Phylogeny, taxonomy, genetics and global heritage ranks of an imperilled, freshwater snail genus Lithasia (Pleuroceridae)

Abstract

Numerous aquatic species are threatened with extinction from habitat elimination or modification. One particularly imperilled group is the freshwater gastropod family Pleuroceridae. Pleurocerids reach their greatest diversity in the southeastern United States, and many species are currently considered extinct, endangered or threatened. One issue hindering efforts to implement conservation management plans for imperilled pleurocerid species is that the taxonomy is in an abysmal state. The taxonomy of pleurocerids is currently based on late 19th- and early 20th-century studies, which used a typological or morphospecies concept. Most biologists today doubt the validity of many of the currently recognized species; however, this does not stop them from assigning conservation ranks in an attempt to determine which species are imperilled or currently stable. We conducted a phylogenetic analysis of the pleurocerid genus Lithasia using morphological and mitochondrial DNA sequence (mtDNA) data in an attempt to delimit species boundaries and test previous taxonomic schemes. We found that the current taxonomy of Lithasia does not reflect species diversity adequately within the genus, with two new undescribed species being discovered. The conservation status ranks of the new, undescribed species are imperilled and would have been overlooked had we relied on the conventional taxonomy. Additionally, the undescribed species' conservation ranks that were previously apparently secure became vulnerable due to being inappropriately assigned as members of formerly widely distributed species instead of the imperilled status they warrant and vice versa, as some taxa that were considered imperilled are now thought to be modestly stable. Our study suggests that conservation ranks should be considered suspect at best in taxonomically poorly known groups until the taxa are reviewed using modern systematic methods.

Correlates of snail shell variation along a unidirectional freshwater gradient in Lithasia geniculata (Haldeman, 1840) (Caenogastropoda: Pleuroceridae) from the Duck River, Tennessee, USA

“…One species, Lithasia geniculata (Haldeman, 1840) from the Duck River in Tennessee, exhibits shell plasticity in an upstream-downstream fashion. Multiple authors have confirmed that L. geniculata has four diagnosable shell forms; once treated as nominal species, they represent one taxon exhibiting continuous variation throughout the river (davis 1974, stein & stansBeRy 1984, Minton & lydeaRd 2003, Minton et al 2008. The smooth more globose-shelled L. geniculata form pinguis occupies the headwaters and is replaced by the more conical duttoniana and fuliginosa forms mid-river.…”

Global diversity of gastropods (Gastropoda; Mollusca) in freshwater

“…Such studies have demonstrated that many currently recognized species are not monophyletic (Minton & Lydeard, 2003;Wethington, 2004) and/or have revealed unrecognized species complexes [e.g., European and North American lymnaeids (Remigio & Blair, 1997;Remigio, 2002); North American pleurocerids (Lydeard et al, 1998); Indonesian pachychiUds (von Rintelen & Glaubrecht, 2005)]. Alternatively, some past studies have overindulged in synonymy, for example Hubendick's (1951) major review of world wide Lymnaeidae recognized only 38 valid species and two genera, while recent studies (e.g., Remigio & Blair, 1997;Kruglov, 2005) have indicated that there are several valid genera and a number of additional species, including several synonymized by Hubendick.…”

Intraspecific models and spatiotemporal context of size–mass relationships in adult dragonflies

“…For example, a phylogenetic analysis of the pleurocerid snail genus Lithasia revealed 2 new imperiled cryptic species that had previously been included inappropriately in a widely distributed species (Minton and Lydeard 2003). Systematic studies can help guide conservation priorities by determining areas of high phylogenetic diversity in the form of evolutionary significant units (Moritz 1994, Faith and Baker 2006.…”