Committee on Evolutionary Biology

The hypothalamic-pituitary-adrenal (HPA) axis releases glucocorticoids (GCs), or stress hormones, during the vertebrate stress response. GCs can both enhance and suppress the immune system depending on whether the experienced stressor is acute or chronic and what aspect of immune function is measured. More research is needed to fully understand how the immune system reacts to stressors. In this study, we examined the effects of chronically raised GCs on innate immune function in Belding's ground squirrels (Urocitellus beldingi). We measured immune function with a bacteria killing ability (BKA) assay, an integrative and functional assessment of an animal's ability to clear a bacterial infection. All studies to date have examined how acute stressors or repeated social stressors impact BKA. This study is the first to our knowledge to investigate how chronically raised GCs impact BKA both before and after an immune challenge. We noninvasively raised GCs in treatment squirrels for six days and then gave them, and a group of untreated (control) squirrels, an injection of lipopolysaccharide (LPS) to stimulate their innate immune system. Treatment squirrels exhibited lower BKA after, but not before, being challenged with LPS. These results suggest that experiencing chronic stress may not be detrimental to immune functioning until an individual is challenged with an infection.

Systematic research on bivalved molluscs (Mollusca: Bivalvia = Pelecypoda) is briefly reviewed in an introduction to a series of papers focusing on seven of the larger branches of the bivalve tree. These are presented in an attempt to summarize current knowledge, to stimulate new research and to highlight needs for future research focus. A revised classification of extant bivalve families (with synonyms and included subfamilies) is presented, based on information compiled from the latest palaeontological, morphological and molecular data. 

The largest Recent family of Bivalvia, the marine Veneridae with approximately 800 species, comprises one of the least understood and most poorly defined molluscan taxa, despite including some of the most economically important and abundant bivalves, for example quahog, Pismo clams, and Manila clams. A review of previous phylogenetic analyses including the superfamily Veneroidea (Veneridae, Petricolidae, Glauconomidae, Turtoniidae, Neoleptonidae) and within the Veneridae shows minimal taxon sampling leading to weak conclusions and few supported synapomorphies. New phylogenetic analyses on 114 taxa tested the monophyly of Veneroidea, Veneridae, and 17 nominal venerid subfamilies, using morphological (conchological, anatomical) data and molecular sequences from mitochondrial (16S, cytochrome oxidase I) and nuclear (28S, histone 3) genes. Morphological analyses using 45 exemplar taxa and 23 traditional characters were highly homoplastic and failed to reconstruct traditional veneroid classification. Full morphological analyses (31 characters) supported the monophyly of Veneroidea and Veneridae but only when certain taxa were excluded, revealing analytical difficulties caused by a suite of characters associated with neotenous or miniaturized morphology. Molecular analyses resulted in substantially higher clade consistency. The combined molecular data set resulted in significant support for a particular topology. The monophyly of Veneridae was supported only when Petricolidae and Turtoniidae were subsumed, and recognized as members with derived or neotenous morphologies, respectively. Morphological character mapping on molecular trees retained a high level of homoplasy, but revealed synapomorphies for major branch points and supported six subfamily groups (Dosiniinae, Gemminae, Samarangiinae, Sunettinae, Tapetinae, combined Chioninae + Venerinae). Glauconomidae and Neoleptonidae are provisionally maintained in Veneroidea pending further study; Petricolinae and Turtoniinae are placed in Veneridae. © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society, 2006, 148, 439–521.

The marine gastropod family Architectonicidae (= Solariidae), commonly known as sundials, comprises about 140 worldwide extant species classified in 11 genera. More than ten times as many names are used in the literature for both Recent and fossil taxa, the latter dating from the Mesozoic (Paleozoic taxa were misinterpreted). Herein we catalog more than 1550 names that have appeared in print at the family-group (10), genus-group (137), and species-group levels (1408). Of the last, nearly 1100 are found to be nomenclatorially available or potentially available. An Appendix is included in which nomenclatural changes are made and/or commented upon. It is demonstrated that Solarium maculatum Link, 1807 was validly introduced and, as Architectonica maculata (Link, 1807), becomes the valid name for the species usually cited as A. picta (Philippi,
1849). The invalid introduction of Heliacus messanensis Bertolaso & Palazzi, 2000 is discussed. The emended spelling of the specific name in the binomen Solatisonax alleryi (G. Seguenza, 1876) is shown to be correctly accepted. Philippia lepida Bayer, 1942, Torinia gyrus depressiuscula Bayer, 1848, Solarium subconcolor von Martens, 1880, Solarium conulus Weinkauff, 1868 and Solarium submoniliferum d’Orbigny, 1852 were proposed as replacement names for multiple preoccupied names and/or misidentifications. These are here restricted to avoid possible confusion. The history and current status of the similarly spelled and inconsistently used nomina Fluxiella and Fluxinella (as placed in Architectonicidae and/or Seguenziidae) are discussed.

Widespread sampling of vertebrates, which comprise the majority of published animal mitochondrial genomes, has led to the view that mitochondrial gene rearrangements are relatively rare, and that gene orders are typically stable across major taxonomic groups. In contrast, more limited sampling within the Phylum Mollusca has revealed an unusually high number of gene order arrangements. Here we provide evidence that the lability of the molluscan mitochondrial genome extends to the family level by describing extensive gene order changes that have occurred within the Vermetidae, a family of sessile marine gastropods that radiated from a basal caenogastropod stock during the Cenozoic Era.
Major mitochondrial gene rearrangements have occurred within this family at a scale unexpected for such an evolutionarily young group and unprecedented for any caenogastropod examined to date. We determined the complete mitochondrial genomes of four species (Dendropoma maximum, D. gregarium, Eualetes tulipa, and Thylacodes squamigerus) and the partial mitochondrial genomes of two others (Vermetus erectus and Thylaeodus sp.). Each of the six vermetid gastropods assayed possessed a unique gene order. In addition to the typical mitochondrial genome complement of 37 genes, additional tRNA genes were evident in D. gregarium (trnK) and Thylacodes squamigerus (trnV, trnLUUR). Three pseudogenes and additional tRNAs found within the genome of Thylacodes squamigerus provide evidence of a past duplication event in this taxon. Likewise, high sequence similarities between isoaccepting leucine tRNAs in Thylacodes, Eualetes, and Thylaeodus suggest that tRNA remolding has been rife within this family. While vermetids exhibit gene arrangements diagnostic of this family, they also share arrangements with littorinimorph caenogastropods, with which they have been linked based on sperm morphology and primary sequence-based phylogenies.
We have uncovered major changes in gene order within a family of caenogastropod molluscs that are indicative of a highly dynamic mitochondrial genome. Studies of mitochondrial genomes at such low taxonomic levels should help to illuminate the dynamics of gene order change, since the telltale vestiges of gene duplication, translocation, and remolding have not yet been erased entirely. Likewise, gene order characters may improve phylogenetic hypotheses at finer taxonomic levels than once anticipated and aid in investigating the conditions under which sequence-based phylogenies lack resolution or prove misleading.

The systematic position and affinities of the marine bivalve genus Hemidonax (Heterodonta, Veneroida) are investigated using comparative sperm ultrastructure, with particular focus on the various groups to which this genus has been assigned [Donacidae (Tellinoidea), Cardiidae (Cardioidea) and Crassatellidae (Crassatelloidea)]. Ultrastructural examination (using transmission electron microscopy) reveals that Hemidonax pictus produces sperm of the aquasperm type, with a short, rounded-conical acrosomal vesicle, a short, barrel-shaped nucleus, a short midpiece (composed of two centrioles and four surrounding mitochondria) and a flagellum containing a conventional 9 + 2 pattern axoneme. The acrosomal vesicle exhibits a wedge-shaped, highly electron-dense, basal ring component, and less dense anterior component (including a thin, electron-lucent layer apically, which may prove to be a useful apomorphy for Hemidonax). A loose, granular deposit of subacrosomal material is located within a narrow invagination traversing most of the length of the vesicle. Comparison with sperm of other heterodont bivalves shows no close connection between Hemidonax and the Donacidae (Tellinoidea) or with the Crassatellidae (or other crassatelloideans). Although certain Veneridae (Veneroidea) and Cardiidae (Cardioidea, especially Fragum) show much better conformity in sperm morphology to that observed in Hemidonax, no complete match could be found among studied taxa. We conclude that Hemidonax should be retained in its own, previously introduced family Hemidonacidae, and the latter be placed incertae sedis within the Euheterodonta.

Isognomon alatus is a sessile intertidal bivalve species that attaches to hard substrata. Within the Florida Keys, where tidal ranges are usually less than 1 m, settlement sites only a few centimetres apart experience drastically different tidal microhabitats. These varying conditions may create morphological gradients that can complicate taxonomic designations. To quantify and characterize the conchological effects of this microhabitat gradient and estimate the degree to which these effects can confuse species identification, I. alatus was studied in relation to tidal position using geometric morphometrics. Isognomon alatus was only found at positions 0.4 m below the highest tide mark, positions exposed to air less than 80% of the time. Below this limit specimen size, immersion time, and area available all covary. Shape differences due to ontogeny were removed using regression and the remaining phenotypic variation within these specimens is significantly correlated with the measured habitat conditions, immersion time being the more robust predictor. The observed phenotype effects are small but can influence species identification. Species assignment tests between I. alatus and the morphologically similar IndoPacific I. ephippium ranged in accuracy from 98 to 90% across microhabitat condition

The reproductive and developmental biology of the sessile gastropod Vermicularia spirata (Philippi, 1836), collected from the Florida Keys, was studied from living and preserved material. Individuals of this species attach themselves to a variety of substrata, but were mainly found embedded in the white sponge Geodia gibberosa. Pallial reproductive structures of both sexes of V. spirata were found greatly to resemble those of Turritella communis, a free-living member of the same family. In both species, animals of both sexes have open pallial ducts formed by two wide, recurved laminae. In the female of V. spirata, the laminae of the pallial oviduct serve as a capsule gland; a pair of side pockets represent a fertilization pouch (possibly doubling as a copulatory bursa) and a seminal receptacle. The functional significance of the extensive, open, pallial sperm duct is not yet clear. Vermicularia spirata is a protandrous hermaphrodite, and small males are free-living; they become attached at about the time they undergo sex reversal. Fertilization is probably brought about by males crawling close to the apertures of the large, sessile females before releasing sperm. Egg capsules are brooded in the females' mantle cavities. Ova of about 300 µm diameter give rise to large (about 600 µm long) swimming-crawling veliger larvae with shells of two and a half whorls. The veligers are capable of metamorphosis at the time of hatching, but siblings from one brood metamorphosed over a two-week period in the laboratory. Juvenile snails grew rapidly by filtering phytoplankton added to their culture water. The life history of V. spirata is well adapted to assure fertilization and recruitment in a species otherwise committed to a sessile, filter-feeding existence.

Siliquariid Tenagodus (synonym: Siliquaria) snails are obligatory sponge commensals, with uncoiling and laterally slitted shells embedded inside Demospongiae hosts, and shell apertures facing the outside allowing for respiratory and gill-filter-feeding activities. Live-collected animals observed in situ within hosts provide the first detailed func-tional morphological study of the group, and form the basis for systematic revision of the western Atlantic members of type genus Tenagodus (Siliquariidae, synonym: Tenagodidae). Three species are recognized. Overall anatomical features of wide-ranging Atlantic T. modestus (Dall, 1881) and T. squamatus (de Blainville, 1827) [= T. anguillae Mörch, 1861] are similar to those previously described for New Zealand Pyxipoma. A third species, Tenagodus bar-badensis sp. nov., is described from Barbados, based on shell characters. The three species live embedded in a few species of halichondriid and thrombid sponges at depths ranging from c. 20 to several hundred metres and show sev-eral characters not previously documented for the family. These include a short compressed-S-shaped osphradium, an anal opening positioned in the posterior mantle cavity, and cuspidate inner marginal radular teeth. Presence of shell septa sealing earlier parts of the shell, first described in the early 1800s but subsequently disputed, was ver-ified. Observations on living T. squamatus demonstrated the use of the large tight-fitting operculum in plunger-like fashion, flushing the mantle cavity and discharging waste material (including faeces from the posteriorly located anus) through the shell slit into the host sponge's aquiferous canal system. Uncoiling shells, shell and mantle slits, and specialized opercular, gill and gut morphology are interpreted as adaptive traits of the sessile mode of life embed-ded in sponge tissue. Actively maintained linkage between snail and sponge water-flow systems provides mutual benefits; these include the allowance for rapid defensive withdrawal and return-to-feeding position of the snail (by using the sponge canal system as a vent or reservoir for displaced water), sanitation of the mantle cavity (waste material can leave the snail through the shell slit at the posterior end of the mantle cavity, avoiding fouling of the gill-feeding system), and by providing increased water flow and, potentially, extra nutritional particles for the sponge (food and waste particles stemming from the snail's activity). The lectotypes selected herein are Serpula anguina Linnaeus, Tenagodus anguillae Mörch, 1861, and Siliquaria modesta Dall, 1881.

Using transmission electron microscopy, sperm morphology was investigated for the first time in a representative of the heterodont bivalve family Glauconomidae. Spermatozoa of Glauco-nome plankta (Iredale, 1936) consist of a head region (acrosomal complex + nucleus), short midpiece and a flagellum. The membrane-bound acrosomal vesicle is attenuate-conical (length 1.1 ± 0.08 µm) with a moderately deep basal invagination extending for most of the vesicle's length. Contents of the vesicle are differentiated into a highly electron-dense basal ring (cylindrical) sheathed by less dense material that also occupies the anterior two-thirds of the vesicle. Finely granular subacrosomal material fills the vesicle invagination and forms a layer between the nuclear apex and the vesicle, but no axial rod is discernible. The nucleus is rod-shaped and straight, 4.4 ± 0.2 µm long and tapers slightly towards the apex. Nuclear contents are highly electron-dense, with the exception of occasional, electron-lucent lacunae. The midpiece consists of a pair of triplet-microtubular centrioles surrounded by four, approximately spherical mitochondria. Highly electron-dense granules of putative glycogen were observed between the mitochondria and around the distal centriole. The distal centriole is anchored to the plasma membrane via satellite fibres and is continuous with the flagellum (the latter 46 ± 3.0 µm long and exhibiting a conventional 9+2 axoneme). Comparison of sperm results does not suggest any especially close relationship between Glauconomidae (as exemplified by G. plankta) and other member families of the superfamily Veneroidea. Elsewhere within the Heterodonta no close relationship with the Corbiculoidea, Myoidea, Mactroidea, Tellinoidea or the Crassatelloidea is indicated by sperm morphology. Most promising seems a possible connection with Arctica (Arcticidae, Arcticoidea), which shows similar acrosomal and nuclear features. Supporting morphological and molecular evidence for this relationship is inconclusive but suggests further study

Marine file clams of family Limidae d'Orbigny, 1846 (+ Radulidae Adams & Adams), characterised by their often colourful mantle and pallial tentacles and by swimming behaviour, are commonly collected and illustrated bivalves. Based on new material from an extensive Florida Keys biodiversity survey plus museum and literature data, western Atlantic species of Lima Bruguière, 1797 (+ Mantellum Röding; Radula Mörch; Limaria Rafinesque; Austrolima Iredale; Meotolima Oyama) and Ctenoides Mörch, 1853 (+ Divaricolima Rovereto) are revised. Lima includes L. marioni Fischer, 1882 (+ L. lata Smith; lectotype selected), and L. caribaea d'Orbigny, 1842 (lectotype selected), distinguished from eastern Atlantic L. lima (Linné) and other species by shell rib number. Ctenoides includes C. scaber (Born, 1778) (+ Ostrea glacialis Gmelin; L. asperula Lamarck; Limaria asperula Link), C. mitis (Lamarck, 1807) (+ L. tenera Sowerby; L. floridana Olsson & Harbison), C. planulatus (Dall, 1886) (lectotype selected), C. sanctipauli Stuardo, 1982, and C. miamiensis, C. obliquus, and C. vokesi, spp. nov. Species distinctions rely mainly on shell characters, although body colour and ornamentation are confirming in some cases. Diagnostic shell characters at the genus-level are supported by new anatomical characters of the gut and tentacles. Known anatomical data for worldwide Lima and Ctenoides species are summarised within a phylogenetic context.

A survey of marine bivalve biodiversity in the Florida Keys, an island archipelago off southern Florida, was compiled from original collecting, museum specimens and the literature. Assembly of over 6000 records resulted in 325 species, 47% of which can be considered common to abundant in the Keys. This represents a 100% increase over the previously known fauna, largely attributable to critical review of museum specimens. Capture of species occurrences from the literature, especially when non-traditional sources (newsletters, agency reports) are excluded, is shown to be least effective, producing only 44% of the total. Bivalve distributions within the Keys show that the fauna is tropical. One-third of the species are wide ranging along the island chain; however, a latitudinal cline in faunal similarity exists from the Upper Keys southwestwards to Dry Tortugas. The fauna of Florida Bay is the most divergent within the study region and also compared to other, ecologically complex, western Atlantic tropical-subtropical regions. Limited historical records indicate little species turnover in the Keys, although population reductions along the main highway and habitat shifts (from natural to artificial substrata) are evident. These results have implications for biodiversity survey methods and, more locally, for management of the Florida Keys National Marine Sanctuary.

The family Omalogyridae comprises some of the smallest known marine snails. Like all micromolluscs, they have been historically neglected and are underrepresented in faunistic surveys. Based on a few focused studies of the family, 15 valid omalogyrid species were previously recognised in the Indian and Pacific Oceans. To these, we add 3 new species based on a morphological analysis of material in the dry collection of the Natural History Museum of Los Angeles County, ap- plying light and scanning electron microscopies. The new species, Ammonicera mcleani, A. mexicana and A. sleursi, are the first omalogyrid species described from the Eastern Pacific coast of North America. Redescriptions of the Australian omalogyrids Ammonicera sucina (Laseron, 1954) and Omalogyra liliputia (Laseron, 1954) are also presented, detailing for the first time ultrastructural aspects of their shell morphology. Additionally, we present here the first record of Am- monicera binodosa Sleurs, 1985b in Sri Lanka, introduce the new combination Ammonicera vangoethemi (Sleurs, 1985c) for Omalogyra vangoethemi, and formally remove Transomalogyra Palazzi & Gaglini, 1979 from Omalogyridae by fixing its type species as Homalogyra densicostata Jeffreys, 1884. Finally, we present lists, geographic records and a bibliogra- phy of all currently recognised omalogyrid species in the Indian, Pacific and Antarctic Oceans, as well as an update to a previously published compilation of the Atlantic and Mediterranean representatives of the family.

Spermatogenic ultrastructure in the marine bivalve mollusc Myochama anomioides (Myochamidae) is described and contrasted with other bivalves, especially other euheterodonts. Small (0.1 μm diameter), primary proacrosomal vesicles produced in spermatocytes give rise to much larger (0.4 μm diameter) secondary proacrosomal vesicles in early spermatids, which in turn form the dished-shaped, definitive acrosomal vesicle (diameter 1.0 μm) of later spermatids. The acrosomal vesicle acquires a deposit of subacrosomal material and comes to lie close to or in contact with the plasma membrane. The acrosomal complex (acrosomal vesicle + subacrosomal material) initially positions itself at the apex of the condensing, fibrous nucleus (the so-called temporary acrosome position), but subsequently begins to move posteriorly. The condensing nucleus becomes markedly folded so that its apex is posteriorly orientated towards the migrating acrosomal complex and the midpiece (mitochondria and centrioles). The close spatial relationship of nuclear apex to acrosomal complex during this folding strongly suggests that acrosomal migration in M. anomioides is assisted, at least in part, by movement of the late spermatid nucleus. Similar nuclear folding has previously been demonstrated in an early stage of fertilization in another anomalodesmatan (Laternula limicola) raising the possibility that one event might be a reversal of the other.