| Abstract |
Although several studies have evaluated the genetic structure and phylogeographic patterns in many species of marine invertebrates, a general model that applies to all of them remains elusive. For example, some species present an admixture of populations with high gene flow, whereas others exhibit more complex patterns. These differences are thought to be due to clear biological aspects, such as direct versus indirect development, or the presence of lecithotrophic versus planktotrophic larvae, but could also be due to environmental pressures that lead to local adaptation. However, very few studies compare animals with similar distributions and different dispersal abilities all within the context of genetic - environmental association. Here, we explore the adaptive and genetic structure patterns in one chiton (Chiton olivaceus), one murex (Hexaplex trunculus) and one abalone (Haliotis tuberculata) species that co-occur in the same sampling locations. Samples were obtained from shallow bottoms along the Cretan coast and ddRAD libraries were prepared and sequenced. The selection of the samples for the ddRAD protocol was informed by mtDNA haplotype networks and the samples were selected in a way that maximized the mtDNA diversity. The data showed evidence of admixture in C. olivaceus and H. tuberculata that is potentially indicating high dispersal ability and/or a recent expansion, whereas H. trunculus exhibited a population pattern with three main groups (North, South & East and Elounda groups) that reflect the geographic distribution of the studied samples and is in accordance with the sea currents in the area. Environmental association tests performed failed to identify loci significantly correlated with a specific environmental parameter, indicative of local adaptation. On the contrary, the population structure of H. trunculus was correlated with three environmental parameters: North/South Aspect, Mean Annual Sea Surface Salinity, Sea Surface Temperature of the warmest month. Moreover, outlier loci tests indicated the existence of 72 outliers, some of which seem to be related with the differentiation of the Elounda group. Since a published genome for the species is not yet available, the role of these loci and the possibility of them being adaptive is yet to be explored. The lack of significant genotype – environment associations could be due to the attributes of the environmental datasets used in this study i.e. to their generality in means of mean annual values that might not be appropriate to reflect the transient genotype-environment interactions. These results clearly exhibit a difference in population patterns that agrees with the different biological cycles of the organisms in question with the abalone and the chiton having a pelagic larval stage, albeit short, and the murex having an intracapsular development. The observed population structure of the murex could be solely attributed to the currents of the study area or the species’ biological cycle or a combination of the two, while the use of a suite of environmental variables could shed light on adaptations of populations to the local environmental pressures. Additionally, the lack of structure observed in the abalone and the chiton could be either be a product of the species biological cycle and dispersal potential or/and to recent expansion while sampling bias especially for H. tuberculata cannot be either excluded or assessed.
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Γενωμική του τοπίου θαλάσσιων ασπονδύλων παράκτιων περιοχών της Κρήτης
