Biogeographical evidence for common vicariance and rare dispersal in a southern Appalachian harvestman (Sabaconidae, Sabacon cavicolens)

Abstract

Aim Species or higher taxa that are obviously dispersal‐limited, but which occupy large geographical distributions, represent a biogeographical paradox. Dispersal must have happened, likely under special and infrequent environmental conditions, but details have been lost to history. The overarching goal of our research is to understand the details of a ‘common vicariance, rare dispersal’ biogeographical history in a widespread but habitat‐specialized harvestman species (Sabacon cavicolens) with a southern Appalachian centre of distribution. Location Eastern North America, southern Appalachians. Methods We assessed cryptic speciation using mitochondrial and nuclear gene DNA sequence data, testing alternative delimitation hypotheses using multispecies coalescent analyses. We also tested whether riverine barriers are associated with mitochondrial genealogical structuring, focusing on multiple rivers in the southern Blue Ridge physiographical province. Finally, we conducted population genetic analyses to assess female‐based range expansion out of the southern Blue Ridge. Results Genetic analyses suggest a large number of species‐level lineages within S. cavicolens, although we prefer a more conservative three‐species hypothesis. These putative species are geographically cohesive and allopatric (Ozarks, Cumberland Plateau, southern Blue Ridge), with the Blue Ridge species including multiple divergent mitochondrial haplogroups. Several genealogical breaks in the Blue Ridge species coincide with riverine barriers, separating mostly allopatric mitochondrial lineages. Contrasting with evidence for constrained gene flow and vicariance, two Blue Ridge haplogroups reveal extensive range expansion both northwards and westwards, resulting in the widespread distribution of closely related haplotypes, and occasional sympatry of dispersive haplotypes. Main Conclusions Hidden beneath the apparently widespread distribution of a single species is a history of old vicariance separating geographically disjunct cryptic species. How these lineages came to occupy such disparate geographies is illustrated by dynamics within the Blue Ridge species, where both in situ vicariance and long‐distance dispersal have shaped a ‘common vicariance, rare dispersal’ biogeographical history.

Pleistocene persistence and expansion in tarantulas on the Colorado Plateau and the effects of missing data on phylogeographical inferences from RADseq

“…Tributaries of the Little Colorado River bisect populations within the Central clade, with identical haplotypes found on each side. Thus, rivers may indeed act as barriers to gene flow to tarantulas at lower elevations, supporting a “riverine barrier hypothesis” as proposed for studies on Opiliones (Hedin & McCormack, 2017; Thomas & Hedin, 2008). At higher elevations on the plateau, however, rivers do not significantly impede gene flow, like the “leaky” barrier scenario used to recently describe the nearby lower Colorado River (Dolby, Dorsey, & Graham, 2019).…”

Is geography an accurate predictor of evolutionary history in the millipede family Xystodesmidae?

“…For example, studies implementing Templeton-Crandall-Sing parsimony and inferring demographic processes using nested clade analysis in millipedes, have generated hypotheses useful for conservation and understanding phylogeographic patterns ( Zigler, Loria & Lewis, 2011 ; Marek & Bond, 2009 ). However, in very old groups of non-mobile invertebrates, the technique of using geographical proximity is more challenging ( Hedin & McCormack, 2017 ; Hendrixson & Bond, 2007 ).…”

“…Among the biodiversity encompassed by these mountains, wingless and low-mobility animals such as millipedes, harvestmen, snails, and salamanders are tightly coupled to their habitat. As a result of its complex topography, varied edaphic qualities, and ancient origins, the Appalachian Mountains have fostered the isolation and diversification of these low-mobility groups resulting in high species diversity in relatively small geographic areas ( Marek, 2010 ; Hedin & McCormack, 2017 ). This is particularly the case for millipedes, and for the past 10–20 million years the group has had the opportunity to diversify in the Appalachian region as a result of its stable mesic environment, calcareous geology (millipedes biomineralize calcium carbonate into their cuticle), and historical contingency ( Briggs, Plint & Pickerill, 1984 ; Shear & Selden, 1995 ).…”

Phylogenomic history of enigmatic pygmy perches: implications for biogeography, taxonomy and conservation

“…On the other hand, biogeographic distributions that cannot be related to ecology or explained by dispersal or vicariance offer enigmatic puzzles that require additional investigation (e.g. [ 8 , 9 ]). Biogeographic knowledge can be further used in applied research, such as assessments of taxonomy and improving conservation legislation [ 10 ].…”