Island biogeography and ecological modeling of the amblypygid Phrynus marginemaculatus in the Florida Keys archipelago

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

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 relaying 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.

Volcanism and palaeoclimate change drive diversification of the world's largest whip spider (Amblypygi)

The tropics contain many of the most biodiverse regions on Earth but the processes responsible for generating this diversity remain poorly understood. This study investigated the drivers of diversification in arthropods with stenotopic ecological requirements and limited dispersal capability using as a model the monotypic whip spider (Amblypygi) genus Acanthophrynus, widespread in the tropical deciduous forests of Mexico. We hypothesized that for these organisms, the tropical deciduous forests serve as a conduit for dispersal, with their disappearance imposing barriers. Given that these forests are located in a region of complex geological history and that they fluctuated in extent during the Pliocene-Pleistocene glacial/interglacial cycles we combine molecular divergence dating, palaeoclimatic niche modelling and ancestral area reconstruction to test if and when habitat fragmentation promoted diversification in Acanthophrynus. Concomitant with the expected role of landscape change, we demonstrate that orogeny of the Trans-Mexican Volcanic Belt, in the Late Miocene or Early Pliocene (6.95-5.21 million years ago), drove the earliest divergence of Acanthophrynus by vicariance. Similarly, as expected, the later onset of glaciations strongly impacted diversification. Whereas a more stable climate in the southern part of the distribution enabled further diversification, a marked loss of suitable habitat during the glaciations only allowed dispersal and diversification in the north to occur later, resulting in a lower overall diversity in this region. Barriers and diversification patterns identified in Acanthophrynus are reflected in the phylogeography of codistributed vertebrates and arthropods, emphasizing the profound impact of Trans-Mexican Volcanic Belt orogeny and glacial/interglacial cycles as drivers of diversification in the Mexican Neotropics.

Comparative analysis of the boundary layer filtering of odor signals in the amblypygid (whip spider) species Paraphrynus laevifrons and Phrynus marginemaculatus

Amblypygids use a pair of modified walking legs (antenniform) as chemosensory and mechanosensory appendages. At the tip of these legs are covered in chemosensory sensilla, which the animals use to sample odor stimuli in their environment by moving the antenniform leg through the air. We designed a set of experiments to measure the filtering effect that aerodynamic boundary layers have on the temporal and spatial structure of chemical stimuli. In addition, two different species of amblypygids (Paraphrynus laevifrons and Phrynus marginemaculatus) that live in two distinct habitats were used for a comparative analysis. Pulses of a tracer molecule were quantified at different distances and flow velocities using an electrochemical detection system. Temporal attributes of the chemical pulses were extracted and were statistically compared across velocities, distances from the appendage, and the two species. Overall, the boundary layer significantly decreased the concentration and increased the duration of pulses for both species. This filtering effect was more pronounced for P. marginemaculatus than P. laevifrons, as the chemical signal was lower in concentration and longer in duration at any distance from the antenniform leg. It is speculated that the difference in boundary layer filtering, as a function of appendage morphology, is tuned to the different types of odor plumes in these animals' native habitats.