Crop-wild hybrids and weed beets are the main source of agronomic concern for sugar beet production all over Europe. In order to understand the dynamics of crop-wild interactions and the evolution of ...weediness in Beta vulgaris, we investigated genetic features of bolting individuals occurring at a local scale, i.e. within two sugar beet fields of the French northern area of sugar beet production. By analysing ploidy level, mitochondrial DNA and microsatellite polymorphism, the genetic diversity and the genetic relationships among three different classes of individuals (variety, in-row and out-row weed-beets) from a given field were examined. Such genetic analyses provide a unique opportunity to obtain evidence for the weeds origin and the evolutionary hypotheses previously stated. All the individuals shared in common the Svulg mitochondrial haplotype, and thus a common maternal origin. Conversely, the large genetic diversity at microsatellite loci highlighted the large diversity of the pollinator plants (cultivated and wild plants) during the-seed production process, as well as during the further evolution of weed beets in the sugar production area.
Using Pectinaria koreni as a biological model of larval dispersal, we coupled the analysis of differently evolving genetic markers (mitochondrial cytochrome oxidase I and four microsatellite loci) to ...hydrodynamic modeling of larval transport in the English Channel. To determine the influence of historical and contemporary processes on the genetic structure of our study populations, genetic relationships between English Channel, Irish Sea, and southern North Sea populations were assessed in relation to the long-term pattern of marine currents and to postglacial colonization pathways. Although significant, low level of overall nuclear genetic differentiation was best explained by the recent origin of populations within the study area and the retention of ancestral polymorphism. Both genetic data sets suggest that two ancestral gene pools contributed to the origin of our study populations, and secondary contacts occurred in the English Channel and southern North Sea as a result of two migration routes around the British Isles. Although Irish Sea and Belgium populations appeared more recently connected, populations of the eastern English Channel were more isolated. English Channel patterns of connectivity indicated high dispersal and gene flow along the French coast, from Normandy to the southern North Sea. Despite significant genetic differentiation between both coasts, migration model selection favored cross-channel gene flow and long-distance migration following the coastlines. Our results highlight the influence of postglacial colonization on genetic patterns in the English Channel, and indicate that contemporary mesoscale connectivity inferred by hydrodynamic modeling cannot, alone, explain the present genetic structure of populations in this area.
Human-mediated biological invasions are known to threaten biodiversity and are often the cause of economic problems, mainly via interspecific interactions with commercially valuable indigenous ...species. The hermaphroditic gastropodCrepidula fornicata(L.) is a successful marine invader of European coasts. In France, it was first recorded in the 1940s and now proliferates, competing with cultured and fished bivalves. To analyze the patterns of spread and the genetic architecture of the populations of this invader, 13 populations, 12 French and 1 native (American) (N = 660) were sexed and analyzed using 8 polymorphic enzyme loci. The majority of the populations showed balanced sex ratios. A high level of genetic diversity was detected in the French populations, contrary to the usual pattern of founder effect frequently reported for invaders. Moreover, most of the introduced populations were shown to be in migration-drift equilibrium. Thus, our results suggest that, in its introduced range,C. fornicatahas stable populations and behaves genetically and demographically in the same way that it does over its native range. The pattern among French populations suggests that the introduction process was complex, and thatC. fornicatafrom France derives from several genetically diverse, but poorly differentiated, source populations. Finally, this dataset also showed that the effects of shell-farmer-mediated transport between bays are only detectable at some specific localities. On the other hand, there was a good fit between patterns of genetic differentiation and the major hydrodynamic features along the French coasts, strongly suggesting that larval dispersal plays an important role in the spread ofC. fornicatain Europe.
Human‐driven translocations of species have diverse evolutionary consequences such as promoting hybridization between previously geographically isolated taxa. This is well illustrated by the solitary ...tunicate, Ciona robusta, native to the North East Pacific and introduced in the North East Atlantic. It is now co‐occurring with its congener Ciona intestinalis in the English Channel, and C. roulei in the Mediterranean Sea. Despite their long allopatric divergence, first and second generation crosses showed a high hybridization success between the introduced and native taxa in the laboratory. However, previous genetic studies failed to provide evidence of recent hybridization between C. robusta and C. intestinalis in the wild. Using SNPs obtained from ddRAD‐sequencing of 397 individuals from 26 populations, we further explored the genome‐wide population structure of the native Ciona taxa. We first confirmed results documented in previous studies, notably (i) a chaotic genetic structure at regional scale, and (ii) a high genetic similarity between C. roulei and C. intestinalis, which is calling for further taxonomic investigation. More importantly, and unexpectedly, we also observed a genomic hotspot of long introgressed C. robusta tracts into C. intestinalis genomes at several locations of their contact zone. Both the genomic architecture of introgression, restricted to a 1.5 Mb region of chromosome 5, and its absence in allopatric populations suggest introgression is recent and occurred after the introduction of the non‐native species. Overall, our study shows that anthropogenic hybridization can be effective in promoting introgression breakthroughs between species at a late stage of the speciation continuum.
A goal of phylogeography is to relate patterns of genetic differentiation to potential historical geographic isolating events. Quaternary glaciations, particularly the one culminating in the Last ...Glacial Maximum ~21 ka (thousands of years ago), greatly affected the distributions and population sizes of temperate marine species as their ranges retreated southward to escape ice sheets. Traditional genetic models of glacial refugia and routes of recolonization include these predictions: low genetic deversity in formerly glaciated areas, with a small number of alleles/haplotypes dominating disproportionately large areas, and high diversity including "private" alleles in glacial refugia. In the Northern Hemisphere, low diversity in the north and high diversity in the south are expected. This simple model does not account for the possibility of populations surviving in relatively small northern periglacial refugia. If these periglacial populations experienced extreme bottlenecks, they could have the low genetic diversity expected in recolonized areas with no refugia, but should have more endemic diversity (private alleles) than recently recolonized areas. This review examines evidence of putative glacial refugia for eight benthic marine taxa in the temperate North Atlantic. All data sets were reanalyzed to allow direct comparisons between geographic patterns of genetic diversity and distribution of particular clades and haplotypes including private alleles. We contend that for marine organisms the genetic signatures of northern periglacial and southern refugia can be distinguished from one another. There is evidence for several periglacial refugia in northern latitudes, giving credence to recent climatic reconstructions with less extensive glaciation.
The success of an exotic species depends notably on its capacity to initiate a new population from a few individuals, to survive genetic bottlenecks and to adapt locally. Species with multiple ...reproductive strategies (e.g. mixed-mating system with both self- and cross-fertilization) can be efficient colonizers. Herein we focus on Corella eumyota, an exotic ascidian that has rapidly invaded English Channel coasts in recent years. Interestingly, this brooding hermaphroditic ascidian is capable of self-fertilization in the laboratory. We developed 12 microsatellite markers from an enriched library of genomic DNA to investigate the level of inbreeding and selfing in two putatively native populations (South Africa, N = 34, and New Zealand, N = 28) and to examine if founder effects were possibly associated with its recent introduction in two French populations (Perros-Guirec, N = 22 and Brest; N = 25). Genetic polymorphism was very low in both native populations (i.e. less than 60% of the loci were polymorphic) and even lower in the introduced populations, one of which was monomorphic at all loci, suggesting a recent bottleneck. Fis and a new method based on multi-locus heterozygosity were used to provide estimates of inbreeding. A high selfing rate was inferred in the South Africa population with both methods (s = 0.90), whereas in the other native population (New Zealand) a lower but significant estimate of selfing rate (s = 0.29) was obtained with the multi-locus method. This variability of population selfing rate might be explained by a mixed-mating system, allowing C. eumyota to reproduce through inbreeding and outbreeding according to mating possibilities; this trait may have favoured the rapid establishment of new populations in Europe.
The rate of introduction of exotic marine species has dramatically increased during the 19th and 20th centuries. Exemplifying this trend, the marine gastropod
Ocinebrellus inornatus was first ...detected outside its native range in 1924 on the American Pacific coast, then in 1995 on the French Atlantic coast. To determine the origin of the French populations of this invasive species, we compared a French population with populations collected in Asia—the native range—and with a population collected in the United States. Analyses of mitochondrial DNA and allozyme polymorphism revealed that the French and American populations were closely related and substantially differentiated from the Asian populations. According to our results, the most likely scenario is that the source population of the French Atlantic coast populations was located in the United States. Indeed, taken altogether, the genetic structure of Asian populations, the time lag separating the introduction on the American Pacific coast from the introduction on the French Atlantic coast and the high level of genetic diversity in the two introduced areas (indicating an absence of major founder events) are hardly compatible with a scenario in which French population resulting only from primary introduction events from the native area. Finally, although similar, the French and American populations were not identical. Thus, even if the main source population of the French populations was located in the United States, the genetic structure of French populations may have been modified by cryptic and recurrent introduction events directly from Asia.
Alvinella pompejana lives on the top of chimneys at deep-sea hydrothermal vents of the East Pacific Rise. It is thought to be one of the most thermotolerant and eurythermal metazoans. Our ...experimental approach combines methods of population genetics and biochemistry, considering temperature as a potential selective factor. Phosphoglucomutase (Pgm-1 locus) is one of the most polymorphic loci of A. pompejana and exhibits four alleles, from which alleles 90 and 100 dominate with frequencies of approximately 0.5 in populations. Results from previous studies suggested that allele 90 might be more thermostable than allele 100. Significant genetic differentiation was found by comparing contrasted microhabitats, especially the young, still hot, versus older and colder chimneys, with allele 90 being at highest frequency on young chimneys. Moreover the frequency of allele 90 was positively correlated with mean temperature at the opening of Alvinella tubes. In parallel, thermostability and thermal optimum experiments demonstrated that allele 90 is more thermostable and more active at higher temperatures than allele 100. This dataset supports an additive model of diversifying selection in which allele 90 is favoured on young hot chimneys but counterbalanced over the whole metapopulation by the dynamics of the vent ecosystem.
Worldwide marine invaders, such as the brown alga Undaria pinnatifida, offer challenging models for unraveling the apparent paradox of sustainable settlement of exotic species over a large spectrum ...of environments. Two intergenic noncoding mitochondrial loci were found to be highly informative at the within-species level. Twenty-five haplotypes were found over the whole dataset (333 base pairs, 524 individuals, and 24 populations). The native range showed striking population genetic structure stemming from low diversity within and high differentiation among populations, a pattern not observed in the introduced range of this seaweed. Contrary to classical expectations of founding effects associated with accidental introduction of exotic species, most of the introduced populations showed high genetic diversity. At the regional scale, genetic diversity and sequence divergence showed contrasting patterns in the two main areas of introduction (Europe and Australasia), suggesting different processes of introduction in the two regions. Gene genealogy analyses point to aquaculture as a major vector of introduction and spread in Europe but implicate maritime traffic in promoting recurrent migration events from the native range to Australasia. The multiplicity of processes and genetic signatures associated with the successful invasion confirms that multiple facets of global change, e.g., aquaculture practices, alteration of habitats, and increased traffic, act in synergy at the worldwide level, facilitating successful pandemic introductions.
Exon Primed Intron Crossing (EPIC) markers provide molecular tools that are susceptible to be variable within species while remaining amplifiable by PCR using potentially universal primers. In this ...study we tested the possibility of obtaining PCR products from 50 EPIC markers on 23 species belonging to seven different phyla (Porifera, Cnidaria, Arthropoda, Nematoda, Mollusca, Annelida, Echinodermata) using 70 new primer pairs. A previous study had identified and tested those loci in a dozen species, including another phylum, Urochordata (Chenuil et al., 2010). Results were contrasted among species. The best results were achieved with the oyster (Mollusca) where 28 loci provided amplicons susceptible to contain an intron according to their size. This was however not the case with the other mollusk Crepidula fornicata, which seems to have undergone a reduction in intron number or intron size. In the Porifera, 13 loci appeared susceptible to contain an intron, a surprisingly high number for this phylum considering its phylogenetic distance with genomic data used to design the primers. For two cnidarian species, numerous loci (24) were obtained. Ecdysozoan phyla (arthropods and nematodes) proved less successful than others as expected considering reports of their rapid rate of genome evolution and the worst results were obtained for several arthropods. Some general patterns among phyla arose, and we discuss how the results of this EPIC survey may give new insights into genome evolution of the study species. This work confirms that this set of EPIC loci provides an easy-to-use toolbox to identify genetic markers potentially useful for population genetics, phylogeography or phylogenetic studies for a large panel of metazoan species. We then argue that obtaining diploid sequence genotypes for these loci became simple and affordable owing to Next-Generation Sequencing development. Species surveyed in this study belong to several genera (Acanthaster, Alvinocaris, Aplysina, Aurelia, Crepidula, Eunicella, Hediste, Hemimysis, Litoditis, Lophelia, Mesopodopsis, Mya, Ophiocten, Ophioderma, Ostrea, Pelagia, Platynereis, Rhizostoma, Rimicaris), two of them, belonging to the family Vesicomydae and Eunicidae, could not be determined at the genus level.
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