (27%). Species delimitation analyses indicated that the 12 named species harbored from 66 to well over 100 putative species. The highest number of species was indicated by the GMYC method (114 species) while the Bayesian Poisson tree processes (bPTP) and the BP&P relying on the Markov chain Monte Carlo Bayesian Phylogenetic model estimated an upper level of 110 species. On the other hand, the recently recommended and relatively conservative distance-based (phylogeny free) ASAP model has the greatest support for 73 species. In either case, nearly all putative species are tightly limited to a single locality, often a small cave system, and sometimes to the surrounding epigean area. Caribbean Phrynus diversity has likely been vastly underestimated, likely due to both morphological crypsis and the ignorance of Caribbean cave fauna. Although mtDNA sequences can suggest species limits, nuclear DNA sequencing and detailed morphological research are necessary to corroborate them and explore whether this phenomenon constitutes species radiation or perhaps just mtDNA divergences as a consequence of, for example, stationary females and actively dispersing males.