A multi-locus genetic assignment technique to assess sources of <Emphasis Type="Italic">Agaricia agaricites</Emphasis> larvae on coral reefs

Assignment of individuals to populations based upon genetic data is an important ecological problem that requires many polymorphic markers, often more than are available using single locus techniques. To demonstrate the utility of amplified fragment length polymorphisms (AFLP) in studying larval dispersal and recruitment in coral populations, two sets of AFLP primers were used to genotype colonies of the coral Agaricia agaricites Linnaeus from three widely separated geographic locations: the Bahamas (23°28′N, 75°42′W) and Key Largo, Florida (24°55′N, 80°31′W—two sites separated by 12 km) in 1995, and the Flower Garden Banks (FGB) in the Gulf of Mexico (27°55′N,93°36′W) in 1997. In addition to adult samples from each site, recruits were collected from settling plates placed on the East FGB for 1 year (1997–1998). The AFLP technique yielded 45 polymorphic markers. An analysis of molecular variance (AMOVA) showed significant genetic differences among the four adult populations, even between the two Key Largo sites. The recruits were significantly different from all adult populations except those from the FGB. Discriminant function analysis and the program AFLPOP were used to assign individuals to populations. Using the adult AFLP-banding patterns to build the statistical models, both procedures correctly assigned the majority of adults to their respective populations in simulations and assigned all but one of the recruits to the Flower Garden population from where they were collected . The AFLP technique provides a simple and adaptable population assignment method for studying recruitment processes in A. agaricites and other coral species. Electronic Supplementary Material Supplementary material is available for this article at     

Evidence for restricted gene flow over small spatial scales in a marine snapping shrimp <Emphasis Type="Italic">Alpheus angulosus</Emphasis>

Despite the apparent absence of geographic barriers, connectivity among marine populations may be restricted by, for example, ecological or behavioral mechanisms. In such cases, populations may show genetic differentiation even over relatively small spatial scales. Here, mitochondrial sequence data from the cytochrome oxidase I (COI) gene and seven polymorphic microsatellite markers were used to investigate fine geographic scale population genetic structure in the snapping shrimp Alpheus angulosus, a member of the A. armillatus species complex, from collections in Florida, Jamaica, and Puerto Rico carried out from 1999 to 2005. The COI data showed a deep divergence that separated these samples into two mitochondrial clades, but this divergence was not supported by the microsatellite data. The COI data reflect past population divergence not reflected in extant population structure on the whole genome level. The microsatellite data also revealed evidence for moderate population structure between populations as close as ∼10 km, and no evidence for isolation by distance, as divergences between near populations were at least as strong as those between more broadly separated populations. Overall, these data suggest a role for restricted gene flow between populations, though the mechanisms that reduce gene flow in this taxon remain unknown.     

Genetic heterogeneity among <Emphasis Type="Italic">Eurytemora affinis</Emphasis> populations in Western Europe

Evolutionary diversification of the broadly distributed copepod sibling species complex Eurytemora affinis has been documented in the northern hemisphere. However, the fine scale geographic distribution, levels of genetic subdivision, evolutionary, and demographic histories of European populations have been less explored. To gain information on genetic subdivision and to evaluate heterogeneity among European populations, we analyzed samples from 8 locations from 58° to 45°N and 0° to 23°E, using 549 base pairs of the mitochondrial cytochrome oxidase subunit I (COI) gene. We discovered three distinct lineages of E. affinis in Western Europe, namely the East Atlantic lineage, the North Sea/English Channel (NSEC) lineage, and the Baltic lineage. These geographically separated lineages showed sequences divergence of 1.7–2.1%, dating back 1.9 million years (CI: 0.9–3.0 My) with no indication of isolation by distance. Genetic divergence in Europe was much lower than among North American lineages. Interestingly, genetic structure varied distinctively among the three lineages: the East Atlantic lineage was divided between the Gironde and the Loire populations, the NSEC lineage comprised one single population unit spanning the Seine, Scheldt and Elbe rivers and the third lineage was restricted to the Baltic Proper (Sweden). We revealed high haplotype diversity in the East Atlantic and the Baltic lineages, whereas in the NSEC lineage haplotype diversity was comparatively low. All three lineages showed signs of at least one demographic expansion event during Pleistocene glaciations that marked their genetic structure. These results provide a preliminary overview of the genetic structure of E. affinis in Europe.     

Historical demography and contemporary spatial genetic structure of an estuarine crab in the northeast Pacific (<Emphasis Type="Italic">Hemigrapsus oregonensis</Emphasis>)

Discrete estuary subpopulations of the mud crab Hemigrapsus oregonensis (Dana, 1851) are connected via larval dispersal. Sequence variation at the mtDNA COI locus was examined in eight populations sampled in 2001–2002 from central California through northern Oregon in the northeast Pacific (36.6–45.8°N) to infer patterns of dispersal and historical connectivity in the region. Strong evidence for persistence since the mid-Pleistocene, with no range truncation resulting from southward shifting temperature isoclines, was provided by a phylogeographic pattern of haplotypes of an older clade distributed throughout the sampled range. A recently derived clade became widespread only north of Cape Blanco after the last glacial maximum. Its clear pattern of restriction to the northern area, in the absence of similarly restricted southern clades, suggests that contemporary dispersal around Cape Blanco is rare (population F _ST = 0.192). Low pairwise differentiation within Oregon and within central California, as well as contrasts between northern and southern groups in the shape of the pairwise mismatch distribution, nucleotide diversity, and Tajima’s D suggest that these regions reflect different demographic histories. Potential mechanisms explaining this latitudinal break include contemporary coastal circulation patterns, selection, and ancient patterns of larval dispersal in the California Current.     

Domoic acid in benthic flatfish on the continental shelf of Monterey Bay,California, USA

Within Monterey Bay, California, USA, the food web transfer of domoic acid (DA), a neurotoxin produced by diatoms of the genus Pseudo-nitzschia, has led to major mortality events of marine mammals and birds. Less visible, and less well known, is whether invertebrates and fish associated with the benthos are also affected by blooms of DA-producing Pseudo-nitzschia spp. This study examines the presence of DA in benthic flatfish offshore of Davenport, California, (37°0′36″N, 122°13′12″W) and within Monterey Bay, California (36°45′0″N, 122°1′48″W), including species that feed primarily in the sediment (benthic-feeding) and species that feed primarily in the water column (benthopelagic-feeding). Flatfish caught between 10 December 2002 and 17 November 2003 at depths of 30–180 m had concentrations of DA in the viscera ranging from 3 to 26 μg DA g⁻¹ of viscera. Although the DA values reported are relatively low, benthic-feeding flatfish were frequently contaminated with DA, especially as compared with the frequency of contamination of flatfish species that feed in the water column. Furthermore, on days in which both benthic-feeding and benthopelagic-feeding flatfish were collected, the former had significantly higher concentrations of DA in the viscera. Curlfin turbot, Pleuronicthys decurrens, the flatfish with both the highest level and frequency of DA contamination, are reported to feed exclusively on polychaetes, suggesting that these invertebrates may be an important vector of the toxin in benthic communities and may pose a risk to other benthic-feeding organisms. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Spatiotemporal variation in the population ecology of scaly slipper lobsters <Emphasis Type="Italic">Scyllarides squammosus</Emphasis> in the Northwestern Hawaiian Islands

Scaly slipper lobster (Scyllarides squammosus) population ecology was examined using tag/recapture information at Necker Island (23°30′N; 164°35′W), Gardner Pinnacles (25°00′N; 168°50′W), Maro Reef (25°30′N; 170°45′W), and Laysan Island (25°48′N; 171°45′W) in the Northwestern Hawaiian Islands (NWHI) USA from 2002 to 2008. Although many aspects of S. squammosus life history and population dynamics were similar to those of other scyllarids, somatic growth differed from its congers. Scyllarides squammosus growth abruptly declined at maturity and, because of this, growth at length was better described using the Schnute as opposed to the more commonly von Bertalanffy growth model. Growth varied among locations, and survival varied among years; thereby being the first documentation of variability in the life history of a scyllarid. This study has expanded knowledge of scyllarid biology and documented that spatiotemporal variability in biological characteristics must be considered to understand and describe the population ecology of this species and probably of other scyllarids.     

Genetic structure of leopard shark (<Emphasis Type="Italic">Triakis semifasciata</Emphasis>) populations in California waters

The leopard shark (Triakis semifasciata) is an important predator in coastal marine ecosystems of California, targeted by recreational and commercial fishermen and of specific interest in fisheries management. From October 2003 to August 2006, 169 leopard sharks were collected from the coast of California (between 40.750°N and 32.678°N) and analyzed for mitochondrial and nuclear genetic structure. Analyses of mtDNA control region sequences revealed relatively low levels of genetic variation (five haplotypes, average pairwise divergence π = 0.0067). In contrast, leopard sharks were highly polymorphic for inter simple sequence repeats (ISSRs), which characterize a broad range of the nuclear genome. The null hypothesis of panmixia in California waters was rejected for both genetic markers, and ISSRs displayed a statistically significant pattern of isolation by distance (IBD) across the species range (P = 0.002). A variety of analyses showed that divergence is most pronounced in the northernmost population of Humboldt Bay. Natal philopatry in T. semifasciata was tested using Siegel-Tukey tests on data partitioned by breeding site status, and sex-specific philopatry was tested by comparing IBD plots between sexes. Although there was some evidence for natal philopatry in leopard sharks (P = 0.038), and population divergence may be related to the proximity of breeding sites (P = 0.064), we found no support for sex-specific philopatry. In addition to identifying a novel set of highly variable genetic markers for use in shark population studies, these results may be used to better inform management decisions for leopard sharks in California.     

Scarred limpets at hydrothermal vents: evidence of predation by deep-sea whelks

The chaotic physical and chemical environment at deep-sea hydrothermal vents has been associated with an ecosystem with few predators, arguably allowing the habitat to provide refuge for vulnerable species. The dominance of endemic limpets with thin, open-coiled shells at north Pacific vents may support this view. To test their vulnerability to predation, the incidence of healed repair scars, which are argued to reflect non-lethal encounters with predators, were examined on the shells of over 5,800 vent limpets of Lepetodrilus fucensis McLean (1988) that were collected from 13 to 18 August 1996. Three vent fields on the Juan de Fuca Ridge at ca. 2,200 m depth were sampled, two within 70 m of 47°56.87′N 129°05.91′W, and one at 47°57.85′N 129°05.15′W with the conspicuous potential limpet predators, the zoarcid fish Pachycara gymninium Anderson and Peden (1988), the galatheid crab Munidopsis alvisca Williams (1988), and the buccinid snail Buccinum thermophilum Harasewych and Kantor (2002). Limpets from the predator-rich vent were most often scarred, a significant difference created by the high incidence of scars on small (<4 mm long) limpets in this sample. Collected with the limpets were small (median shell diameter 4.4 mm) buccinids. They, rather than the larger, more conspicuous mobile fishes and crabs are argued to be the shell-damaging predator. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

MtDNA population structure and gene flow in lingcod (<Emphasis Type="Italic">Ophiodon elongatus</Emphasis>): limited connectivity despite long-lived pelagic larvae

Lingcod, Ophiodon elongatus Girard, have a 3-month pelagic larval stage and are an important recreational and commercial species on the west coast of North America. Cytochrome-c oxidase I sequences from tissue samples were used to characterize population structure and infer patterns of gene flow from California to Alaska. No significant genetic structure was found when estimates of Wright’s F _ST (i.e., Φ_ST) were generated among all populations sampled. Nesting populations within regions, however, indicated that the inner coast of Washington State is distinct, a result corroborating previous allozyme work. Coalescent-based estimates of gene flow indicate that although migration can be high from an evolutionary perspective, nearly half of all comparisons among populations showed no gene flow in at least one direction. From an ecological perspective, moderate migration rates (Nm < 10) among most populations provide surprisingly limited connectivity at large (∼ 1,000 km) and small (∼100 km) spatial scales. Coalescent-based estimates also show that gene flow between the inner and the outer coasts is asymmetric, a result consistent with prevailing surface currents. Because the expected inter-locus variances for coalescent-based estimates of gene flow are likely large, future work will benefit from analyses of nuclear DNA markers. However, limited demographic connectivity on large spatial scales may help explain why stock recovery has been uneven, with greater recovery in the northern (87% rebuilt) than in the southern (24% rebuilt) fishery region, supporting a regional management strategy. These results suggest that despite a 3-month pelagic larval stage, some areas may be effectively closed with respect to both population dynamics and fishery management issues.     

Population connectivity in the temperate damselfish <Emphasis Type="Italic">Parma microlepis</Emphasis>: analyses of genetic structure across multiple spatial scales

This study investigated the utility of microsatellite markers for providing information on levels of population connectivity for a low dispersing reef fish in New South Wales (NSW), Australia, at scales ≤400 km. It was hypothesized that the temperate damselfish Parma microlepis, which produces benthic eggs and has limited post-settlement dispersal, would exhibit spatial genetic structure and a significant pattern of isolation-by-distance (IBD). A fully nested hierarchical sampling design incorporating three spatial scales (sites, location and regions, separated by 1–2, 10–50 and 70–80 km respectively) was used to determine genetic variability at seven microsatellite loci. Broad-scale genetic homogeneity and lack of IBD was well supported by single and multi-locus analyses. The proportion of the total genetic variation attributable to differences among regions, locations or sites was effectively zero (Φ/R-statistics ≤0.007). The geographic distribution of genetic diversity and levels of polymorphism (H _E 0.21–0.95) indicate high mutation rates, large effective population sizes, and high rates of gene flow. Significant gene flow may be driven by factors influencing pre-settlement dispersal, including the East Australian Current (EAC) and habitat continuity. Genetic connectivity may not reflect demographically important connectivity, but does imply that P. microlepis populations are well connected from an evolutionary perspective. Total observed genetic diversity was accounted for within 1–2 km of reef and could be represented within small Marine Protected Areas. Reef fishes in NSW which have life histories similar to P. microlepis (e.g. pre-settlement durations ≥2 weeks) are also likely to exhibit genetic homogeneity. Genetic markers are, therefore, most likely to provide information on demographically relevant connectivity for species with lower dispersal capabilities, small population sizes, short life spans, and whose habitats are rare, or patchily distributed along-shore. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Geographic clines and stepping-stone patterns detected along the East Pacific Rise in the vetigastropod Lepetodrilus elevatus reflect species crypticism

Three different molecular markers (i.e. seven allozyme loci, two nuclear gene loci and, mtCOI DNA sequences) were used to assess the genetic structure of the vent gastropod Lepetodrilus elevatus collected from three vent fields along the East Pacific Rise (13°N, 9°50′N and 17°S). While allozymes and nuclear loci suggested a strong stepping-stone pattern, a multivariate analysis performed on allozymic frequencies showed the presence of two distinct evolutionary lineages: the first situated in the north from 13°N to 9°50′N and the second in the south from 9°50′N to 17°S. The analysis of mitochondrial DNA sequences confirmed the separation of L. elevatus into two distinct clades with a divergence of 6.5%, which is consistent with the interspecific level of sequence variation in other vent species. A divergence time of 6–14 Mya was estimated between the two clades from previous clock calibrations. Our results suggest that these taxa followed an allopatric speciation between the northern and southern parts of the EPR with a recent demographic expansion of the southern clade to the north and a subsequent secondary contact (clade hybridisation). This speciation was probably reinforced by a habitat specialisation of the two cryptic species because the southern clade was mainly found associated with mussel-dominated communities and the northern clade with tubeworm-dominated communities. However, the analysis of shell morphology failed to separate the two cryptic species based on this sole criterion although they differed from Lepetodrilus elevatus galriftensis (Galapagos population) by a higher shell elevation. Within each clade, genetic differentiation was not related to the distance across populations and could be within vent field as important as between fields. While both clades appear to be in expansion since their speciation, significant excesses in heterozygotes suggest a very recent and local bottleneck at 17°S, probably due to massive site extinction in this region.     

Worms without borders: genetic diversity patterns in four Brazilian <Emphasis Type="Italic">Ototyphlonemertes</Emphasis> species (Nemertea,Hoplonemertea)

Understanding the evolutionary processes from recent demographic history is especially difficult for interstitial organisms due to their poorly known natural history. In this study, the genetic variation and population history of the four Ototyphlonemertes (Diesing in Sitz ber Math Nat Kl Akad Wiss Wien 46:413–416, 1863) species were evaluated from samples collected along the Brazilian coast (between 27°31′S and 13°00′W) in 2006. The mitochondrial region cytochrome c oxidase subunit 3 (COX3) is analyzed to assess the genetic variation of these dioecious species. Although these species have a sympatric distribution along the coast, our data suggest that their levels of differentiation and their demographic histories differ sharply. There is strong evidence of gene flow among demes in O. erneba and O. evelinae, and their level of structuring is much lower than for the other two species. Indeed, the COX3 fragment reveals cryptic lineages in O. lactea and O. parmula. The results seem to contradict the high genetic structuring and low intrapopulational variability expected with the ecological constriction and habitat discontinuity faced by these organisms, meaning that there might be gene flow among populations or their dispersal capability has been underestimated.     

Habitat modification affects recruitment of abalone in central New Zealand

The habitat experienced during early life-history stages can determine the number and quality of individuals that recruit to adult populations. In a field experiment, biogenic habitat complexity was manipulated (presence or absence of foliose macroalgae) at two depths (2–3 m and 5–6 m) and the habitat-dependent effects on recruitment of the black foot abalone (Haliotis iris) were examined at three field sites along the south coast of Wellington, New Zealand (41°20′S, 174°47′E), between July and November 2005. Recruit density (<5 weeks post-settlement) was measured on cobbles covered with crustose coralline algae. Habitats of low complexity (barrens treatments) had consistently greater densities of recruits than habitats of high complexity (algae treatments). However, recruits in algae habitats were larger, and for deep habitats, there was greater survival in algae habitats compared with barrens habitats. While depth had no significant effect on early recruit (<2 weeks post-settlement) density, late recruit (<5 weeks post-settlement) density was greater in shallow habitats, and so it seems recruit survival was greater in shallow habitats. In this experiment, algal habitat complexity had strong effects on early recruit abundance, but habitat-dependent variations in recruit growth and survival may modify initial patterns of abundance and determine recruitment to adult abalone populations.     

Characterizing the resident, fermentative microbial consortium in the hindgut of the temperate-zone herbivorous fish, Hermosilla azurea (Teleostei: Kyphosidae)

The zebraperch, Hermosilla azurea Jenkins and Evermann, a warm-temperate marine fish species with a strictly macroalgal diet, has a relatively long digestive tract with an enlarged hindgut and an associated blind caecum (HC). In zebraperch sampled off Santa Catalina Island, California (33°19′42′′N; 118°18′37′′W) in years 1995 through 2001, direct cell counts, gut epithelium assessment of bacterial attachment, and short-chain fatty acid (SCFA) analyses verified that the zebraperch HC possesses a dense and morphologically diverse, fermentative microbiota. Bacterial cell counts and morphological diversity were significantly higher in HC contents compared to anterior gut regions, suggesting that microbial populations were growing along the digestive tract. Similarly, electron micrographs of the HC epithelium revealed attached microbes, further supporting the possibility that these organisms constitute resident microbiota. Five different SCFAs were detected in all three regions of the digestive tract, but levels were up to three times greater in HC contents. Acetate was consistently the prevailing SCFA in all gut regions. Sequence analysis of bacterial 16S rDNA was used to identify predominant bacterial groups in HC contents. Of the seven main bacterial types identified, Enterovibrio spp. were the dominant bacteria in HC contents followed by species of Bacteroides,Faecalibacterium, and Desulfovibrio. Taken together, our findings show that the zebraperch HC harbors a consortium of microbes that appears to assist in the breakdown of algal polysaccharides in the herbivorous diet of the fish.     

Low levels of global genetic differentiation and population expansion in the deep-sea teleost <Emphasis Type="Italic">Hoplostethus atlanticus</Emphasis> revealed by mitochondrial DNA sequences

The orange roughy Hoplostethus atlanticus is a well-known commercial species with a global distribution. There is no consensus about levels of connectivity among populations despite a range of techniques having been applied. We used cytochrome c oxidase subunit I (COI) and cytochrome b sequences to study genetic connectivity at a global scale. Pairwise Φ_ST analyses revealed a lack of significant differentiation among samples from New Zealand, Australia, Namibia, and Chile. However, low but significant differentiation (Φ_ST = 0.02–0.13, P < 0.05) was found between two Northeast Atlantic sites and all the other sites with COI. AMOVA and the haplotype genealogy confirmed these results. The prevalent lack of genetic differentiation is probably due to active adult dispersal under the stepping-stone model. Demographic analyses suggested the occurrence of two expansion events during the Pleistocene period.     

Geographical subdivision,demographic history and gene flow in two sympatric species of intertidal snails, <Emphasis Type="Italic">Nerita scabricosta</Emphasis> and <Emphasis Type="Italic">Nerita funiculata</Emphasis>, from the tropical eastern Pacific

The patchy distribution of rocky intertidal communities in the tropical eastern Pacific (TEP) may impose severe constraints on the genetic connectivity among populations of marine invertebrates associated with this habitat. In this study, we analyzed a portion of the mitochondrial cytochrome c oxidase subunit I (COI) gene in two sympatric species of marine snails, Nerita scabricosta and Nerita funiculata, common inhabitants of the rocky intertidal from the Gulf of California (Sea of Cortez) and outer Pacific coast of the southern Baja California (Baja) peninsula to northern South America, to assess genetic connectivity among populations of each species. One of our aims was to determine whether the morphological, behavioral, and ecological differences observed among populations of both species throughout their range in the TEP corresponded to population genetic differences. In addition, we were interested in elucidating the demographic history of both species. We found no evidence of genetic structure throughout the Gulf of California and outer coast of the Baja peninsula region for either species. Comparisons between Gulf of California/Baja and Panama populations, however, showed significant genetic differentiation for N. scabricosta, but not for N. funiculata. The genetic differences between Mexican and Panamanian populations of N. scabricosta were consistent with previously reported ecological and behavioral differences for this species between these two distant regions. However, previously reported size differences between northern and central/southern Gulf of California individuals of N. scabricosta do not correspond with our findings of genetic connectivity among these populations. Results from neutrality tests (Tajima’s D and Fu’s F _S), the mismatch distribution, and Bayesian skyline analyses suggested that both species have experienced dramatic population expansions dating to the Pleistocene.     

Sperm polymorphism and genetic divergence in the mussel Perumytilus purpuratus

For the first time in a marine bivalve species, geographic intraspecific variation in sperm morphology in the Chilean mussel, Perumytilus purpuratus, is reported. Samples were obtained in December 2010 from the rocky intertidal at three locations: Antofagasta (23o44′01.08′′S, 70o26′26.11′′W), Valparaíso (32o57′23.07′′S, 71o33′01.86′′W), and Valdivia (39°50′44.26′′S, 73°25′51.99′′W). Scanning electron microscopy was used to describe sperm traits, and genetic data were obtained by sequencing a 16S mtDNA 427-bp fragment. The results showed geographic intraspecific variation with two statistically significant patterns of genetically differentiated sperm morphologies. One genetic clade was found for Antofagasta and Valparaíso, displaying a unique sperm morphotype with a short acrosome accounting for 26 % of the head length, and the other from Valdivia, with a larger acrosome occupying 47 % of the head length. These results will lead to new research to distinguish among alternative hypotheses: the presence of cryptic species, incipient speciation, or a polymorphism in sperm traits of P. purpuratus.     

Geographic and ontogenetic variation in the diet and daily ration of the bonnethead shark, <Emphasis Type="Italic">Sphyrna tiburo</Emphasis>, from the eastern Gulf of Mexico

To examine variation in diet and daily ration of the bonnethead shark, Sphyrna tiburo (Linnaeus 1758), animals were collected from three areas in the eastern Gulf of Mexico: northwest Florida (∼29°40′N, 85°13′W), Tampa Bay near Anclote Key (∼28°10′N, 82°42.5′W), and Florida Bay (∼24°50′N, 80°48′W) from March through September, 1998–2000. In each area, diet was assessed by life stage (young-of-the year, juveniles, and adults) and quantified using five indices: percent by number (%N), percent by weight (%W), frequency of occurrence (%O), index of relative importance expressed on a percent basis (%IRI), and %IRI based on diet category (%IRI_DC). Diet could not be assessed for young-of-the-year in Tampa Bay or Florida Bay owing to low sample size. Diet analysis showed an ontogenetic shift in northwest Florida. Young-of-the-year stomachs from northwest Florida (n = 68, 1 empty) contained a mix of seagrass and crustaceans while juvenile stomachs (n = 82, 0 empty) contained a mix of crabs and seagrass and adult stomachs (n = 39, 1 empty) contained almost exclusively crabs. Crabs made up the majority of both juvenile and adult diet in Tampa Bay (n = 79, 2 empty, and n = 88, 1 empty, respectively). Juvenile stomachs from Florida Bay (n = 72, 0 empty) contained seagrass and a mix of crustaceans while adult stomachs contained more shrimp and cephalopods (n = 82, 3 empty). Diets in northwest Florida and Tampa Bay were similar. The diet in Florida Bay was different from those in the other two areas, consisting of fewer crabs and more cephalopods and lobsters. Plant material was found in large quantities in all stomachs examined from all locations (>15 %IRI_DC in 6 of the 7 life stage-area combinations, >30 %IRI_DC in 4 of the 7 combinations, and 62 %IRI_DC in young-of-the-year diet in northwest Florida). Using species- and area-specific inputs, a bioenergetic model was constructed to estimate daily ration. Models were constructed under two scenarios: assuming plant material was and was not part of the diet. Overall, daily ration was significantly different by sex, life stage, and region. The bioenergetic model predicted increasing daily ration with decreasing latitude and decreasing daily ration with ontogeny regardless of the inclusion or exclusion of plant material. These results provide evidence that bonnetheads continuously exposed to warmer temperatures have elevated metabolism and require additional energy consumption to maintain growth and reproduction. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Small-scale genetic structure in the sea palm Postelsia palmaeformis Ruprecht (Phaeophyceae)

Documenting the scale of movement among populations is an important challenge for marine ecology. Using nine microsatellite markers, evidence of genetic structure in a marine kelp, the sea palm Postelsia palmaeformis Ruprecht, was examined in the vicinity of Cape Flattery, Washington state, USA (48° 24′ N, 124°44′ W). Genetic clustering analysis implemented without reference to geographic structure strongly suggested that a number of distinct genetic clusters existed among the 245 plants sampled in August in the years 1997–2001. Subsequent analysis showed that clustering was associated with geographically defined populations both among (km scale) and within (m scale) sampling sites. F _st analysis of geographically defined populations revealed significant genetic differentiation among populations of plants as little as 5 m apart, evidence of genetic structuring at even smaller scales, and a sharp increase in F _st across populations separated by up to 23 m. F _st values were also high and approximately unchanging (F _st=0.470) for populations separated by greater distances (up to 11 km), consistent with a scenario of rare dispersal by detached, floating plants carried by variable currents. The results corroborate natural history observations suggesting that P. palmaeformis has extremely short (1–3 m) spore dispersal distances, and indicate that the dynamics of sea palm populations are more affected by local processes than recruitment from distant populations.     

Genome-size variation in bivalve molluscs determined by flow cytometry

Six of the nine described species of the mole crab genus Emerita are distributed in the Americas, two [E. analoga (Stimpson, 1857) and E. rathbunae Schmitt, 1935] on the west coast, and four [E. benedicti Schmitt, 1935, E. brasiliensis Schmitt, 1935, E. portoricensis Schmitt, 1935 and E. talpoida (Say, 1817)] on the east. The presence of an extended planktonic larval stage in all Emerita species suggests high dispersal potential and the possibility of extensive gene flow among conspecific populations. Two taxa were sampled to study the extent of gene flow between widely separated conspecific populations: E. analoga (California and Chile) and E. talpoida (Massachusetts, South Carolina, and the west coast of Florida), while all other taxa were characterized from a single location. Portions of two mitochondrial genes, cytochrome oxidase I (COI) and 16S ribosomal RNA (16S rRNA) were sequenced. For data analysis, approximately 500 bp (COI) and 400 bp (16S rRNA) were examined. Estimated genetic divergence of 5.41% in COI between E. talpoida populations sampled from the Gulf of Mexico and the Atlantic coast, and 3.47% between E. analoga sampled in Chile and California, indicates that in both cases there has been no recent gene flow between disjunct populations. Additional molecular and morphological studies are necessary to decide whether disjunct populations should be accorded specific status. We predict that many marine invertebrates with antitropical distributions similar to E. analoga may consist of sibling species. In contrast to relationships inferred earlier from distribution patterns, parsimony analyses of both COI and 16S rRNA data yield similar phylogenetic trees in which E. analoga is separated from a clade composed of other species in the Americas; a bootstrap value (67%) in the COI inferred tree marginally supports the separation, but the same tree topology with a higher bootstrap value (84%) is obtained with 16S rRNA sequence data. Genetic divergence among the taxa indicates that the Emerita species constitute an old group and that distribution of species has been modified by past climatic and geological events.