Charles Lydeard

The Global Decline of Nonmarine Mollusks

Abstract Invertebrate species represent more than 99% of animal diversity; however, they receive much less publicity and attract disproportionately minor research effort relative to vertebrates. Nonmarine mollusks (i.e., terrestrial and freshwater) are one of the most diverse and imperiled groups of animals, although not many people other than a few specialists who study the group seem to be aware of their plight. Nonmarine mollusks include a number of phylogenetically disparate lineages and species-rich assemblages that represent two molluscan classes, Bivalvia (clams and mussels) and Gastropoda (snails, slugs, and limpets). In this article we provide an overview of global nonmarine molluscan biodiversity and conservation status, including several case studies documenting the diversity and global decline of nonmarine mollusks. We conclude with a discussion of the roles that mollusks and malacologists should play in conservation, including research, conservation management strategies, and education and outreach.

CHAPTER 17 – The Phylogenetic Utility of the Mitochondrial Cytochrome b Gene for Inferring Relationships among Actinopterygian Fishes

The objective of this chapter is to test the phylogenetic utility of the mitochondrial cytochrome b gene by analyzing the relationships of monophyletic Actinopterygii or ray-finned fishes at different hierarchic levels. Modern actinopterygians are the most diverse of all vertebrate groups and include more than 25,000 species. In order to assess the utility of the cytochrome b gene, actinopterygian fishes representing a diverse array of taxa and divergence times were selected. Facts and figures supporting phylogenetic hypothesis of actinopterygian fishes, including only the taxa, are examined based on morphological data from various sources. Although this chapter focuses on the cytochrome b gene, this study serves as a model for further studies that examines the utility of other genes. It lists the actinopterygian species examined in this study and their current classification. The mitochondrial cytochrome b gene sequences for the remaining 18 ray-finned fishes were retrieved from GenBank. The results of Cytochrome b sequence variation, base compositional bias, and amino acids differences are very important from the analytical point of view as is the assessment of the phylogenetic utility of the mitochondrial cytochrome b gene arrived at by examining taxonomic congruence between molecular- and morphological-based phylogenetic hypotheses.

Phylogeographic analysis of the threatened and endangered superconglutinate-producing mussels of the genus Lampsilis (Bivalvia: Unionidae)

Several species of freshwater unionid mussels in the genus Lampsilis exhibit a remarkable reproductive strategy. Female mussels of these species enclose their larvae in a minnow‐like lure, called a ‘superconglutinate’, to attract piscivorous fishes. When a fish attempts to ingest the superconglutinate the lure ruptures and the larvae are released to parasitize the fish. Of the four species of mussel which exhibit this strategy and are endemic to the Gulf Coast drainages of the southeastern United States, three are protected under the Endangered Species Act, and one is recognized as imperilled. Phylogenetic analysis of nucleotide sequences of the mitochondrial 16S ribosomal RNA and the first subunit of the cytochrome oxidase c genes was conducted on 18 individual specimens representing these four species and six outgroup taxa. Phylogenetic analyses of these data support the monophyly of the superconglutinate‐producing mussels, and indicates a strong geographical component to the data. The zoogeographic patterns of the four taxa included in the study are congruent with those seen in freshwater vertebrates, and are consistent with a vicariant pattern resulting from fluctuations in sea level during the Pleistocene. Despite the strong geographical structuring of the data, only one species, Lampsilis subangulata, was recovered as monophyletic. The authors attribute the lack of support for the monophyly of the remaining species to insufficient sequence variation and the recent origin of the ancestor of these taxa. Based on these data, any future captive breeding projects aimed at augmenting or re‐establishing populations should do so only from the appropriate source populations so as to maintain the genetic integrity of these nascent species.

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

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.

Identification of 'extinct' freshwater mussel species using DNA barcoding

Freshwater mollusks are highly imperiled, with 70% of the North American species extinct, endangered, or at risk of extinction. Impoundments and other human impacts on the Coosa River of Alabama, Georgia and Tennessee of the southeastern USA alone are believed to have caused 50 mollusk species extinctions, but uncertainty over boundaries among several putatively closely related species makes this number preliminary. Our examination of freshwater mussels collected during an extensive survey of the upper‐drainage basin, DNA barcoding and molecular phylogenetic analyses confirm the rediscovery of four morphospecies in the genus Pleurobema (Unionidae) previously thought to be extinct from the upper Coosa basin. A fifth ‘extinct’ form was found in an adjoining basin. Molecular data show that the Coosa morphologies represent at least three species‐level taxa: Pleurobema decisum, P. hanleyianum and P. stabile. Endemism is higher than currently recognized, both at the species level and for multispecies clades. Prompt conservation efforts may preserve some of these taxa and their ecosystem.

Prodigious polyphyly in imperilled freshwater pearly-mussels (Bivalvia: Unionidae): a phylogenetic test of species and generic designations

Abstract Unionid bivalves or freshwater pearly-mussels (Unionoidea: Unionidae) serve as an exemplary system for examining many of the problems facing systematists and conservation biologists today. Most of the species and genera were described in the late 1800s and early 1900s, but few phylogenetic studies have been conducted to test conventional views of species and classification. Pearly-mussels of Gulf Coastal drainages of the southeastern United States from the Escambia (southern Alabama to Florida) to the Suwannee Rivers (Florida) are a unique fauna comprised of approximately 100 species, with about 30 endemic to the region. In this study, mitochondrial cytochrome c oxidase subunit I and 16S rRNA gene sequences were used to test the monophyly and to estimate evolutionary relationships of five unionid species representing three different genera. The molecular phylogenies depict all three genera as polyphyletic. The prodigious polyphyly exhibited within unionids is due to incorrect notions of homology and false assumptions about missing anatomical data. In contrast, the molecular phylogeny provides evidence to support the recognition of all five unionid species as distinct evolutionary entities. Furthermore, molecular genealogical evidence supports the elevation of Quincuncina infucata (Conrad) of the Suwannee River to species level, for which Q. kleiniana (Lea) is available.

The Genera of Pleurobemini (Bivalvia: Unionidae: Ambleminae)

Abstract: The unionid tribe Pleurobemini is diverse but poorly-understood phylogenetically. Current classification recognizes two highly diverse genera, Elliptio Rafinesque, 1819 and Pleurobema Rafinesque, 1820, besides the moderately diverse Fusconaia Simpson, 1900, and several genera with one to three species. However, classification at the species and genus level has been problematic. Molecular data and re-examination of shell morphology and anatomy indicate new groupings of these taxa. Several genera proposed by early workers such as Rafinesque and Swainson are available, but are poorly-characterized and are often overlooked. We analyzed two mitochondrial genes, cox1 and nad1, for 50 species assigned to Pleurobemini, including the type species of each genus and as many other species as possible. Although the majority of studied species in Elliptio, Pleurobema, and Fusconaia show close affinities to the respective type species, the affinities of others are problematic. Genera or subgenera such as Eurynia Rafinesque, 1819, Sintoxia Rafinesque, 1820, and Pleuronaia Frierson, 1927, generally regarded as subjective synonyms, apply to some clades. Other clades or unaffiliated species have no available name. Quincuncina burkei (Walker, 1922), the type of the genus Quincuncina Ortmann, 1922, is assigned to Fusconaia Simpson, 1900. Fusconaia apalachicola (Williams and Fradkin, 1999), F. ebenus (Lea, 1831), F. rotulata (Wright, 1899) (also listed as Obovaria rotulata), F. succissa (Lea, 1852), Cyclonaias tuberculatus (Rafinesque, 1820), Uniomerus Conrad, 1853, and the Quincuncina infucata (Conrad, 1834) complex are all excluded from Pleurobemini. The first three are placed in the new genus Reginaia Campbell and Lydeard; Uniomerus Conrad, 1853 is assigned to Quadrulini; and the remainder belong in the pustulosa Lea, 1831 group of Quadrulini (genus Rotundaria Rafinesque, 1820).

Pulmonate phylogeny based on 28S rRNA gene sequences: A framework for discussing habitat transitions and character transformation

Pulmonate snails occupy a wide range of marine, estuarine, freshwater and terrestrial environments. Non-terrestrial forms are supposed to be basal in pulmonate evolution but the groups phylogeny is not well resolved either morphologically or on the basis of available DNA sequence data. The lack of a robust phylogeny makes it difficult to understand character polarization and habitat transformation in pulmonates. We have investigated pulmonate relationships using 27 new sequences of 28S rRNA from pulmonates and outgroups, augmented with data from GenBank. The complete alignments comprised about 3.8kb. Maximum parsimony, maximum likelihood and Bayesian analyses of alignments generated under different assumptions are reported. Complete alignments appear to have a degree of substitution saturation so where there is conflict between hypothesised relationships more weight is given to analyses where regions of random similarity are excluded and which are not affected by this complication. Monophyly of the five main pulmonate groups was robustly supported in almost all analyses. The marine group Amphiboloidea and the freshwater Glacidorbidae are the most basal. The remaining pulmonates (Siphonariidae, Hygrophila and Eupulmonata) form a moderately-supported monophyletic group in all analyses bar one probably affected by saturation of substitutions. Siphonariidae, a predominantly marine and intertidal family, and Eupulmonata (mainly terrestrial with marine, estuarine and freshwater species) form a strongly supported clade that is the sister group to Hygrophila (freshwater). Multiple colonizations of freshwater and terrestrial habitats by pulmonate snails are suggested. No analyses strongly support the possibility of habitat reversions. The colonizations of freshwater by Hygrophila and of land by Stylommatophora were apparently phylogenetically independent although it cannot yet be excluded that there were transient terrestrial phases in the history of the former group or freshwater phases in the latter.

The evolution of reproductive isolation in a simultaneous hermaphrodite, the freshwater snail Physa

BackgroundThe cosmopolitan freshwater snail Physa acuta has recently found widespread use as a model organism for the study of mating systems and reproductive allocation. Mitochondrial DNA phylogenies suggest that Physa carolinae, recently described from the American southeast, is a sister species of P. acuta. The divergence of the acuta/carolinae ancestor from the more widespread P. pomilia appears to be somewhat older, and the split between a hypothetical acuta/carolinae/pomilia ancestor and P. gyrina appears older still.ResultsHere we report the results of no-choice mating experiments yielding no evidence of hybridization between gyrina and any of four other populations (pomilia, carolinae, Philadelphia acuta, or Charleston acuta), nor between pomilia and carolinae. Crosses between pomilia and both acuta populations yielded sterile F1 progeny with reduced viability, while crosses between carolinae and both acuta populations yielded sterile F1 hybrids of normal viability. A set of mate-choice tests also revealed significant sexual isolation between gyrina and all four of our other Physa populations, between pomilia and carolinae, and between pomilia and Charleston acuta, but not between pomilia and the acuta population from Philadelphia, nor between carolinae and either acuta population. These observations are consistent with the origin of hybrid sterility prior to hybrid inviability, and a hypothesis that speciation between pomilia and acuta may have been reinforced by selection for prezygotic reproductive isolation in sympatry.ConclusionsWe propose a two-factor model for the evolution of postzygotic reproductive incompatibility in this set of five Physa populations consistent with the Dobzhansky-Muller model of speciation, and a second two-factor model for the evolution of sexual incompatibility. Under these models, species trees may be said to correspond with gene trees in American populations of the freshwater snail, Physa.

Molecular systematics of Fusconaia (Bivalvia: Unionidae: Ambleminae)

Abstract: The genus Fusconaia Simpson, 1900, as currently recognized, includes ~12 species in the tribe Pleurobemini. Two species are federally listed and several more are imperiled in part or all of their ranges; one species is probably extinct. However, classification at the species and genus level has been problematic, and it is unknown whether imperiled populations represent merely local ecophenotypic variations or endemic species. To provide additional evidence on the systematics of this group and to help establish conservation priorities, we sequenced two mitochondrial genes for all available species of Fusconaia as well as representatives of other genera of Pleurobemini and several outgroups. Both cox1 and nad1 provided well-resolved phytogenies. Some putative species show little molecular differentiation, supporting their synonymization. In particular, Fusconaia flava (Rafinesque, 1820), F. cerina (Conrad, 1838), and the easternmost populations previously assigned to F. askewi (Marsh, 1896) are not differentiated by our data. Although the majority of Fusconaia places in a well-supported clade that includes F. flava, the type species, others do not. “Fusconaia” barnesiana (Lea, 1838), the type of Pleuronaia Frierson, 1927, places with “Lexingtonia” dollabelloides (Lea, 1840) and “Pleurobema” gibberum (Lea, 1838). “Fusconaia” ebenus (Lea, 1831) and “F.” rotulata (Wright, 1899) form a distinct clade outside of Pleurobemini. “Fusconaia” succissa (Lea, 1852) is assigned to the pustulosa group of Quadrula (subgenus Rotundaria), along with Quincuncina infucata (Conrad, 1834). Conversely, the type species of Quincuncina, Quincuncina burkei Walker, 1922, is assigned to Fusconaia. Populations in the Ozark region assigned to F. flava and populations in the Suwannee River system assigned to Quincuncina infucata probably deserve species-level recognition.