Development of tetranucleotide microsatellite markers for the cushion star, Asterina gibbosa, and cross-species amplification

Connectivity Among Populations of the Top Shell Gibbula divaricata in the Adriatic Sea

Genetic connectivity studies are essential to understand species diversity and genetic structure and to assess the role of potential factors affecting connectivity, thus enabling sound management and conservation strategies. Here, we analyzed the patterns of genetic variability in the marine snail Gibbula divaricata from five coastal locations in the central-south Adriatic Sea (central Mediterranean) and one in the adjacent northern Ionian Sea, using 21 described polymorphic microsatellite loci. Observed and expected heterozygosity varied from 0.582 to 0.635 and 0.684 to 0.780, respectively. AMOVA analyses showed that 97% of genetic variation was observed within populations. Nevertheless, significant, although small, genetic differentiation was found among nearly all of the pairwise F ST comparisons. Over a general pattern of panmixia, three groups of populations were identified: eastern Adriatic populations, western Adriatic populations, and a third group represented by the single northern Ionian Sea population. Nonetheless, migration and gene flow were significant between these groups. Gibbula divaricata is thought to have a limited dispersal capacity related to its lecithotrophic trochophore larval stage. Our results indicated high levels of self-recruitment and gene flow that is mainly driven through coastline dispersion, with populations separated by the lack of suitable habitats or deep waters. This stepping-stone mode of dispersion together with the high levels of self-recruitment could lead to higher levels of population structuring and differentiation along the Adriatic Sea. Large effective population sizes and episodic events of long-distance dispersal might be responsible for the weak differentiation observed in the analyzed populations. In summary, the circulation system operating in this region creates natural barriers for dispersion that, together with life-history traits and habitat requirements, certainly affect connectivity in G. divaricata. However, this scenario of potential differentiation seems to be overridden by sporadic events of long-distance dispersal across barriers and large effective population sizes.

Isolation of microsatellite loci for the endangered vermetid gastropod Dendropoma lebeche using Illumina MiSeq next generation sequencing technology

Dendropoma petraeum, considered the primary vermetid reef-building species in the Mediterranean, has recently been shown to be a species complex of at least four cryptic species. These species have highly restricted, non-overlapping distributions, causing concern for their conservation status. To better study the genetic diversity of these populations, we selected one of these species, Dendropoma lebeche (Templado et al. in Mediterr Mar Sci 17(1):13-31, 2016), which is restricted to the western Mediterranean, for microsatellite marker development using Illumina MiSeq. We provide an initial survey of 29 polymorphic microsatellite loci for D. lebeche. Genetic analyses identified 2-11 alleles per locus across the 30 samples examined. Observed and expected heterozygosities ranged from 0.067 to 0.800 and 0.064 to 0.770, respectively. None of the loci deviated from Hardy-Weinberg equilibrium or showed signs of being under selective pressure. Significant linkage disequilibrium was found between two loci. We also show the cross-species amplification of these microsatellite markers in the other three species of the complex, the Tyrrhenian-Sicilian lineage, D. cristatum (Biondi, 1859), the Levantine lineage, D. anguliferum (Monterosato, 1878) and Dendropoma sp. found along the Ionian-Aegean coasts, suggesting their potential utility for future phylogenetic and evolutionary studies.

Looking for morphological evidence of cryptic species in Asterina Nardo, 1834 (Echinodermata: Asteroidea). The redescription of Asterina pancerii (Gasco, 1870) and the description of two new species

Three species of the genus Asterina are known to inhabit the Mediterranean Sea and the north-eastern Atlantic Ocean: Asterina gibbosa (Pennant, 1777), A. pancerii (Gasco, 1870) and A. phylactica Emson & Crump, 1979. Differentiation of these species has primarily been based only on subtle characters (some highly debatable), such as colour or size. Therefore, this study aimed to review the morphological data characterising members of the genus, to incorporate new characters that may clarify morphological analyses and to couple morphological data with molecular evidence of differentiation based on the analysis of partial sequences of the cytochromec oxidase subunitI (COI) and 18S rDNA (18S) genes and two anonymous nuclear loci (AgX2 and AgX5). The different lineages and cryptic species identified from the molecular analysis were then morphologically characterised, which was challenging given the limited number of diagnostic characters. Two of the five monophyletic lineages obtained molecularly (COI divergence >4%), further supported by differences in morphological characters and reproductive behaviour, are proposed as new species: Asterina martinbarriosi, sp. nov. from the Canary Islands, Spain (eastern central Atlantic Ocean) and Asterina vicentae, sp. nov. from Tarragona, north-eastern Spain (western Mediterranean Sea).

Development and characterization of 26 novel microsatellite loci for the trochid gastropod Gibbula divaricata (Linnaeus, 1758), using Illumina MiSeq next generation sequencing technology

In the present study we used the high-throughput sequencing technology Illumina MiSeq to develop 26 polymorphic microsatellite loci for the marine snail Gibbula divaricata. Four to 32 alleles were detected per locus across 30 samples analyzed. Observed and expected heterozygosities ranged from 0.130 to 0.933 and from 0.294 to 0.956, respectively. No significant linkage disequilibrium existed. Seven loci deviated from Hardy-Weinberg equilibrium that could not totally be explained by the presence of null alleles. Sympatric distribution with other species of the genus Gibbula, as G. rarilineata and G. varia, lead us to test the cross utility of the developed markers in these two species, which could be useful to test common biogeographic patterns or potential hybridization phenomena, since morphological intermediate specimens were found.