Aim: Freshwater mussels share habitat and are parasites of freshwater fishes during the larval life stage. Therefore, models of fish biogeography may also explain the historical biogeography of freshwater mussels. We tested this assumption using predictions of three biogeographic models constructed for northern Gulf of Mexico drainages on a freshwater mussel species complex. Specifically, we tested (1) if speciation was due to vicariant events of fluctuating sea levels that separated lineages east-west of the Mobile Basin (Central Gulf Coast speciation hypothesis), (2) if the timing of divergences occurred 8.5–3.5 MYA (Gulf Coast allopatric speciation model) and (3) if diversification in Mississippi River populations was recent and for evidence of population increase consistent with range expansion into northern deglaciated regions (Pleistocene glaciation model). Location: Eastern North America. Taxon: Freshwater mussels (Bivalvia: Unionidae), Lampsilis teres and L. floridensis. Methods: We collected 249 specimens from 73 localities across the group's distribution. We used three molecular markers (COI, NDI & ITSI) to conduct time calibrated Bayesian phylogenetic analyses, phylogeographic analyses (AMOVA & SAMOVA) and demographic analyses including Bayesian skyline plots. Results: Lampsilis teres and L. floridensis are allopatric species whose distributions meet at the eastern edge of the Mobile Basin. Speciation was estimated to occur in the late Miocene. Populations from isolated river systems surrounding the Gulf of Mexico are almost all monophyletic. Mississippi drainage samples formed a shallow clade with recent diversification and showed evidence of recent population expansion. Main conclusions: The historical biogeography of the L. teres species complex is broadly consistent with tested ichthyofaunal models. The timing of speciation and intraspecific divergences correspond to low sea-level events suggesting that Gulf Coast sea-level fluctuations are responsible for dispersal (sea-level recession) and subsequent cladogenesis (sea-level inundation). Consistent with numerous other freshwater studies, we found the Mobile Basin to be a suture zone, which may be due to the narrow, offshore continental shelf.
Bibliographical noteFunding Information:
Many people assisted with field collecting of mussels including Jeff Garner, John Harris, Mike Davis, Shelby Marr, Bernard Sietman, Don Hubbs, Jason Wisniewski, Josh Obermeyer, Carla Atkinson, Michael Buntin, Paul Johnson, Paul Hartfield, Todd Slack, Bob Jones, Ben Bosman, Clint Robertson, Tony Brady, Jennifer Grunewald, Patric Harper, Matt Duplessis, Chase Smith, Sandy Pursifull, Jordan Holcomb, Matt Rowe, Paul Freeman, Karen Herrington, John Johansen, Savannah Reach, Jesse Hollifield, Kevin Cummings, Rachel Vinsel, Andrew Hazzard and Danny Walsh. We thank Caitlin Beaver and Chase Smith for assistance in the genetics laboratory. The use of museum collections, specifically tissue for molecular analysis from the Arkansas State University Museum of Zoology, Bell Museum of Natural History, Florida Museum of Natural History, Illinois Natural History Survey and Texas A&M Natural Resources Institute, greatly improved this study. We thank Lisa and Jeff Garner, Meenu and Rahul Saraf, Stuart McGregor, Emily Olsen & Eric Puls, and Josh Obermeyer for their hospitality during field excursions. Specimens collected by S.K. were done under the following collecting permits: Arkansas (050320162), Alabama (2016109109668680), Illinois (A16.6004) and Mississippi (0624161) in 2016. Collecting in Texas by C.R. was done under permit SPR-0511-142. No federally protected species were collected for this research. This work was funded by the Wally Dayton Wildlife Fellowship, Moos Graduate Research Fellowship in Aquatic Biology (University of Minnesota), Joyce Davenport Fellowship, Dayton Research Grant & Dayton Fellowship (Bell Museum of Natural History), Minnesota Agricultural Experiment Station and U.S. Geological Survey. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the US Government.
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- North America
- Pleistocene glaciation
- sea-level changes