Recognition of a highly restricted freshwater snail lineage (Physidae: Physella) in southeastern Oregon: convergent evolution, historical context, and conservation considerations

Abstract

Non-marine mollusks have the highest number of documented extinctions of any major taxonomic group. Given their conservation status and the numerous cases of taxonomic uncertainty concerning freshwater mollusks in particular, the recognition of potentially endangered species is critically important. Here, we evaluate the genetic distinctiveness and phylogenetic position of a freshwater snail restricted to a series of geothermal springs within the Owyhee River drainage in Oregon (the 'Owyhee wet-rock physa'). Because these snails closely resemble Physella (Petrophysa) zionis, a wet-rock physa that occurs in a small area in Zion National Park (Utah), the Owyhee wet-rock physa is presumably either closely related to or represents a disjunct population of P. zionis. However, phylogenetic analyses of sequences of mitochondrial cytochrome oxidase I and nuclear first and second internal transcribed spacer gene regions indicate that the Owyhee wet-rock physa is genetically distinct from other physid species. Despite exhibiting similar morphologies, the Owyhee wetrock physa and P. zionis are distantly related physids; instead, the Owyhee wet-rock physa is most closely related to a population of physids from central California. These results suggest that convergent evolution may be responsible for the similar shell morphologies of the Owyhee wetrock physa and P. zionis. Furthermore, the close relationship between physid populations in southeastern Oregon and central California suggests a historical connection between the Owyhee River and river drainages to the south. Finally, we recommend that the Owyhee wet-rock physa be considered critically endangered based on its extremely limited distribution.

Phylogeography and genetics of the globally invasive snail Physa acuta Draparnaud 1805, and its potential to serve as an intermediate host to larval digenetic trematodes

“…Additionally the presumed sister species P. spelunca has only been recovered from Wyoming [ 78 ] and did not have support as the sister species to P. acuta from our analyses. Anecdotally, recent molecular genetic studies of Physa [ 79 – 81 ] may demonstrate a greater number of independent taxonomic units from Western waterways relative to the Eastern USA, suggesting that biogeographically the west may have been important in physid diversification .…”

Molecular species delimitation refines the taxonomy of native and nonnative physinine snails in North America

“…This represented a modestly supported (BS 88) clade that consisted of specimens identified either as one of a host of formerly valid nominal species or as a previously recognized but still unnamed candidate taxon 38 , and were not identified by their collectors. This was further divided into two subclades, the first of which was highly supported (BS 98) and consisted of three forms (13–15) from western North America that were either grouped into a single species or regarded as three separate taxa in different analyses.…”

“…Each group had little intraspecific variation (all 0.4%) and strong bootstrap support (100), and differed from a sister taxon by 4.1 to 4.3%. One of these (form 15) is known to be morphologically distinctive and restricted to a single spring complex in eastern Oregon (and was included in our sample of new specimens), informally named the Owyhee wet-rock physa 38 ; it also exhibited an amino acid COI sequence divergent from all other members of Physinae and a diagnostic H3 sequence. On those grounds, we recognize it as a candidate taxon (CS 8).…”

“…Regardless of its origins, its presence in the Snake River was questioned in a subsequent study of newly acquired and museum specimens from the Snake River 37 , whose authors countered that not only was P. natricina sufficiently morphologically and genetically discrete to merit recognition, but that the thousands of other specimens in their dataset were P. gyrina , not P. acuta . Adding to the regional complexity is a candidate species from a spring complex in Oregon in the Owyhee River basin, a tributary to the Snake River, that appears to constitute a valid taxon that has yet to be described 38 , and the suspected presence of an unknown number of introduced species as well as native species of dubious validity 30 .…”

Untangling species identity in gastropods with polymorphic shells in the genus Bolma Risso, 1826 (Mollusca, Vetigastropoda)

“…These findings are consistent with the hypothesis that their morphological similarity may be a result of local adaptation to similar environments. Convergent evolution of shell-shape among phylogenetically divergent species experiencing similar environmental selection pressures has been widely documented (even though not always formally tested) in molluscs, including the freshwater limpets of the African genus Burnupia (Albrecht et al 2004), freshwater snails inhabiting geothermal springs in Oregon (Physa Draparnaud, 1801;Moore et al 2015), the hydrothermal vent snails Alviniconcha Okutani & Ohta, 1988(Johnson et al 2015 and the bathyal gastropod genus Gemmuloborsonia Shuto, 1989 (Puillandre et al 2010a). Along with these examples, our study suggested that shell shape in Bolma is highly adaptive and therefore has poor species-level significance.…”