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Campbell D.C.,Paleontological Research Institution | Lydeard C.,National Science Foundation
American Malacological Bulletin | Year: 2012

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). Source


Campbell D.C.,Paleontological Research Institution | Lydeard C.,National Science Foundation
American Malacological Bulletin | Year: 2012

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. Source


Kosloski M.,Cornell University | Kosloski M.,Paleontological Research Institution
Journal of Experimental Marine Biology and Ecology | Year: 2011

The ability to assign lethal traces left on prey to particular durophagous predators enhances our understanding of predation pressure in the fossil record. To determine whether stone crabs (Menippe mercenaria Say 1818) leave diagnostic traces in the act of feeding on hard clams (Mercenaria mercenaria Linnaeus 1758), live clams were offered to crabs in laboratory aquaria over several months and the fragments produced during predation were examined for diagnostic breakage patterns. These fragments were then compared both macroscopically and using scanning electron microscopy to the fracture patterns produced by tumbling clams in a rock tumbler which simulated breakage during transport in the surf zone, and crushing clams using an Instron which simulated breakage resulting from sediment compaction. Fossil specimens of Mercenaria mercenaria were also examined to determine whether the criteria for recognizing predation traces generated experimentally could be recognized. While not all acts of predation produce diagnostic traces, when larger fragments (greater than 50% shell remaining) are produced during feeding, predatory-diagnostic breakage ranges from 70 to 80%. Macroscopic breakage patterns generated during the predation experiments were also present in fossil specimens. Damage caused by abiotic mechanisms (tumbling and crushing) is highly unlikely to be confused with damage produced by this predator. © 2010 Elsevier B.V. Source


Mikkelsen P.M.,Paleontological Research Institution
American Malacological Bulletin | Year: 2011

What can living marine bivalves tell us about speciation in the marine environment? Three sets of literature data on Recent marine bivalves are analyzed for insight into the mechanisms behind bivalve speciation processes. (1) A dataset of all marine bivalves described as new to science during the years 2000-2009 (381 species in 135 published papers) reveals that malacologists are still describing undiscovered biodiversity, based largely upon newly collected expedition material. New species include those of both large and small body size (0.86-500 mm, mean 28 mm), from 51 bivalve families, all oceanic basins, and a wide range of water depths (intertidal to 7,333 m, mean 444 m). External shell characters dominate the diagnoses but are increasingly supplemented by anatomical, molecular, and phylogenetic evidence. Endemism is low (2.6%) when stated as such although another 57% of species were described as (thus far) restricted to a particular geographic region, habitat, or both. High percentages of deep-water and otherwise (geographically or ecologically) restricted species, plus several case studies, suggest that physiological specialization, in the form of bathymetrie limits, unique dietary adaptations, or host/symbiont associations, plays an important role in setting up barriers to gene flow in marine bivalves. (2) Bivalve species complexes [i.e., closely related, cryptic (possibly sibling) species with obscure morphological boundaries, or highly variable single species] also imply factors involved in ongoing speciation. Seven recently studied marine taxa are presented in which species complexes are either revealed or resolved by molecular data. Apparent barriers to gene flow are in most cases physiological (sympatric), or (in two cases) physical (allopatric), and in one case can be readily broken down by anthropogenic transport. (3) Two recent published phylogenetic analyses are discussed that show (a) disparately sized sister taxa with their synapomorphies (glochidia in Unionoidea; chemosymbiotic bacteria and mucus-tube feeding in Lucinoidea; cruciform muscle and long siphons in Tellinoidea; aortic bulb in Veneroidea) as recognized innovations that facilitated radiation of the more species-rich sister, and (b) polytomies in Lucinoidea that suggest rapid ongoing evolutionary change in several clades. Together these three sets of published data defeat the concept of a Marine Speciation Paradox in bivalves - speciation clues are merely subtler in marine bivalves and most often act at the physiological, rather than physical, level. Source


Dietl G.P.,Paleontological Research Institution | Dietl G.P.,Cornell University
Palaeontology | Year: 2013

A major challenge facing conservation biology today is predicting how often species will be able to adapt to environmental change. We need to know which, and under what environmental conditions, ecologically important traits are likely to evolve and keep species in the evolutionary game. Conservation biologists currently lack enough data across a broad range of traits and taxa to address this problem, which impedes the development of scenarios of possible adaptive management responses. Here I outline how trait-based data and methods that palaeobiologists use to address the long-term dynamics of evolving lineages can be applied to address this challenge. We need an impassioned community-wide effort to view evolutionary stasis with an ecological lens. © The Palaeontological Association. Source

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