Occurrence of the parasite genus Hematodinium (Alveolata: Syndinea) in the water column

Crustaceans worldwide are infected with alveolate parasites of the genus Hematodinium, causing substantial losses to langoustine and crab fisheries. The distinct seasonality in Hematodinium occurrence in their decapod hosts, as well as unsuccessful attempts at transmission, suggest the existence of life stages outside their benthic crustacean hosts. We used a nested polymerase chain reaction method to detect Hematodinium rDNA in the environment and in potential alternative hosts. Environmental samples from the Clyde Sea, Scotland, were screened during the April release of dinospores and during June and August, when infection prevalence is rare in benthic crustaceans. Hematodinium rDNA was amplified in 15% (14/94) of isolated langoustine larvae, and in 12% (13/111) of crab larvae. In addition, Hematodinium rDNA was present in mixed plankton samples devoid of decapod larvae, but including the 2 μm-10 mm fraction of particulate organic matter in the water column, containing phytoplankton and other zooplankton. These results indicate that Hematodinium occurs in the water column and is harboured by planktonic organisms, including larval stages of the crustacean hosts, when infections are at their lowest in adult hosts.     

Semilunar postlarval settlement periodicity ensuing from semilunar larval release cycle in the Nihonotrypaea harmandi (Crustacea,Decapoda, Axiidea,Callianassidae) population on an intertidal sandflat in an open marine coastal embayment

Many decapod crustaceans in marine intertidal habitats release larvae toward coastal oceans, from which postlarvae (decapodids: settling-stage larvae) return home. Decapodid settlement processes are poorly understood. Previous studies showed that in Kyushu, Japan, the callianassid shrimp population on an intertidal sandflat of an open bay joining the coastal ocean near a large estuary released eight batches of larvae basically in a semilunar cycle from June through October and that decapodids performed diel vertical migration, occurring in the water column nocturnally. We conducted (a) frequent sampling for population density and size-composition on the sandflat through one reproductive season, (b) planktonic and benthic sampling for decapodids around the bay mouth, and (c) current meter deployment at three points across the bay mouth for tidal harmonic analysis. On the sandflat, six batches of newly-settled decapodids (settlers) occurred in a semilunar periodicity until October, with peaks occurring 0–3 days before syzygy dates except for the first one. For larval Batches 1–4, buoyancy-driven shoreward subsurface currents during July to mid-October would transport some pre-decapodid-stage larvae (zoeae) toward the bay. The absence of expected settler Batches 7–8 would be due to the converse subsurface currents caused by water-column mixing and seasonal winds after mid-October, carrying zoeae offshore. Once in the bay, phasing of night and nighttime-averaged shoreward tidal current explained the settlement pattern for Batches 1–4. For Batches 5–6 occurring in mid-September to mid-October, water currents generated by seasonal wind and tidal forcings may have caused peak settlement after the time expected from tidally-driven decapodid transport.     

Flux of decapod larvae and juveniles at a station in the lower Canal de Mira (Ria de Aveiro,Portugal) during one lunar month

Summary

Emigration and immigration of decapod larvae from estuaries depend on timing of larvae occurrence in the water column relative to the tidal, tidal amplitude and day cycles. The phase relation of these natural cycles varies with tidal regime and geographically, resulting in different time-patterns of hatching of first stage larvae and of presence of late stage larvae in the water column. Vertical migration behaviour according to phase of tide also controls transport inside estuaries. These mechanisms were investigated in a field study conducted on the northwest coast of Portugal where neap ebb tides occur during the night around the quarters of the moon. Flux of decapod larvae through one sampling station was measured during one lunar month at the Canal de Mira (Ria de Aveiro) in the spring of 1990. The sampling programme was comprised of a set of 25-h fixed station studies, separated by 25-h intervals during which no sampling took place. Plankton samples were collected with a pump every hour at three depths. Current velocity and direction at the standard depths, as well as height of the water column, were also measured every hour. Hourly instantaneous flux of larvae through a 1-m-wide vertical section of the Canal de Mira was calculated for the most abundant forms. A total number of 13 combinations of species and larval stages were analyzed, belonging to the families Atelecyclidae, Pirimelidae, Portunidae, Pilumnidae, Grapsidae, Palaemonidae, Crangonidae and Thalassinidae. Patterns of net larval flux along the lunar month could be grouped into three types. Type 1 includes first zoeas that were consistently exported to the sea. Type 2 comprises late zoeas, megalops and juveniles that were consistently imported into the estuary. First zoeas that were imported during some of the 25-h studies but were exported during the others were included in Type 3; in species of this type import periods appeared to alternate with export periods according to lunar phase. Flux of Type 1 larvae followed a semi-lunar pattern. Release activity of Type 1 zoeas took place during the night and started during neap tides around the quarters of the moon, but maximum releases occurred 3–4 h after high tide of average amplitude tides, 3–4 days after the quadratures. These observations agree with the hypothesis that hatching is timed to occur on ebb tides of the largest possible amplitude so that larvae are easily dispersed from areas with a high density of predator fishes. However, based on other observations on the Portuguese coast, it cannot be ruled out that hatching might depend on a minimum number of hours of darkness experienced by the females. Larvae included in Type 2 comprise forms that may have been retained inside the estuary for the entire larval phase, as well as one form that was imported from shelf waters. No semi-lunar pattern of import was detected in this last form. Fluctuations of net flux observed in Type 3 larvae, as well in other forms that were not included in any of the types, were more difficult to explain. These larvae were first zoeas of species belonging to different taxonomic, morphological and ecological groups and may show a diversity of adaptations to the way of life of the adults. Imports and exports of larvae depended not only on time-patterns of abundance, but also on time-patterns of larval vertical distribution. As a general rule, larval stages showed patterns of depth distribution that were consistent with vertical migration rhythmic behaviours synchronized with the tidal cycle. Though the effect was not always statistically significant, first-stage larvae were closer to the surface during ebb, especially during the night, enhancing seaward transport. On the contrary, later zoeal stages, megalops and juveniles were usually closer to the surface during flood, suggesting migration to the water column during this phase of the tide and landward transport.     

Diversity,biomass and production of decapod crustacean larvae in a changing environment

Summary

There is a latitudinal gradient in the species richness of Decapoda with pelagic larvae. For example, only two species of Brachyura are found around Svalbard, 54 species are known from the English Channel and ~100 from the Atlantic coast of the Iberian peninsula. The distributions of many species are limited by effects of temperature. Intermoult times of larvae are inversely related to temperature. In the field the size of larvae is inversely related to temperature, the relationship tending to increase in significance in successive larval stages. The timing of the seasonal occurrence of larvae of decapod species in the plankton is also related to temperature, to a greater extent than are seasonal cycles of the holoplankton. These effects of temperature on larval development influence the biomass and production of the larvae in the plankton. Some potential effects of climate change on the distributions and dynamics of planktonic larvae of decapods and consequent changes in their diversity, biomass and production can be predicted insofar as temperature is a limiting factor.     

Polymorphism in developmental mode and its effect on population genetic structure of a spionid polychaete, Pygospio elegans

Population genetic structure of sedentary marine species is expected to be shaped mainly by the dispersal ability of their larvae. Long-lived planktonic larvae can connect populations through migration and gene flow, whereas species with nondispersive benthic or direct-developing larvae are expected to have genetically differentiated populations. Poecilogonous species producing different larval types are ideal when studying the effect of developmental mode on population genetic structure and connectivity. In the spionid polychaete Pygospio elegans, different larval types have been observed between, and sometimes also within, populations. We used microsatellite markers to study population structure of European P. elegans from the Baltic Sea (BS) and North Sea (NS). We found that populations with planktonic larvae had higher genetic diversity than did populations with benthic larvae. However, this pattern may not be related to developmental mode, since in P. elegans, developmental mode may be associated with geography. Benthic larvae were more commonly seen in the brackish BS and planktonic larvae were predominant in the NS, although both larval types also are found from both areas. Significant isolation-by-distance (IBD) was found overall and within regions. Most of the pair-wise F(ST) comparisons among populations were significant, although some geographically close populations with planktonic larvae were found to be genetically similar. However, these results, together with the pattern of IBD, autocorrelation within populations, as well as high estimated local recruitment, suggest that dispersal is limited in populations with planktonic larvae as well as in those with benthic larvae. The decrease in salinity between the NS and BS causes a barrier to gene flow in many marine species. In P. elegans, low, but significant, differentiation was detected between the NS and BS (3.34% in AMOVA), but no clear transition zone was observed, indicating that larvae are not hampered by the change in salinity.     

Closing the larval loop: linking larval ecology to the population dynamics of marine benthic invertebrates

The majority of marine benthic invertebrates exhibit a complex life cycle that includes separate planktonic larval, and bottom-dwelling juvenile and adult phases. To understand and predict changes in the spatial and temporal distributions, abundances, population growth rate, and population structure of a species with such a complex life cycle, it is necessary to understand the relative importance of the physical, chemical and biological properties and processes that affect individuals within both the planktonic and benthic phases. To accomplish this goal, it is necessary to study both phases within a common, quantitative framework defined in terms of some common currency. This can be done efficiently through construction and evaluation of a population dynamics model that describes the complete life cycle.

Two forms that such a model might assume are reviewed: a stage-based, population matrix model, and a model that specifies discrete stages of the population, on the bottom and in the water column, in terms of simultaneous differential equations that may be solved in both space and time. Terms to be incorporated in each type of model can be formulated to describe the critical properties and processes that can affect populations within each stage of the life cycle. For both types of model it is shown how this might be accomplished using an idealized balanomorph barnacle as an example species. The critical properties and processes that affect the planktonic and benthic phases are reviewed. For larvae, these include benthic adult fecundity and fertilization success, growth and larval stage duration, mortality, larval behavior, dispersal by currents and turbulence, and larval settlement. It is possible to predict or estimate empirically all of the key terms that should be built into the larval and benthic components of the model. Thus, the challenge of formulating and evaluating a full life cycle model is achievable. Development and evaluation of such a model will be challenging because of the diverse processes which must be considered, and because of the disparities in the spatial and temporal scales appropriate to the benthic and planktonic larval phases. In evaluating model predictions it is critical that sampling schemes be matched to the spatial and temporal scales of model resolution.     

Marine bivalves: Distribution of mero-planktonic shell-bearing larvae in eastern north Atlantic surface waters

Larval shells of benthic marine bivalves occur frequently in plankton samples from temperate to tropical eastern North Atlantic waters. At many sites their abundance is higher than fifty specimens per cubic meter of surface water, thus outnumbering the other planktonic components with calcareous shells. Generally they are more frequent in nearshore water masses than far from land, but it could be shown that not only faunas on continental shelves, but also on oceanic inlands and on submarine elevations, produce larvae, which can be found far out in the ocean.Although it cannot be excluded that long-transported bivalve larvae have also been found in these samples, two arguments seem to assure that the bulk of these shells has been produced in the neighbouring shallow-water areas: decreasing abundance as well as increasing size of shells with increasing distance from the shallow-water area (this applies both to island and continental shelves).The bulk of bivalve shells is concentrated in surface waters. However, shells have also been found with decreasing abundance in water depths down to 600 m. The size distribution in the water column is qualitatively similar for water masses close to the coast and far from land; large shells occur in the upper 50 m, but average diameter decreases below this depth. However, far from land in water depths of 500–600 m they can reach sizes up to about 0.5 mm in diameter (according to one specimen). Generally, shell sizes are larger in corresponding water depth levels far from than in those close to land.The occurrence of larval shells of bivalves throughout the eastern North Atlantic also has wide paleogeographic implications. Since no specific determinations of these bivalves have been tried, it is unknown in which water depths their parental generations occur. However, it can be assumed that eastern North Atlantic island shelves and peaks of submarine guyots and other subsurface elevations which reach to within a few hundred. meters of the surface, can be populated by faunas from eastern Atlantic continental margins being transported by off-shore currents far into the ocean. Since the islands and presumably guyots, etc. as well, produce pelagic larval assemblages from their own benthic molluscan faunas, it can easily be assumed that larval shells can be transported across the ocean by surface and subsurface currents.     

Ecology of larval herring in relation to the oceanography of the Gulf of Maine

The dynamics of larval herring in the north-eastern Gulf ofMaine are reviewed with reference to the important physicaland biological oceanographic processes of the region. Particularattention is given to the apparently conflicting hypothesesof larval drift from the tidally well-mixed spawning areas tonursery areas, and larval retention in spawning areas for aperiod of several months. Both processes have been reportedfor the eastern Maine-Grand Manan spawning area of the Gulfof Maine, but the relative importance of each to larval survivalthrough the winter and recruitment to the juvenile stage isnot clear. Both transport and retention are interpreted in lightof oceanographic processes that might impart variability, especiallybetween years, in the proportion of larvae transported awayversus that retained. Results of recent survey cruises in theGulf of Maine show both hypotheses to have merit. It is suggestedthat (i) interannual differences in slope water intrusions intothe Gulf of Maine as they affect the residual circulation, (ii)the lunar periodicity in the intensity of tidal mixing in relationto hatching times, and (iii) the potential for variable spawninglocations relative to the tidal fronts, may affect the distributionsof herring larvae immediately after hatching in the fall, andmay control the proportion of larvae that are advected awaywith the residual currents versus that retained in the vicinityof spawning. It is also suggested that those processes thataffect larval distributions and survival in the fall are importantin determining the overwintering distributions of larvae inthe Gulf of Maine, where the subtle influences of variable foodregimes and water temperatures could potentially exact largeinterannual differences in winter survival and recruitment tothe juvenile stage.     

Swimming Speed of Larval Snail Does Not Correlate with Size and Ciliary Beat Frequency

Many marine invertebrates have planktonic larvae with cilia used for both propulsion and capturing of food particles. Hence, changes in ciliary activity have implications for larval nutrition and ability to navigate the water column, which in turn affect survival and dispersal. Using high-speed high-resolution microvideography, we examined the relationship between swimming speed, velar arrangements, and ciliary beat frequency of freely swimming veliger larvae of the gastropod Crepidula fornicata over the course of larval development. Average swimming speed was greatest 6 days post hatching, suggesting a reduction in swimming speed towards settlement. At a given age, veliger larvae have highly variable speeds (0.8–4 body lengths s⁻¹) that are independent of shell size. Contrary to the hypothesis that an increase in ciliary beat frequency increases work done, and therefore speed, there was no significant correlation between swimming speed and ciliary beat frequency. Instead, there are significant correlations between swimming speed and visible area of the velar lobe, and distance between centroids of velum and larval shell. These observations suggest an alternative hypothesis that, instead of modifying ciliary beat frequency, larval C. fornicata modify swimming through adjustment of velum extension or orientation. The ability to adjust velum position could influence particle capture efficiency and fluid disturbance and help promote survival in the plankton.     

Seasonal distribution and duration of the planktonic stage of Dover sole, Solea solea, larvae in the Bay of Biscay: an hypothesis

The possibility of deriving a prediction about the effect of seasonal variations in the duration of the planktonic larval phase on the dispersal of larval Dover sole was investigated. During six cruises, from February to May 1992, the distribution of sole larvae was studied along a 100-km transect, from the offshore spawning grounds to the coastal nurseries of the Bay of Biscay (France). Samples ( n = 189) were collected with a suprabenthic sampler, and vertical profiles of water temperature and salinity were recorded simultaneously. Counts of otolith increments of larval stage 4b (onset of metamorphosis) were used to estimate the duration of the planktonic life. Duration of the larval phase decreases by about 15 days (37%) with water temperature increase (between 8° in February and 11.2° C in May). Sole larvae occur from the coastal area to 100 km offshore. Within the same cruise, no difference in the duration of the planktonic life was observed between the larvae caught in the onshore and the offshore area. In spite of seasonal differences in abundance, the extent and the shape of the larval distributions during the period of study suggest that the seasonal variations in the duration of the planktonic life did not affect the larval distribution.     

Larval settlement of the nemertean egg predator Carcinonemertes errans on the Dungeness crab,Metacarcinus magister

Due to their habitat specificity, marine parasites present excellent systems for studying the processes and patterns of larval settlement. Settlement of Carcinonermertes errans, an egg predator of the Dungeness crab, is described here for the first time. Upon contact with a host individual, competent larvae of C. errans settled on the crab's exoskeleton and migrated under the abdominal flap within 24 h. When removed from the host, recently settled worms retained their larval characteristics. After 48 h on the host, however, metamorphosis proceeded and larvae became juvenile worms. Additional field studies showed that competent larvae were present in the waters of the Coos Bay Estuary during the months of August through early November, could infect crab hosts directly from the water column, and exhibited density‐dependent gregarious settlement.     

Dispersal of Deep-Sea Larvae from the Intra-American Seas: Simulations of Trajectories using Ocean Models

Using data on ocean circulation with a Lagrangian larval transport model, we modeled the potential dispersal distances for seven species of bathyal invertebrates whose durations of larval life have been estimated from laboratory rearing, MOCNESS plankton sampling, spawning times, and recruitment. Species associated with methane seeps in the Gulf of Mexico and/or Barbados included the bivalve "Bathymodiolus" childressi, the gastropod Bathynerita naticoidea, the siboglinid polychaete tube worm Lamellibrachia luymesi, and the asteroid Sclerasterias tanneri. Non-seep species included the echinoids Cidaris blakei and Stylocidaris lineata from sedimented slopes in the Bahamas and the wood-dwelling sipunculan Phascolosoma turnerae, found in Barbados, the Bahamas, and the Gulf of Mexico. Durations of the planktonic larval stages ranged from 3 weeks in lecithotrophic tubeworms to more than 2 years in planktotrophic starfish. Planktotrophic sipunculan larvae from the northern Gulf of Mexico were capable of reaching the mid-Atlantic off Newfoundland, a distance of more than 3000?km, during a 7- to 14-month drifting period, but the proportion retained in the Gulf of Mexico varied significantly among years. Larvae drifting in the upper water column often had longer median dispersal distances than larvae drifting for the same amount of time below the permanent thermocline, although the shapes of the distance-frequency curves varied with depth only in the species with the longest larval trajectories. Even species drifting for >2 years did not cross the ocean in the North Atlantic Drift.     

Synchronous spawning in a recently established population of the zebra mussel,Dreissena polymorpha,in western Lake Erie,USA

Seasonal patterns of reproduction in a newly established population of Dreissena polymorpha are described for a site in the western basin of Lake Erie. Reproduction was monitored by histological examination of gonads, analysis of shell length-dry weight relationships, and following abundance of planktonic and settling larvae. Patterns of planktonic larval abundance and settling showed a distinct bimodal pattern in July and August, but conflicted with histological and length-dry weight data that showed spawning was a brief, highly synchronous event occurring in late August. Differences between histological data and abundance of larvae in the plankton can be explained as resulting from drift of larvae from disjunct populations of D. polymorpha which spawned earlier, into the study area. Veliger larvae were present in the plankton at low densities throughout the warm months before and after periods of peak abundances. The presence of these larvae can be explained by a combination of asynchronous spawning among local populations and postponed settlement by planktonic larvae.     

The spatial patchiness of Pacific herring larvae

Synopsis The spatial patchiness at age was measured for Pacific herring,Clupea harengus pallasi, larvae of a small coastal inlet. Lloyd's index of patchiness decreased from 3.8 at hatching to a minimum of 1.5 at 25–30 d and then increased to 2.5 at 50 d. This two-cycle pattern resembles that measured by others for the larvae of other species of schooling pelagic fishes. It differs by being several times lower in magnitude. This is attributed to two factors: (1) a rapid reduction in patchiness from a relatively high level in the demersal egg interval to a lower level in the planktonic larval interval as larvae are released into the water column over a period of 2–4 days, and (2) foraging by larval herring for prey that are larger, more dilute, and less patchy than the prey of other, smaller pelagic fish larvae.     

The peril of the plankton

The pelagic environment is characterized by unevenly distributed resources and risks. Such unpredictability presents adaptive challenges to diverse planktonic organisms including the larvae of benthic marine invertebrates. Estimates of mortality during planktonic development are highly variable, ranging from 0% to 100% per day. Predation is considered a significant source of this mortality, but what explains the variability in estimates of the mortality of marine invertebrate larvae? While differential exposure of larval prey to predators may explain these widely variable estimates, adaptations that reduce vulnerability of marine larvae to predators may also be important. Although there are excellent reviews of predation upon larvae and of larval mortality and defenses, nearly 15 years have elapsed since these topics were formally reviewed. Here, we highlight recent advances in understanding the behavioral, chemical, and morphological defenses that larvae possess and assess their effectiveness in reducing the risk of predation. While recent work confirms that larval mortality is generally high, it also demonstrates that larvae can reduce their risk of predation in several ways, including: (1) temporarily escaping the benthos during vulnerable early stages, (2) producing chemical compounds that reduce palatability, (3) possessing morphological defenses such as spines and shells, and (4) exhibiting induced defensive responses whereby larvae can alter their behavior, morphology, and life histories in the presence of predators. Taken together, these studies indicate that marine invertebrate larvae possess a sophisticated suite of defensive phenotypes that have allowed them to persist in the life cycle of benthic invertebrates for eons.     

Transport of molluscan larvae through a shallow estuary

Dispersal of invertebrate larvae is determined by larval swimmingbehavior, the length of planktonic development and the hydrodynamicregime. Larvae of estuarine invertebrates must refrain fromexport or invade an estuary after development in the ocean.This study investigates retention patterns of estuarine molluscsby measuring time series of larval abundance in relation tohydrodynamic processes. Previous investigations of larval dynamicshave generally focused on larger estuarine systems that areoften stratified and have relatively long hydraulic residencetimes. The estuary studied in this investigation supports densepopulations of infaunal clams yet has a water depth to tidalamplitude ratio near unity. To access processes affecting larvalretention, the circulation patterns of the estuary were measuredwith time series of salinity, temperature, pressure and horizontalvelocity. Transport rates of larvae between ocean and estuary,and within the estuary proper, were calculated from velocityand larval concentration time series. The daily residence timeof the estuary was determined for the summer spawning period.The results demonstrate that molluscan larvae were routinelytransported between the estuary and nearshore zone in tidalflows. Based on the magnitude of the horizontal current velocities,passive transport of larvae predominates during most of thetidal cycle in the estuary. Residence time calculations suggestthat the ability of larvae to remain in the estuary throughlarval development is unlikely, and there was no evidence ofselective retention of mature bivalve larvae in the estuary.Rather, larvae are exported rapidly from the estuary and undergodevelopment in the coastal ocean. Mesoscale physical processesin the coastal ocean probably control variation in the deliveryof larvae back to estuarine systems. Recruitment to this andsimilar estuaries must therefore be dependent on invasion.     

Ultrastructural evidence for nutritional exchange between brooding unionid mussels and their glochidia larvae

Abstract. The life history of unionid bivalve molluscs includes retention of developing embryos within the gills of parental mussels. This brooding behavior may facilitate nutrient transfer to the glochidia larvae, i.e., matrotrophy. To address this possibility, morphological relationships between brood chambers and developing larvae of Pyganodon cataracta and Utterbackia imbecillis were examined with TEM, and larval shells were observed with SEM, for features that could be associated with the uptake of dissolved materials. Early in brooding, glochidia are enclosed in a vitelline membrane that physically contacts numerous cilia and microvilli of the epithelial cells lining the brood chamber (marsupium). The vitelline membrane subsequently disappears. Lamellar tissues of parental mussels initially have large deposits of glycogen that diminish during the course of brooding. Septa separating brood chambers from adjacent secondary water tubes have numerous mitochondria and microvilli, suggesting the potential for active transport of materials into or out of the marsupia. Since punctae (pores) in the larval shells become filled with an organic matrix early in brooding, they are unlikely to be involved in nutrient exchange. Ultrastructure of the brood chamber and physical contact between the parental mussel and larvae are consistent with a nutritive role for retention of glochidia in the marsupia.     

Loss of larval parasitism in parasitengonine mites

Larval Parasitengona are typically parasites, yet at least 29 species of water mites and one species of Trombidiidae forgo larval feeding and any association with a host. Species with non-feeding larvae are isolated cases within species groups or genera where the remaining species have parasitic larvae. Species without larval parasitism occur in at least 14 genera, eight families and four superfamilies of water mites; the loss of larval parasitism is presumably polyphyletic, having occurred at least 21 times. Lineages of water mites with non-feeding larvae frequently exist in parallel with almost identical populations or species that have parasitic larvae. Thus, there is tremendous potential for studies comparing the relative merits of the two life history strategies. Comparisons indicate that adults from lineages with non-parasitic larvae produce smaller numbers of larger eggs; the extra nutrition included in larger eggs permits the larvae to forgo feeding. Non-feeding larvae frequently have wider dorsal plates but reduced leg length, setal length and sclerotization when compared to parasitic larvae from sister lineages. The adults of lineages with non-feeding larvae are frequently smaller in comparison to adults of sister lineages with parasitic larvae. There is no apparent pattern in relation to habitat: lineages lacking larval parasitism occur in streams, temporary ponds and the littoral and planktonic regions of permanent lakes. © Rapid Science Ltd. 1998     

Population structure of the spotted babylon, Babylonia areolata in three wild populations along the Chinese coastline revealed using AFLP fingerprinting

Many marine gastropods are sedentary as adults but have planktonic larvae which can potentially be dispersed over large distances. Consequently larval transport is expected to play a prominent role in facilitating gene flow and determining population structure. The spotted babylon (Babylonia areolata) is a dioecious species possessing an approximately two week planktonic larval stage. We analyzed the population structure of the spotted babylon using amplified fragment length polymorphism (AFLP). One hundred and sixteen AFLP loci were analyzed in 63 individuals from three populations and revealed a high level of genetic diversity, with all individuals harboring a unique banding pattern. AMOVA results and an assignment test revealed that population differentiation was present. PCoA, pairwise F_ST and UPGMA tree all revealed that gene flow might be present only on a small geographic scale (around 160 km), but, over a large distance (around 1000 km), only reduced gene flow occurred. A mantel test indicated a highly significant positive correlation between genetic differentiation and geographical distance.