Genetic structure of the high dispersal Atlanto-Mediterreanean sea star Astropecten aranciacus revealed by mitochondrial DNA sequences and microsatellite loci AbstractTo investigate the impact of potential marine barriers on gene-flow in high dispersal marine invertebrates, we assessed the population genetic structure of the sea star Astropecten aranciacus. Samples were obtained from nine locations within the Atlantic and the Mediterranean Sea including populations east of the Siculo-Tunisian Strait. We obtained both DNA sequence data of the mitochondrial control region and genotype data at four microsatellite loci. Both markers were highly polymorphic and showed a great level of genetic diversity. Genetic differentiation between populations (F (ST)) was in general low, particularly for nuclear data, as is often the case in high dispersal marine invertebrates. Nevertheless, both marker sets indicated a significant genetic differentiation of the population from the island of Madeira to most other populations. Our results also demonstrate a clear pattern of isolation-by-distance supported by both mitochondrial and nuclear markers. Therefore, we conclude that larval dispersal of A. aranciacus is somewhat limited even within the basins of the Atlantic, the west Mediterranean and the east Mediterranean. Microsatellite loci further revealed genetic differentiation between the three basins; however, it is not clear whether this is truly caused by marine barriers. Genetic differentiation between basins might also be a result of isolation-by-distance allowing for any grouping to be significant as long as geographical neighbors are clustered together. Although levels of genetic differentiation were less pronounced in mirosatellite data, both datasets were coherent and revealed similar patterns of genetic structure in A. aranciacus. 1Genetic structure of the high dispersal Atlanto-Mediterreanean sea star Astropecten aranciacus revealed by mitochondrial DNA sequences and microsatellite loci Deborah E. Zulliger, Samuel Tanner, Markus Ruch and Georg Ribi AbstractTo investigate the impact of potential marine barriers on gene flow in high dispersal marine invertebrates, we assessed the population genetic structure of the sea star Astropecten aranciacus. Samples were obtained from nine locations within the Atlantic and the Mediterranean Sea including populations east of the Siculo-Tunisian Strait. We obtained both DNA sequence data of the mitochondrial control region and genotype data at four microsatellite loci. Both markers were highly polymorphic and showed a great level of genetic diversity. Genetic differentiation between populations (F ST ) was in general low, particularly for nuclear data, as is often the case in high dispersal marine invertebrates. Nevertheless, both marker sets indicated a significant genetic differentiation of the population from the island of Madeira to most other populations. Our results also demonstrate a clear pattern of isolation-by-distance supported by both mitochondrial and nuclear markers. The...

Local adaptation is one possible response of organisms to survive in a changing environment. However, the genetic basis of adaptation is not well understood, especially in nonmodel species. To infer recurrent patterns of local adaptation, we investigated whether the same putative adaptive loci reoccur in related species. We performed genome scans using amplified fragment length polymorphism (AFLP) markers on populations of five Alpine Brassicaceae species sampled across a wide range of environmental conditions. To identify markers potentially under directional selection, we performed outlier and environmental association analyses using a set of topo-climatic variables available as GIS layers. Several AFLP loci showed signatures of adaptation, of which one, found in Cardamine resedifolia (Cre_P1_212.5), was associated with precipitation. We sequence-characterized this candidate locus and genotyped single nucleotide polymorphisms (SNPs) found within this locus for all species. Testing for environmental associations of SNPs revealed the same association of this locus in Arabis alpina but not in other study species. Cumulative statistical evidence indicates that locus Cre_P1_212.5 is environmentally relevant or is linked to a gene under selection in our study range. Furthermore, the locus shows an association to the same potentially selective factor in at least one other related species. These findings help to identify trends in plant adaptation in Alpine ecosystems in response to particular environmental parameters.

With over 150 described species, Astropecten Gray (Paxillosida:Astropectinidae) is one of the most species-rich genera among sea stars. This diversity is remarkable, because most species of Astropecten have a long-lived planktotrophic larval stage, which would be expected to lead to a low speciation rate. The taxonomy of this genus is complex and not well resolved, and phylogenetic relationships have only been addressed in the beginning of the last century. In order to resolve general taxonomic issues, identify speciation patterns and estimate species diversity within the genus Astropecten, we inferred a molecular phylogeny of 117 specimens of Astropecten belonging to 40 species from around the world using mitochondrial DNA (mtDNA) sequences of 12S rRNA, 16S rRNA and cytochrome oxidase subunit I (COI). We compared the resulting molecular phylogeny to a previously published morphological one by Döderlein and investigated the possibility of morphological convergence in species from different geographic regions. Finally, we also aimed at identifying potentially problematic descriptions and/or signs of cryptic speciation in Astropecten. The global molecular phylogeny exhibited three main clades, each containing specimens of the same geographic region: 1. the IndoPacific; 2. the Neotropics; and 3. the eastern Atlantic and Mediterranean. Phylogenetic inferences based on mtDNA indicate that morphological and ecological convergence has taken place in Astropecten, resulting in allopatric non-sister taxa with similar morphologies and habitat preferences. The comparison to Döderlein’s morphological phylogeny reveals congruence on the whole but many discrepancies on a local scale, indicating that meaningful morphological characters are not easily identified and categorized in Astropecten. Our results also reveal that A. polyacanthus Müller & Tröschel and A. indicus Döderlein are species-complexes; cryptic speciation may have occurred within each of these morphospecies. Furthermore, several variants, previously presumed to be conspecific, exhibit genetic distances large enough to justify recognizing them as separate species.