Molecular phylogeny of the Forcipulatacea (Asteroidea: Echinodermata): systematics and biogeography

We present a comprehensively sampled three‐gene phylogeny of the monophyletic Forcipulatacea, one of three major lineages within the crown‐group Asteroidea. We present substantially more Southern Hemisphere and deep‐sea taxa than were sampled in previous molecular studies of this group. Morphologically distinct groups, such as the Brisingida and the Zoroasteridae, are upheld as monophyletic. Brisingida is supported as the derived sister group to the Asteriidae (restricted), rather than as a basal taxon. The Asteriidae is paraphyletic, and is broken up into the Stichasteridae and four primary asteriid clades: (1) a highly diverse boreal clade, containing members from the Arctic and sub‐Arctic in the Northern Hemisphere; (2) the genus Sclerasterias; (3) and (4) two sister clades that contain asteriids from the Antarctic and pantropical regions. The Stichasteridae, which was regarded as a synonym of the Asteriidae, is resurrected by our results, and represents the most diverse Southern Hemisphere forcipulatacean clade (although two deep‐sea stichasterid genera occur in the Northern Hemisphere). The Labidiasteridae is artificial, and should be synonymized into the Heliasteridae. The Pedicellasteridae is paraphyletic, with three separate clades containing pedicellasterid taxa emerging among the basal Forcipulatacea. Fossils and timing estimates from species‐level phylogeographic studies are consistent with prior phylogenetic hypotheses for the Forcipulatacea, suggesting diversification of basal taxa in the early Mesozoic, with some evidence for more widely distributed ranges from Cretacous taxa. Our analysis suggests a hypothesis of an older fauna present in the Antarctic during the Eocene, which was succeeded by a modern Antarctic fauna that is represented by the recently derived Antarctic Asteriidae and other forcipulatacean lineages. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162 , 646–660.     

Gamete Recognition and Egg Activation in Sea Urchins

SYNOPSIS. Free-spawning marine invertebrates face the challengeof ensuring that gametes of the same species come into contact,recognize, bind to and fuse with one another once they havebeen released by the adults. Coordinated spawning, chemoattractionand specific cell-cell recognition events help to overcome thischallenge. One marine invertebrate, the sea urchin, has servedas a model system for the study of gamete recognition and fertilizationfor over 100 years. Recent biochemical and molecular advancesin this area have begun to address the questions that have beenraised by the results of elegant physiological observations.The picture of fertilization that is emerging is characterizedby highly specific cell-cell interactions between proteins onthe surfaces of the gametes. These proteins then mediate thebinding and subsequent events that lead to activation of theegg and delivery of the male genetic material. Because of theserecent insights, the sea urchin egg is in a position to provideanswers to one of the central debates in developmental biology—themechanism of egg activation. Does the sperm deliver an activatingfactor? Does sperm binding trigger a receptor-mediated signal?Or is the mechanism a complex combination? With the tools andknowledge gained from the study of sea urchin fertilization,testing of these hypotheses should be feasible in the near future.     

Primers for the amplification of nuclear introns in sea stars of the family Asteriidae

We describe polymerase chain reaction primers that consistently amplify three intron regions of approximately 2 kb in total length for two nuclear protein‐coding genes (ATP synthase beta subunit and elongation factor‐1 alpha subunit) in sea stars of the family Asteriidae. The introns are moderately polymorphic at the species level (average within‐species percentage of site differences = 0.42%, range 0–1.44%), are evolving at about 29% as fast as mitochondrial sequences in the same species and are alignable at the genus or family level, making them suitable for phylogenetic and population genetic analyses.     

Molecular phylogeny of the Valvatacea (Asteroidea: Echinodermata)

The Valvatacea is one the most ecologically important, taxonomically diverse, and widespread groups of post‐Palaeozoic (i.e. modern) Asteroidea. Classification within the group has been historically problematic. We present a comprehensively sampled, three‐gene (12S, 16S, early‐stage histone H3) molecular phylogenetic analysis of the Valvatacea. We include five of the six families within the Paxillosida, the monotypic Notomyotida, and 13 of the 16 families of the living Valvatida. The Solasteridae is removed from the Velatida (Spinulosacea) and joins the Ganeriidae and the Leilasteridae as members of the clade containing the Asterinidae. The Poraniidae is supported as the sister group to the large cluster of Valvatacea. Asteropseids and poraniids are phylogenetically distant, contrary to morphological evidence. Several goniasterid‐like ophidiasterids, such as Fromia and Neoferdina are supported as derived goniasterids rather than as Ophidiasteridae. The Benthopectinidae (Notomyotida) are supported as members of the Paxillosida as are two members of the Pseudarchasterinae that have traditionally been considered members of the Goniasteridae. Our data suggest that Antarctic valvataceans may be derived from sister taxa in adjacent regions. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 769–788.     

Genetic subdivision and morphological variation in a freshwater snail species complex formerly referred to as Viviparus georgianus (Lea)

Genetic and morphological variation was studied in a brooding (ovoviviparous) and morphologically variable freshwater snail [ Viviparus georgianus (Lea)] species complex in southern Georgia and Florida. Eleven populations were clustered into three genetically isolated, allopatric groups characterized by 7 to 14 diagnostic loci out of the 38 loci examined. These allopatric groups were identified as V. georgianus (in eastern and southern Florida), V. limi (in the Ocblockonee River) and V. goodrichi (in the Florida panhandle). Nei's standard genetic distances between the species were large (0.23-0.52) compared to intraspecific distances (0.00-0.06). Hierarchical F-statistics for differentiation among sites within drainage systems (F_SD) for V. goodrichi and V. georgianus were large (0.519 and 0.387, respectively). The F_DT values (differentiation among drainage systems within the total area sampled) were negative or close to zero, so most of the intraspecific genetic differentiation was due to differences among populations within drianage systems, rather than to differences among systems. Canonical discriminant analysis of nine shell morphological measurements separated all three species with little overlap. Principal components analysis of the shell morphology revealed intraspecific variation among sites possibly due to environmental effects. This study demonstrates the marked genetic and morphological variation among and within drainage systems in freshwater prosobranchs.