And So We Meet Again: Allopatric Divergence and Secondary Contact with Gene Flow is a Recurring Them
Perry, Blair W. blair.perry@uta.edu
Schield, Drew R.
Adams, Richard H. Department of Biology
University of Texas at Arlington Arlington, Texas, USA
Card, Daren C.
Department of Biology
University of Texas at Arlington Arlington, Texas, USA
Department of Organismic and Evolutionary Biology Museum of Comparative Zoology
Harvard University
Cambridge, Massachusetts, USA
Jezkova, Tereza
Department of Biology
Miami University of Ohio Oxford, Ohio, USA
Pasquesi, Giulia I. M.
Nikolakis, Zachary L.
Row, Kristopher Department of Biology
University of Texas at Arlington Arlington, Texas, USA
Meik, Jesse M.
Department of Biological Sciences Tarleton State University Stephenville, Texas, USA
Smith, Cara F.
Mackessy, Stephen P.
School of Biological Sciences
University of Northern Colorado
Greeley, Colorado, USA
Castoe, Todd A. Department of Biology
University of Texas at Arlington Arlington, Texas, USA
The study of recently diverged lineages whose geographic ranges come into contact can provide insight into the early stages of speciation and the potential roles of reproductive isolation in generating and maintaining species. Such insight can also be important for understanding the strategies and challenges for delimiting species within recently diverged species complexes. Here, we used mitochondrial and nuclear genetic data to study population structure, gene flow, and demographic history across a geographically widespread rattlesnake clade, the western rattlesnake species complex (Crotalus cerberus, C. viridis, C. oreganus, and relatives), which contains multiple lineages with ranges that geographically overlap or contact one another. We find evidence that pervasive gene flow has broadly influenced patterns of present-day genetic diversity. Our results suggest that lineage diversity has been shaped largely by drift and divergent selection in isolation, followed by secondary contact in which reproductive isolating mechanisms appear weak and insufficient to prevent introgression, even between anciently diverged lineages. The complexity of divergence and secondary contact with gene flow among lineages also provides new context for why delimiting species within this complex has been historically difficult and contentious.