Conservation Genetics of a Critically Endangered Limpet Genus and Rediscovery of an Extinct Species

Diarmaid Ó Foighil,Jingchun Li,John B Burch,Ryan Evans,Taehwan Lee,Paul Johnson,Samuel T Turvey

doi:10.1371/journal.pone.0020496

Abstract

BackgroundA third of all known freshwater mollusk extinctions worldwide have occurred within a single medium-sized American drainage. The Mobile River Basin (MRB) of Alabama, a global hotspot of temperate freshwater biodiversity, was intensively industrialized during the 20th century, driving 47 of its 139 endemic mollusk species to extinction. These include the ancylinid limpet Rhodacmea filosa, currently classified as extinct (IUCN Red List), a member of a critically endangered southeastern North American genus reduced to a single known extant population (of R. elatior) in the MRB.Methodology/Principal FindingsWe document here the tripling of known extant populations of this North American limpet genus with the rediscovery of enduring Rhodacmea filosa in a MRB tributary and of R. elatior in its type locality: the Green River, Kentucky, an Ohio River Basin (ORB) tributary. Rhodacmea species are diagnosed using untested conchological traits and we reassessed their systematic and conservation status across both basins using morphometric and genetic characters. Our data corroborated the taxonomic validity of Rhodacmea filosa and we inferred a within-MRB cladogenic origin from a common ancestor bearing the R. elatior shell phenotype. The geographically-isolated MRB and ORB R. elatior populations formed a cryptic species complex: although overlapping morphometrically, they exhibited a pronounced phylogenetic disjunction that greatly exceeded that of within-MRB R. elatior and R. filosa sister species.Conclusions/Significance Rhodacmea filosa, the type species of the genus, is not extinct. It persists in a Coosa River tributary and morphometric and phylogenetic analyses confirm its taxonomic validity. All three surviving populations of the genus Rhodacmea merit specific status. They collectively contain all known survivors of a phylogenetically highly distinctive North American endemic genus and therefore represent a concentrated fraction of continental freshwater gastropod biodiversity. We recommend the establishment of a proactive targeted conservation program that may include their captive propagation and reintroduction.

Highlights

Surface freshwater habitats support a disproportionate share of the earth’s biodiversity: they embody 0.01% of the planet’s water [1] but contain .9% of described animal species, including one third of vertebrates [2]
North American drainages experienced a major wave of impoundment during the early-mid 20th century and,2% (,100,000 km) of high-quality, free-flowing rivers remain of an estimated original U.S figure of 5,200,000 km [6]
Damming completely transforms dynamic lotic habitats, turning free-flowing rivers into chains of reservoirs with severe consequences for endemic biotas [7]. This is most starkly evident in the southeastern United States Mobile River Basin (MRB; Fig. 1), a global hotspot of temperate freshwater fish and mollusk diversity characterized by extraordinary levels of endemism, including 40 fish species [8] and 34 mussel and 105 snail species [9,10] found nowhere else

Summary

Introduction

Surface freshwater habitats support a disproportionate share of the earth’s biodiversity: they embody 0.01% of the planet’s water [1] but contain .9% of described animal species, including one third of vertebrates [2]. Damming completely transforms dynamic lotic habitats, turning free-flowing rivers into chains of reservoirs with severe consequences for endemic biotas [7] This is most starkly evident in the southeastern United States Mobile River Basin (MRB; Fig. 1), a global hotspot of temperate freshwater fish and mollusk diversity characterized by extraordinary levels of endemism, including 40 fish species [8] and 34 mussel and 105 snail species [9,10] found nowhere else. The Mobile River Basin (MRB) of Alabama, a global hotspot of temperate freshwater biodiversity, was intensively industrialized during the 20th century, driving 47 of its 139 endemic mollusk species to extinction These include the ancylinid limpet Rhodacmea filosa, currently classified as extinct (IUCN Red List), a member of a critically endangered southeastern North American genus reduced to a single known extant population (of R. elatior) in the MRB

Methods

Results

Conclusion