Phylogeography of the sea star Marthasterias glacialis (Asteroidea, Echinodermata): deep genetic divergence between mitochondrial lineages in the north-western mediterranean

We explore the phylogeography of the broadcast spawner Marthasterias glacialis along south Europe and Azores. Sequences of the cytochrome c oxidase gene from 225 specimens, belonging to 10 localities, were analysed. We found 73 haplotypes grouped within two lineages (divergence 2.9%). One lineage was Atlanto–Mediterranean, whereas another one was exclusively Mediterranean. Estimation of lineages split goes back to 830,000–580,000 (±120,000) years ago. This suggests that sea-level oscillations during the Pleistocene glaciations promoted gene flow interruption, lineage divergence between basins and cryptic speciation. Secondary contact between populations allowed a recolonization of the Mediterranean by the Atlantic lineage. When animals of the Atlanto–Mediterranean lineage were considered separately, F _st index and AMOVA did not show significant differences between populations along either the Iberian Peninsula or basins. Isolation by distance between populations was not detected, and only populations of Plymouth and Azores showed significant differences to all the others. The remoteness of Azores islands might explain the structure of this population. Haphazard arrival of larvae and local extinctions rather than contemporary restricted gene flow might be responsible for the distinctive population structure of Plymouth.     

Molecular evidence for multiple lineages in the gorgonian family Plexauridae (Anthozoa: Octocorallia)

Octocorals are diverse and abundant on many marine hard substrates, and, within this group, members of the family Plexauridae are an important component of tropical reef assemblages, especially in the Caribbean. To understand historical relationships within this large and diverse assemblage, and to test the monophyly of the family and some of its genera, DNA sequences of two mitochondrial loci (msh1 and ND2, ~1,185 bp) were analyzed from 46 species in 21 genera from deep and shallow waters in the tropical western Atlantic and in the tropical western and eastern Pacific (plus 9 taxa in the closely related Gorgoniidae and 1 species of the more distantly related Alcyoniidae). Five strongly supported clades were recovered. Three large clades correspond roughly to the Plexauridae, Paramuriceidae, and Gorgoniidae, and two smaller clades were comprised of taxa previously assigned to several families. Astrogorgia sp. did not group with any of the clades. The mutual relationships among the five clades remain unclear. Several genera previously regarded as unrelated appear to be grouped among the three families; e.g. Hypnogorgia sp. (Paramuriceidae) falls within a clade consisting of both Pacific and Atlantic Muricea spp. (Plexauridae), while Swiftia sp., Scleracis sp., and an Atlantic Thesea sp. (all Paramuriceidae) group with the gorgoniids. In several instances, genera containing Atlantic and Pacific species were recovered as monophyletic (Muricea spp., Bebryce spp.). However, in at least three cases (Echinomuricea spp., Thesea spp., Villogorgia spp.), placement of Atlantic and Pacific species in the same genus may reflect convergence of sclerite morphology. The results indicate a strong need for reexamination of octocoral taxonomy using a combination of molecular, morphological, and chemical evidence.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00227-005-1592-y.Communicated by J.P. Grassle, New Brunswick     

Genetic divergence among three sympatric species of Mediterranean Patella (Archaeogastropoda)

Patella caerulea L., P. aspera Lam. (=P. ulyssiponensis Gmelin). P. rustica L. (=P. lusitanica Gmelin) are coexisting Mediterranean species of the genus Patella. P. caerulea and P. rustica have a haploid complement of n=9 with seven metacentric and two telocentric chromosomes, while P. aspera has a haploid complement of n=8 without telocentric chromosomes. To better define the phylogenetic relationships among these three species, an electrophoretic analysis of 12 enzyme coding loci was performed on samples of the three species collected from Laigueglia (Liguria, Italy) in 1989. On the whole, genotypic frequencies were in agreement with Hardy-Weinberg expectations and no significant differences were observed among the populations of the three species as far as their genetic structure is concerned. Nearly 50% of the sampled loci were diagnostic. Nei's genetic distance was 0.82 between P. caerulea and P. aspera, 0.97 between P. aspera and P. rustica and 0.94 between P. caerulea and P. rustica. By greatly separating P. rustica from the other two species, results of the electrophoretic analysis are consistent with the traditional view, which regards P. aspera and P. caerulea as more closely related than P. rustica on the basis of radular teeth morphology. Using genetic distances and the assumptions of the molecular clock, lineages leading to P. aspera and to P. caerulea may have diverged from the stem common to P. rustica ca. 18 million years ago.     

Reproductive success of nesting male longear sunfish (Lepomis megalotis peltastes)

Summary Although a few male longear sunfish nest solitarily, most territorial males excavate their nest in dense aggregations. The importance of sexual selection in the evolution of this breeding system was evaluated by 1) examining the influence of certain male and nest characteristics on spawning success and 2) by comparing the success of social and solitary nesters. Among group nesters, females spawned preferentially with males nesting early within a spawning period and occupying central nests. Male size and nest diameter were negatively correlated with nesting day and hence spawning success. However, female discrimination using these traits directly could not be demonstrated. The reproductive success of social and solitary males was compared by counting the larvae in their nests several days after spawning. Successful males (with larvae) were more likely than males without larvae to be encountered later in the breeding season and to nest in small groups or solitarily. Spawning period (of which there were 5 or 6 in a season) was significantly correlated with larval abundance in the nest, while male size was not. Social and solitary males were equally successful, but aggregations may nonetheless result from sexual selection: males unlikely to attract females may nest around more attractive males to steal fertilizations from them. High spawning synchrony may prevent attractive males from renesting elsewhere once other nesters aggregate around them.     

Horizontal movement of ocean sunfish, <Emphasis Type="Italic">Mola mola</Emphasis>, in the northwest Atlantic

Data were retrieved from 25 ocean sunfish (Mola mola) that were tagged with pop-up satellite archival tags in the southern Gulf of Maine (n = 6), off Nantucket Island (n = 17), and off the coast of Georgia (n = 2) between September 2005 and March 2008. Tags remained attached from 7 to 242 days, with a mean attachment period of (X ± SD) 107.2 ± 80.6 days. Ocean sunfish tagged in the Gulf of Maine and southern New England left those areas in the late summer and early autumn and moved south along the continental shelf break. Fish traveled as far south as the Bahamas and the Gulf of Mexico. By moving south, sunfish experienced similar mean sea surface temperatures throughout the tagging period. The maximum straight-line distance traveled by a tagged Mola mola was 2,520 km in 130 days. Two tagged ocean sunfish entered the Gulf of Mexico, one in the December and one in July. Movements were associated with frontal features created by the Gulf Stream and fish moved farther offshore in 2007 when the Gulf Stream was deflected from the shelf break.     

Distribution and diversity of mtDNA lineages among southern right whales (Eubalaena australis) from Australia and New Zealand

Using a biopsy dart system, samples of skin tissue were collected from southern right whales (Eubalaena australis) in 1995 on two wintering grounds, southwest Australia (n = 20) and the Auckland Islands of New Zealand (n = 20); and on offshore feeding grounds at Latitudes 40 to 43°, south of Western Australia (n = 5). A variable section of the mitochondrial DNA control-region (289 nucleotides) was amplified and sequenced from these 45 individuals (21 males, 20 females and 4 of unknown sex), distinguishing a total of seven unique sequences (i.e. mtDNA haplotypes). Two haplotypes were found on both wintering grounds (including a common type representing 45% of each sample), and five types were unique to only one wintering ground. An analysis of variance adapted for molecular information revealed significant genetic differentiation between the two wintering grounds (p = 0.017). The feeding-ground sample was too small for statistical comparison with the wintering grounds, but included two haplotypes found only in the Auckland Islands as well as the common haplotype found on both wintering grounds. The nucleotide diversity and differentiation of mtDNA among the right whales was similar to that among humpback whales (Megaptera novaeangliae) from the same regions (Baker et al. 1998), but haplotype diversity was significantly reduced, perhaps as a result of more intensive hunting during the last century and continued illegal hunting during this century. Received: 16 March 1998 / Accepted: 18 December 1998     

Gene flow among giant clam (Tridacna gigas) populations in Pacific does not parallel ocean circulation

Tridacna gigas (L.) populations were sampled from 13 locations throughout the west Pacific in 1990–1991 and screened for allozyme variation at seven polymorphic loci. Significant genetic differences were found between the few large stocks of T. gigas remaining in the world. Cluster analysis identified two major regional groups of populations: a Central Pacific group consisting of Kiribati and the Marshall Islands, and a West Pacific group comprising all other populations. Within the latter group, the Great Barrier Reef populations were significantly differentiated from those in the Solomon Islands. The main routes of gene flow did not run parallel with known major surface currents as might be expected, but crossed them. Gene exchange was limited east-west between the Central and West Pacific groups and the GBR and the Solomon Islands. The lack of correspondence between the major surface currents and the routes of gene flow suggests that the genetic structure of T. gigas reflects historical patterns of migration that no longer occur, rather than presentday dispersal. These findings raise fundamental questions concerning the origin and maintenance of genetic diversity in Pacific faunas, and have important implications for the mariculture and conservation of T. gigas.     

Polymorphic color vision in white-faced capuchins (Cebus capucinus): Is there foraging niche divergence among phenotypes?

Many species of platyrrhine primates are characterised by sex-linked color vision polymorphism. This presents an opportunity to study the biology and ecology of individuals with different phenotypes living in the same group. Several evolutionary processes could maintain polymorphic genes in populations. In this study, we evaluate the hypothesis that foraging niche divergence among monkeys explains the presence of multiple color vision phenotypes. Specifically, we test whether dichromats and trichromats differ in foraging time devoted to cryptic vs brightly colored resources. We did not find any differences in foraging time spent on different food types by dichromatic and trichromatic monkeys in two groups of white-faced capuchins (Cebus capucinus) living in a tropical dry forest. We conclude that in so far as these variables are concerned, niche divergence does not likely explain color vision polymorphism in our study population.     

Distribution and abundance of choanoflagellates (Acanthoecidae) in the coastal cold ocean of Newfoundland, Canada

Water samples from six bays were taken over a 5-year period (1988 to 1992) to determine the distribution and abundance of loricate choanoflagellates in coastal Newfoundland, and to assess the impact that these organisms might have on this cold ocean food web. Scanning electron microscopy was used to study the morphology of these flagellates, allowing us to identify 11 species of loricate choanoflagellates. Parvicorbicula socialis (Meunier) Deflandre was the most abundant species (80 × 10³ cells l⁻¹), particularly during the spring diatom bloom. Single-cell species, such as Bicosta spini fera (Throndsen) Leadbeater and Calliacantha natans (Grontved) Leadbeater, were found more commonly after the spring diatom bloom in the summer months. Many of the single-cell choanoflagellates were attached to bacteria-rich microaggregates and debris in the water column and in unpoisoned sediment traps. The P. socialis cell flux was calculated to be 5.3 × 10⁶ cells m⁻² d⁻¹ in late May sediment traps. P. socialis in the upper 100 m of the water column was removing 0.3% of the standing crop of bacteria each day (April/May), and the equivalent of 7.4% of the daily bacterial production over the water column. Diel studies of P. socialis in Conception Bay suggest that the sharp decline in population numbers observed in midnight samples may be related to the high number of grazing zooplankton observed during the same period. Pelagic tunicate and zooplankton fecal pellets were found to contain large numbers of choanoflagellate costae, thus providing a direct link from the microbial loop to the macrozooplankton. Received: 17 March 1997 / Accepted: 9 May 1997     

Genetic, morphological, and chemical divergence in the sponge genus Latrunculia (Porifera: Demospongiae) from New Zealand

We undertook a comprehensive study of Latrunculia in New Zealand to determine the relationship between taxonomic, environmental, and chemical variation within the genus. Sponges were collected from five locations around New Zealand: Three Kings Islands, Tutukaka, Wellington, Kaikoura, and Doubtful Sound. Allozyme electrophoresis at nine polymorphic loci indicated that sponges from each geographic location were genetically distinct, and that they displayed genetic differences of the magnitude usually associated with reproductively isolated species (Nei's D between locations =0.375-2.476). Additionally, the comparisons revealed that the green and brown colour morphs of Latrunculia that are sympatric at Three Kings Islands and Kaikoura are distinct from each other, and that there are two genetic groups within the green sponges in Doubtful Sound. On the basis of genetic data we conclude that there are at least eight species of Latrunculia in New Zealand waters, not one to four as had been previously thought. Morphological comparisons of the eight genetic species based on skeletal characters (i.e. skeletal organisation of the choanosome, spicule composition, size, and geometry) indicated that the eight Latrunculia species fell into only two morphological groups that could be easily diagnosed on the basis of discorhabd type. Within these two primary morphological groups, skeletal characteristics among the eight species largely overlap and are not diagnostic. These findings emphasise the limitations of traditional taxonomic methods based solely on skeletal characters for distinguishing species of Latrunculia. However, multivariate analysis (MANOVA and CDA) based on six measured skeletal variables did reveal significant morphological variation among the species (Pillai's Trace=3.28, F=6.90, P<0.0001), supporting the division of the genus into eight species. Comparisons of chemical extracts from Latrunculia also showed that the amounts of five different bioactive compounds (discorhabdins A, B, C, D, and J) varied predictably among the eight species. This finding suggests that discorhabdin variation within Latrunculia, previously thought to be associated with intra-specific environmental variability, is more likely to reflect differences among species rather than phenotypic plasticity. Our results also highlight the importance of thorough taxonomic studies associated with marine natural products research to understand fully the variation in bioactive properties among individuals. The potential processes underlying the unusually high speciation rates in New Zealand Latrunculia that are indicated in our study are discussed.     

Application of various mathematical models to data from the uptake of methyl mercury in bluegill sunfish (Lepomis macrochirus)

Evaluated and compared are the results of various mathematical models to data from the uptake of methyl mercury in bluegill sunfish (Lepomis macrochirus). Data were obtained from the direct uptake of methyl mercury from water in bluegill at 9°C and at a CH₃HgCl concentration of 0.2 ppb. The models considered are: (1) linear uptake relationship; (2) first-order kinetics, one-compartment or single-exponential model; (3) combination of first-order kinetics and the linear uptake relationship, designated as slope-exponential model; (4) two-compartment or double-exponential model; (5) three-compartment model, including a storage compartment for the build up of contaminant, designated as storage model; (6) three-compartment model, allowing two routes of elimination, designated the “Y” model; (7) an empirical uptake relationship having the form of a rectangular hyperbola.A comparison of the nonlinear models showed that the empirical model had fewer convergence problems in obtaining parameter estimates and its parameter values had less variation. The best fit was made by the “Y” model, the empirical model gave one of the smaller values of the residual mean squares, and other nonlinear models had computational convergence difficulties. The lack of computational problems and the comparitively small residual mean squares resulted in the selection of and the preference for the empirical model for use in describing the individual and interactive effects of temperature and methyl mercury concentration on the direct uptake of methyl mercury from water by bluegill.     

Evolutionary relationships among deep-sea mytilids (Bivalvia: Mytilidae) from hydrothermal vents and cold-water methane/sulfide seeps

A protein electrophoretic survey of mytilids inhabiting deep-sea hydrothermal vents and cold-water methane/sulfide seeps revealed electromorph patterns diagnostic of 10 distinct species. From hydrothermal vents located at sites on the Galápagos Rift, the Mid-Atlantic Ridge, and the Mariana Back Arc Basin, we detected four species of mytilids. Six additional species were detected from three cold-water seep sides in the Gulf of Mexico. The patchy distribution and temporal stability of seeps may provide a greater opportunity for mytilid diversification and persistence than vent sites Nei's genetic distances (D) between species were relatively large (range: 0.528 to ) both within and among habitat types. This pronounced degree of genetic differentiation suggests a relatively ancient common ancestor for the group. Phylogenetic trees were generated using distance Wagner and parsimony analyses of allozyme and morphological characters. The tree topologies obtained from both methods support: (1) the hypothesis that a seep ancestor gave rise to the deep-sea hydrothermal vent mytilids, (2) a historical progression from shallow-water to deep-water habitats, and (3) a co-evolutionary progression from external to internal localization of bacterial symbionts. Whether the seep mytilid taxa constitute paraphyletic or polyphyletic groups remains unresolved. Our phylogenetic hypotheses also provide a benchmark for the phylogeny of mytilid bacterial symbionts.     

Movement patterns of large bigeye tuna (Thunnus obesus) in the open ocean, determined using ultrasonic telemetry

 The horizontal and vertical movements of large bigeye tuna (Thunnus obesus Lowe, 1839; 25 to 50 kg) captured in the south Pacific Ocean (French Polynesia) were determined using pressure-sensitive ultrasonic transmitters. Bigeye tuna swam within the first 100 m below the surface during the night-time and at depths between 400 and 500 m during the daytime. The fish exhibited clear relationships with the sound scattering layer (SSL). They followed its vertical movements at dawn and dusk, and were probably foraging on the organisms of the SSL. Bigeye tuna did, however, make regular rapid upward vertical excursions into the warm surface layer, most probably in order to regulate body temperature and, perhaps, to compensate for an accumulated oxygen debt (i.e. to metabolize lactate). The characteristics of these dives differ from those reported from previous studies on smaller bigeye tuna (∼12 kg) near the main Hawaiian Islands. During the daytime, the large fish in French Polynesia made upward excursions approximately only every 2.5 h, whereas smaller fish in Hawaiian waters made upward excursions approximately every hour. Our data are the first observations on the role of body size in the vertical behavior of bigeye tuna. Received: 9 September 1998 / Accepted: 25 November 1999     

Geographic and bathymetric patterns of mitochondrial 16S rRNA sequence divergence among deep-sea amphipods,Eurythenes gryllus

The physical uniformity of the deep sea suggests a lack of absolute barriers to faunal dispersal, and thus genetic homogeneity in broadly distributed species is expected. The deep-sea amphipod Eurythenes gryllus Lichtenstein (Crustacea: Lysianassoidea) is considered a panoceanic, cold-water stenotherm, with a vertical depth distribution from 184 to 6500 m. We surveyed mtDNA sequence diversity in E. gryllus to assess genetic diversity and population structure in different oceans and across traditionally defined bathyal and abyssal zones. DNA sequences (437 nucleotides length) from the mitochondrial large-subunit ribosomal RNA gene (16S rRNA) of 95 individuals, collected between 1982 and 1990 from 14 locations in the central North Pacific (including multiple samples on the slope of a seamount), castern and western North Atlantic, and the Arctic Ocean, were obtained. Our analysis of DNA sequence diversity indicates (1) genetic homogeneity among sites within the same depth zone at the scale of ocean basins; and (2) genetically divergent, cryptic taxa distributed at different depths, with the greatest diversity in the bathyal zone. These observations suggest that ecological and physical conditions are important isolating mechanisms that may lead to speciation in this group.     

Evolutionary genetics of marine Mysis spp. (Crustacea: Mysidacea)

Inter-and intraspecific allozyme differentiation in the mysid crustacean genus Mysis in the North Atlantic region was studied in order to evaluate earlier concepts of evolutionary and systematic relationships and to assess patterns of subdivision within widespread taxa. The results support a relatively ancient divergence of the marine and non-marine species of the genus, and are generally in line with the current subgeneric tridivision into Mysis s.str., Michteimysis and Auricomysis. However, the North American littoral species M. gaspensis should be returned to subgenus Mysis s.str. from its present position in Michteimysis with M. mixta. The closest observed affinities within Mysis s.str. were between M. gaspensis and the freshwater M. relicta group, and between M. oculata and M. litoralis. Intraspecific differentiation among North European coastal populations of M. oculata and M. litoralis was moderately strong (F _ST0.1), suggesting population bottlenecks and limited dispersal in the post-glacial time. On the other hand, ransoceanic differences were not essentially greater, indicating the systematic homogeneity and long-term dispersal capacity in the marine species. This contrasts with the strong genetic and systematic fragmentation earlier found within the circumboreal M. relicta species group.