Self‐recruitment and sweepstakes reproduction amid extensive gene flow in a coral‐reef fish

Identifying patterns of larval dispersal within marine metapopulations is vital for effective fisheries management, appropriate marine reserve design, and conservation efforts. We employed genetic markers (microsatellites) to determine dispersal patterns in bicolour damselfish (Pomacentridae: Stegastes partitus). Tissue samples of 751 fish were collected in 2004 and 2005 from 11 sites encompassing the Exuma Sound, Bahamas. Bayesian parentage analysis identified two parent–offspring pairs, which is remarkable given the large population sizes and 28 day pelagic larval duration of bicolour damselfish. The two parent–offspring pairs directly documented self‐recruitment at the two northern‐most sites, one of which is a long‐established marine reserve. Principal coordinates analyses of pair‐wise relatedness values further indicated that self‐recruitment was common in all sampled populations. Nevertheless, measures of genetic differentiation (F_ST) and results from assignment methods suggested high levels of gene flow among populations. Comparisons of heterozygosity and relatedness among samples of adults and recruits indicated spatially and temporally independent sweepstakes events, whereby only a subset of adults successfully contribute to subsequent generations. These results indicate that self‐recruitment and sweepstakes reproduction are the predominant, ecologically‐relevant processes that shape patterns of larval dispersal in this system.     

Historical human activities reshape evolutionary trajectories across both native and introduced ranges

The same vectors that introduce species to new ranges could move them among native populations, but how human‐mediated dispersal impacts native ranges has been difficult to address because human‐mediated dispersal and natural dispersal can simultaneously shape patterns of gene flow. Here, we disentangle human‐mediated dispersal from natural dispersal by exploiting a system where the primary vector was once extensive but has since ceased. From 10th to 19th Centuries, ships in the North Atlantic exchanged sediments dredged from the intertidal for ballast, which ended when seawater ballast tanks were adopted. We investigate genetic patterns from RADseq‐derived SNPs in the amphipod Corophium volutator (n = 121; 4,870 SNPs) and the annelid Hediste diversicolor (n = 78; 3,820 SNPs), which were introduced from Europe to North America, have limited natural dispersal capabilities, are abundant in intertidal sediments, but not commonly found in modern water ballast tanks. We detect similar levels of genetic subdivision among introduced North American populations and among native European populations. Phylogenetic networks and clustering analyses reveal population structure between sites, a high degree of phylogenetic reticulation within ranges, and phylogenetic splits between European and North American populations. These patterns are inconsistent with phylogeographic structure expected to arise from natural dispersal alone, suggesting human activity eroded ancestral phylogeographic structure between native populations, but was insufficient to overcome divergent processes between naturalized populations and their sources. Our results suggest human activity may alter species' evolutionary trajectories on a broad geographic scale via regional homogenization and global diversification, in some cases precluding historical inference from genetic data.     

Balearic insular isolation and large continental spread framed the phylogeography of the western Mediterranean Cheirolophus intybaceus s.l. (Asteraceae)

Recent Quaternary geological and climate events have shaped the evolutionary histories of plant species in the Mediterranean basin, one of the most important hotspots of biodiversity. Genetic analyses of the western Mediterranean Cheirolophus intybaceus s.l. (Asteraceae) based on AFLP were conducted to establish the relationships between its close species and populations, to reconstruct the phylogeography of the group and to analyse potential unidirectional versus bidirectional dispersals between the Ibero‐Provençal belt and the Balearic Islands. AFLP data revealed two main genetic groups, one constituted by the Balearic populations and Garraf (NE Iberia) and the other formed by the remaining mainland populations that were further sub‐structured into two geographically separated subgroups (SE + E Iberia and NE Iberia + SW France). Genetic diversity and spatial structure analyses suggested a mid‐Pleistocene scenario for the origin of C. intybaceus in southern Iberia, followed by dispersal to the north and a single colonisation event of the Balearic archipelago from the near Dianic NE Iberian area. This hypothesis was supported by paleogeographic data, which showed the existence of terrestrial connections between the continent and the islands during the Middle–Late Pleistocene marine regressions, whereas the more recent single back‐colonisation of the mainland from Mallorca might be explained by several hypotheses, such as long‐distance dispersal mediated by migratory marine birds or sea currents.     

Probability of successful larval dispersal declines fivefold over 1 km in a coral reef fish

A central question of marine ecology is, how far do larvae disperse? Coupled biophysical models predict that the probability of successful dispersal declines as a function of distance between populations. Estimates of genetic isolation-by-distance and self-recruitment provide indirect support for this prediction. Here, we conduct the first direct test of this prediction, using data from the well-studied system of clown anemonefish (Amphiprion percula) at Kimbe Island, in Papua New Guinea. Amphiprion percula live in small breeding groups that inhabit sea anemones. These groups can be thought of as populations within a metapopulation. We use the x- and y-coordinates of each anemone to determine the expected distribution of dispersal distances (the distribution of distances between each and every population in the metapopulation). We use parentage analyses to trace recruits back to parents and determine the observed distribution of dispersal distances. Then, we employ a logistic model to (i) compare the observed and expected dispersal distance distributions and (ii) determine the relationship between the probability of successful dispersal and the distance between populations. The observed and expected dispersal distance distributions are significantly different (p < 0.0001). Remarkably, the probability of successful dispersal between populations decreases fivefold over 1 km. This study provides a framework for quantitative investigations of larval dispersal that can be applied to other species. Further, the approach facilitates testing biological and physical hypotheses for the factors influencing larval dispersal in unison, which will advance our understanding of marine population connectivity.     

Similarity in temporal variation in sex‐biased dispersal over short and long distances in the dark‐eyed junco,Junco hyemalis

Patterns of sex‐biased dispersal (SBD) are typically consistent within taxa, for example female‐biased in birds and male‐biased in mammals, leading to theories about the evolutionary pressures that lead to SBD. However, generalizations about the evolution of sex biases tend to overlook that dispersal is mediated by ecological factors that vary over time. We examined potential temporal variation in between‐ and within‐population dispersal over an 11‐year period in a bird, the dark‐eyed junco (Junco hyemalis). We measured between‐population dispersal patterns using genetic assignment indices and found yearly variation in which sex was more likely to have immigrated. When we measured within‐population spatial genetic structure and mark–recapture dispersal distances, we typically found yearly SBD patterns that mirrored between‐population dispersal, indicating common eco‐evolutionary causes despite expected differences due to the scale of dispersal. However, in years without detectable between‐population sex biases, we found genetic similarity between nearby males within our population. This suggests that, in certain circumstances, ecological pressures may act on within‐population dispersal without affecting dispersal between populations. Alternatively, current analytical tools may be better able to detect within‐population SBD. Future work will investigate potential causes of the observed temporal variation in dispersal patterns and whether they have greater effects on within‐population dispersal.     

Microsatellite DNA markers for analysis of population structure in the sea urchin Centrostephanus rodgersii

We describe the development of 13 variable microsatellites developed to investigate population structure and dispersal in the sea urchin Centrostephanus rodgersii. This species is the dominant grazing herbivore in southeast Australian coastal waters and has the ability to modify benthic community structure. The microsatellites we identified showed a range of allele numbers (4–21) and expected heterozygosity (0.32–0.91) in two sampled populations. Contrary to previous findings in free‐spawning marine invertebrates, genotype proportions in neither population deviated significantly from Hardy–Weinberg expectations.     

Fine‐scale patterns of genetic divergence within and between morphologically variable subspecies of the sea urchin Heliocidaris erythrogramma (Echinometridae)

The spatial scale over which genetic divergences occur between populations and the extent that they are paralleled by morphological differences can vary greatly among marine species. In the present study, we use a hierarchical spatial design to investigate genetic structure in Heliocidaris erythrogramma occurring on near shore limestone reefs in Western Australia. These reefs are inhabited by two distinct subspecies: the thick‐spined Heliocidaris erythrogramma armigera and the thin‐spined Heliocidaris erythrogramma erythrogramma, each of which also have distinct colour patterns. In addition to pronounced morphological variation, H. erythrogramma exhibits a relatively short (3–4 days) planktonic phase before settlement and metamorphosis, which limits their capacity for dispersal. We used microsatellite markers to determine whether patterns of genetic structure were influenced more by morphological or life history limitations to dispersal. Both individual and population‐level analyses found significant genetic differentiation between subspecies, which was independent of geographical distance. Genetic diversity was considerably lower within H. e. erythrogramma than within H. e. armigera and genetic divergence was four‐fold greater between subspecies than among populations within subspecies. This pattern was consistent even at fine spatial scales (< 5 km). We did detect some evidence of gene flow between the subspecies; however, it appears to be highly restricted. Within subspecies, genetic structure was more clearly driven by dispersal capacity, although weak patterns of isolation‐by‐distance suggest that there may be other factors limiting gene exchange between populations. Our results show that spatial patterns of genetic structure in Western Australian H. erythrogramma is influenced by a range of factors but is primarily correlated with the distribution of morphologically distinct subspecies. This suggests the presence of reproductive barriers to gene exchange between them and demonstrates that morphological variation can be a good predictor of genetic divergence. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 578–592.     

Phenological match drives pollen‐mediated gene flow in a temporally dimorphic tree

• Variation in flowering phenology is common in natural populations, and is expected to be, together with inter‐mate distance, an important driver of effective pollen dispersal. In populations composed of plants with temporally separated sexual phases (i.e. dichogamous or heterodichogamous populations), pollen‐mediated gene flow is assumed to reflect phenological overlap between complementary sexual phases. In this study, we conducted paternity analyses to test this hypothesis in the temporally dimorphic tree Acer opalus.
• We performed spatially explicit analyses based on categorical and fractional paternity assignment, and included tree size, pair‐wise genetic relatedness and morph type as additional predictors. Because differences between morphs in flowering phenology may also influence pollination distances, we modelled separate pollen dispersal kernels for the two morphs.
• Extended phenological overlap between male and female phases (mainly associated with inter‐morph crosses) resulted in higher siring success after accounting for the effects of genetic relatedness, morph type and tree size, while reduced phenological overlap (mainly associated with intra‐morph crosses) resulted in longer pollination distances achieved. Siring success also increased in larger trees.
• Mating patterns could not be predicted by phenology alone. However, as heterogeneity in flowering phenology was the single morph‐specific predictor of siring success, it is expected to be key in maintaining the temporal dimorphism in A. opalus, by promoting not only a prevalent pattern of inter‐morph mating, but also long‐distance pollination resulting from intra‐morph mating events.

     

Biased dispersal of Metrioptera bicolor,a wing dimorphic bush‐cricket

In the highly fragmented landscape of central Europe, dispersal is of particular importance as it determines the long‐term survival of animal populations. Dispersal not only secures the recolonization of patches where populations went extinct, it may also rescue small populations and thus prevent local extinction events. As dispersal involves different individual fitness costs, the decision to disperse should not be random but context‐dependent and often will be biased toward a certain group of individuals (e.g., sex‐ and wing morph‐biased dispersal). Although biased dispersal has far‐reaching consequences for animal populations, immediate studies of sex‐ and wing morph‐biased dispersal in orthopterans are very rare. Here, we used a combined approach of morphological and genetic analyses to investigate biased dispersal of Metrioptera bicolor, a wing dimorphic bush‐cricket. Our results clearly show wing morph‐biased dispersal for both sexes of M. bicolor. In addition, we found sex‐biased dispersal for macropterous individuals, but not for micropters. Both, morphological and genetic data, favor macropterous males as dispersal unit of this bush‐cricket species. To get an idea of the flight ability of M. bicolor, we compared our morphological data with that of Locusta migratoria and Schistocerca gregaria, which are very good flyers. Based on our morphological data, we suggest a good flight ability for macropters of M. bicolor, although flying individuals of this species are seldom observed.     

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.     

Population structure and dispersal of the coral‐excavating sponge Cliona delitrix

Some excavating sponges of the genus Cliona compete with live reef corals, often killing and bioeroding entire colonies. Important aspects affecting distribution of these species, such as dispersal capability and population structure, remain largely unknown. Thus, the aim of this study was to determine levels of genetic connectivity and dispersal of Cliona delitrix across the Greater Caribbean (Caribbean Sea, Bahamas and Florida), to understand current patterns and possible future trends in their distribution and effects on coral reefs. Using ten species‐specific microsatellite markers, we found high levels of genetic differentiation between six genetically distinct populations: one in the Atlantic (Florida‐Bahamas), one specific to Florida and four in the South Caribbean Sea. In Florida, two independent breeding populations are likely separated by depth. Gene flow and ecological dispersal occur among other populations in the Florida reef tract, and between some Florida locations and the Bahamas. Similarly, gene flow occurs between populations in the South Caribbean Sea, but appears restricted between the Caribbean Sea and the Atlantic (Florida‐Bahamas). Dispersal of C. delitrix was farther than expected for a marine sponge and favoured in areas where currents are strong enough to transport sponge eggs or larvae over longer distances. Our results support the influence of ocean current patterns on genetic connectivity, and constitute a baseline to monitor future C. delitrix trends under climate change.     

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.     

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.     

Boomeranging around Australia: Historical biogeography and population genomics of the anti‐equatorial fish Microcanthus strigatus (Teleostei: Microcanthidae)

The geographic distributions of marine fishes have been shaped by ancient vicariance and ongoing dispersal events. Some species exhibit anti‐equatorial distributions, inhabiting temperate regions on both sides of the tropics while being absent from equatorial latitudes. The perciform fish Microcanthus strigatus (the stripey) exhibits such a distribution with disjunct populations occurring in East Asia, Hawaii, Western Australia, and the southwest Pacific. Here, we examine the historical biogeography and evolutionary history of M. strigatus, based on more than 80 specimens sampled from the four major populations. We analysed 36 morphological characters, three mitochondrial markers, and two sets of 7,120 and 12,771 single‐nucleotide polymorphisms from the nuclear genome. Our results suggest that M. strigatus represents a cryptic species complex comprising at least two genetically distinct populations worthy of species‐level recognition, with one population exhibiting strong genetic structuring but with intermittent, historical gene flow. We provide evidence for a southwest Pacific origin for the ancestral Microcanthus and explain how past connectivity between these regions might have given rise to the relationships observed in present‐day marine fauna. Our ancestral range reconstructions and molecular‐clock analyses support a southwest Pacific centre of origin for Microcanthus, with subsequent colonization of Western Australia through the Bass Strait followed by transequatorial dispersals to the Northern Hemisphere during the Pleistocene. Our results detail an anti‐tropical dispersal pattern that is highly unusual and previously undocumented, thereby emphasizing the importance of integrative systematics in the evaluation of widespread species.     

Higher investment in flight morphology does not trade off with fecundity estimates in a poleward range‐expanding damselfly

1. Evolutionary increases in dispersal‐related traits are frequently documented during range expansions. Investment in flight‐related traits is energetically costly and a trade‐off with fecundity may be expected during range expansion. 2. However, in contrast to wing‐dimorphic species, this trade‐off is not general in wing‐monomorphic species. In the absence of a dispersal‐‐fecundity trade‐off, an increased investment in clutch size at the expansion front is expected possibly at a cost of reduced offspring size. 3. The study evaluated investment in female flight morphology and fecundity‐related traits (clutch size, hatchling size) and potential trade‐offs among these traits in replicated populations of the poleward range‐expanding damselfly Coenagrion scitulum. 4. Females at the expansion front had a higher relative thorax length, indicating an increased investment in flight; this can be explained by spatial sorting of dispersal ability or in situ natural selection at the expansion front. Edge females produced larger hatchlings, however, this pattern was totally driven by the population‐specific thermal larval regimes and could not be attributed to the range expansion per se. By contrast, clutch sizes did not differ between core and edge populations. There was no signal of a dispersal–fecundity trade‐off either for a trade‐off between clutch size and hatchling size. 5. These results indicate that evolution of a higher dispersal ability at the expansion front of C. scitulum does not trade off with investment in fecundity, hence a dispersal–fecundity trade‐off is unlikely to slow down range expansion of this species.     

Scale‐dependent post‐establishment spread and genetic diversity in an invading mollusc in South America

Aims Our study aimed to characterize the dispersal dynamics and population genetic structure of the introduced golden mussel Limnoperna fortunei throughout its invaded range in South America and to determine how different dispersal methods, that is, human‐mediated dispersal and downstream natural dispersal, contribute to genetic variation among populations. Location Paraná–Uruguay–Río de la Plata watershed in Argentina, Brazil, Paraguay and Uruguay. Methods We performed genetic analyses based on a comprehensive sampling strategy encompassing 22 populations (N = 712) throughout the invaded range in South America, using the mitochondrial cytochrome c oxidase subunit I (COI) gene and eight polymorphic nuclear microsatellites. We employed both population genetics and phylogenetic analyses to clarify the dispersal dynamics and population genetic structure. Results We detected relatively high genetic differentiation between populations (F_ST = ?0.041 to 0.111 for COI, ?0.060 to 0.108 for microsatellites) at both fine and large geographical scales. Bayesian clustering and three‐dimensional factorial correspondence analyses consistently revealed two genetically distinct clusters, highlighting genetic discontinuities in the invaded range. Results of all genetic analyses suggest ship‐mediated ‘jump’ dispersal as the dominant mode of spread of golden mussels in South America, while downstream natural dispersal has had limited effects on contemporary genetic patterns. Main conclusions Our study provides new evidence that post‐establishment dispersal dynamics and genetic patterns vary across geographical scales. While ship‐mediated ‘jump’ dispersal dominates post‐establishment spread of golden mussels in South America, once colonies become established in upstream locations, larvae produced may be advected downstream to infill patchy distributions. Moreover, genetic structuring at fine geographical scales, especially within the same drainages, suggests a further detailed understanding of dynamics of larval dispersal and settlement in different water systems. Knowledge of the mechanisms by which post‐establishment spread occurs can, in some cases, be used to limit dispersal of golden mussels and other introduced species.     

Sex‐specific graphs: Relating group‐specific topology to demographic and landscape data

Sex‐specific genetic structure is a commonly observed pattern among vertebrate species. Facing differential selective pressures, individuals may adopt sex‐specific life history traits that ultimately shape genetic variation among populations. Although differential dispersal dynamics are commonly detected in the literature, few studies have used genetic structure to investigate sex‐specific functional connectivity. The recent use of graph theoretic approaches in landscape genetics has demonstrated network capacities to describe complex system behaviours where network topology represents genetic interaction among subunits. Here, we partition the overall genetic structure into sex‐specific graphs, revealing different male and female dispersal dynamics of a fisher (Pekania [Martes] pennanti) metapopulation in southern Ontario. Our analyses based on network topologies supported the hypothesis of male‐biased dispersal. Furthermore, we demonstrated that the effect of the landscape, identified at the population level, could be partitioned among sex‐specific strata. We found that female connectivity was negatively correlated with snow depth, whereas connectivity among males was not. Our findings underscore the potential of conducting sex‐specific analysis by identifying landscape elements or configuration that differentially promotes or impedes functional connectivity between sexes, revealing processes that may otherwise remain cryptic. We propose that the sex‐specific graph approach would be applicable to other vagile species where differential sex‐specific processes are expected to occur.     

Genetic differentiation and reduced genetic diversity at the northern range edge of two species with different dispersal modes

Theory predicts that genetic variation should be reduced at range margins, but empirical support is equivocal. Here, we used genotyping‐by‐sequencing technology to investigate genetic variation in central and marginal populations of two species in the marine gastropod genus Crepidula. These two species have different development and dispersal types and might therefore show different spatial patterns of genetic variation. Both allelic richness and the proportion of private alleles were highest in the most central populations of both species, and lower at the margin. The species with low dispersal, Crepidula convexa, showed high degrees of structure throughout the range that conform to the pattern found in previous studies using other molecular markers. The northernmost populations of the high‐dispersing species, Crepidula fornicata, are distinct from more central populations, although this species has been previously observed to have little genetic structure over much of its range. Although genetic diversity was significantly lower at the range margin, the absolute reduction in diversity observed with these genomewide markers was slight, and it is not yet known whether there are functional consequences for the marginal populations.     

The interplay of dispersal limitation,rivers, and historical events shapes the genetic structure of an Amazonian frog

Disentangling the impact of landscape features such as rivers and historical events on dispersal is a challenging but necessary task to gain a comprehensive picture of the evolution of diverse biota such as that found in Amazonia. Adenomera andreae, a small, territorial, terrestrial frog species of the Amazonian forest represents a good model for such studies. We combined cytochrome b sequences with 12 microsatellites to investigate the genetic structure at two contrasted spatial scales in French Guiana: along a ～6‐km transect, to evaluate dispersal ability, and between paired bank populations along a ～65‐km stretch of the Approuague river, to test the effect of rivers as barriers to dispersal. We observed significant spatial genetic structure between individuals at a remarkably small geographical scale, and conclude that the species has a restricted dispersal ability that is probably tied to its life‐history traits. Mitochondrial and microsatellite data also indicate a high level of differentiation among populations on opposite banks of the river, and, in some cases, among populations on the same riverbank. These results suggest that the observed population structure in A. andreae is the result of restricted dispersal abilities combined with the action of rivers and Quaternary population isolation. Given that Amazonia hosts a great portion of anurans, as well as other small vertebrates, that display life‐history traits comparable with A. andreae, we argue that our analyses provide new insights into the complex interactions among evolutionary processes shaping Amazonian biodiversity. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 356–373.     

Linking DNA sequences to morphology: cryptic diversity and population genetic structure in the marine nematode Thoracostoma trachygaster (Nematoda,Leptosomatidae)

Derycke, S., De Ley, P., De Ley, I.T., Holovachov, O., Rigaux, A. & Moens, T. (2010). Linking DNA sequences to morphology: cryptic diversity and population genetic structure in the marine nematode Thoracostoma trachygaster (Nematoda, Leptosomatidae).—Zoologica Scripta, 39, 276–289. Recent taxonomic and population genetic studies have revealed the presence of substantial cryptic diversity through sequence analysis of nematode morphospecies classified in different major clades. Correct interpretations of intra‐ and interspecific genetic variation require certainty about the conspecificity of the sequenced specimens, which in turn must depend on appropriate protocols with built‐in verifiability procedures. In this study, we performed a population genetic study in the free‐living marine nematode Thoracostoma trachygaster, a member of one of the earliest major clades to diverge in nematode phylogeny. We collected 367 nematodes from 11 populations located in the Californian Bight, all of which were video captured before DNA extraction to document and verify their individual morphology. Sequences for the cytochrome c oxidase subunit 1 (COI), D2D3 and 18S genes showed eight deeply divergent clades, and using a reverse taxonomy approach, six of these clades proved to be other morphospecies than T. trachygaster. Phylogenetic analyses of COI, internal transcribed spacer and D2D3 showed evidence for two sympatrically distributed cryptic species within the morphospecies T. trachygaster. Population genetic analyses of the most widespread cryptic species showed a moderate genetic structuring (Φ_ST = 0.28), and 18% of this genetic variation was caused by differences between populations north and south of Point Conception. Within the southern Californian Bight, some genetic differentiation could be attributed to differences between populations north and south of Malibu, supporting the idea of a barrier to gene flow near Los Angeles region. The results for T. trachygaster support the contention that species diversity within free‐living nematodes is underestimated, and that dispersal of marine nematodes from tidal environments associated with kelp holdfasts is substantial at scales of a few 100 km.