Active buoyancy adjustment increases dispersal potential in benthic marine animals.

While the study of dispersal and connectivity in the ocean typically centres on pelagic species and planktonic larval stages of benthic species, the present work explores an overlooked locomotor means in post-settlement benthic stages that redefines their dispersal potential. Members of the echinoderm class Holothuroidea colonize a diversity of marine environments world-wide, where they play key ecological and economical roles, making their conservation a priority. Holothuroids are commonly called sea cucumbers or sea slugs to reflect their slow movements and are assumed to disperse chiefly through pelagic larvae. The present study documents and explores their unexpected ability to actively modify their buoyancy, leading them to tumble or float at speeds orders of magnitudes faster than through benthic crawling. Two focal species representing different taxonomic orders, geographic distributions and reproductive strategies were studied over several years. Active buoyancy adjustment (ABA) was achieved through a rapid increase in water-to-flesh ratio by up to 740%, leading to bloating, and simultaneously detachment from the substrate. It occurred as early as 6 months post settlement in juveniles and was recorded in wild adult populations. In experimental trials, ABA was triggered by high conspecific density, decreasing salinity and increasing water turbidity. Based on field video footage, ABA-assisted movements generated speeds of up to 90 km/day. These findings imply that displacement during planktonic larval stages may not supersede the locomotor capacity of benthic stages, challenging the notion of sedentarity. Combining the present results and anecdotal reports, ABA emerges as a generalized means of dispersal among benthic animals, with critical implications for world-wide management and conservation of commercially and ecologically significant species.

Barcoding Atlantic Canada's mesopelagic and upper bathypelagic marine fishes.

DNA barcode sequences were developed from 557 mesopelagic and upper bathypelagic teleost specimens collected in waters off Atlantic Canada. Confident morphological identifications were available for 366 specimens, of 118 species and 93 genera, which yielded 328 haplotypes. Five of the species were novel to the Barcode of Life Database (BOLD). Most of the 118 species conformed to expectations of monophyly and the presence of a "barcode gap", though some known weaknesses in existing taxonomy were confirmed and a deficiency in published keys was revealed. Of the specimens for which no firm morphological identification was available, 156 were successfully identified to species, and a further 11 to genus, using their barcode sequences and a combination of distance- and character-based methods. The remaining 24 specimens were from species for which no reference barcode is yet available or else ones confused by apparent misidentification of publicly available sequences in BOLD. Addition of the new sequences to those previously in BOLD contributed support to recent taxonomic revisions of Chiasmodon and Poromitra, while it also revealed 18 cases of potential cryptic speciation. Most of the latter appear to result from genetic divergence among populations in different ocean basins, while the general lack of strong horizontal environmental gradients within the deep sea has allowed morphology to be conserved. Other examples of divergence appear to distinguish individuals living under the sub-tropical gyre of the North Atlantic from those under that ocean's sub-polar gyre. In contrast, the available sequences for two myctophid species, Benthosema glaciale and Notoscopelus elongatus, showed genetic structuring on finer geographic scales. The observed structure was not consistent with recent suggestions that "resident" populations of myctophids can maintain allopatry despite the mixing of ocean waters. Rather, it indicates that the very rapid speciation characteristic of the Myctophidae is both on-going and detectable using barcodes.

Influence of Benthic Macrofauna as a Spatial Structuring Agent for Juvenile Haddock (Melanogrammus aeglefinus) on the Eastern Scotian Shelf, Atlantic Canada.

We examined the habitat of juvenile haddock on the eastern Scotian Shelf (off Nova Scotia, Canada) in relation to grab-sampled benthic macrofaunal invertebrate species assemblages in order to determine whether there were significant differences in benthic macrofauna between areas of historically persistent high and low juvenile haddock abundance. Our analyses were conducted over two spatial scales in each of two years: among banks (Emerald, Western and Sable Island), approximately 60 km distant from each other, and between areas of high and low juvenile haddock abundance at distances of 10 to 30 km-all in an area that had not experienced groundfishing in the decade prior to sampling. We also examined fine-scale (10s of metres) within-site variability in the macrofauna and used surficial sediment characteristics, along with hydrographic variables, to identify environmental correlates. PERMANOVA identified statistically significant differences in biomass, density and composition of the benthos associated with juvenile haddock abundance; however it was difficult to determine whether the results had biological relevance. Post hoc tests showed that these differences occurred only on Sable Island Bank where both fish and benthos may have been independently responding to sediment type which was most different there (100% sand in the area of low haddock abundance vs. 22% gravel in the area of high haddock abundance). In total, 383 benthic taxa representing 13 phyla were identified. Annelida was the most specious phylum (36.29% of taxa, representing 33 families), followed by Arthropoda (with Crustaceans, mostly Amphipoda, accounting for 25.07% of the total number of taxa). The strongest pattern in the macrofauna was expressed at the largest scale, between banks, accounting for approximately 25% of the variation in the data. Emerald Bank, deeper, warmer and saltier than the Western and Sable Island Banks, had a distinctive fauna.

Genetic structure of capelin (Mallotus villosus) in the northwest Atlantic Ocean.

Capelin (Mallotus villosus) is a commercially exploited, key forage-fish species found in the boreal waters of the North Pacific and North Atlantic Oceans. We examined the population structure of capelin throughout their range in the Canadian northwest Atlantic Ocean using genetic-based methods. Capelin collected at ten beach and five demersal spawning locations over the period 2002 through 2008 (N = 3,433 fish) were genotyped using six polymorphic microsatellite loci. Temporally distinct samples were identified at three beach spawning locations: Chance Cove, Little Lawn and Straitsview, Newfoundland. Four capelin stocks are assumed for fisheries management in the northwest Atlantic Ocean based on meristics, morphometrics, tag returns, and seasonal distribution patterns. Our results suggested groupings that were somewhat different than the assumed structure, and indicate at least seven genetically defined populations arising from two ancestral populations. The spatial mosaic of capelin from each of the two basal cluster groups explains much of the observed geographic variability amongst neighbouring samples. The genetic-defined populations were resolved at Jost's Dest ≥ 0.01 and were composed of fish collected 1) in the Gulf of St. Lawrence, 2) along the south and east coasts of Newfoundland, 3) along coastal northern Newfoundland and southern Labrador, 4) along coastal northern Labrador, 5) near the Saguenay River, and at two nearshore demersal spawning sites, 6) one at Grebes Nest off Bellevue Beach on the east coast of Newfoundland, and 7) one off the coast of Labrador at Domino Run. Moreover, the offshore demersal spawners on the Scotian Shelf and Southeast Shoal appeared to be related to the inshore demersal spawners at Grebes Nest and in Domino Run and to beach spawners from the Gulf of St. Lawrence.

Proteomic analysis of eggs from Mytilus edulis females differing in mitochondrial DNA transmission mode.

Many bivalves have an unusual mechanism of mitochondrial DNA (mtDNA) inheritance called doubly uniparental inheritance (DUI) in which distinctly different genomes are inherited through the female (F genome) and male (M genome) lineages. In fertilized eggs that will develop into male embryos, the sperm mitochondria remain in an aggregation, which is believed to be delivered to the primordial germ cells and passed to the next generation through the sperm. In fertilized eggs that will develop into female embryos, the sperm mitochondria are dispersed throughout the developing embryo and make little if any contribution to the next generation. The frequency of embryos with the aggregated or dispersed mitochondrial type varies among females. Previous models of DUI have predicted that maternal nuclear factors cause molecular differences among unfertilized eggs from females producing embryos with predominantly dispersed or aggregated mitochondria. We test this hypothesis using females of each of the two types from a natural population. We have found small, yet detectable, differences of the predicted type at the proteome level. We also provide evidence that eggs of females giving the dispersed pattern have consistently lower expression for different proteasome subunits than eggs of females giving the aggregated pattern. These results, combined with those of an earlier study in which we used hatchery lines of Mytilus, and with a transcriptomic study in a clam that has the DUI system of mtDNA transmission, reinforce the hypothesis that the ubiquitin-proteasome system plays a key role in the mechanism of DUI and sex determination in bivalves. We also report that eggs of females giving the dispersed pattern have higher expression for arginine kinase and enolase, enzymes involved in energy production, whereas ferritin, which is involved in iron homeostasis, has lower expression. We discuss these results in the context of genetic models for DUI and suggest experimental methods for further understanding the role of these proteins in DUI.

From sea to sea: Canada's three oceans of biodiversity.

Evaluating and understanding biodiversity in marine ecosystems are both necessary and challenging for conservation. This paper compiles and summarizes current knowledge of the diversity of marine taxa in Canada's three oceans while recognizing that this compilation is incomplete and will change in the future. That Canada has the longest coastline in the world and incorporates distinctly different biogeographic provinces and ecoregions (e.g., temperate through ice-covered areas) constrains this analysis. The taxonomic groups presented here include microbes, phytoplankton, macroalgae, zooplankton, benthic infauna, fishes, and marine mammals. The minimum number of species or taxa compiled here is 15,988 for the three Canadian oceans. However, this number clearly underestimates in several ways the total number of taxa present. First, there are significant gaps in the published literature. Second, the diversity of many habitats has not been compiled for all taxonomic groups (e.g., intertidal rocky shores, deep sea), and data compilations are based on short-term, directed research programs or longer-term monitoring activities with limited spatial resolution. Third, the biodiversity of large organisms is well known, but this is not true of smaller organisms. Finally, the greatest constraint on this summary is the willingness and capacity of those who collected the data to make it available to those interested in biodiversity meta-analyses. Confirmation of identities and intercomparison of studies are also constrained by the disturbing rate of decline in the number of taxonomists and systematists specializing on marine taxa in Canada. This decline is mostly the result of retirements of current specialists and to a lack of training and employment opportunities for new ones. Considering the difficulties encountered in compiling an overview of biogeographic data and the diversity of species or taxa in Canada's three oceans, this synthesis is intended to serve as a biodiversity baseline for a new program on marine biodiversity, the Canadian Healthy Ocean Network. A major effort needs to be undertaken to establish a complete baseline of Canadian marine biodiversity of all taxonomic groups, especially if we are to understand and conserve this part of Canada's natural heritage.

Paternal mtDNA and maleness are co-inherited but not causally linked in mytilid mussels.

BACKGROUND: In marine mussels of the genus Mytilus there are two mitochondrial genomes. One is transmitted through the female parent, which is the normal transmission route in animals, and the other is transmitted through the male parent which is an unusual phenomenon. In males the germ cell line is dominated by the paternal mitochondrial genome and the somatic cell line by the maternal. Research to date has not allowed a clear answer to the question of whether inheritance of the paternal genome is causally related to maleness. METHODOLOGY/PRINCIPAL FINDINGS: Here we present results from hybrid crosses, from triploid mussels and from observations of sperm mitochondria in fertilized eggs which clearly show that maleness and presence of the paternal mitochondrial genome can be decoupled. These same results show that the female mussel has exclusive control of whether her progeny will inherit the mitochondrial genome of the male parent. CONCLUSIONS/SIGNIFICANCE: These findings are important in our efforts to understand the mechanistic basis of this unusual mode of mitochondrial DNA inheritance that is common among bivalves.

Pleistocene glaciation events shape genetic structure across the range of the American lobster, Homarus americanus.

A north/south discontinuity along the northeastern coast of North America in the genetic structure of the American lobster (Homarus americanus) was detected using a suite of 13 microsatellite loci assessed using spatial analyses. Population genetic data laid over existing data on physiographic changes and sea-surface temperatures were used to reconstruct the Pleistocene distribution of this species. A postglacial northern-edge colonization model best explains the relative genetic homogeneity of the northern region compared to the southern region centred in the Gulf of Maine. Population genetic analyses identified significant structure (range of standardized theta 0-0.02) but no significant evidence for isolation by distance. The novel application of spatial genetic analyses to a marine species allowed us to interpret these results by providing a greater insight into the evolutionary factors responsible for shaping the genetic structure of this species throughout is natural range.

Genetic variation underlying protein expression in eggs of the marine mussel Mytilus edulis.

Study of the genetic basis of gene expression variation is central to attempts to understand the causes of evolutionary change. Although there are many transcriptomics studies estimating genetic variance and heritability in model organisms such as humans there is a lack of equivalent proteomics studies. In the present study, the heritability underlying egg protein expression was estimated in the marine mussel Mytilus. We believe this to be the first such measurement of genetic variation for gene expression in eggs of any organism. The study of eggs is important in evolutionary theory and life history analysis because maternal effects might have profound effects on the rate of evolution of offspring traits. Evidence is presented that the egg proteome varies significantly between individual females and that heritability of protein expression in mussel eggs is moderate to high suggesting abundant genetic variation on which natural selection might act. The study of the mussel egg proteome is also important because of the unusual system of mitochondrial DNA inheritance in mussels whereby different mitochondrial genomes are transmitted independently through female and male lineages (doubly uniparental inheritance). It is likely that the mechanism underlying this system involves the interaction of specific egg factors with sperm mitochondria following fertilization, and its elucidation might be advanced by study of the proteome in females having different progeny sex ratios. Putative identifications are presented here for egg proteins using MS/MS in Mytilus lines differing in sex ratio. Ontology terms relating to stress response and protein folding occur more frequently for proteins showing large expression differences between the lines. The distribution of ontology terms in mussel eggs was compared with those for previous mussel proteomics studies (using other tissues) and with mammal eggs. Significant differences were observed between mussel eggs and mussel tissues but not between the two types of eggs.

Nucleotide content gradients in maternally and paternally inherited mitochondrial genomes of the mussel Mytilus.

Several studies have shown that in vertebrate mtDNAs the nucleotide content at fourfold degenerate sites is well correlated with the site's time of exposure to the single-strand state, as predicted from the asymmetrical model of mtDNA replication. Here we examine whether the same explanation may hold for the regional variation in nucleotide content in the maternal and paternal mtDNAs of the mussel Mytilus galloprovincialis. The origin of replication of the heavy strand (O(H)) of these genomes has been previously established. A systematic search of the two genomes for sequences that are likely to act as the origin of replication of the light strand (O(L)) suggested that the most probable site lies within the ND3 gene. By adopting this O(L) position we calculated times of exposure for 0(FD) (nondegenerate), 2(FD) (twofold degenerate), and 4(FD) (fourfold degenerate) sites of the protein-coding part of the genome and for the rRNA, tRNA and noncoding parts. The presence of thymine and absence of guanine at 4(FD) sites was highly correlated with the presumed time of exposure. Such an effect was not found for the 2(FD) sites, the rRNA, the tRNA, or the noncoding parts. There was a trend for a small increase in cytosine at 0(FD) sites with exposure time, which is explicable as the result of biased usage of 4(FD) codons. The same analysis was applied to a recently sequenced mitochondrial genome of Mytilus trossulus and produced similar results. These results are consistent with the asymmetrical model of replication and suggest that guanine oxidation due to single-strand exposure is the main cause of regional variation of nucleotide content in Mytilus mitochondrial genomes.

Segregation of sperm mitochondria in two- and four-cell embryos of the blue mussel Mytilus edulis: Implications for the mechanism of doubly uniparental inheritance of mitochondrial DNA.

Species of the family Mytilidae have 2 mitochondrial genomes, one that is transmitted through the egg and one that is transmitted through the sperm. In the Mytilus edulis species complex (M. edulis, M. galloprovincialis, and M. trossulus) there is also a strong mother-dependent sex-ratio bias in favor of one or the other sex among progeny from pair matings. In a previous study, we have shown that sperm mitochondria enter the egg and that their behavior during cell division is different depending on whether the egg originated from a female- or male-biased mother. Specifically, in eggs from females that produce mostly or exclusively daughters, sperm mitochondria disperse randomly among cells after egg division. In eggs from females that produce predominantly sons, sperm mitochondria tend to stay together in the same cell. Here, we extend these observations and show that in 2- and 4-cell embryos from male-biased mothers most sperm mitochondria are located near or at the cleavage furrow of the major cell, in contrast to embryos from female-biased mothers where there is no preferential association of sperm mitochondria with the cleavage furrow. This observation provides evidence for an early developmental mechanism through which sperm mitochondria are preferentially channeled into the primordial cells of male embryos, thus making the paternal mitochondrial genome the dominant mtDNA component of the male germ line.

Development, characterisation, inheritance, and cross-species utility of American lobster (Homarus americanus) microsatellite and mtDNA PCR-RFLP markers.

Effective management of exploited species demands contemporary knowledge of population structure and mating patterns. Genetic markers can prove useful in providing this knowledge. Despite its commercial importance, genetic markers for American lobster (Homarus americanus) are limited. We developed 12 tetra- and 1 trinucleotide microsatellite loci for American lobster that exhibit little stuttering after PCR amplification. Gene diversity of these loci ranged from 0.516 to 0.929. A four-locus multiplex permits rapid genotyping of progeny in parentage experiments with a paternity exclusion probability over the four loci of 97.8%. We examined the loci for conformity to Hardy-Weinberg expectations (HWE) and linkage using individuals from one location and found that four loci deviated from HWE. We also tested inheritance and pairwise linkage using 48 embryos from each of two females. With the exception of two loci that were derived from the same clone and separated by 72 bp, no evidence of linkage was found. We, for the first time, demonstrate the occurrence of multiple paternity in American lobster. We also observed an apparent occurrence of dispermic androgenesis, possibly the first documentation of such an event within a species. Ten of the loci amplified in European lobster (Homarus gammarus), although two were monomorphic and one deviated significantly from HWE. We quantified mitochondrial DNA (mtDNA) sequence variation through the use of PCR amplification of two DNA fragments, followed by digestion with restriction enzymes; eight haplotypes were detected. One of the two fragments amplified in European lobster. Both sets of markers should prove useful for population discrimination purposes, and the microsatellites, in particular the four-locus multiplex, should prove highly amenable to rapidly addressing questions about mating patterns.