Intraspecific Genetic Admixture and the Morphological Diversification of an Estuarine Fish Population Complex (original) (raw)
Related papers
Journal of Fish Biology, 1991
Larvae of anadromous rainbow smelt originating in various spawning tributaries are retained in the St Lawrence estuary. We proposed that these smelt represent one population genetically differentiated from adjacent populations characterized by geographically distinct larval retention areas. We also analysed four landlocked populations to evaluate the phylogenetic basis of dwarf and normal-sized phenotypes and their relation to anadromous smelt. A phylogenetic distinction was revealed between anadromous and landlocked smelt, with only one of the two mtDNA phylogenetic groups of anadromous fish observed among landlocked smelt. Significant geographical heterogeneity in the distribution of mtDNA genotypes was observed among landlocked smelt, suggesting that dwarfism in smelt may be polyphyletic in origin. St Lawrence smelt were genetically identical but distinct from adjacent populations, supporting the proposition that population genetic structure reflects the number of larval retention zones rather than spawning sites.
Canadian Journal of Fisheries and Aquatic Sciences, 1998
Ecological isolation through resource partitioning is invoked as a major factor for explaining the persistence of genetically distinct yet closely related sympatric populations. Two genetically distinct sympatric populations of anadromous rainbow smelt (Osmerus mordax) exist in the middle estuary of the St. Lawrence River. The persistence of these coexisting populations in sympatry is in conflict with current theoretical concepts predicting population richness. In the present study, we performed mtDNA PCR-RFLP analysis of 922 larvae from 33 sampling stations to test the hypothesis that the larvae belonging to the two sympatric smelt populations of the St. Lawrence middle estuary are spatially segregated and that such segregation may promote the persistence of the populations. Results clearly revealed spatial homogeneity in the relative distribution of larvae from the two populations. Consequently, they did not support our working hypothesis that larvae belonging to the two sympatric...
Molecular Ecology, 1993
Two morphologically and ecologically distinct forms of smelt, Osmerus, reside sympatrically in Lake Utopia, south-western New Brunswick, Canada. The 'normalsized' form matures at greater than 200 mm standard length, averages about 31-33 gill rakers, and spawns in lake outlets. By contrast, the 'dwarf-sized' form matures at less than 150 mm standard length, averages 34-36 gill rakers, and spawns in small streams 3-5 weeks later than the normal form. We tested whether these sympatric forms represented ecological polymorphism within a single population or two reproductively isolated demes by assaying variation within and between forms by mitochondrial DNA (mtDNA) restriction site and nuclear minisatellite DNA analyses. Analysis of smelt mtDNA with twelve restriction enzymes resolved ten composite genotypes (differing by an average 0.27% sequence divergence) which differed markedly in frequency between the forms. Net percentage sequence divergence between the forms wasO.l6%. A Wagner parsimony/ bootstrapping analysis of the restriction site presencelabsence matrix, however, suggested that there were no significant distinctions between dwarf and normal smelt based on the phylogeny of composite genotypes. Hybridization studies of genomic DNA digests with a minisatellite probe indicated both that nuclear restriction fragment differentiation and the frequency of specific fragments differed significantly between the forms. Significant genetic differentiation between the sympatric forms demonstrates that they are distinct gene pools and reproductively isolated. Our molecular evidence for reproductive isolation between dwarf and normal smelt in Lake Utopia, coupled with the persistent morphological and ecological differentiation between them, argues strongly that they are behaving as distinct species.The Lake Utopia Osmerus populations provide further illustration of the potential for rapid differentiation to the level of biological species in postglacial environments.
Genetic versus demographic stock structure of rainbow smelt in a large fragmented lake
Journal of Great Lakes Research, 2020
Identification of fish stocks plays an important role in fisheries management, but stock identification often depends on the techniques used and the management goals as much as on actual population structure. Historically, stocks were identified by place of capture, population demography and morphology, but genetic stock identification has become a standard approach. Here, we evaluate the stock structure of rainbow smelt (Osmerus mordax) in three basins of Lake Champlain separated by causeways using genotype data from six microsatellite loci and 26 years of demographic data. No genetic differences among rainbow smelt from the different basins were evident, which suggests that gene flow occurs among basins. However, length, age, and catch-per-unit-effort of rainbow smelt suggests asynchronous population dynamics in the different basins, and thus each basin may hold populations that are at least partially isolated from one another. Consequently, we conclude that while rainbow smelt in Lake Champlain consist of at least three demographic stocks they may form only a single genetic stock. Our results concur with other studies that suggest care should be taken when only a single method of stock identification is used.
Marine Ecology Progress Series, 2011
Contemporary genetic spatial structure in north temperate marine species is likely the culmination of multiple vicariant and dispersive cycles. Here we evaluate spatial genetic structure in an estuarine fish, rainbow smelt Osmerus mordax, from coastal Newfoundland, Canada, using data from both mtDNA (ND5) sequences and nuclear loci (11 microsatellites). Sequence analysis of ND5 identified a previously unrecognized genetic discontinuity between 2 hypothesized glacial clades in southeastern Newfoundland. Microsatellite based tests for directional selection identified a locus (Omo11, p < 0.001) that mirrored mtDNA clades in the geographic distribution of its 2 common alleles but did not display elevated differentiation following correction for heterozygosity. Bayesian multilocus clustering of the remaining micro satellite loci supported the presence of 2 predominant groups, for which the spatial distribution was also largely consistent with those of the mtDNA and Omo11 clades. Taken together, the similarity in microsatellite and mtDNA clines supports the hypothesis that contemporary spatial structure in smelt reflects historical landscape isolation maintained by low dispersal and selective processes producing reinforcement between diverging populations. As genetic structure in northern marine and estuarine species may be largely determined by historical glacial cycles of vicariance, contemporary estimates of connectivity should be interpreted in the context of both past and present landscape structure.
Genetic Differentiation of Three Key Anadromous Fish Populations of the Hudson River
Estuaries, 1996
Large, recreationally or commercially important populations of Atlantic sturgeon (Acipenser oxyrinchus), American shad (Alosa sapidissima), and striped bass (Morone saxatilis) occur in the Hudson River. Members of the Hudson River populations of these fishes also occur over a broad range along the Atlanti~coast where they mix with conspecifics from other anadromous populations. For management purposes, it is imperative to be able to discriminate among individual stocks so that weak stocks may be protected and harvest may be allocated equitably. Because of their sensitivity and resistance to environmentally-induced temporal variation, molecular approaches have been increasingly employed in stock identification studies. However, post-Pleistocene recolonization of the Hudson River must have occurred less than 10,000 years ago-a relatively brief period for genetic divergence among populations. We tested whether various measures of DNA variation between Hudson River populations and adjacent populations of Atlantic sturgeon, American shad, and striped bass were sufficient to discriminate among their conspecific populations. American shad populations surveyed for mtDNA variation were highly diverse genotypically, but genotypic frequencies among the populations of the Connecticut, Hudson, and Delaware rivers were statistically homogeneous (p > 0.05). In contrast, Atlantic sturgeon (surveyed for mtDNA variation) and striped bass (surveyed for mtDNA and nuclear DNA variation) populations of the Hudson River were not genotypically diverse, but they were differentiated from northern and southern populations. Our results suggest higher gene flow (and lesser homing fidelity) among American shad populations in comparison with the two other species.
Biological Journal of the Linnean Society, 2009
Vicariant geographic isolation and resource partitioning have long been independently identified as processes contributing to the morphological divergence of closely-related species. However, little is known about the extent to which vicariant history influences the adaptive ecological divergence associated with resource partitioning and trophic specialization within species. The present study thus quantified the contribution of vicariant historical genetic divergence to the adaptive contemporary morphological divergence of intraspecific feeding specialists in the Rainbow smelt (Pisces: Osmerus mordax). This species is characterized by the polyphyletic origin of two lacustrine feeding specialists originating in two intraspecific lineages associated with independent glacial refuges. The historical genetic segregation was initiated approximately 350 000 years ago, whereas the lacustrine trophic segregation arose within the past 10 000 years. Wild caught lacustrine smelt populations were grouped a priori based on known historical genetic identities (Acadian and Atlantic mitochondrial DNA clades) and contemporary feeding specializations (microphageous and macrophageous morphotypes). The present study demonstrated that independent suites of correlated morphological traits are associated with either vicariant history or contemporary feeding specializations. Second, functionally-similar feeding specialists exhibit distinct morphologies resulting largely from vicariant historical processes. Although, the evolutionary processes producing historical phenotypes remains unknown, the results obtained demonstrate how adaptive radiation associated with ecological resource partitioning and feeding specializations can be strongly influenced by intraspecific phenotypic diversification resulting from relatively recent vicariant histories.
Genetic and morphometric divergence in threespine stickleback in the Chignik catchment, Alaska
Ecology and Evolution, 2013
Divergent selection pressures induced by different environmental conditions typically lead to variation in life history, behavior, and morphology. When populations are locally adapted to their current environment, selection may limit movement into novel sites, leading to neutral and adaptive genetic divergence in allopatric populations. Subsequently, divergence can be reinforced by development of pre-or postzygotic barriers to gene flow. The threespine stickleback, Gasterosteus aculeatus, is a primarily marine fish that has invaded freshwater repeatedly in postglacial times. After invasion, the established freshwater populations typically show rapid diversification of several traits as they become reproductively isolated from their ancestral marine population. In this study, we examine the genetic and morphometric differentiation between sticklebacks living in an open system comprising a brackish water lagoon, two freshwater lakes, and connecting rivers. By applying a set of microsatellite markers, we disentangled the genetic relationship of the individuals across the diverse environments and identified two genetic populations: one associated with brackish and the other with the freshwater environments. The "brackish" sticklebacks were larger and had a different body shape than those in freshwater. However, we found evidence for upstream migration from the brackish lagoon into the freshwater environments, as fish that were genetically and morphometrically similar to the lagoon fish were found in all freshwater sampling sites. Regardless, few F1-hybrids were identified, and it therefore appears that some preand/or postzygotic barriers to gene flow rather than geographic distance are causing the divergence in this system.
Molecular Ecology, 2011
The capelin (Mallotus villosus) is a widespread marine fish species for which previous work has identified geographically distinct mtDNA clades, the frontiers of which are well within adult and larval dispersal capabilities. Here, we use AFLPs to test for the presence of nuclear gene flow among clades. In addition, we evaluate genetic structuring within one clade, the Northwest Atlantic (NWA). We found that each of the mtDNA clades corresponds with a unique nuclear DNA genetic cluster. Within the NWA clade, we detected individuals with small but significant amounts of genetic ancestry from other clades, likely due to historical introgression. Further support for historical introgression comes from analyses of variance in locus-specific differentiation, which support introgression between some clades and divergence without gene flow between others. Within the NWA, we identified two genetic clusters that correspond to sites in geographically adjacent areas. However, these clusters differ primarily at 'outlier' loci, and a genetic subdivision (K = 2) was not supported by genetic clustering programs using neutral loci. Significant neutral F ST differentiation was found only between sites that otherwise differed at outlier loci. Thus, these populations may be in the initial stages of 'isolation by adaptation'. These results suggest strong between-clade reproductive isolation despite opportunities for gene flow and support the hypothesis that selection can contribute to divergence in otherwise 'open' systems.