A test of the vicariance hypothesis of western North American freshwater biogeography

Aim The biogeography of western North American freshwater molluscs has traditionally been attributed to vicariance associated with late Tertiary rearrangement of landscape based on distributional evidence and the putatively limited dispersal ability of these organisms. We examined the phylogeography of a widely ranging western springsnail (Pyrgulopsis wongi Hershler, 1989) to test this hypothesis and evaluate the relative importance of vicariance and dispersal in structuring the distribution of this species. Location Southwestern Great Basin (California and Nevada), United States of America. Method Two mitochondrial genes (COI, NDI) were sequenced for 28 populations of P. wongi spanning its entire geographic range, which consists of 10 topographically closed drainage basins. We also sequenced eight closely related congeners, as well as the type species of the closely related eastern North American genus Floridobia Hershler & Thompson, 2002, which was used as the outgroup. Phylogenies based on the combined data set were obtained using several methods, and networks for each gene were generated as an additional means of examining relationships among haplotypes. Partitioning of haplotype variation was studied using amova , migration between populations was estimated using a coalescent‐based method (mdiv ), and divergence times were inferred using a locally calibrated molecular clock and mdiv . Results Pyrgulopsis wongi is subdivided into narrowly localized and widely distributed lineages that diverged in the Pleistocene, well after the inception of the contemporary regional landscape. While large Φ_ST values and the localized geographic distributions of most haplotypes imply absence or negligible contemporary dispersal of this spring‐dwelling snail, the pattern of phylogeographic structuring, presence of a few widespread haplotypes, and results of the mdiv analyses suggest geologically recent dispersal across drainage divides. Main conclusions Phylogeography of P. wongi conflicts with the traditional vicariance model as it is not structured by the contemporary landscape and is instead indicative of geologically recent dispersal. In the absence of evidence that dispersal of this species occurred through surface water connections during the relevant (Quaternary) time frame, we conjecture that spread may have instead been mediated by transport on waterfowl or via upland stream capture. The non‐concordance between phylogeography and landscape reported in this and other recent studies of Pyrgulopsis suggests that members of this diverse and imperiled genus should not be managed using an a priori, ‘watershed as conservation unit’ approach.     

Phylogenetic relationships of the Cochliopinae (Rissooidea: Hydrobiidae): an enigmatic group of aquatic gastropods

Phylogenetic analysis based on a partial sequence of the mitochondrial cytochrome c oxidase subunit I gene was performed for 26 representatives of the aquatic gastropod subfamily Cochliopinae, 6 additional members of the family Hydrobiidae, and outgroup species of the families Rissoidae and Pomatiopsidae. Maximum-parsimony analysis yielded a single shortest tree which resolved two monophyletic groups: (1) a clade containing all cochliopine taxa with the exception of Antroselates and (2) a clade composed of Antroselates and the hydrobiid genus Amnicola. The clade containing both of these monophyletic groups was depicted as more closely related to members of the family Pomatiopsidae than to other hydrobiid snails which were basally positioned in our topology. New anatomical evidence supports recognition of the cochliopine and Antroselates-Amnicola clades, and structure within the monophyletic group of cochliopines is largely congruent with genitalic characters. However, the close relationship between the Pomatiopsidae and these clades is in conflict with commonly accepted classifications and suggests that a widely accepted scenario for genitalic evolution in these snails is in need of further study.     

Assembly of a micro-hotspot of caenogastropod endemism in the southern Nevada desert,with a description of a new species of Tryonia (Truncatelloidea,Cochliopidae)

Newly obtained and previously published sequences of the cytochrome c oxidase subunit I (COI) gene were analyzed to examine the biogeographic assembly of the caenogastropod fauna (belonging to the families Assimineidae, Cochliopidae, and Hydrobiidae) of an isolated spring along the lower Colorado River in southern Nevada (Blue Point Spring). Based on available COI clock calibrations, the three lineages that comprise this fauna are 2.78–1.42 million years old, which is roughly coeval or slightly younger than the age of Blue Point Spring (inferred from local fossil spring deposits). Two of the lineages—endemic Pyrgulopsis coloradensis and Assiminea aff. infima—are most closely related to snails in the Death Valley area (well to the west) and likely colonized Blue Point Spring by transport on birds. A single haplotype was detected in both of these snails, suggesting that they may have only recently colonized Blue Point Spring. The third lineage—endemic Tryonia infernalis, newly described herein based on morphological and molecular evidence—is most closely related to a geographically proximal species in a lower Colorado River tributary (Tryonia clathrata); the split between these taxa may be the product of vicariance (severance of a prior drainage connection) or a separate jump dispersal event. The considerable genetic diversity in Tryonia infernalis (three haplotypes differing by 0.6% mean sequence divergence) suggests a possibly lengthy history of local differentiation. Our findings also identify Blue Point Spring as a new micro-hotspot of groundwater-dependent biodiversity in Nevada and will assist ongoing efforts to protect and conserve these imperiled ecosystems.     

The endemic gastropod fauna of Lake Titicaca: correlation between molecular evolution and hydrographic history

Lake Titicaca, situated in the Altiplano high plateau, is the only ancient lake in South America. This 2- to 3-My-old (where My is million years) water body has had a complex history that included at least five major hydrological phases during the Pleistocene. It is generally assumed that these physical events helped shape the evolutionary history of the lake's biota. Herein, we study an endemic species assemblage in Lake Titicaca, composed of members of the microgastropod genus Heleobia, to determine whether the lake has functioned as a reservoir of relic species or the site of local diversification, to evaluate congruence of the regional paleohydrology and the evolutionary history of this assemblage, and to assess whether the geographic distributions of endemic lineages are hierarchical. Our phylogenetic analyses indicate that the Titicaca/Altiplano Heleobia fauna (together with few extralimital taxa) forms a species flock. A molecular clock analysis suggests that the most recent common ancestor (MRCAs) of the Altiplano taxa evolved 0.53 (0.28-0.80) My ago and the MRCAs of the Altiplano taxa and their extralimital sister group 0.92 (0.46-1.52) My ago. The endemic species of Lake Titicaca are younger than the lake itself, implying primarily intralacustrine speciation. Moreover, the timing of evolutionary branching events and the ages of two precursors of Lake Titicaca, lakes Cabana and Ballivián, is congruent. Although Lake Titicaca appears to have been the principal site of speciation for the regional Heleobia fauna, the contemporary spatial patterns of endemism have been masked by immigration and/or emigration events of local riverine taxa, which we attribute to the unstable hydrographic history of the Altiplano. Thus, a hierarchical distribution of endemism is not evident, but instead there is a single genetic break between two regional clades. We also discuss our findings in relation to studies of other regional biota and suggest that salinity tolerance was the most likely limiting factor in the evolution of Altiplano species flocks.     

Mitochondrial DNA sequences reveal extensive cryptic diversity within a western American springsnail

We analysed cytochrome c oxidase subunit I and NADH dehydrogenase subunit I sequence variation among 29 populations of a widely ranging southwestern springsnail (Pyrgulopsis micrococcus) and 18 regional congeners. Cladistic analyses of these sequences depict P. micrococcus as a polyphyletic composite of five well-supported clades. Sequence divergences among these clades and subclades imply the possible occurrence of as many as seven or eight cryptic species in addition to P. micrococcus. Our finding that P. micrococcus contains multiple, genetically distinct and geographically restricted lineages suggests that diversification within this highly speciose aquatic genus has been structured in large part by the operation of terrestrial barriers to gene flow. However, these sequence data also indicate that recent dispersal among hydrographically separated areas has occurred within one of these lineages, which we attribute to passive transport on migratory waterbirds.     

Phylogenetic relationships within the aquatic snail genus Tryonia: implications for biogeography of the North American Southwest

We examined the phylogenetic relationships among 23 species of the North American aquatic snail genus Tryonia (Hydrobiidae), 10 additional representatives of the subfamily Cochliopinae, and two outgroups. Maximum parsimony analysis of a 601-base-pair sequence from the mitochondrial COI gene did not support monophyly of the genus nor its subgenus Paupertryonia. A clade composed of the type species of Tryonia and 16 congeners was strongly supported by the COI data and congruent with recently discovered variation in female genitalic morphology. This "true Tryonia" clade included two large western subclades having a sister-group relationship. The phylogenetic structure of one of these subclades is congruent with vicariant events associated with late Neogene history of the lower Colorado River drainage. The other subclade mirrors development of the modern Rio Grande rift and inception of modern topography in the southwestern Great Basin during the late Neogene. Both subclades are represented in the composite Tryonia fauna of the Amargosa River basin, whose assembly is attributed to the complex geological history of the Death Valley region.     

Redescription of Marstonia comalensis (Pilsbry & Ferriss, 1906), a poorly known and possibly threatened freshwater gastropod from the Edwards Plateau region (Texas)

Marstonia comalensis, a poorly known nymphophiline gastropod (originally described from Comal Creek, Texas) that has often been confused with Cincinnatia integra, is re-described and the generic placement of this species, which was recently allocated to Marstonia based on unpublished evidence, is confirmed by anatomical study. Marstonia comalensis is a large congener having an ovate-conic, openly umbilicate shell and penis having a short filament and oblique, squarish lobe bearing a narrow gland along its distal edge. It is well differentiated morphologically from congeners having similar shells and penes and is also genetically divergent relative to those congeners that have been sequenced (mtCOI divergence 3.0-8.5%). A Bayesian analysis of a small COI dataset resolved Marstonia comalensis in a poorly supported sub-clade together with Marstonia hershleri, Marstonia lustrica and Marstonia pachyta. The predominantly new records presented herein indicate that Marstonia comalensis was historically distributed in the upper portions of the Brazos, Colorado, Guadalupe and Nueces River basins, south-central Texas. The species has been live collected at only 12 localities and only two of these have been re-visited since 1993. These data suggest that the conservation status of this snail, which has a critically imperiled (G1) NatureServe ranking and was recently proposed for federal listing, needs to be re-assessed.     

Phylogeography of an endangered Western North American springsnail

We provide the first genetic analysis of the Bruneau Hot Springsnail (Pyrgulopsis bruneauensis), a federally listed (endangered) hydrobiid gastropod that is distributed in spring-fed habitats along a short reach of the Bruneau River in southwestern Idaho and threatened with extinction by groundwater withdrawal. Partial sequences of mitochondrial cytochrome c oxidase subunit I (COI) and NADH dehydrogenase subunit I (NDI) were obtained from 51 specimens from six sites spanning the narrow geographic range of P. bruneauensis. A Bayesian analysis of the combined dataset resolved this species as a well supported clade which differed from other regional congeners by 4.66–10.62% sequence divergence (COI). The 11 observed COI haplotypes in P. bruneauensis formed two divergent (1.42 ± 0.7%) subgroups that co-occurred at five of the six collecting sites. COI haplotype diversity was substantial (ranging up to 0.9111) in all but one sample, while nucleotide diversity was low (<0.01). AMOVA detected small but significant variation among sites, although only one sample was significantly differentiated by pairwise comparisons. Haplotype composition varied widely among the collecting localities and no obvious geographic pattern was detected. These findings suggest that translocation of snails, which was considered as a possible measure in the P. bruneauensis recovery plan, should be preceded by assays to ensure selection of appropriately genetically diverse source populations.     

PERMANENT GENETIC RESOURCES: Microsatellite markers for the threatened Bliss Rapids snail (Taylorconcha serpenticola) and cross-amplification in its congener, T. insperata

We developed and tested microsatellite markers to investigate population structure of a threatened North American freshwater gastropod, Taylorconcha serpenticola. Of the 21 primer pairs that were evaluated, 11 were readily optimized and scored, providing amplification of 12 loci that were screened for 820 specimens from 29 populations. The number of alleles across 11 of these polymorphic loci ranged from three to 20 and the observed heterozygosity varied from 0.0061 to 0.7561. All loci yielded suitable amplification products in the second species of Taylorconcha (T. insperata) and three proved to be diagnostic for these congeners, demonstrating that these markers are also useful for species identification studies.     

Phylogenetic relationships of North American nymphophiline gastropods based on mitochondrial DNA sequences

Phylogenetic relationships of 36 nymphophiline species representing 10 genera were inferred from mtCOI sequence data and compared to recent morphology-based classifications of this group. Parsimony and maximum likelihood analyses of the molecular data set suggested monophyly of the North American nymphophilines and a sister or otherwise close relationship between this fauna and a European species assigned to the subfamily. Results also supported a previously hypothesized close relationship between the predominantly freshwater nymphophilines and the brackish-water genus Hydrobia . Our analyses resolved a North American nymphophiline subclade composed of Floridobia , Nymphophilus , and Pyrgulopsis , and depicted the remaining North American genera ( Cincinnatia , Marstonia , Notogillia , Rhapinema , Spilochlamys , Stiobia ) as either a monophyletic or paraphyletic group. Two of the large North American genera ( Floridobia , Marstonia ) were supported as monophyletic groups while monophyly of Pyrgulopsis , a western North American group containing > 100 species, was equivocal. North American nymphophiline phylogeny implies that vicariance of eastern and western North American groups was followed by a secondary invasion of eastern coastal areas from the west. We attribute this to dispersal of salt-tolerant progenitors along the Gulf of Mexico coast