Page last updated
13 January 2014
pre 2003 MUSSELp Literature
Molecular Phylogenetic Analysis of Two Problematic Freshwater Mussel Genera (Unio and Gonidea) and a Re-Evaluation of the Classification of the Nearctic Unionidae (Bivalvia: Palaeoheterodonta: Unionoida)
by Daniel L. Graf
Published 2002, Journal of Molluscan Studies 68: 65-71. Online access.
Abstract. The freshwater mussel genera Unio (Palearctic) and Gonidea (Pacific Nearctic drainages) have been difficult to place in the classification of the Unionidae. This has been principally due to (1) a lack of appreciation for derived vs. ancestral characters and (2) a decoupling of taxonomy from evolutionary theory. To test cladistically the positions of Unio and Gonidea relative to the well-studied Nearctic genera of the Atlantic/Gulf of Mexico drainages, partial nuclear large-ribosomal subunit (28S rDNA) sequences were obtained from representative freshwater mussel lineages, including three genera from Southeast Asia. The phylogenetic reconstruction differs from the traditional placement of Unio among the Ambleminae; instead, Unio falls sister to anodontine mussels. Gonidea is sister to the remaining Nearctic Ambleminae, and these are distinct from the Asian amblemine genera. Based on these results, the classification of the New World Unionidae is updated [i.e., Unioninae (= Unionini + Anodontini) + Ambleminae], and synapomorphies of the family are discussed.
Evolutionary relationships among the higher taxa of freshwater mussels (Bivalvia: Unionoida): inferences on phylogeny and character evolution from analyses of DNA sequence data
by Walter R. Hoeh, Arthur E. Bogan, Kevin S. Cummings & Sheldon I. Guttman
Published 2002, Malacological Review 31/32(2): 123-141.
Abstract. Doubt regarding the history of phylogenies within the Unionoida have hampered attempts to understand evolution within the group and to establish a stable classification system. To test alternative hypotheses of unionoid phylogeny, 630 base pairs of DNA sequence for the cytochrome c oxidase subunit I (COI) gene were obtained from 30 species representing the higher taxa within the Unionoida (=ingroup) and one species (Neotrigonia margaritacea) representing the Trigonioida (=outgroup). Both parsimony and neighbor-joining algorithms were employed to generate phylogenetic trees from the COI nucleotide sequences. All phylogenetic analyses produced trees with the following topology: ((((Unionidae [except Coelatura], Margaritiferidae), Coelatura), (Mutelidae, Mycetopodidae)), Hyriidae). The Hyriidae, Margaritiferidae, Mutelidae, Mycetopodidae, and Etherioidea were supported as monophyletic groups while the Unionidae and Unionoidea were judged paraphyletic. These phylogenetic relationships suggest that (1) hyriids, rather than margaritiferids, are a product of the most basal cladogenic event in the ancestral unionoid lineage, (2) the lineage ancestral to unionoids arose on one of the Gondwanan landmasses, (3) the glochidium is the ancestral unionoid larval type, and (4) endobranchial brooding is ancestral in unionoids followed by a transition to tetrageny which subsequently gave rise to ectobranchy.
A Phylogenetic Perspective on the Evolution of the Unionoida (Mollusca Bivalvia Palaeoheterodonta): Using Pattern to Test Hypotheses of Macroevolutionary Process
by Daniel L. Graf
Ph.D. dissertation defended April 2001, University of Michigan, Ann Arbor, Michigan (available on-line).
Abstract. The Unionoida, commonly known as freshwater pearly mussels or naiades, is a diverse, ancient order of strictly continental, freshwater bivalves. Most previous discussions of freshwater mussel evolution pre-dated the widespread acceptance of phylogenetic systematics and modern biogeographic theory. As a result, our understanding of the macroevolutionary processes behind the present diversity has been limited to untested narratives. This is unfortunate, as the age, distribution, and diversity of freshwater mussels makes them useful for studying divergences ranging from the Mesozoic to the Quaternary.
This dissertation documents four cladistic studies of the Unionoida. Because no single character or taxon set is appropriate across all levels of freshwater mussel phylogeny, four specific topics are addressed using separate but overlapping analyses of morphology and mitochondrial and nuclear DNA. The first analysis (Chapter 2) applies a strictly morphological character set to test the position of the Hyriidae among the Unionoida. Chapters 3 and 4 address the phylogeny and brooding character evolution among the Nearctic Unionidae using a combined (mitochondrial + nuclear) character set. Chapter 5 returns to the Hyriidae of the Australasian and Neotropical regions, using molecular characters to test hypotheses of biogeographic process. Chapter 6, the last analytical chapter, tests the position of the Nearctic genera relative to the global Unionoidea.
The seventh chapter reviews the macroevolution of the Unionoida from a phylogenetic perspective based on the results of these four studies.
Molecular phylogenetic analysis of 28S rDNA supports a Gondwanan origin for Australasian Hyriidae (Mollusca: Bivalvia: Unionoida)
By Daniel L. Graf & Diarmaid Ó Foighil
Published 2000, Vie Milieu 50: 245-254.
Abstract. The Hyriidae (Mollusca: Bivalvia: Unionoida) have a disjunct distribution, occurring on South America, Australia, and New Zealand. Most previous macroevolutionary studies of the Hyriidae pre-dated widespread acceptance of both continental drift and phylogenetic systematics. For this study, we applied molecular phylogenetic techniques to test the hypothesis that the observed disjunction of Australasian hyriids across the Tasman Sea is due to the disintegration of Gondwanaland (>80 million years ago). We sequenced a fragment of 28S rDNA for representative hyriid Velesunionini (Australia), Hyridellini (Australia and New Zealand), and Hyriinae (South America) and for outgroups belonging to the unionoid families Margaritiferidae and Unionidae. The topology of the single 28S tree [i.e., (Margaritiferidae, Unionidae, (Velesunionini, (Hyridellini, Hyriinae)))] recovered by both maximum parsimony and maximum likelihood did not support a monophyletic Australasian clade, and the branch lengths were consistent with Mesozoic vicariance. We also acquired COI sequences for the Australian subset of mussels to corroborate the 28S branch lengths. Our results suggest that (1) the Hyriidae pre-date the break up of Gondwanaland and (2) the New Zealand Hyridellini are relics rather than colonizers. Alternative long-distance dispersal hypotheses are discussed in the context of our results, historical geology, and mussel life history.
Data. grafofoighil2000b_28S.txt | grafofoighil2000b_coi.txt
The Evolution of Brooding Characters Among the Freshwater Pearly Mussels (Mollusca: Bivalvia: Unionoidea) of North America
by Daniel L. Graf & Diarmaid Ó Foighil
Published 2000, Journal of Molluscan Studies 66: 157-170. Online access.
Abstract. Brooding characters have figured prominently in the classification of North American freshwater pearly mussels (Bivalvia: Unionoidea). The purpose of our study was to phylogenetically evaluate hypotheses of brooding character evolution in order to test homology statements suggested by earlier taxonomic systems of the Unionoidea. Parsimony analysis of partial COI sequences from 29 species of freshwater mussels and 13 outgroups were used to derive a phylogeny. Thirteen brooding characters (e.g., brooding period, marsupium arrangement, structure of interlamellar septa, etc.) were traced onto this phylogeny. Results indicate that long-term brooding (bradytictia) is the derived state among North American freshwater mussels; short-term brooding (tachytictia) is plesiomorphic. Bradytictia evolved independently in the Anodontinae and Lampsilini, with unique morphological modifications derived in those clades to facilitate long-term brooding. The evolution of bradytictia among temperate clades is discussed.
The Etherioidea Revisited: A Phylogenetic Analysis of Hyriid Relationships (Mollusca: Bivalvia: Paleoheterodonta: Unionoida)
By Daniel L. Graf
Published 2000, Occasional Papers of the University of Michigan Museum of Zoology (729): 1-21. On DeepBlue.
Abstract. Almost all freshwater pearly mussels (Order Unionoida) have one of two types of parasitic larvae, either glochidia or lasidia. The most widely accepted hypothesis of freshwater mussel higher classification divides the order into two superfamilies, the Unionoidea and Etherioidea [= Muteloidea], based solely upon larval type. To test this hypothesis, specifically the relationships of the Hyriidae (which have glochidia), a morphological data set compiled from both larval and adult life history stages was analyzed phylogenetically using parsimony. Results indicate that hyriids, despite their development including a parasitic glochidium, share a more recent common ancestor with the Etherioidea than with any unionoidean. The Etherioidea (Hyriidae, (Iridinidae, Etheriidae)) is diagnosed by at least three adult anatomical synapomorphies. The lasidium-type larva is hypothesized to be derived from glochidia. The bearing of these results on the biogeography, character evolution, and classification of the Unionoida is discussed.
Conservation Status of Freshwater Mussels of the United States and Canada
by Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris & R.J. Neves
Published 1993, Fisheries 18(9): 6-22.
Abstract. The American Fisheries Society (AFS) herein provides a list of all native freshwater mussels (families Margaritiferidae and Unionidae) in the United States and Canada. This report also provides state and provincial distributions; a comprehensive review of the conservation status of all taxa; and references on biology, conservation, and distribution of freshwater mussels. The list includes 297 native freshwater mussels, of which 213 taxa (71.7%) are considered endangered, threatened, or of special concern. Twenty-one taxa (7.1%) are listed as endangered but possibly extinct, 77 (25.9%) as endangered but extant, 43 (14.5%) as threatened, 72 (24.2%) as of special concern, 14 (4.7%) as undetermined, and only 70 (23.6%) as currently stable. The primary reasons for the decline of freshwater mussels are habitat destruction from dams, channel modification, siltation, and the introduction of nonindigenous mollusks. The high numbers of imperiled freshwater mussels in the United States and Canada, which harbor the most diverse fauna in the world, portend a trajectory toward an extinction crisis that, if unchecked, will severely impoverish one of our richest components of aquatic biodiversity.