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      Mitochondrial sequence data indicate “Vicariance by Erosion” as a mechanism of species diversification in North American Ptomaphagus (Coleoptera, Leiodidae, Cholevinae) cave beetles

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      Subterranean Biology

      Pensoft Publishers

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          Abstract

          Small carrion beetles (Coleoptera: Leiodidae: Cholevinae) are members of cave communities around the world and important models for understanding the colonization of caves, adaptation to cave life, and the diversification of cave-adapted lineages. We developed a molecular phylogeny to examine the diversification of the hirtus-group of the small carrion beetle genus Ptomaphagus. The hirtus-group has no surface-dwelling members; it consists of 19 short-range endemic cave- and soil-dwelling species in the central and southeastern United States of America. Taxonomic, phylogenetic and biogeographic data were previously interpreted to suggest the hirtus-group diversified within the past 350,000 years through a series of cave colonization and speciation events related to Pleistocene climate fluctuations. However, our time-calibrated molecular phylogeny resulting from the analysis of 2,300 nucleotides from five genes across three mitochondrial regions ( cox1, cytb, rrnL- trnL- nad1) for all members of the clade paints a different picture. We identify three stages of diversification in the hirtus-group: (1) ~10 million years ago (mya), the lineage that develops into P.shapardi, a soil-dwelling species from the Ozarks, diverged from the lineage that gives rise to the 18 cave-obligate members of the group; (2) between 8.5 mya and 6 mya, seven geographically distinct lineages diverged across Kentucky, Tennessee, Alabama and Georgia; six of these lineages represent a single species today, whereas (3) the ‘South Cumberlands’ lineage in Tennessee and Alabama diversified into 12 species over the past ~6 my. While the events triggering diversification during the first two stages remain to be determined, the distributions, phylogenetic relationships and divergence times in the South Cumberlands lineage are consistent with populations being isolated by vicariant events as the southern Cumberland Plateau eroded and fragmented over millions of years.

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          Most cited references 32

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          Ecoregions of the Conterminous United States

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            Recent divergence with gene flow in Tennessee cave salamanders (Plethodontidae: Gyrinophilus) inferred from gene genealogies.

            Cave organisms occupy a special place in evolutionary biology because convergent morphologies of many species demonstrate repeatability in evolution even as they obscure phylogenetic relationships. The origin of specialized cave-dwelling species also raises the issue of the relative importance of isolation vs. natural selection in speciation. Two alternative hypotheses describe the origin of subterranean species. The 'climate-relict' model proposes allopatric speciation after populations of cold-adapted species become stranded in caves due to climate change. The 'adaptive-shift' model proposes parapatric speciation driven by divergent selection between subterranean and surface habitats. Our study of the Tennessee cave salamander complex shows that the three nominal forms (Gyrinophilus palleucus palleucus, G. p. necturoides, and G. gulolineatus) arose recently and are genealogically nested within the epigean (surface-dwelling) species, G. porphyriticus. Short branch lengths and discordant gene trees were consistent with a complex history involving gene flow between diverging forms. Results of coalescent-based analysis of the distribution of haplotypes among groups reject the allopatric speciation model and support continuous or recurrent genetic exchange during divergence. These results strongly favour the hypothesis that Tennessee cave salamanders originated from spring salamanders via divergence with gene flow.
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              Can we agree on an ecological classification of subterranean animals?

               Boris Sket (2008)
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                Author and article information

                Journal
                Subterranean Biology
                SB
                Pensoft Publishers
                1314-2615
                1768-1448
                January 07 2019
                January 07 2019
                : 29
                : 35-57
                Article
                10.3897/subtbiol.29.31377
                © 2019

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