Genetic Patchiness Research Articles

Genetic patchiness of the endangered giant clam Tridacna maxima from Peninsular Malaysia

Genetic patchiness of the endangered giant clam Tridacna maxima from Peninsular Malaysia

High connectivity among Vesicomyid bivalves from cold seeps and deep-sea fans of Congo

Chemosynthetic ecosystems are scattered in the deep ocean, harbouring highly specialized communities, among which the degree of connectivity and dispersal is scarcely studied. This gap is largely due to limited range distribution, either real or due to highly partial exploration, preventing the availability of a sufficient number of samples for population genetic analysis. For the few species that escaped this gap, large-scale panmixia was often reported, raising wonders as to the evolutionary mechanisms involved in the first steps of speciation. Vesicomyid bivalves are one of the most abundant groups of chemosynthetic fauna, for which depth was proposed as an essential driver of differentiation. Early stages of speciation are thus expected to involve genetic differentiation along depth gradients. The vesicomyid bivalve Christineconcha regab was studied across widely separated localities along the Western African margin, from the cold-seeps of Regab pockmarks located at 3150 m depth on the Congo margin to the turbiditic lobes of the Congo deep-sea fan located at 5000 m depth, using mitochondrial (COI) sequences and eight microsatellite loci. Despite rather high density in relation to high organic matter availability, results obtained showed rather low levels of genetic diversity at both mtDNA and microsatellites. The main consistent pattern of differentiation was observed across depths from Regab pockmark (South-Western part) and lobe areas (Lobe B and C). This is likely due to the largest sample sizes characterizing Regab_SW and Lobe C allowing the detection of faint genetic differentiation, and possibly to a stronger signature in the demographically declining (thus acknowledgedly under sampled) Lobe B. Other significant results were not congruent among markers, suggesting low statistical power due to limited sample size or the occurrence of chaotic genetic patchiness. Altogether, the results suggest the occurrence of effective gene flow at regional scale, and departure from equilibrium in the recently discovered lobes of the Congo River, possibly resulting from unstable environmental conditions and recurrent events of extinction recolonization.

Chaotic Genetic Patchiness in the Highly Valued Atlantic Stalked Barnacle Pollicipes pollicipes From the Iberian Peninsula: Implications for Fisheries Management

The stalked barnacle Pollicipes pollicipes inhabits rocky shores from the Atlantic coasts of Brittany (France) to Senegal. Because of the culinary traditions of southern Europe, stalked barnacles represent an important target species for local fisheries on the Iberian Peninsula. To manage this fishery sustainably, it is therefore important to assess the dynamics of local populations over the Iberian coast, and how they are interconnected at a wider scale using finely tuned genetic markers. In this work, a new enriched library of GT microsatellites for P. pollicipes was prepared and sequenced using Ion Torrent™ Next Gen-Sequencing Technology. 1,423 adults and juveniles were sampled in 15 localities of three geographic regions: southern Portugal, Galicia and Asturias (both in northern Spain). Twenty polymorphic loci arranged in five multiplex PCRs were then tested and validated as new molecular tools to address the spatial and temporal genetic patterns of P. pollicipes. Our results revealed high genetic diversity among adults. However, juveniles were genetically more structured than their adult counterparts, which alternatively displayed much more connectivity among the three studied regions. The lack of spatial genetic heterogeneity in adults may be due to the overlapping of several generations of settlers coming from different geographic origins, which mainly depends on the orientation of residual currents along the coast during reproduction. The genetic differentiation of juveniles may indeed be congruent with Iberian Peninsula hydrodynamics, which can produce chaotic genetic patchiness (CGP) at small temporal scales due to sweepstake reproductive success, collective dispersal and/or self-recruitment. Remarkably, most of the genetic heterogeneity of juveniles found in this work was located in Galicia, which could represent an admixture between distinct metapopulations or an old refuge for the most northern populations. To conclude, high genetic variation in P. pollicipes can lead to the false impression of population panmixia at the Iberian scale by masking more restricted and current-driven larval exchanges between regions. This possibility should be taken into consideration for further specific management and conservation plans for the species over the Iberian Peninsula.

Sweepstake reproductive success and collective dispersal produce chaotic genetic patchiness in a broadcast spawner.

A long-standing paradox of marine populations is chaotic genetic patchiness (CGP), temporally unstable patterns of genetic differentiation that occur below the geographic scale of effective dispersal. Several mechanisms are hypothesized to explain CGP including natural selection, spatiotemporal fluctuations in larval source populations, self-recruitment, and sweepstake reproduction. Discriminating among them is extremely difficult but is fundamental to understanding how marine organisms reproduce and disperse. Here, we report a notable example of CGP in the Antarctic limpet, an unusually tractable system where multiple confounding explanations can be discounted. Using population genomics, temporally replicated sampling, surface drifters, and forward genetic simulations, we show that CGP likely arises from an extreme sweepstake event together with collective larval dispersal, while selection appears to be unimportant. Our results illustrate the importance of neutral demographic forces in natural populations and have important implications for understanding the recruitment dynamics, population connectivity, local adaptation, and resilience of marine populations.

Impact of cyclones on hard coral and metapopulation structure, connectivity and genetic diversity of coral reef fish

Cyclones have one of the greatest effects on the biodiversity of coral reefs and the associated species. But it is unknown how stochastic alterations in habitat structure influence metapopulation structure, connectivity and genetic diversity. From 1993 to 2018, the reefs of the Capricorn Bunker Reef group in the southern part of the Great Barrier Reef were impacted by three tropical cyclones including cyclone Hamish (2009, category 5). This resulted in substantial loss of live habitat-forming coral and coral reef fish communities. Within 6–8 years after cyclones had devastated, live hard corals recovered by 50–60%. We show the relationship between hard coral cover and the abundance of the neon damselfish (Pomacentrus coelestis), the first fish colonizing destroyed reefs. We present the first long-term (2008–2015 years corresponding to 16–24 generations of P. coelestis) population genetic study to understand the impact of cyclones on the meta-population structure, connectivity and genetic diversity of the neon damselfish. After the cyclone, we observed the largest change in the genetic structure at reef populations compared to other years. Simultaneously, allelic richness of genetic microsatellite markers dropped indicating a great loss of genetic diversity, which increased again in subsequent years. Over years, metapopulation dynamics were characterized by high connectivity among fish populations associated with the Capricorn Bunker reefs (2200 km2); however, despite high exchange, genetic patchiness was observed with annual strong genetic divergence between populations among reefs. Some broad similarities in the genetic structure in 2015 could be explained by dispersal from a source reef and the related expansion of local populations. This study has shown that alternating cyclone-driven changes and subsequent recovery phases of coral habitat can greatly influence patterns of reef fish connectivity. The frequency of disturbances determines abundance of fish and genetic diversity within species.

Genetic and phenotypic variation exhibit both predictable and stochastic patterns across an intertidal fish metapopulation.

Interactions among selection, gene flow, and drift affect the trajectory of adaptive evolution. In natural populations, the direction and magnitude of these processes can be variable across different spatial, temporal, or ontogenetic scales. Consequently, variability in evolutionary processes affects the predictability or stochasticity of microevolutionary outcomes. We studied an intertidal fish, Bathygobius cocosensis (Bleeker, 1854), to understand how space, time, and life stage structure genetic and phenotypic variation in a species with potentially extensive dispersal and a complex life cycle (larval dispersal preceding benthic recruitment). We sampled juvenile and adult life stages, at three sites, over three years. Genome-wide SNPs uncovered a pattern of chaotic genetic patchiness, that is, weak-but-significant patchy spatial genetic structure that was variable through time and between life stages. Outlier locus analyses suggested that targets of spatially divergent selection were mostly temporally variable, though a significant number of spatial outlier loci were shared between life stages. Head shape, a putatively ecologically responsive (adaptive) phenotype in B.cocosensis also exhibited high temporal variability within sites. However, consistent spatial relationships between sites indicated that environmental similarities among sites may generate predictable phenotype distributions across space. Our study highlights the complex microevolutionary dynamics of marine systems, where consideration of multiple ecological dimensions can reveal both predictable and stochastic patterns in the distributions of genetic and phenotypic variation. Such considerations probably apply to species that possess short, complex life cycles, have large dispersal potential and fecundities, and that inhabit heterogeneous environments.

Transcriptome Expression of Biomineralization Genes in Littoraria flava Gastropod in Brazilian Rocky Shore Reveals Evidence of Local Adaptation.

Understanding how selection shapes population differentiation and local adaptation in marine species remains one of the greatest challenges in the field of evolutionary biology. The selection of genes in response to environment-specific factors and microenvironmental variation often results in chaotic genetic patchiness, which is commonly observed in rocky shore organisms. To identify these genes, the expression profile of the marine gastropod Littoraria flava collected from four Southeast Brazilian locations in ten rocky shore sites was analyzed. In this first L. flava transcriptome, 250,641 unigenes were generated, and 24% returned hits after functional annotation. Independent paired comparisons between 1) transects, 2) sites within transects, and 3) sites from different transects were performed for differential expression, detecting 8,622 unique differentially expressed genes. Araçá (AR) and São João (SJ) transect comparisons showed the most divergent gene products. For local adaptation, fitness-related differentially expressed genes were chosen for selection tests. Nine and 24 genes under adaptative and purifying selection, respectively, were most related to biomineralization in AR and chaperones in SJ. The biomineralization-genes perlucin and gigasin-6 were positively selected exclusively in the site toward the open ocean in AR, with sequence variants leading to pronounced protein structure changes. Despite an intense gene flow among L. flava populations due to its planktonic larva, gene expression patterns within transects may be the result of selective pressures. Our findings represent the first step in understanding how microenvironmental genetic variation is maintained in rocky shore populations and the mechanisms underlying local adaptation in marine species.

Chaotic genetic structure and past demographic expansion of the invasive gastropod Tritia neritea in its native range, the Mediterranean Sea

To better predict population evolution of invasive species in introduced areas it is critical to identify and understand the mechanisms driving genetic diversity and structure in their native range. Here, we combined analyses of the mitochondrial COI gene and 11 microsatellite markers to investigate both past demographic history and contemporaneous genetic structure in the native area of the gastropod Tritia neritea, using Bayesian skyline plots (BSP), multivariate analyses and Bayesian clustering. The BSP framework revealed population expansions, dated after the last glacial maximum. The haplotype network revealed a strong geographic clustering. Multivariate analyses and Bayesian clustering highlighted the strong genetic structure at all scales, between the Black Sea and the Adriatic Sea, but also within basins. Within basins, a random pattern of genetic patchiness was observed, suggesting a superimposition of processes involving natural biological effects (no larval phase and thus limited larval dispersal) and putative anthropogenic transport of specimens. Contrary to the introduced area, no isolation-by-distance patterns were recovered in the Mediterranean or the Black Seas, highlighting different mechanisms at play on both native and introduced areas, triggering unknown consequences for species’ evolutionary trajectories. These results of Tritia neritea populations on its native range highlight a mixture of ancient and recent processes, with the effects of paleoclimates and life history traits likely tangled with the effects of human-mediated dispersal.

Patterns of genetic variation in leading-edge populations of Quercus robur: genetic patchiness due to family clusters

The genetic structure of populations at the edge of species distribution is important for species adaptation to environmental changes. Small populations may experience non-random mating and differentiation due to genetic drift but larger populations, too, may have low effective size, e.g., due to the within-population structure. We studied spatial population structure of pedunculate oak, Quercus robur, at the northern edge of the species’ global distribution, where oak populations are experiencing rapid climatic and anthropogenic changes. Using 12 microsatellite markers, we analyzed genetic differentiation of seven small to medium size populations (census sizes 57–305 reproducing trees) and four populations for within-population genetic structures. Genetic differentiation among seven populations was low (Fst = 0.07). We found a strong spatial genetic structure in each of the four populations. Spatial autocorrelation was significant in all populations and its intensity (Sp) was higher than those reported in more southern oak populations. Significant genetic patchiness was revealed by Bayesian structuring and a high amount of spatially aggregated full and half sibs was detected by sibship reconstruction. Meta-analysis of isoenzyme and SSR data extracted from the (GD)2 database suggested northwards decreasing trend in the expected heterozygosity and an effective number of alleles, thus supporting the central-marginal hypothesis in oak populations. We suggest that the fragmented distribution and location of Finnish pedunculate oak populations at the species’ northern margin facilitate the formation of within-population genetic structures. Information on the existence of spatial genetic structures can help conservation managers to design gene conservation activities and to avoid too strong family structures in the sampling of seeds and cuttings for afforestation and tree improvement purposes.

Investigation of mechanisms underlying chaotic genetic patchiness in the intertidal marbled crab Pachygrapsus marmoratus (Brachyura: Grapsidae) across the Ligurian Sea

BackgroundStudies on marine community dynamics and population structures are limited by the lack of exhaustive knowledge on the larval dispersal component of connectivity. Genetic data represents a powerful tool in understanding such processes in the marine realm. When dealing with dispersion and connectivity in marine ecosystems, many evidences show patterns of genetic structure that cannot be explained by any clear geographic trend and may show temporal instability. This scenario is usually referred to as chaotic genetic patchiness, whose driving mechanisms are recognized to be selection, temporal shifts in local population dynamics, sweepstakes reproductive success and collective dispersal.In this study we focused on the marbled crab Pachygrapsus marmoratus that inhabits the rocky shores of the Mediterranean Sea, Black Sea and East Atlantic Ocean, and disperses through planktonic larvae for about 1 month. P. marmoratus exhibits unexpectedly low connectivity levels at local scale, although well-defined phylogeographic patterns across the species’ distribution range were described. This has been explained as an effect of subtle geographic barriers or due to sweepstake reproductive success. In order to verify a chaotic genetic patchiness scenario, and to explore mechanisms underlying it, we planned our investigation within the Ligurian Sea, an isolated basin of the western Mediterranean Sea, and we genotyped 321 individuals at 11 microsatellite loci.ResultsWe recorded genetic heterogeneity among our Ligurian Sea samples with the occurrence of genetic clusters not matching the original populations and a slight inter-population divergence, with the geographically most distant populations being the genetically most similar ones. Moreover, individuals from each site were assigned to all the genetic clusters. We also recorded evidences of self-recruitment and a higher than expected within-site kinship.ConclusionsOverall, our results suggest that the chaotic genetic patchiness we found in P. marmoratus Ligurian Sea populations is the result of a combination of differences in reproductive success, en masse larval dispersion and local larval retention. This study defines P. marmoratus as an example of marine spawner whose genetic pool is not homogenous at population level, but rather split in a chaotic mosaic of slightly differentiated genetic patches derived from complex and dynamic ecological processes.

Oceanographic features and limited dispersal shape the population genetic structure of the vase sponge Ircinia campana in the Greater Caribbean

Understanding population genetic structure can help us to infer dispersal patterns, predict population resilience and design effective management strategies. For sessile species with limited dispersal, this is especially pertinent because genetic diversity and connectivity are key aspects of their resilience to environmental stressors. Here, we describe the population structure of Ircinia campana, a common Caribbean sponge subject to mass mortalities and disease. Microsatellites were used to genotype 440 individuals from 19 sites throughout the Greater Caribbean. We found strong genetic structure across the region, and significant isolation by distance across the Lesser Antilles, highlighting the influence of limited larval dispersal. We also observed spatial genetic structure patterns congruent with oceanography. This includes evidence of connectivity between sponges in the Florida Keys and the southeast coast of the United States (>700 km away) where the oceanographic environment is dominated by the strong Florida Current. Conversely, the population in southern Belize was strongly differentiated from all other sites, consistent with the presence of dispersal-limiting oceanographic features, including the Gulf of Honduras gyre. At smaller spatial scales (<100 km), sites showed heterogeneous patterns of low-level but significant genetic differentiation (chaotic genetic patchiness), indicative of temporal variability in recruitment or local selective pressures. Genetic diversity was similar across sites, but there was evidence of a genetic bottleneck at one site in Florida where past mass mortalities have occurred. These findings underscore the relationship between regional oceanography and weak larval dispersal in explaining population genetic patterns, and could inform conservation management of the species.

Is post-bleaching recovery of Acropora hyacinthus on Palau via spread of local kin groups?

Palau suffered massive mortality of reef corals during the 1998 mass bleaching, and understanding recovery from that catastrophic loss is critical to management for future impacts. Many reef species have shown significant genetic structure at small scales while apparently absent at large scales, a pattern often referred to as chaotic genetic patchiness. Here we use hierarchical sampling of population structure scored from a panel of microsatellite markers for the coral Acropora hyacinthus across the islands of Yap, Ngulu and Palau to evaluate hypotheses about the mechanisms of previously described chaotic genetic structure. As with previous studies, we find no isolation-by-distance within or between the three islands and high genetic structure between sites separated by as little as ~ 10 km on Palau. Using kinship among individual colonies, however, we find higher mean pairwise relatedness coefficients among individuals within sampling sites. Comparing population structure among hierarchical sampling scales, we show that the pattern of chaotic genetic patchiness reported previously appears to derive from genetic patches of local kin groups at small spatial scales. Genetic distinction of Palau from neighboring islands and high kinship among individuals within these kinship neighborhoods implies that the coral reefs of Palau apparently recovered through a mosaic of rare thermally tolerant colonies that survived the 1998 mass bleaching and are now spreading and recolonizing reefs as local kin groups. This pattern of recovery on Palau gives us a better understanding for effective coral reef conservation strategies in which protecting these rare survivors wherever they occur, rather than specific areas of reef habitat, is critical to increase coral reef resilience.

Chaotic genetic patchiness in the pelagic teleost fish Sardina pilchardus across the Siculo-Tunisian Strait

ABSTRACT This investigation aims at assessing patterns of spatial genetic structure of the teleost fish Sardina pilchardus across the Siculo-Tunisian Strait (a well-known discontinuous biogeographic area) and delineating putative genetic stocks within the species. For this purpose, a total of 180 specimens, collected from 11 locations stretching across the western and eastern Mediterranean coasts of Tunisia, were analysed genetically by means of 18 nuclear allozyme loci. The outcome of this study revealed strong genetic differentiation among populations, with the marked genetic distinctiveness of the central Tunisian population at Mahdia. Despite the delineation of seven well-defined genetic groups, no significant correlation was found between genetic and geographic distances. Besides, the recorded population subdivision did not align with biogeographic boundaries, suggesting the presence of chaotic genetic patchiness. Recent genetic bottlenecks were evidenced in S. pilchardus populations. Patchy migration patterns were recorded among the examined pairs of sardine populations. Among the recorded 16 polymorphic loci, GPI-2 and SOD appeared to be subject to natural selection. Patterns of population genetic differentiation and structuring were not found to be driven by outlier loci that appeared to be under selection. Furthermore, the detected neutral GPI-1 locus was found to be responsible for most of the genetic variation among identified genetic clusters. Hence, natural selection cannot cause the detected genetic heterogeneity among sardine samples. Different explanations to the origin of chaotic genetic patterns, observed within S. pilchardus, were discussed.

Small-scale population genetic structure of the sand bubbler crab Scopimera ryukyuensis in the Ryukyu Islands, Japan.

Generally, the gene flow of marine organisms is well maintained, but some local populations of coastal species are genetically differentiated even on a small scale (genetic patchiness). Small-scale isolation can be crucial for understanding genetic diversity within a species. The present study examined the population genetic structure of the sand bubbler crab Scopimera ryukyuensis, which is endemic to the Ryukyu Islands in the northwestern Pacific. A total of 52 haplotypes of mitochondrial cytochrome c oxidase subunit I were recovered from 197 specimens collected from four islands. The haplotype and nucleotide diversities were relatively high in thecentral Ryukyus (Amami-Oshima and Okinawa Islands) with some exceptions but were low at the southern edge of the geographical distribution of the species, i.e., the southern Ryukyus (Ishigaki and Iriomote Islands). Pairwise FST analysis suggested that the gene flow of S. ryukyuensis was largely restricted. The local populations of the species are differentiated among islands, except for stations on Ishigaki Island and a station on Iriomote Island. Moreover, a clear intra-island population genetic structure was observed within Amami-Oshima and Iriomote Islands, e.g., only 20 km between stations. Small-scale isolation among local populations may be a common tendency for coastal species in the Ryukyu Islands, considering the results of previous studies on corals.

Using genetics to inform restoration and predict resilience in declining populations of a keystone marine sponge

Genetic tools can have a key role in informing conservation management of declining populations. Genetic diversity is an important determinant of population fitness and resilience, and can require careful management to ensure sufficient variation is present. In addition, population genetics data reveal patterns of connectivity and gene flow between locations, enabling mangers to predict recovery and resilience, identify areas of local adaptation, and generate restoration plans. Here, we demonstrate a conservation genetics approach to inform restoration and management of the loggerhead sponge (Spheciospongia vesparium) in the Florida Keys, USA. This species is a dominant, habitat-forming component of marine ecosystems in the Caribbean region, but in Florida has suffered numerous mass mortality events. We developed microsatellite markers and used them to genotype sponges from 14 locations in Florida and a site each in The Bahamas, Belize and Barbuda. We found that genetic diversity levels were similar across all sites, but inbreeding and bottleneck signatures were present in Florida. Populations are highly structured at the regional scale, whilst within Florida connectivity is present in a weak isolation by distance pattern, coupled with chaotic genetic patchiness. Evidence of a weak barrier to gene flow was found in Florida among sites situated on opposite sides of the islands in the Middle Keys. Loggerhead sponge populations in Florida are vulnerable in the face of mass mortalities due to low connectivity with other areas in the region, as well as distance-limited and unpredictable local connectivity patterns. However, our discovery of Florida’s high genetic diversity increases hope for resilience to future perturbations. These results provide valuable insight for sponge restoration practice in Florida.

Demographic, Taxonomic, and Genetic Characterization of the Snook Species Complex (Centropomus spp.) along the Leading Edge of Its Range in the Northwestern Gulf of Mexico

AbstractA recent increase in the abundance of snook species (Centropomus spp.) in Texas has been generally associated with a broad‐scale warming trend of Texas’ inshore waters, closure of the commercial fishery in 1987, and fairly conservative restrictions on recreational catch implemented at the same time. Despite this observed increase in abundance, little is known about the snook species complex in Texas, including uncertainty about recent changes in distribution and abundance, taxonomy, and population structure. Here, abundance and distribution data from a long‐running fishery‐independent (FIN) data set were analyzed in synergy with mitochondrial DNA (mtDNA) and microsatellite genotypes to answer basic questions about the snook species complex in Texas. The main findings from this work are as follows: (1) based on trends observed in FIN data, snook are increasing in abundance and expanding their range northward in Texas; (2) based on mtDNA sequencing, the two most common species of snook in Texas are the Common Snook C. undecimalis and Largescale Fat Snook C. mexicanus; (3) a third species, the Mexican Snook C. poeyi, occurs but only rarely; and (4) patterns from microsatellite genotypes suggest that the two predominant species, Common Snook and Largescale Fat Snook, probably constitute single genetic stocks in Texas, although evidence of chaotic genetic patchiness was also observed. This latter finding might be a general expectation for populations that are on the leading edge of an expanding species range and implies that management measures in Texas should be directed toward conservation of suitable habitat corridors offering environmental and habitat refugia as well as measures (e.g., stock enhancement) that increase the probability of survival of small, localized populations.

A novel integrative approach elucidates fine-scale dispersal patchiness in marine populations

Dispersal is one of the main determining factors of population structure. In the marine habitat, well-connected populations with large numbers of reproducing individuals are common but even so population structure can exist on a small-scale. Variation in dispersal patterns between populations or over time is often associated to geographic distance or changing oceanographic barriers. Consequently, detecting structure and variation in dispersal on a fine-scale within marine populations still remains a challenge. Here we propose and use a novel approach of combining a clustering model, early-life history trait information from fish otoliths, spatial coordinates and genetic markers to detect very fine-scale dispersal patterns. We collected 1573 individuals (946 adults and 627 juveniles) of the black-faced blenny across a small-scale (2 km) coastline as well as at a larger-scale area (<50 kms). A total of 178 single nucleotide polymorphism markers were used to evaluate relatedness patterns within this well-connected population. In our clustering models we categorized SHORT-range dispersers to be potential local recruits based on their high relatedness within and low relatedness towards other spatial clusters. Local retention and/or dispersal of this potential local recruitment varied across the 2 km coastline with higher frequency of SHORT-range dispersers towards the southwest of the area for adults. An inverse pattern was found for juveniles, showing an increase of SHORT-range dispersers towards the northeast. As we rule out selective movement and mortality from one year to the next, this pattern reveals a complex but not full genetic mixing, and variability in coastal circulation is most likely the main driver of this fine-scale chaotic genetic patchiness within this otherwise homogeneous population. When focusing on the patterns within one recruitment season, we found large differences in temperatures (from approx. 17 °C to 25 °C) as well as pelagic larval duration (PLD) for juveniles from the beginning of the season and the end of the season. We were able to detect fine-scale differences in LONG-range juvenile dispersers, representing distant migrants, depending on whether they were born at the beginning of the season with a longer PLD, or at the end of the reproductive season. The ability to detect such fine-scale dispersal patchiness will aid in our understanding of the underlying mechanisms of population structuring and chaotic patchiness in a wide range of species even with high potential dispersal abilities.

Along-shelf connectivity and circumpolar gene flow in Antarctic silverfish (Pleuragramma antarctica)

The Antarctic silverfish (Pleuragramma antarctica) is a critically important forage species with a circumpolar distribution and is unique among other notothenioid species for its wholly pelagic life cycle. Previous studies have provided mixed evidence of population structure over regional and circumpolar scales. The aim of the present study was to test the recent population hypothesis for Antarctic silverfish, which emphasizes the interplay between life history and hydrography in shaping connectivity. A total of 1067 individuals were collected over 25 years from different locations on a circumpolar scale. Samples were genotyped at fifteen microsatellites to assess population differentiation and genetic structuring using clustering methods, F-statistics, and hierarchical analysis of variance. A lack of differentiation was found between locations connected by the Antarctic Slope Front Current (ASF), indicative of high levels of gene flow. However, gene flow was significantly reduced at the South Orkney Islands and the western Antarctic Peninsula where the ASF is absent. This pattern of gene flow emphasized the relevance of large-scale circulation as a mechanism for circumpolar connectivity. Chaotic genetic patchiness characterized population structure over time, with varying patterns of differentiation observed between years, accompanied by heterogeneous standard length distributions. The present study supports a more nuanced version of the genetic panmixia hypothesis that reflects physical-biological interactions over the life history.

Genetic variation in Irish Sea brown crab (Cancer pagurusL.): implications for local and regional management

AbstractUnderstanding demographic processes over multiple spatial scales is vital for the optimization of conservation/management strategies, particularly for commercially harvested taxa such as the brown crab (Cancer pagurusL). Brown crab population genetic structure was investigated at (i) a local scale within the Irish Sea, which included comparisons with the Lundy No Take Zone (NTZ) and (ii) across the NE Atlantic. The results indicate that the brown crab does not exhibit strong spatial structure either within the Irish Sea or at the regional level, suggesting high gene flow within and among the Irish Sea, English Channel and North Sea. Comparisons between the Lundy NTZ and harvested areas revealed similarly high levels of genetic diversity. An intriguing result was that the Lundy NTZ sample exhibited a degree of genetic patchiness (ephemeral geographically unpatterned differentiation) which may indicate elevated recruitment skews within the NTZ. Overall, the results support the view that brown crabs within the sampled area belong to a single genetically panmictic stock and that if breeding stock sizes are maintained genetic drift will not be strong enough to reduce neutral genetic diversity. The highly connected nature of this species requires international cooperation for sustainable management, an important component of which will be the application of more powerful population genomic approaches to assess finer scale aspects of stock structure as well drivers of genetic patchiness reported for the species. This is a timely consideration in light of potential future misalignments between biological and geopolitical stock boundaries in the Irish Sea following Brexit.

Complex genetic structure revealed in the circum-Antarctic broadcast spawning sea urchin Sterechinus neumayeri

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 601:153-166 (2018) - DOI: https://doi.org/10.3354/meps12648 Complex genetic structure revealed in the circum-Antarctic broadcast spawning sea urchin Sterechinus neumayeri Karen J. Miller1,*, Helena P. Baird2, Jake van Oosterom3, Julie Mondon3, Catherine K. King2 1Australian Institute of Marine Science, UWA Oceans Institute, 35 Stirling Highway, Crawley, WA 6009, Australia 2Australian Antarctic Division, 203 Channel Highway, Kingston, TAS 7050, Australia 3Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Geelong, VIC 3216, Australia *Corresponding author: k.miller@aims.gov.au ABSTRACT: Patterns and mechanisms of gene flow and larval dispersal in the Antarctic marine environment are still poorly understood, despite the current threat of rapid climate change and the need for such information to inform conservation and management efforts. Studies on Antarctic brooding marine invertebrates have demonstrated limited connectivity, concurrent with life history expectations; however, no equivalent data are available for broadcast spawning species for which we might expect a higher capacity for larval dispersal. Here, we have used microsatellite DNA markers and mitochondrial DNA sequence data to explore patterns of genetic structure and infer larval dispersal patterns across spatial scales of <500 m to 1400 km in the broadcast spawning sea urchin Sterechinus neumayeri. We show genetic differentiation at small spatial scales (<1 km), but genetic homogeneity over moderate (1-25 km) and large spatial scales (1000 km), consistent with patterns described as chaotic genetic patchiness. Self-recruitment appears common in S. neumayeri, and genotypes of larvae collected from the water column provide preliminary evidence that the adult population structure is maintained through variability among larval cohorts. Genetic similarity at large spatial scales may represent evolutionary connectivity on a circum-Antarctic scale, and likely also reflects a history of shelf recolonisation after isolation in glacial refugia. KEY WORDS: Gene flow · Larval dispersal · Migration · Chaotic genetic patchiness · Microsatellites · Echinoid Full text in pdf format Supplementary material PreviousNextCite this article as: Miller KJ, Baird HP, van Oosterom J, Mondon J, King CK (2018) Complex genetic structure revealed in the circum-Antarctic broadcast spawning sea urchin Sterechinus neumayeri. Mar Ecol Prog Ser 601:153-166. https://doi.org/10.3354/meps12648 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 601. Online publication date: August 09, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.