High Levels Of Self-recruitment Research Articles

Regional-scale genetic differentiation of the stony coral Desmophyllum dianthus in the southwest Pacific Ocean is consistent with regional-scale physico-chemical oceanography

Deep-sea corals are diverse and abundant in New Zealand’s EEZ and the southwest Pacific Ocean. We assessed genetic diversity and gene flow of the deep-sea scleractinian (stony cup coral) Desmophyllum dianthus in five areas (Kermadec Ridge, Louisville Seamount Chain, Chatham Rise, Campbell Plateau, Macquarie Ridge), and applied dispersal kernels estimated from drifters observations and seascape genetics to compare with observed connectivity patterns and regional physico-chemical data. We observed pronounced between-region genetic differentiation, high levels of self-recruitment, but also high connectivity between distant sites (e.g., at the Kermadec Ridge inside the New Zealand EEZ, and the Louisville Seamount Chain outside the New Zealand EEZ). Genetic diversity was marginally highest at the Kermadec Ridge, whilst populations on the Chatham Rise showed evidence of unique genetic diversity that may be driven by converging ocean currents. Overall, patterns of genetic connectivity were consistent with oceanographic predictions of dispersal routes. Seascape genetic analyses indicated that environmental variables most often related to physical seafloor habitat characteristics were important predictors of regional-scale genetic differentiation of D. dianthus. Our research shows that current spatial closures within the New Zealand EEZ and surrounding high seas areas do not encompass the extent of genetic diversity and connectivity for D. dianthus, which parallels research for other deep-sea taxa in the region. Future measures implemented to protect deep-sea coral biodiversity require consideration of complex connectivity patterns and migration routes amongst taxa, at various spatial scales. This study demonstrates that a combined gene flow, seascape genetics and dispersal kernel modelling approach can provide a robust evaluation of connectivity in deep-sea environments to inform management decision making at the scale of the southwest Pacific Ocean.

Fine‐scale population structure of Collichtys lucidus populations inferred from microsatellite markers

The spinyhead croaker Collichthys lucidus (Richardson) is a small sciaenid species distributed along the inshore waters of northwestern Pacific Ocean, and now has been listed as Key Protected Commercial Sources of Aquatic Animals and Plants in China. To delineate stock boundaries and inform conservation policy for its management, samples were collected from eight locations across the Chinese coastal waters and analyzed at nine microsatellite loci. C. lucidus populations showed low genetic diversity (expected heterozygosity = 0.445–0.542; observed heterozygosity = 0.392–0.539; Polymorphism Information Content = 0.268–0.684). Strong genetic fdifferentiation (Fst = 0.065–0.510, all significant after Bonferroni correction) among all populations and high levels of self-recruitment (89.2%–91.5%) were observed, which suggested limited genetic exchange for this species. Clustering results of discriminant analysis of principal components and STRUCTURE found strong support for obvious genetic clusters (populations FZ, XM and SZ vs. populations SH, YRE, ZS, WZ and ND). The results of the present study not only supported the phylogeographic pattern of north-south differentiation, but also suggested that C. lucidus populations may be predominantly sustained by self-replenishment rather than by recruitment from distant populations.

Connectivity Among Populations of the Top Shell Gibbula divaricata in the Adriatic Sea.

Genetic connectivity studies are essential to understand species diversity and genetic structure and to assess the role of potential factors affecting connectivity, thus enabling sound management and conservation strategies. Here, we analyzed the patterns of genetic variability in the marine snail Gibbula divaricata from five coastal locations in the central-south Adriatic Sea (central Mediterranean) and one in the adjacent northern Ionian Sea, using 21 described polymorphic microsatellite loci. Observed and expected heterozygosity varied from 0.582 to 0.635 and 0.684 to 0.780, respectively. AMOVA analyses showed that 97% of genetic variation was observed within populations. Nevertheless, significant, although small, genetic differentiation was found among nearly all of the pairwise FST comparisons. Over a general pattern of panmixia, three groups of populations were identified: eastern Adriatic populations, western Adriatic populations, and a third group represented by the single northern Ionian Sea population. Nonetheless, migration and gene flow were significant between these groups. Gibbula divaricata is thought to have a limited dispersal capacity related to its lecithotrophic trochophore larval stage. Our results indicated high levels of self-recruitment and gene flow that is mainly driven through coastline dispersion, with populations separated by the lack of suitable habitats or deep waters. This stepping-stone mode of dispersion together with the high levels of self-recruitment could lead to higher levels of population structuring and differentiation along the Adriatic Sea. Large effective population sizes and episodic events of long-distance dispersal might be responsible for the weak differentiation observed in the analyzed populations. In summary, the circulation system operating in this region creates natural barriers for dispersion that, together with life-history traits and habitat requirements, certainly affect connectivity in G. divaricata. However, this scenario of potential differentiation seems to be overridden by sporadic events of long-distance dispersal across barriers and large effective population sizes.

Regional genetic structure of sandfish Holothuria (Metriatyla) scabra populations across the Philippine archipelago

The sandfish, Holothuria (Metriatyla) scabra Jaeger, 1833 is a commercially-valuable tropical sea cucumber species which is overexploited throughout much of its distributional range, the Philippine archipelago included. The need for management interventions to sustain the fishery is recognized. However, the lack of knowledge on the genetic structure of natural populations needs to be addressed to guide management initiatives. The present study examined genetic diversity and spatial patterns of genetic structure of sandfish populations across the Philippine archipelago. Population genetic analysis using 11 microsatellite markers revealed weak yet significant regional genetic structure among 15 H. scabra populations across the Philippine archipelago (FST = 0.016; P < 0.0001). Six genetic groups broadly concordant with marine biogeographic regions were identified. Genetic connectivity was strongest among populations situated in the center of the archipelago (internal seas; FST = 0.002, P > 0.05). Peripheral locations exhibited limited gene flow (Philippine Sea, South China Sea, Sulu Sea and Celebes Sea; mean FST = 0.023, P < 0.0001), with significant genetic relatedness further suggesting relative isolation or high levels of self-recruitment. Excluding the two most divergent Sulu Sea populations, there was a significant signal of isolation-by-distance for the rest of the Philippine populations, suggesting that geographic distance between coastal habitats coupled with oceanographic circulation largely influence genetic structure. There was no signature of genetic bottlenecks for any population, although effective population sizes (Ne) were larger for central populations compared to peripheral populations. This study provides information on genetic stocks which has important implications to genetic resource management of Philippine sandfish populations to support sustainability of the fishery.

Population genetic signatures of a climate change driven marine range extension

Shifts in species distribution, or ‘range shifts’, are one of the most commonly documented responses to ocean warming, with important consequences for the function and structure of ecosystems, and for socio-economic activities. Understanding the genetic signatures of range shifts can help build our knowledge of the capacity of species to establish and persist in colonised areas. Here, seven microsatellite loci were used to examine the population connectivity, genetic structure and diversity of Octopus tetricus, which has extended its distribution several hundred kilometres polewards associated with the southwards extension of the warm East Australian Current along south-eastern Australia. The historical distribution and the range extension zones had significant genetic differences but levels of genetic diversity were comparable. The population in the range extension zone was sub-structured, contained relatively high levels of self-recruitment and was sourced by migrants from along the entire geographic distribution. Genetic bottlenecks and changes in population size were detected throughout the range extension axis. Persistent gene flow from throughout the historical zone and moderate genetic diversity may buffer the genetic bottlenecks and favour the range extension of O. tetricus. These characteristics may aid adaptation, establishment, and long-term persistence of the population in the range extension zone.

Regional genetic differentiation among populations of Cladocora caespitosa in the Western Mediterranean

Cladocora caespitosa is the only reef-forming zooxanthellate scleractinian in the Mediterranean Sea. This endemic coral has suffered severe mortality events at different Mediterranean sites owing to anomalous summer heat waves related to global climate change. In this study, we assessed genetic structure and gene flow among four populations of this species in the Western Mediterranean Sea: Cape Palos (SE Spain), Cala Galdana (Balearic Islands), Columbretes Islands, and L’Ametlla (NE Spain). The results obtained from Bayesian approaches, F ST statistics, and Bayesian analysis of migration rates suggest certain levels of genetic differentiation driven by high levels of self-recruitment, a fact that is supported by egg-retention mechanisms. Conversely, genetic connectivity among distant populations, even if generally low, seems to be related to sporadic dispersal events through regional surface currents linked to the spawning period that occurs at the end of summer-beginning of autumn. These features, together with a certain isolation of the Columbretes Islands, could explain the regional genetic differentiation found among populations. These results help to better understand population structure and connectivity of the species and will serve as an approach for further studies on different aspects of the biology and ecology of C. caespitosa.

Limited transport and recolonization potential in shallow tidal estuaries

Evidence of limited larval exchange and high levels of self‐recruitment in marine populations continues to accumulate, implying that marine systems are not as open as we once believed. In estuaries, some organisms with long larval periods, such as crab and bivalve species, are capable of long‐distance transport, while others, including many polychaete and gastropod species with crawling or brooded larvae, lack long‐distance larval dispersal mechanisms and may disperse as juveniles and adults. To predict transport rates and colonization potentials of macrofaunal life stages transported in the water column, we use a combined hydrodynamic and particle tracking model. We vary particle release location to investigate how different habitats (i.e., main channel, lower sandflat, high sandflat, tidal creek) will contribute to the supply of colonists in different parts of the estuary. Most particles traveled short distances and settled within their release habitat. Slightly negatively buoyant particles (corresponding to small larvae) traveled much farther than more negatively buoyant particles (corresponding to larger, heavier larvae and juveniles). Particles released from high intertidal locations had lower rates of transport and transfer among habitats compared to lower intertidal sites. Other influences on organism transport include timing of release (with respect to tide), release location within the water column, tidal range, and magnitude of freshwater flood events. In general, estuarine communities dominated by organisms with limited dispersal periods are likely to be recruitment limited and limited in their ability to reach mature community states when subject to increasing frequencies or spatial extent of disturbance.