Gulf Coast vicariance shapes phylogeographic history of a North American freshwater mussel species complex

Abstract

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- MYA (Gulf Coast allopatric speciation model) and (3) if diversification in MississippiRiver 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.

Biogeography of freshwater mussels (Bivalvia: Unionida) in Texas and implications on conservation biology

“…Those events caused fluctuating sea levels and changes in stream connections, which are hypothesized to have resulted in speciation events and faunal exchange (Conner & Suttkus, 1986; MacGuigan et al, 2021; Near et al, 2003). Similar findings have been made for freshwater mussels endemic to GOM basins found in northern Mexico to Louisiana (Keogh et al, 2021; Pieri et al, 2018; Smith et al, 2021) .…”

Strong, Recent Selective Sweeps Reshape Genetic Diversity in Freshwater BivalveMegalonaias nervosa

“…S1, Supplementary Material online). Inference of ancient population expansion is consistent with a species range expansion at the end of the last glaciation as greater habitat became available after glaciers receded ( Elderkin et al 2007 ; Keogh et al 2021 ). Diversity π and Tajima’s D varies across scaffolds, with a roughly normal distribution genomewide ( fig.…”

Novel Pipeline for Large-Scale Comparative Population Genetics

“…CO1 is expected to be more conservative than some other markers, such as microsatellites, which are commonly used for analysis below the species level in detecting differences among individuals within species (Liu et al, 2020). However, there is evidence that there is sufficient variability in CO1 to detect major population divisions and phylogeographic history (e.g., April et al, 2012, Bernatchez & Wilson, 1998, Keogh et al, 2021, Witt & Hebert, 2000). CO1 has been used to answer questions at a variety of temporal scales, including drawing conclusions about demographic history, divergence times, and events occurring millions of years ago (Attiná et al, 2021, Choi et al, 2020, Havel et al, 2000, Jossart et al, 2017, Reed et al, 2006, Stark et al, 2021, Talbot et al, 2016).…”