Spatial and temporal patterns of larval dispersal in a coral‐reef fish metapopulation: evidence of variable reproductive success

Many marine organisms can be transported hundreds of kilometres during their pelagic larval stage, yet little is known about spatial and temporal patterns of larval dispersal. Although traditional population‐genetic tools can be applied to infer movement of larvae on an evolutionary timescale, large effective population sizes and high rates of gene flow present serious challenges to documenting dispersal patterns over shorter, ecologically relevant, timescales. Here, we address these challenges by combining direct parentage analysis and indirect genetic analyses over a 4‐year period to document spatial and temporal patterns of larval dispersal in a common coral‐reef fish: the bicolour damselfish (Stegastes partitus). At four island locations surrounding Exuma Sound, Bahamas, including a long‐established marine reserve, we collected 3278 individuals and genotyped them at 10 microsatellite loci. Using Bayesian parentage analysis, we identified eight parent‐offspring pairs, thereby directly documenting dispersal distances ranging from 0 km (i.e., self‐recruitment) to 129 km (i.e., larval connectivity). Despite documenting substantial dispersal and gene flow between islands, we observed more self‐recruitment events than expected if the larvae were drawn from a common, well‐mixed pool (i.e., a completely open population). Additionally, we detected both spatial and temporal variation in signatures of sweepstakes and Wahlund effects. The high variance in reproductive success (i.e., ‘sweepstakes’) we observed may be influenced by seasonal mesoscale gyres present in the Exuma Sound, which play a prominent role in shaping local oceanographic patterns. This study documents the complex nature of larval dispersal in a coral‐reef fish, and highlights the importance of sampling multiple cohorts and coupling both direct and indirect genetic methods in order disentangle patterns of dispersal, gene flow and variable reproductive success.     

Determining parentage and relatedness from genetic markers sheds light on patterns of marine larval dispersal

Population connectivity, the extent to which geographically separated subpopulations exchange individuals and are demographically linked, is important to the scientific management of marine living resources. In theory, the design of a marine protected area, for example, depends on an explicit understanding of how dispersal of planktonic larvae affects metapopulation structure and dynamics ( Botsford et al. 2001 ). In practice, for most marine metazoans with planktonic larvae, the mean and variance of the distances that larvae disperse are unobservable quantities, owing to the small sizes of larvae and the very large volumes through which they are distributed. Simulation of dispersal kernels with models that incorporate oceanography and limited aspects of larval biology and behaviour, coupled with field studies of larval distribution, abundance, and settlement, have provided the best available approaches to date for understanding connectivity of marine populations ( Cowen et al. 2006 ). On the other hand, marine population connectivity has often been judged by spatial variation in the frequencies of alleles and genotypes, although the inherent limitations of this indirect approach to measuring larval dispersal have often been overlooked ( Hedgecock et al. 2007 ). More recently, researchers have turned to genetic methods and highly polymorphic markers that can provide direct evidence of population connectivity in the form of parentage or relatedness of recruits (e.g. Jones et al. 2005 ). In this issue, Christie et al. (2010) provide a particularly elegant example, in which both indirect and novel direct genetic methods are used to determine the major ecological processes shaping dispersal patterns of larval bicolour damselfish Stegastes partitus, a common and widespread reef fish species in the Caribbean Basin ( Fig. 1 ).

Figure 1 Open in figure viewer PowerPoint The bicolour damselfish Stegastes partitus shows substantial self‐recruitment of juveniles to their natal coral reef habitat. Below, a male guarding an artificial nest made from PVC pipe; differential reproductive success of parents or differential survival of egg clutches or the larvae that hatch from them may account for signals of sweepstakes reproductive success in this species (photo credits: top, Bill Harward; bottom, Darren Johnson).     

Parentage analyses identify local dispersal events and sibling aggregations in a natural population of Millepora hydrocorals,a free‐spawning marine invertebrate

Dispersal is a critical process for the persistence and productivity of marine populations. For many reef species, there is increasing evidence that local demography and self‐recruitment have major consequences on their genetic diversity and adaptation to environmental change. Yet empirical data of dispersal patterns in reef‐building species remain scarce. Here, we document the first genetic estimates of self‐recruitment and dispersal distances in a free‐spawning marine invertebrate, the hydrocoral Millepora cf. platyphylla. Using twelve microsatellite markers, we gathered genotypic information from 3,160 georeferenced colonies collected over 27,000 m² of a single reef in three adjacent habitats in Moorea, French Polynesia; the mid slope, upper slope, and back reef. Although the adult population was predominantly clonal (85% were clones), our parentage analysis revealed a moderate self‐recruitment rate with a minimum of 8% of sexual propagules produced locally. Assigned offspring often settled at <10 m from their parents and dispersal events decrease with increasing geographic distance. There were no discrepancies between the dispersal distances of offspring assigned to parents belonging to clonal versus nonclonal genotypes. Interhabitat dispersal events via cross‐reef transport were also detected for sexual and asexual propagules. Sibship analysis showed that full siblings recruit nearby on the reef (more than 40% settled at <30 m), resulting in sibling aggregations. Our findings highlight the importance of self‐recruitment together with clonality in stabilizing population dynamics, which may ultimately enhance local sustainability and resilience to disturbance.     

Spatial patterns of self‐recruitment of a coral reef fish in relation to island‐scale retention mechanisms

Oceanographic features influence the transport and delivery of marine larvae, and physical retention mechanisms, such as eddies, can enhance self‐recruitment (i.e. the return of larvae to their natal population). Knowledge of exact locations of hatching (origin) and settlement (arrival) of larvae of reef animals provides a means to compare observed patterns of self‐recruitment ‘connectivity’ with those expected from water circulation patterns. Using parentage inference based on multiple sampling years in Moorea, French Polynesia, we describe spatial and temporal variation in self‐recruitment of the anemonefish Amphiprion chrysopterus, evaluate the consistency of net dispersal distances of self‐recruits against the null expectation of passive particle dispersal and test the hypothesis that larvae originating in certain reef habitats (lagoons and passes) would be retained and thus more likely to self‐recruit than those originating on the outer (fore) reef. Estimates of known self‐recruitment were consistent across the sampling years (~25–27% of sampled recruits). For most (88%) of these self‐recruits, the net distance between hatching and settlement locations was within the maximum dispersal distance expected for a neutrally buoyant passive particle based on the longest duration of the larval dispersive phase and the average direction and speed of current flow around Moorea. Furthermore, a parent of a given body size on the outer (fore) reef of Moorea was less likely to produce self‐recruits than those in passes. Our findings show that even a simple dispersal model based on net average flow and direction of alongshore currents can provide insight into landscape‐scale retention patterns of reef fishes.     

Self‐recruitment in a Caribbean reef fish: a method for approximating dispersal kernels accounting for seascape

Characterizing patterns of larval dispersal is essential to understanding the ecological and evolutionary dynamics of marine metapopulations. Recent research has measured local dispersal within populations, but the development of marine dispersal kernels from empirical data remains a challenge. We propose a framework to move beyond point estimates of dispersal towards the approximation of a simple dispersal kernel, based on the hypothesis that the structure of the seascape is a primary predictor of realized dispersal patterns. Using the coral reef fish Elacatinus lori as a study organism, we use genetic parentage analysis to estimate self‐recruitment at a small spatial scale (<1 km). Next, we determine which simple kernel explains the observed self‐recruitment, given the influx of larvae from reef habitat patches in the seascape at a large spatial scale (up to 35 km). Finally, we complete parentage analyses at six additional sites to test for export from the focal site and compare these observed dispersal data within the metapopulation to the predicted dispersal kernel. We find 4.6% self‐recruitment (CI_95%: ±3.0%) in the focal population, which is explained by the exponential kernel y = 0.915^x (CI_95%: y = 0.865^x, y = 0.965^x), given the seascape. Additional parentage analyses showed low levels of export to nearby sites, and the best‐fit line through the observed dispersal proportions also revealed a declining function y = 0.77^x. This study lends direct support to the hypothesis that the probability of larval dispersal declines rapidly with distance in Atlantic gobies in continuously distributed habitat, just as it does in the Indo‐Pacific damselfishes in patchily distributed habitat.     

The role of marine reserves in the replenishment of a locally impacted population of anemonefish on the Great Barrier Reef

The development of parentage analysis to track the dispersal of juvenile offspring has given us unprecedented insight into the population dynamics of coral reef fishes. These tools now have the potential to inform fisheries management and species conservation, particularly for small fragmented populations under threat from exploitation and disturbance. In this study, we resolve patterns of larval dispersal for a population of the anemonefish Amphiprion melanopus in the Keppel Islands (southern Great Barrier Reef). Habitat loss and fishing appear to have impacted this population and a network of no‐take marine reserves currently protects 75% of the potential breeders. Using parentage analysis, we estimate that 21% of recruitment in the island group was generated locally and that breeding adults living in reserves were responsible for 79% (31 of 39) of these of locally produced juveniles. Overall, the network of reserves was fully connected via larval dispersal; however, one reserve was identified as a critical source of larvae for the island group. The population in the Keppel Islands also appears to be well‐connected to other source populations at least 60 km away, given that 79% (145 of 184) of the juveniles sampled remained unassigned in the parentage analysis. We estimated the effective size of the A. melanopus metapopulation to be 745 (582–993 95% CI) and recommend continued monitoring of its genetic status. Maintaining connectivity with populations beyond the Keppel Islands and recovery of local recruitment habitat, potentially through active restoration of host anemone populations, will be important for its long‐term persistence.     

Large‐scale,multidirectional larval connectivity among coral reef fish populations in the Great Barrier Reef Marine Park

Larval dispersal is the key process by which populations of most marine fishes and invertebrates are connected and replenished. Advances in larval tagging and genetics have enhanced our capacity to track larval dispersal, assess scales of population connectivity, and quantify larval exchange among no‐take marine reserves and fished areas. Recent studies have found that reserves can be a significant source of recruits for populations up to 40 km away, but the scale and direction of larval connectivity across larger seascapes remain unknown. Here, we apply genetic parentage analysis to investigate larval dispersal patterns for two exploited coral reef groupers (Plectropomus maculatus and Plectropomus leopardus) within and among three clusters of reefs separated by 60–220 km within the Great Barrier Reef Marine Park, Australia. A total of 69 juvenile P. maculatus and 17 juvenile P. leopardus (representing 6% and 9% of the total juveniles sampled, respectively) were genetically assigned to parent individuals on reefs within the study area. We identified both short‐distance larval dispersal within regions (200 m to 50 km) and long‐distance, multidirectional dispersal of up to ~250 km among regions. Dispersal strength declined significantly with distance, with best‐fit dispersal kernels estimating median dispersal distances of ~110 km for P. maculatus and ~190 km for P. leopardus. Larval exchange among reefs demonstrates that established reserves form a highly connected network and contribute larvae for the replenishment of fished reefs at multiple spatial scales. Our findings highlight the potential for long‐distance dispersal in an important group of reef fishes, and provide further evidence that effectively protected reserves can yield recruitment and sustainability benefits for exploited fish populations.     

USING ISOLATION BY DISTANCE AND EFFECTIVE DENSITY TO ESTIMATE DISPERSAL SCALES IN ANEMONEFISH

Robust estimates of dispersal are critical for understanding population dynamics and local adaptation, as well as for successful spatial management. Genetic isolation by distance patterns hold clues to dispersal, but understanding these patterns quantitatively has been complicated by uncertainty in effective density. In this study, we genotyped populations of a coral reef fish (Amphiprion clarkii) at 13 microsatellite loci to uncover fine‐scale isolation by distance patterns in two replicate transects. Temporal changes in allele frequencies between generations suggested that effective densities in these populations are 4–21 adults/km. A separate estimate from census densities suggested that effective densities may be as high as 82–178 adults/km. Applying these effective densities with isolation by distance theory suggested that larval dispersal kernels in A. clarkii had a spread near 11 km (4–27 km). These kernels predicted low fractions of self‐recruitment in continuous habitats, but the same kernels were consistent with previously reported, high self‐recruitment fractions (40–60%) when realistic levels of habitat patchiness were considered. Our results suggested that ecologically relevant larval dispersal can be estimated with widely available genetic methods when effective density is measured carefully through cohort sampling and ecological censuses, and that self‐recruitment studies should be interpreted in light of habitat patchiness.     

Dispersal in the spiny damselfish,Acanthochromis polyacanthus,a coral reef fish species without a larval pelagic stage

The spiny damselfish, Acanthochromis polyacanthus, is widely distributed throughout the Indo‐Australian archipelago. However, this species lacks a larval dispersal stage and shows genetic differentiation between populations from closely spaced reefs. To investigate the dispersal strategy of this unique species, we used microsatellite markers to determine genetic relatedness at five dispersal scales: within broods of juveniles, between adults within a collection site (~30 m²), between sites on single reefs, between nearby reefs in a reef cluster, and between reef clusters. We sampled broods of juveniles and adults from seven reefs in the Capricorn‐Bunker and Swain groups of the Great Barrier Reef. We found that extra‐pair mating is rare and juveniles remain with their parents until fledged. Adults from single sites are less related than broods but more related than expected by chance. However, there is no evidence of inbreeding suggesting the existence of assortative mating and/or adult migration. Genetic differences were found between all of the reefs tested except between Heron and Sykes reefs, which are separated only by a 2‐km area of shallow water (less than 10 m). There was a strong correlation between genetic distance, geographical distance and water depth. Apparently, under present‐day conditions spiny damselfish populations are connected only between sites of shallow water, through dispersal of adults over short distances. Assuming that dispersal behaviour has not changed, the broad distribution of A. polyacanthus as a species is likely based on historical colonization patterns when reefs were connected by shallow water at times of lower sea levels.     

Larval dispersal and movement patterns of coral reef fishes,and implications for marine reserve network design

Well‐designed and effectively managed networks of marine reserves can be effective tools for both fisheries management and biodiversity conservation. Connectivity, the demographic linking of local populations through the dispersal of individuals as larvae, juveniles or adults, is a key ecological factor to consider in marine reserve design, since it has important implications for the persistence of metapopulations and their recovery from disturbance. For marine reserves to protect biodiversity and enhance populations of species in fished areas, they must be able to sustain focal species (particularly fishery species) within their boundaries, and be spaced such that they can function as mutually replenishing networks whilst providing recruitment subsidies to fished areas. Thus the configuration (size, spacing and location) of individual reserves within a network should be informed by larval dispersal and movement patterns of the species for which protection is required. In the past, empirical data regarding larval dispersal and movement patterns of adults and juveniles of many tropical marine species have been unavailable or inaccessible to practitioners responsible for marine reserve design. Recent empirical studies using new technologies have also provided fresh insights into movement patterns of many species and redefined our understanding of connectivity among populations through larval dispersal. Our review of movement patterns of 34 families (210 species) of coral reef fishes demonstrates that movement patterns (home ranges, ontogenetic shifts and spawning migrations) vary among and within species, and are influenced by a range of factors (e.g. size, sex, behaviour, density, habitat characteristics, season, tide and time of day). Some species move <0.1–0.5 km (e.g. damselfishes, butterflyfishes and angelfishes), <0.5–3 km (e.g. most parrotfishes, goatfishes and surgeonfishes) or 3–10 km (e.g. large parrotfishes and wrasses), while others move tens to hundreds (e.g. some groupers, emperors, snappers and jacks) or thousands of kilometres (e.g. some sharks and tuna). Larval dispersal distances tend to be <5–15 km, and self‐recruitment is common. Synthesising this information allows us, for the first time, to provide species, specific advice on the size, spacing and location of marine reserves in tropical marine ecosystems to maximise benefits for conservation and fisheries management for a range of taxa. We recommend that: (i) marine reserves should be more than twice the size of the home range of focal species (in all directions), thus marine reserves of various sizes will be required depending on which species require protection, how far they move, and if other effective protection is in place outside reserves; (ii) reserve spacing should be <15 km, with smaller reserves spaced more closely; and (iii) marine reserves should include habitats that are critical to the life history of focal species (e.g. home ranges, nursery grounds, migration corridors and spawning aggregations), and be located to accommodate movement patterns among these. We also provide practical advice for practitioners on how to use this information to design, evaluate and monitor the effectiveness of marine reserve networks within broader ecological, socioeconomic and management contexts.     

Ontogenetic and spatial variation in size‐selective mortality of a marine fish

Although body size can affect individual fitness, ontogenetic and spatial variation in the ecology of an organism may determine the relative advantages of size and growth. During an 8‐year field study in the Bahamas, we examined selective mortality on size and growth throughout the entire reef‐associated life phase of a common coral‐reef fish, Stegastes partitus (the bicolour damselfish). On average, faster‐growing juveniles experienced greater mortality, though as adults, larger individuals had higher survival. Comparing patterns of selection observed at four separate populations revealed that greater population density was associated with stronger selection for larger adult size. Large adults may be favoured because they are superior competitors and less susceptible to gape‐limited predators. Laboratory experiments suggested that selective mortality of fast‐growing juveniles was likely because of risk‐prone foraging behaviour. These patterns suggest that variation in ecological interactions may lead to complex patterns of lifetime selection on body size.     

Genetic assignment of recruits reveals short‐ and long‐distance larval dispersal in Pocillopora damicornis on the Great Barrier Reef

Understanding connectivity of coral populations among and within reefs over ecologically significant timescales is essential for developing evidence‐based management strategies, including the design of marineprotected areas. Here, we present the first assessment of contemporary connectivity among populations of two Molecular Operational Taxonomic Units (MOTUs) of the brooding coral Pocillopora damicornis. We used individual‐based genetic assignment methods to identify the proportions of philopatric and migrant larval recruits, settling over 12 months at sites around Lizard Island (northern Great Barrier Reef [GBR]) and over 24 months at sites around the Palms Islands (central GBR). Overall, we found spatially and temporally variable rates of self‐recruitment and dispersal, demonstrating the importance of variation in local physical characteristics in driving dispersal processes. Recruitment patterns and inferred dispersal distances differed between the two P. damicornis MOTUs, with type α recruits exhibiting predominantly philopatric recruitment, while the majority of type β recruits were either migrants from identified putative source populations or assumed migrants based on genetic exclusion from all known populations. While P. damicornis invests much energy into brooding clonal larvae, we found that only 15% and 7% of type α and type β recruits, respectively, were clones of sampled adult colonies or other recruits, challenging the hypothesis that reproduction is predominantly asexual in this species on the GBR. We explain high rates of self‐recruitment and low rates of clonality in these MOTUs by suggesting that locally retained larvae originate predominantly from spawned gametes, while brooded larvae are mainly vagabonds.     

Patterns and persistence of larval retention and connectivity in a marine fish metapopulation

Connectivity, the demographic linking of local populations through the dispersal of individuals, is one of the most poorly understood processes in population dynamics, yet has profound implications for conservation and harvest strategies. For marine species with pelagic larvae, direct estimation of connectivity remains logistically challenging and has mostly been limited to single snapshots in time. Here, we document seasonal and interannual patterns of larval dispersal in a metapopulation of the coral reef fish Amphiprion polymnus. A 3‐year record of larval trajectories within and among nine discrete local populations from an area of approximately 35 km was established by determining the natal origin of settled juveniles through DNA parentage analysis. We found that spatial patterns of both self‐recruitment and connectivity were remarkably consistent over time, with a low level of self‐recruitment at the scale of individual sites. Connectivity among sites was common and multidirectional in all years and was not significantly influenced by seasonal variability of predominant surface current directions. However, approximately 75% of the sampled juveniles could not be assigned to parents within the study area, indicating high levels of immigrations from sources outside the study area. The data support predictions that the magnitude and temporal stability of larval connectivity decreases significantly with increasing distance between subpopulations, but increases with the size of subpopulations. Given the considerable effort needed to directly measure larval exchange, the consistent patterns suggest snapshot parentage analyses can provide useful dispersal estimates to inform spatial management decisions.     

Dispersal of a nearshore marine fish connects marine reserves and adjacent fished areas along an open coast

Marine species with pelagic larvae typically exhibit little population structure, suggesting long‐distance dispersal and high gene flow. Directly quantifying dispersal of marine fishes is challenging but important, particularly for the design of marine protected areas (MPAs). Here, we studied kelp rockfish (Sebastes atrovirens) sampled along ~25 km of coastline in a boundary current‐dominated ecosystem and used genetic parentage analysis to identify dispersal events and characterize them, because the distance between sedentary parents and their settled offspring is the lifetime dispersal distance. Large sample sizes and intensive sampling are critical for increasing the likelihood of detecting parent–offspring matches in such systems and we sampled more than 6,000 kelp rockfish and analysed them with a powerful set of 96 microhaplotype markers. We identified eight parent–offspring pairs with high confidence, including two juvenile fish that were born inside MPAs and dispersed to areas outside MPAs, and four fish born in MPAs that dispersed to nearby MPAs. Additionally, we identified 25 full‐sibling pairs, which occurred throughout the sampling area and included all possible combinations of inferred dispersal trajectories. Intriguingly, these included two pairs of young‐of‐the‐year siblings with one member each sampled in consecutive years. These sibling pairs suggest monogamy, either intentional or accidental, which has not been previously demonstrated in rockfishes. This study provides the first direct observation of larval dispersal events in a current‐dominated ecosystem and direct evidence that larvae produced within MPAs are exported both to neighbouring MPAs and to proximate areas where harvest is allowed.     

Fine‐scale genetic structure and inferences on population biology in the threatened Mediterranean red coral,Corallium rubrum

Identifying microevolutionary processes acting in populations of marine species with larval dispersal is a challenging but crucial task because of its conservation implications. In this context, recent improvements in the study of spatial genetic structure (SGS) are particularly promising because they allow accurate insights into the demographic and evolutionary processes at stake. Using an exhaustive sampling and a combination of image processing and population genetics, we highlighted significant SGS between colonies of Corallium rubrum over an area of half a square metre, which sheds light on a number of aspects of its population biology. Based on this SGS, we found the mean dispersal range within sites to be between 22.6 and 32.1 cm, suggesting that the surveyed area approximately corresponded to a breeding unit. We then conducted a kinship analysis, which revealed a complex half‐sib family structure and allowed us to quantify the level of self‐recruitment and to characterize aspects of the mating system of this species. Furthermore, significant temporal variations in allele frequencies were observed, suggesting low genetic drift. These results have important conservation implications for the red coral and further our understanding of the microevolutionary processes acting within populations of sessile marine species with a larval phase.     

Reduced genetic diversity and increased reproductive isolation follow population‐level loss of larval dispersal in a marine gastropod

Population‐level consequences of dispersal ability remain poorly understood, especially for marine animals in which dispersal is typically considered a species‐level trait governed by oceanographic transport of microscopic larvae. Transitions from dispersive (planktotrophic) to nondispersive, aplanktonic larvae are predicted to reduce connectivity, genetic diversity within populations, and the spatial scale at which reproductive isolation evolves. However, larval dimorphism within a species is rare, precluding population‐level tests. We show the sea slug Costasiella ocellifera expresses both larval morphs in Florida and the Caribbean, regions with divergent mitochondrial lineages. Planktotrophy predominated at 11 sites, 10 of which formed a highly connected and genetically diverse Caribbean metapopulation. Four populations expressed mainly aplanktonic development and had markedly reduced connectivity, and lower genetic diversity at one mitochondrial and six nuclear loci. Aplanktonic dams showed partial postzygotic isolation in most interpopulation crosses, regardless of genetic or geographic distance to the sire's source, suggesting that outbreeding depression affects fragmented populations. Dams from genetically isolated and neighboring populations also exhibited premating isolation, consistent with reinforcement contingent on historical interaction. By increasing self‐recruitment and genetic drift, the loss of dispersal may thus initiate a feedback loop resulting in the evolution of reproductive isolation over small spatial scales in the sea.     

Long‐distance dispersal and local retention of larvae as mechanisms of recruitment in an island population of a coral reef fish

Abstract Although recruitment of pelagic larvae is a fundamental and well‐documented process in the dynamics of benthic marine populations, identifying the sources of recruitment, or the degree to which populations are connected via dispersal of larvae, has remained elusive for most marine taxa. In this study we used natural environmental markers (trace elements) recorded in fish otoliths (ear stones) as tags of natal origin. Specifically, we used the otolith core and edge chemistries of a locally endemic wrasse (Coris bulbifrons) from Lord Howe Island (LHI), Australia, and a widely distributed species (Coris picta) from three potential mainland source regions, to determine the likely sources of recruitment to C. picta populations on LHI. The use of a local endemic species, which is by definition self‐recruiting, is a novel approach for ground‐truthing the dispersal history of non‐endemic coral reef fish. Discriminant function analyses were able to separate LHI from mainland fish, using both edge and core signatures, with a high degree of accuracy, suggesting at least some of the C. picta collected on LHI were of local origin. This result was corroborated when half of the C. bulbifrons and LHI C. picta were introduced as unknowns into a discriminant function analysis using the remaining C. bulbifrons, LHI C. picta, and the mainland C. picta as a training data set. Overall, our findings suggest that both long distance dispersal and local retention are important sources of recruitment to populations of C. picta on LHI and that otolith chemistry of endemic species could be a useful benchmark for determining the prevalence of self‐recruitment in insular populations of other widespread species.     

Nonsignificant isolation by distance implies limited dispersal

Understanding the scale of dispersal is an important consideration in the conservation and management of many species. However, in species in which the high‐dispersal stage is characterized by tiny gametes or offspring, it may be difficult to estimate dispersal directly. This is the case for many marine species, whose pelagic larvae are dispersed by ocean currents by several days or weeks before beginning a benthic, more sedentary, adult stage. As consequence of the high‐dispersal larval stage, many marine species have low genetic structure on large spatial scales (Waples 1998 ; Hellberg 2007 ). Despite the high capacity for dispersal, some tagging studies have found that a surprising number of larvae recruit into the population they were released from (self‐recruitment). However, estimates of self‐recruitment are not informative about mean dispersal between subpopulations. To what extent are limited dispersal estimates from tagging studies compatible with high potential for dispersal and low genetic structure? In this issue, a study on five species of coral reef fish used isolation by distance (IBD) between individuals to estimate mean dispersal distances (Puebla et al. 2012 ). They found that mean dispersal was unexpectedly small (<50 km), given relatively low IBD slopes and long pelagic durations. This study demonstrates how low genetic structure is compatible with limited dispersal in marine species. A comprehensive understanding of dispersal in marine species will involve integrating methods that estimate dispersal over different spatial and temporal scales. Genomic data may increase power to resolve these issues but must be applied carefully to this question.     

A genetic approach to estimating natal dispersal distances and self‐recruitment in resident rainforest birds

Natal dispersal is a fundamental component of the ecology and evolutionary history of birds, yet is often prohibitively difficult to study. We characterized natal dispersal for the first time in a bird using molecular genetic parentage analyses in a tropical rainforest understory species, the chestnut‐backed antbird (Thamnophilidae: Myrmeciza exsul). Median natal dispersal distance was ～800 m (mean = 931 ± 84 (SE) m, n = 48), with ～90% of all distances < 1500 m. We found no evidence of sex‐biased dispersal. An index of self‐recruitment (i.e. individuals establishing a territory within the population of origin) was higher in sites largely or entirely surrounded by non‐forest, suggesting birds are reluctant to disperse out of preferred forest habitat. Via simulations, we confirmed that the genetic data had sufficient resolution to correctly identify parent‐offspring dyads, but lacked resolution to identify other relationships (full‐sib and half‐sib) with confidence. Chestnut‐backed antbirds have measurable self‐recruitment rates caused by short natal dispersal distances, and self‐recruitment may be amplified by reluctance to disperse out of sites bordered by non‐forest. Some tropical forest understory birds have naturally short dispersal distances, and our results have implications for understanding how species will be affected by fragmented landscapes and for the design of reserves.     

QUANTIFYING EVOLUTIONARY POTENTIAL OF MARINE FISH LARVAE: HERITABILITY,SELECTION, AND EVOLUTIONARY CONSTRAINTS

For many marine fish, intense larval mortality may provide considerable opportunity for selection, yet much less is known about the evolutionary potential of larval traits. We combined field demographic studies and manipulative experiments to estimate quantitative genetic parameters for both larval size and swimming performance for a natural population of a common coral‐reef fish, the bicolor damselfish (Stegastes partitus). We also examined selection on larval size by synthesizing information from published estimates of selective mortality. We introduce a method that uses the Lande–Arnold framework for examining selection on quantitative traits to empirically reconstruct adaptive landscapes. This method allows the relationship between phenotypic value and fitness components to be described across a broad range of trait values. Our results suggested that despite strong viability selection for large larvae and moderate heritability (h²= 0.29), evolutionary responses of larvae would likely be balanced by reproductive selection favoring mothers that produce more, smaller offspring. Although long‐term evolutionary responses of larval traits may be constrained by size‐number trade‐offs, our results suggest that phenotypic variation in larval size may be an ecologically important source of variability in population dynamics through effects on larval survival and recruitment to benthic populations.