Biogeography of the Macrhybopsis aestivalis complex (Teleostei: Cyprinidae): emphasis on speciation and ancient heterospecific mitochondrial transfer
2022
Hoagstrom, Christopher W. | Echelle, Anthony A.
The Macrhybopsis aestivalis complex (nine recognized species of small-bodied, riverine cyprinids) is predicted to have diversified allopatrically in response to prehistoric reorganizations of rivers tributary to the Gulf of México. To flesh out details of this hypothesis, we derived, from previous work, a mitochondrial (ND2) chronogram for interpretation against the background of a published nuclear gene phylogeny (S7 intron 1), paleo-geomorphology, and other species with congruent biogeographies. The complex arose in the Early Miocene and potentially occupied most of its present range by Late Miocene-Early Pliocene. Biogeography is largely consistent with allopatric speciation and secondary contact driven by Neogene river-course rearrangements. One exceptional case of ecologically driven speciation is indicated for an undescribed form in the Ohio River drainage. Heterospecific mtDNA fixation is indicated in the Arkansas and Red rivers as well as in a case of ancient exchange involving M. meeki or M. gelida from outside the complex. A novel result is the suggestion that interspecific mtDNA sharing can exist over millions of years before donor and recipient lineages start to diverge mitochondrially. Additional study is needed to fully resolve the phylogeography of the complex, especially in the Wabash River, Upper Tennessee River, and the southern Mississippi Embayment. Finally, biogeographic considerations and critique of a prior, morphologically based revision of the M. aestivalis complex indicate a need to revisit the synonymy of presently unrecognized M. sterletus with M. aestivalis in the Río Grande drainage. Hypotheses presented are potentially applicable to biogeographies of other riverine fishes.
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