Riverscape genetic variation, migration patterns, and morphological variation of the threatened Round Rocksnail, Leptoxis ampla

Abstract

Within riverine systems, headwater populations are hypothesized to harbour higher amounts of genetic distinctiveness than populations in the main stem of a river and display increased genetic diversity in large, downstream habitats. However, these hypotheses were mostly developed with insects and fish, and they have not been tested on many invertebrate lineages. Pleuroceridae gastropods are of particular ecological importance to rivers of eastern North America, sometimes comprising over 90% of macroinvertebrate biomass. Yet, virtually nothing is known of pleurocerid landscape genetics, including whether genetic diversity follows predictions made by hypotheses developed on more mobile species. Moreover, the commonly repeated hypothesis that intraspecific morphological variation in gastropods results from ecophenotypic plasticity has not been well tested on pleurocerids. Using 2bRAD‐seq to discover single nucleotide polymorphisms, we show that the threatened, Cahaba River endemic pleurocerid, Leptoxis ampla, has limited gene flow among populations and that migration is downstream‐biased, conflicting with previous hypotheses. Both tributary and main stem populations harbour unique genomic profiles, and genetic diversity was highest in downstream populations. Furthermore, L. ampla shell morphology was more correlated with genetic differences among individuals and populations than habitat characteristics. We anticipate similar genetic and demographic patterns to be seen in other pleurocerids, and hypotheses about gene flow and population demographics that were based on more mobile taxa often, but not always, apply to freshwater gastropods. From a conservation standpoint, genetic structure of L. ampla populations suggests distinctive genetic diversity is lost with localized extirpation, a phenomenon common across the range of Pleuroceridae.

Genomic data reveal deep genetic structure but no support for current taxonomic designation in a grasshopper species complex

“…Spatial models had strong statistical support up to K = 3–5 (Figure a), but layers beyond K = 3 contributed relatively little to total covariance (Figure b). construct analyses showed strong genetic admixture for all K values (e.g., Whelan et al, ) and only genetic assignments for K = 3–4 were partially compatible with the presence of the two main genetic clusters revealed by structure and faststructure (Figure and Figure ).…”

Conservation genomics reveals low genetic diversity and multiple parentage in the threatened freshwater mussel,Margaritifera hembeli

“…However, fine-scale relationships and migration 462 patterns among populations that our SNP-based approach illuminated are novel. Sampled sites 463 appeared to demonstrate an isolation-by-distance effect, which is a general pattern seen in many 464 freshwater organisms (Meffe and Vrijenhoek 1988;Whelan et al 2019). Furthermore, AMOVA 465 indicated significant genetic structure with a genetic break occurring between collection sites 466 north and south of the Red River, with further significant genetic structure between populations 467 in the north and south.…”

Range reduction of Oblong Rocksnail,Leptoxis compacta, shapes riverscape genetic patterns

“…Pleurocerids are found east of the Rocky Mountains in North America, with most of their diversity concentrated in the southeastern United States (Lydeard & Mayden, 1995;Strong & Köhler, 2009). Pleurocerids lack a highly vagile veliger larval stage seen in many aquatic gastropod groups, and they are thought to move large distances only when washed downstream (Whelan et al, 2019;Whelan, Johnson & Harris, 2015). Only one study has been published on landscape and conservation genomics of pleurocerids, and that study focused exclusively on a single species, Leptoxis ampla (Whelan et al, 2019).…”

“…Pleurocerids lack a highly vagile veliger larval stage seen in many aquatic gastropod groups, and they are thought to move large distances only when washed downstream (Whelan et al, 2019;Whelan, Johnson & Harris, 2015). Only one study has been published on landscape and conservation genomics of pleurocerids, and that study focused exclusively on a single species, Leptoxis ampla (Whelan et al, 2019). Many freshwater species, including L. ampla, display common riverscape genetic patterns such as increased genetic diversity in downstream populations and isolation by distance (Hughes, Schmidt & Finn, 2009;Paz-Vinas et al, 2015).…”