Reciprocal phenotypic plasticity in a predator-prey interaction between larval amphibians

In biological interactions, phenotypic change in interacting organisms induced by their interaction partners causes a substantial shift in some environmental factor of the partners, which may subsequently change their phenotype in response to that modified environmental factor. Few examples of such arms-race-like plastic responses, known as reciprocal phenotypic plasticity, have been identified in predator-prey interactions. We experimentally identified a reciprocal defensive plastic response of a prey species against a predator with a predaceous phenotype using a model system of close predator-prey interaction. Rana pirica tadpoles (the prey species) were reared with larvae of the salamander Hynobius retardatus (the predator species) having either a predaceous or a typical, nonpredaceous phenotype. The H. retardatus larvae with the predaceous phenotype, which is known to be induced by the presence of R. pirica tadpoles, induced a more defensive phenotype in the tadpoles than did larvae with the typical phenotype. The result suggests that the reciprocal phenotypic plasticity of R. pirica tadpoles is in response to a phenotype-specific signal under a close-signal recognition process.     

Flexible defense strategies: competition modifies investment in behavioral vs. morphological defenses

Competition is predicted to affect the expression of inducible defenses, but because costs of behavioral and morphological antipredator defenses differ along resource gradients, its effects on defenses may depend on the traits considered. We tested the predictions from different defense models in tadpoles of the common frog Rana temporaria, which exhibit both types of defenses. In an outdoor experiment, we exposed the tadpoles to nonlethal predators (Aeshna dragonfly larvae) and to a gradient of intraspecific competition. Morphological responses did not follow any of the expected patterns, since investment in defense was not affected by resource level. Instead, tail depth decreased in the absence of predators. Behavioral defenses followed a state-dependent model. Overall, the defense strategy of the tadpoles revealed a shift from morphological and behavioral defenses at low tadpole density to morphological defense only at high density. This difference probably reflects the different efficiency of the defenses. Hiding is an effective means of defense, but it is unsustainable when resources are scarce. Morphological responses become more important with increasing density to compensate for the increase in behavioral risk-taking. Our results indicate that competition can strongly affect reaction norms of inducible defenses and highlight the importance of integrating ecological parameters that affect the cost-benefit balance of phenotypic plasticity.     

A trade-off between prey- and predator-induced polyphenisms in larvae of the salamander Hynobius retardatus

Organisms in natural habitats participate in complex ecological interactions that include competition, predation, and foraging. Under natural aquatic environmental conditions, amphibian larvae can simultaneously receive multiple signals from conspecifics, predators, and prey, implying that predator-induced morphological defenses can occur in prey and that prey-induced offensive morphological traits may develop in predators. Although multiple adaptive plasticity, such as inducible defenses and inducible offensive traits, can be expected to have not only ecological but also evolutionary implications, few empirical studies report on species having such plasticity. The broad-headed larval morph of Hynobius retardatus, which is induced by crowding with heterospecific anuran (Rana pirica) larvae, is a representative example of prey-induced polyphenism. The morph is one of two distinct morphs that have been identified in this species; the other is the typical morph. In this paper, we report that typical larval morphs of Hynobius can respond rapidly to a predatory environment and show conspicuous predator-induced plasticity of larval tail depth, but that broad-headed morphs cannot respond similarly to a predation threat. Our findings support the hypothesis that induction or maintenance of adaptive plasticity (e.g., predator-induced polyphenism) trades off against other adaptive plastic responses (e.g., prey-induced polyphenism). For a species to retain both an ability to forage for larger prey and an ability to more effectively resist predation makes sense in light of the range of environments that many salamander larvae experience in nature. Our results suggest that the salamander larvae clearly discriminate between cues from prey and those from predators and accurately respond to each cue; that is, they adjust their phenotype to the current environment.     

Survival trade-offs between two predator-induced phenotypes in Pacific treefrogs (Pseudacris regilla)

In many organisms, specific predator species induce defensive phenotypes that are qualitatively different from the phenotypes induced by other predator species. This differential induction implies that there is no optimal phenotype that works best against all predators. However, few studies have actually tested the hypothesis that each predator-induced phenotype provides the highest survival rate in encounters with the predator that induced that phenotype. In this experiment, I reared Pacific treefrog (Pseudacris regilla) larvae with chemical cues from two different predators (bluegill sunfish and predaceous diving-beetle larvae), and without predator cues. The Pacific treefrog larvae in the three treatments differed in their morphology and foraging behavior. I then exposed tadpoles from each treatment to free-foraging predaceous diving beetles and bluegill sunfish. Tadpoles survived best when exposed to the predator whose cues they were reared with, and worst when exposed to the other predator. In both predator environments, the tadpoles reared in the nonpredator control treatment had intermediate survival between the two predator-induced groups. Thus, there is no generalized "antipredator" response to these predators; rather, there was a clear trade-off in survival abilities between the predators.     

Mechanism of predator–prey detection and behavioral responses in some anuran tadpoles

Predator–prey relationship was studied in three sympatric species of anuran tadpoles. The study design consisted of allowing predaceous Hoplobatrachus tigerinus tadpoles to devour prey tadpoles (Sphaerotheca breviceps and Bufo melanostictus) placed in a plastic tub (five tadpoles of each species, stage ~27) in 30 min. In trials without refugia, more tadpoles of Bufo fell prey compared to Sphaerotheca. In contrast, provision of refugia using hydrilla plant reversed predation risk of the two species. The swimming speed (V _max = 64.55 ± 1.45 cm/s) of Hoplobatrachus tadpoles was much higher compared to the prey species (Bufo: 3.6 ± 0.4 cm/s; Sphaerotheca: 27.6 ± 1.6 cm/s). Poor swimming ability may account for the observed vulnerability of the Bufo tadpoles to predation especially in clear waters; refugia overcame predation to some extent. On the other hand, Sphaerotheca tadpoles that swim faster than the toad tadpoles were less vulnerable in open areas; refugia actually hindered swimming and increased predation. Experiments with association choice tests show that predaceous tadpoles detect prey based on both visual and chemical cues. On the other hand, the prey tadpoles detected predator based exclusively on chemical rather than visual cues. The antipredator defense strategy of the toad tadpoles is manifested in the form of reduced movements, remaining still for longer times and, increased burst speed. The present findings also suggest that in both prey species predator detection has a genetic basis since naive tadpoles with no prior exposure to predators exhibit fright response on first encounter with them.     

Novel features of an inducible defense system in larval tree frogs (Hyla chrysoscelis)

Organisms in aquatic ecosystems must often tolerate variable environmental conditions, including an uncertain risk of predation. Individuals that can maintain plastic defenses against predation will increase their survival when predators are present, but will not incur the costs of these defenses when the risk of predation is low and the defense is not induced. Larvae of the pond-breeding anuran Hyla chrysoscelis develop a conspicuous phenotype in the presence of predators consisting of a brightly colored tail and a deeper tail fin. In this study, I attempted to identify the source of the chemical signal that induces this defensive morphology in this species. I tested whether metabolites alone, originating from the prey but passing through the predator, were able to induce the same morphological response as the combination of alarm signals released directly by attacked conspecifics, and metabolites. I used morphometric and tail conspicuousness data to assess tadpole response to the perceived risk of predation by larval odonate predators (Anax junius). I also tested whether this inducing cue could be recognized across species by measuring the morphological response of H. chrysoscelis tadpoles exposed to cues emitted when tadpoles of a closely related genus (Pseudacris crucifer) were consumed. Tadpoles exhibited a clean graded response of both overall shape and tail morphology in response to all cues, corresponding to their relative reliability as indicators of a risk of predation. H. chrysoscelis tadpoles were also able to respond to cues emitted when tadpoles of a closely related genus were consumed by predators. These results illustrate that tadpoles of this species are able to respond to metabolites alone without alarm signals, and that interspecific chemical communication is a primary mechanism for predator avoidance in this inducible defense system.     

Threat-sensitive generalization of predator recognition by larval amphibians

Despite the importance of acquired predator recognition in mediating predator–prey interactions, we know little about the specific characteristics that prey use to distinguish predators from non-predators. Recent experiments with mammals and fish indicate that some prey lacking innate predator recognition have the ability to display anti-predator responses upon their first encounter with those predators if they are similar to predators that the prey has recently learned to recognize. This phenomenon is referred to as generalization of predator recognition. In this experiment, we documented for the first time that larval amphibians (woodfrog, Rana sylvatica) have the ability to generalize the recognition of known predators to closely related novel predators. Moreover, we demonstrated that this ability is dependent on the level of risk associated with the known predator. When red-bellied newt, Cynops pyrrhogaster (known predator), was paired with simulated low risk, tadpoles displayed fright responses to newts and novel tiger salamanders, Ambystoma tigrinum, but not to novel African clawed frogs, Xenopus laevis. However, when the newt was paired with simulated high risk, tadpoles generalized their responses to both tiger salamanders and African clawed frogs. Larval anurans seem to have a wider generalization frame than other animals.     

Vortex formation and foraging in polyphenic spadefoot toad tadpoles

Animal aggregations are widespread in nature and can exhibit complex emergent properties not found at an individual level. We investigate one such example here, collective vortex formation by congeneric spadefoot toad tadpoles: Spea bombifrons and Spea multiplicata. Tadpoles of these species develop into either an omnivorous or a carnivorous (cannibalistic) morph depending on diet. Previous studies show that S. multiplicata are more likely to develop into omnivores and feed on suspended organic matter in the water body. The omnivorous morph is frequently social, forming aggregates that move and forage together and form vortices in which they adopt a distinctive slowly rotating circular formation. This behaviour has been speculated to act as a means to agitate the substratum in ponds and thus could be a collective foraging strategy. Here we perform a quantitative investigation of the behaviour of tadpoles within aggregates. We found that only S. multiplicata groups exhibited vortex formation, suggesting that social interactions differ between species. The probability of collectively forming a vortex, in response to introduced food particles, increased for higher tadpole densities and when tadpoles were hungry. Individuals inside a vortex moved faster and exhibited higher (by approximately 27%) tailbeat frequencies than those outside the vortex, thus incurring a personal energetic cost. The resulting environmental modification, however, suggests that vortex behaviour may be an adaptation to actively create and exploit a resource patch within the environment.     

Predicted Genetic Consequences of Strong Fertility Selection Due to Pollinator Loss in an Isolated Population of Primula sieboldii

Previous studies demonstrated strong fertility selection for a self-fertile, homostyle morph due to pollinator loss in an isolated population of Primula sieboldii , an endangered heterostylous species. To predict genetic consequences of the selection we developed a deterministic genetic model based on a classical "supergene" model, and we studied the effects of pollinator availability and inbreeding depression on temporal changes of morph frequencies through model simulation. Because of the severe pollinator limitation experienced by the population, fast, irreversible loss of the thrum morph from the population was predicted, even if high inbreeding depression was assumed. To prevent the breakdown of the normal breeding system of the species, morph frequency monitoring for timely active management should be implemented. Active management should include hand pollinations and pollinator therapy—reintroduction and reestablishment of suitable pollinator populations. The method we adopted in this study to parametrize pollinator availability can be used widely in conservation modeling for a range of plant species that have multiple mating types with different degrees of self-incompatibility.     

Genetic relationships within and between clonal and solitary forms of the sea anemone Anthopleura elegantissima revisited: evidence for the existence of two species

Along the temperate Pacific coast of North America, the actiniarian sea anemone Anthopleura elegantissima exhibits two discrete life-history phenotypes. Although both forms sexually produce planula larvae, the clonal morph can also asexually propagate by fission, whereas the solitary morph does not. Whether the two forms constitute one or two species has long been contested. Hand originally designated the two forms as conspecifics, whereas Francis – on the basis of differences in microhabitat, biogeographic range and phenotypic frequencies – argued that the two forms constituted a sibling-species pair. From the results of an electrophoretic survey in which they pooled allelic frequencies across several geographic locations, Smith and Potts subsequently argued that the two forms were not genetically differentiated, and therefore represented a single species. We re-examined the relationship between the forms electrophoretically, substantially extending the geographic range and doubling the sample sizes beyond those used by Smith and Potts, and not pooling allelic frequencies in our analyses. Our analysis of patterns of genetic variation at ten highly polymorphic allozyme loci shows that although no fixed genetic differences distinguish the two forms, there are significant differences in allele frequencies between clonal and solitary A.␣elegantissima at every site we sampled throughout their range of sympatry (over 1000 km); within each form, however, there is little detectable genetic differentiation among populations. We therefore conclude that the two forms represent recently reproductively isolated taxa, and propose that the clonal form retain the binomial A. elegantissima (Brandt, 1835), whereas the solitary form be described and named a new species, Anthopleura sp. Received: 28 August 1996 / Accepted: 25 September 1996     

How flexible is phenotypic plasticity? Developmental windows for trait induction and reversal

Inducible defenses allow prey to modulate their phenotypic responses to the level of predation risk in the environment and reduce the cost of constitutive defenses. Inherent in this statement is that prey must alter their phenotypes during development in order to form these defenses. This has lead many ecologists and evolutionary biologists to call for studies that examine developmental plasticity to provide insights into the importance of development in controlling the trajectories of trait formation, the integration of phenotypes over ontogeny, and the establishment of developmental windows for trait formation and reversal. By moving away from studies that focus on a single point in development, we can obtain a more complete understanding of the phenotypic decisions and limitations of prey. We exposed freshwater snails (Helisoma trivolvis) to environments in which predatory water bugs (Belostoma flumineum) were always absent, always present, or added and removed at different points in development. We discovered that snails formed morphological defenses against water bugs. Importantly, after the initial induction of defenses, snails showed similar developmental trajectories as snails reared without predators. Further, the snails possessed wide developmental windows for inducible defenses that extended past sexual maturity. However, being induced later in development appeared to have an associated cost (i.e., decreased shell thickness) that was not found when water bugs were always present. This epiphenotype (i.e., new shell formation as an extension of the current shell) suggests that resource limitation plays an important role in responses to temporal variation in predation risk and may have critical ecological costs that limit the benefits of the inducible defense. Lastly, the ability of snails to completely reverse their defenses was limited to early in ontogeny due to the constraints associated with modular growth of shell material. In sum, we demonstrate that taking a developmental perspective is extremely valuable for understanding the ecology of inducible defenses.     

Antipredator defenses along a latitudinal gradient in Rana temporaria

Antipredator defenses are expected to decrease toward higher latitudes because predation rates are predicted to decrease with latitude. However, latitudinal variation in predator avoidance and defense mechanisms has seldom been studied. We studied tadpole antipredator defenses in seven Rana temporaria populations collected along a 1500-km latitudinal gradient across Sweden, along which previous studies have found increasing tadpole growth and development rates. In a laboratory common garden experiment, we measured behavioral and morphological defenses by raising tadpoles in the presence and absence of a predator (Aeshna dragonfly larva) in two temperature treatments. We also estimated tadpole survival in the presence of free-ranging predators and compared predator densities between R. temporaria breeding ponds situated at low and high latitudes. Activity and foraging were generally positively correlated with latitude in the common garden experiment. While all populations responded to predator presence by decreasing activity and foraging, high-latitude populations maintained higher activity levels in the presence of the predator. All populations exhibited defensive morphology in body and tail shape. However, whereas tail depth tended to increase with latitude in the presence of predator, it did not change with latitude in the absence of the predator. Predator presence generally increased larval period and decreased growth rate. In the southern populations, predator presence tended to have a negative effect on metamorphic size, whereas in the northern populations predators had little or a positive effect on size. Latitude of origin had a strong effect on survival in the presence of a free-ranging predator, with high-latitude tadpoles experiencing higher mortality than those from the low latitudes. In the wild, predator densities were significantly lower in high-latitude than in mid-latitude breeding ponds. Although the higher activity level in the northern populations seems to confer a significant survival disadvantage under predation risk, it is probably needed to maintain the high growth and development rates. However, the occurrence of R. temporaria at high latitudes may be facilitated by the lower predator densities in the north.     

Personality trait differences between mainland and island populations in the common frog (Rana temporaria)

Understanding and predicting species range expansions is an important challenge in modern ecology because of rapidly changing environments. Recent studies have revealed that consistent within-species variation in behavior (i.e., animal personality) can be imperative for dispersal success, a key process in range expansion. Here we investigate how habitat isolation can mediate differentiation of personality traits between recently founded island populations and the main population. We performed laboratory studies of boldness and exploration across life stages (tadpoles and froglets) using four isolated island populations and four mainland populations of the common frog (Rana temporaria). Both tadpoles and froglets from isolated populations were bolder and more exploratory than conspecifics from the mainland. Although the pattern can be influenced by possible differences in predation pressure, we suggest that this behavioral differentiation might be the result of a disperser-dependent founder effect brought on by an isolation-driven environmental filtering of animal personalities. These findings can have important implications for both species persistence in the face of climate change (i.e., range expansions) and ecological invasions as well as for explaining rapid speciation in isolated patches.     

Genetic Structure of Herpetofauna on Halmahera Island,Indonesia: Implications for Aketajawe‐Lolobata National Park

Abstract: Genetic variation within species—a priority for biodiversity conservation—is influenced by natural selection, demography, and stochastic events such as genetic drift. We evaluated the role of these factors in 14 codistributed species of reptiles and amphibians on the Indonesian island of Halmahera by testing whether their molecular variation was correlated with geographic distance, ecology, riverine barriers, or Halmahera's paleoisland precursors. We found support for isolation by distance effects in four species. Two of these four were also significantly affected either by rivers or by ecology. A fifth species was significantly affected by ecology and a sixth was significantly affected by Halmahera's paleoislands. [Correction added after publication 9 December 2009: the previous sentence was edited for clarity.] These findings—the most comprehensive survey of multispecies genetic variation on Halmahera to date—bode well for the efficacy of the recently established Aketajawe‐Lolobata National Park in conserving a substantial component of vertebrate genetic variation on this island. Future success of conservation efforts will depend crucially, of course, on funding for and enforcement of conservation management of this park.     

Genetic structure of local populations and divergence between growth forms in a clonal invertebrate,the Caribbean octocoral Briareum asbestinum

Although the genetic structure of many populations of marine organisms show little deviation from panmixia, in those marine species with limited larval dispersal, patterns of microgeographic genetic differentiation may be common. The octocoral Briareum asbestinum should show local population differentiation because colonies reproduce asexually by fragmentation, most matings occur between colonies in very close proximity, and the sexually produced larvae and sperm appear to disperse only short distances. Variability in secondary chemistry of individual B. asbestinum colonies from different populations in close proximity also suggests local population differentiation. We determined the genetic composition of local populations by surveying allozyme variation of three shallow and two deep populations within a 300 m² area at San Salvador Island, Bahamas and at a site 161 km away on Little San Salvador, Bahamas in July 1990. As B. asbestinum occurs as either an erect branching form or an encrusting mat often at the same sites, we sampled both morphs to examine the extent of genetic exchange between them. Five of 21 loci were polymorphic and most populations showed a deficit of heterozygotes. Allele frequencies differed significantly between morphs at each site where they occurred together. The mean genetic distance (D=0.065) between morphs is consistent with the interpretation that the two morphs are genetically isolated. Despite the close spatial proximity of the San Salvador populations, both the branching and encrusting morphs showed significant genetic heterogeneity among neighboring populations. Similarly, pooled allelic frequencies for samples collected from the islands of San Salvador and Little San Salvador differed significantly at 1 locus for the branching morph and at 3 out of 5 loci for the encrusting morph.     

Amphibian embryo and parental defenses and a larval predator reduce egg mortality from water mold

Water molds attack aquatic eggs worldwide and have been associated with major mortality events in some cases, but typically only in association with additional stressors. We combined field observations and laboratory experiments to study egg stage defenses against pathogenic water mold in three temperate amphibians. Spotted salamanders (Ambystoma maculatum) wrap their eggs in a protective jelly layer that prevents mold from reaching the embryos. Wood frog (Rana sylvatica) egg masses have less jelly but are laid while ponds are still cold and mold growth is slow. American toad (Bufo americanus) eggs experience the highest infection levels. They are surrounded by thin jelly and are laid when ponds have warmed and mold grows rapidly. Eggs of all three species hatched early when infected, yielding smaller and less developed hatchlings. This response was strongest in B. americanus. Precocious hatching increased vulnerability of wood frog hatchlings to invertebrate predators. Finally, despite being potential toad hatchling predators, R. sylvatica tadpoles can have a positive effect on B. americanus eggs. They eat water mold off infected toad clutches, increasing their hatching success.     

Suitability of Golf Course Ponds for Amphibian Metamorphosis When Bullfrogs Are Removed

Abstract:  Managing areas designed for human recreation so that they are compatible with natural amphibian populations can reduce the negative impacts of habitat destruction. We examined the potential for amphibians to complete larval development in golf course ponds in the presence or absence of overwintered bullfrog tadpoles ( Rana catesbeiana ), which are frequently found in permanent, human-made ponds. We reared larval American toads ( Bufo americanus ), southern leopard frogs ( R. sphenocephala ), and spotted salamanders ( Ambystoma maculatum ) with 0 or 5 overwintered bullfrog tadpoles in field enclosures located in ponds on golf courses or in experimental wetlands at a reference site. Survival to metamorphosis of American toads, southern leopard frogs, and spotted salamanders was greater in ponds on golf courses than at reference sites. We attributed this increased survival to low abundance of insect predators in golf course ponds. The presence of overwintered bullfrogs, however, reduced the survival of American toads, southern leopard frogs, and spotted salamanders reared in golf course ponds, indicating that the suitability of the aquatic habitats for these species partly depended on the biotic community present. Our results suggest that ponds in human recreational areas should be managed by maintaining intermediate hydroperiods, which will reduce the presence of bullfrog tadpoles and predators, such as fish, and which may allow native amphibian assemblages to flourish.     

Ecological and physiological differences between two colour morphs of the coral Pocillopora damicornis

Pocillopora damicornis (Linnaeus) is a ubiquitous branching coral found throughout the Indo-Pacific region. Like many other species of coral, P. damicornis displays a large range of morphologies. At One Tree Island, it occurs as two distinct morphs that are easily distinguished by the presence or absence of pink pigmentation. The two colour morphs of P. damicornis were found to differ in their distribution and abundance in the One Tree Island Lagoon. The brown morph was more abudant than the pink morph in the shallows (<1 m),whereas the pink morph was more abundant at deeper sites (>3 m). The two morphs also differed physiologically. The brown morph tended to have a greater calcification rate than the pink morph, regardless of environmental conditions. However, the difference in the calcification rate between the two morphs became non-significant under shaded conditions (5% full sunlight), indicating some degree of physiological plasticity of the morphs. The pink colour in P. damicornis was due to a hydrophilic pigment with a major peak absorbance at 560 nm. The expression of pink pigment had both genetic and phenotypic components. The brown morph has a reduced genetic capacity to express the pigment relative to the pink morph. On the other hand, pigment expression could be induced by light in the pink morph. Although genetic differences ultimately determine the differences between the two morphs of P. damicornis, the extent of pigment expression is under some degree of environmental influence.     

Genetic connectivity among color morphs and Pacific archipelagos for the flame angelfish, <Emphasis Type="Italic">Centropyge loriculus</Emphasis>

Color variation is used in taxonomic classification of reef fishes, but it may not reliably indicate evolutionary divergence. In the central Pacific, there are three color morphs of the flame angelfish, Centropyge loriculus: a red morph that occurs primarily in the Hawaiian archipelago, the endemic Marquesan color morph with reduced black markings, and an orange morph that occurs throughout the rest of Oceania. The red and orange morphs co-occur at Johnston Atoll (1,300 km south of Hawai’i), but intermediate forms have not been reported. To determine whether the three color morphs represent distinct evolutionary lineages, we compared 641 base pairs of mitochondrial cytochrome b. Forty-one closely related haplotypes were observed in 116 individuals. Analysis of molecular variance (AMOVA) indicated no significant genetic structure among color morphs (Φ_ST = 0.011, P = 0.147). Likewise, there was no significant pairwise structure between sampling locations, separated by up to 5,700 km, after a Bonferroni correction (Φ_ST = 0.000–0.080, P = 0.0130–0.999). Genetic studies in conjunction with larval distribution data indicate that Centropyge species are highly dispersive. While there is a strong geographic component to the distribution of color morphs in C. loriculus, we find no evidence for corresponding genetic partitioning. We do not rule out an adaptive role for color differentiation, but our data do not support emerging species.     

Effects of habitat fragmentation on the genetic structure and connectivity of the black-lipped pearl oyster Pinctada margaritifera populations in French Polynesia

Habitat destruction leading to increased fragmentation is detrimental to species by reducing population size and genetic diversity and by restraining population connectivity. However, little is known about the effects of naturally fragmented habitats on wild populations, especially when it comes to marine benthic invertebrates with long pelagic larval duration. In this framework, we investigated the connectivity and genetic diversity variation among nine wild populations of the black-lipped pearl oyster, Pinctada margaritifera, throughout French Polynesia using ten microsatellite DNA markers. Despite the naturally fragmented habitat (South Pacific oceanic islands), we found high values of genetic diversity and population admixture, indicating connectivity at small and large spatial scales within sampled sites of the Tuamotu, and between the Society and Tuamotu Archipelagos. In the meantime, habitat geomorphology increased genetic drift in populations occurring in small, closed lagoons. Significant genetic structure not correlated to geographic distance was detected mainly between closed and open lagoons. The Marquesas Islands hosted the most divergent populations, likely a result of vicariance. Our results also highlight that migration patterns among lagoons are not symmetrical. Altogether, the general pattern of gene flow, nonsymmetrical migration rates among populations, absence of isolation by distance and absence of recent extinction events found in our study strongly suggest that P. margaritifera populations of French Polynesia follow an asymmetrical island model of dispersal.