Piero Cossu

Small-scale morphological and genetic differentiation in the Mediterranean killifish Aphanius fasciatus (Cyprinodontidae) from a coastal brackish-water pond and an adjacent pool in northern Sardinia

Two samples of Aphanius fasciatuscollected in the Pilo pond (northern Sardinia, Italy) and in an adjacent pool of small surface area were analysed morphologically (235 individuals) and genetically (a subsample of 58 individuals). The aims of the present study were (i) to test the hypothesis that different predation pressures may be associated with morphological and/or genetic differences between samples from each habitat and (ii) to assess the level of divergence between the two populations. Morphological analysis was based on the relative size of fins because it has been shown to be associated with predation pressure. The relative caudal fin area (caudal fin area/total body surface) was smaller in specimens from the pool, in both males and females, whereas no differences were found for the dorsal and anal fin areas. Caudal fins with higher aspect ratio (fin depth/fin length) were found in fish from the pool but not in the pond, due to a higher fin depth. We hypothesised that specimens from the pool would show smaller caudal fin area, since they are subject to lower predation pressure. Random amplification of polymorphic DNA (RAPD) analysis revealed a relatively high degree of both within- and between-sample genetic heterogeneity. The pond and pool samples exhibited heterozygosities, which did not differ significantly by t-test. Between-sample genetic divergence was highlighted by the coancestry coefficient (h = 0.301 ± 0.059, P < 0.001) and analysis of molecular variance (AMOVA) (variance between sites = 41%, P < 0.001). Genetic divergence between sites with a relatively high genetic diversity within both samples suggested that the population in the pool did not originate from a single colonisation event with a small number of founders. The genetic divergence between the two populations is consistent with their differences in fin size.

Mitochondrial DNA reveals genetic structuring of Pinna nobilis across the Mediterranean Sea.

Pinna nobilis is the largest endemic Mediterranean marine bivalve. During past centuries, various human activities have promoted the regression of its populations. As a consequence of stringent standards of protection, demographic expansions are currently reported in many sites. The aim of this study was to provide the first large broad-scale insight into the genetic variability of P. nobilis in the area that encompasses the western Mediterranean, Ionian Sea, and Adriatic Sea marine ecoregions. To accomplish this objective twenty-five populations from this area were surveyed using two mitochondrial DNA markers (COI and 16S). Our dataset was then merged with those obtained in other studies for the Aegean and Tunisian populations (eastern Mediterranean), and statistical analyses (Bayesian model-based clustering, median-joining network, AMOVA, mismatch distribution, Tajima’s and Fu’s neutrality tests and Bayesian skyline plots) were performed. The results revealed genetic divergence among three distinguishable areas: (1) western Mediterranean and Ionian Sea; (2) Adriatic Sea; and (3) Aegean Sea and Tunisian coastal areas. From a conservational point of view, populations from the three genetically divergent groups found may be considered as different management units.

Genetic structure of Octopus vulgaris (Mollusca, Cephalopoda) from the Mediterranean Sea as revealed by a microsatellite locus

Abstract An investigation of the genetic variability of Octopus vulgaris, an intensively harvested species, was carried out using a mi crosatellite locus as genetic marker. Samples from one eastern At lantic and nine Mediterranean locations were analysed. In each population, the number of alleles at locus Ov06 varied from four to seven and was 21 overall. Observed and expected heterozy‐gosity values ranged from 0.310 to 0.655 and 0.506 to 0.841, re spectively. Permutation tests and the positive average value of FIS showed significant departures from the Hardy‐Weinberg equilibri um, due to a deficit of heterozygotes. FST showed high levels of genetic divergence among the populations. Genetic distance val ues ranged from 0.0004 to 7.1520. Isolation‐by‐distance was not evident either by the Mantel test or multidimensional scaling. Mi crosatellite results are consistent with a previous allozyme study, and suggest that the common octopus does not form a single panmictic unit in the Mediterranean. From a fishery perspective, this information leads to the conclusion that the management of O. vulgaris should be planned on a local level.

New records of the pygmy mussel Xenostrobus securis (Bivalvia: Mytilidae) in brackish-water biotopes of the western Mediterranean provide evidence of its invasive potential

The present study reports new records of the invasive pygmy mussel Xenostrobus securis in six brackish-water localities in the western Mediterranean. Until now X. securis , whose native range includes southern Australia and New Zealand, was also known from the northern Adriatic Sea and southern France. Along the coast of northern Tuscany (Italy) X. securis invaded brackish-water canals in the area between the port of Leghorn and the mouth of the Arno River. Moreover, this mussel has been found in one inner site of the Gulf of Olbia (north-eastern Sardinia, Italy) and at the mouth of the Fluvia River (northern Catalonia, Spain). As an ecosystem engineer, X. securis is an ecologically important species, heavily altering pre-existing benthic communities. Given that its presence in other western Mediterranean sites is highly possible, we recommend a closer monitoring of brackish-water biotopes.

Patterns of spatial genetic structuring in the endangered limpet Patella ferruginea: implications for the conservation of a Mediterranean endemic

Patella ferruginea Gmelin, 1791 is an endangered marine gastropod endemic to the Western Mediterranean. Its range is restricted to the Sardinian-Corsican region (SCR), North Africa, a few scattered sites in Southern Spain, and Sicily. Inter-simple sequence repeat (ISSR) markers and three different mitochondrial DNA (mtDNA) regions, Cytochrome c Oxidase subunit I, 12S (small-subunit ribosomal RNA gene) and 16S (large-subunit ribosomal RNA gene), were used to investigate the presence of genetic population structuring. The mtDNA sequences showed very low levels of genetic differentiation. Conversely, ISSRs showed the presence of two main genetic groups, corresponding to Spain, North Africa and Sicily and the SCR. The SCR was further split into two subgroups. The ISSR results suggest that, on a regional scale, the genetic structure of P. ferruginea is mainly determined by the restriction of gene flow by dispersal barriers. On a more local scale human harvesting may play a crucial role in population structuring by increasing the effect of genetic drift.

Morphological differentiation in the ragworm, Hediste diversicolor (Polychaeta, Nereididae), as revealed by variation of paragnath number and distribution

Variation in the number and distribution of paragnaths in populations of the ragworm, Hediste diversicolor, from 14 localities across a large part of its European range was analysed. Significant inter‐population variation was revealed by ANOVA applied to (i) the number of paragnaths in each zone of the pharynx, (ii) the number of paragnaths in each of the two belts (maxillary and oral), (iii) the total number of paragnaths on the pharynx and (iv) the measures of asymmetry for paired zones. No geographical pattern of morphological variation was detected by multidimensional scaling on population centroids and no signals of morphological population substructuring were found. Explanations of variation in paragnath number and pattern among populations may reflect local differences in diet or dominant mode of feeding. Factor analysis suggested that the two belts of the pharynx behave as separate functional units in feeding activities. The comparison with two samples of the other nereidid, Perinereis cultrifera, showed only a moderate distinction between the two species. We recommend use of the paragnath pattern and number coupled with other kinds of markers when addressing the analysis of species boundaries or subtle population differentiation.

The First Mitogenome of the Cyprus Mouflon (Ovis gmelini ophion): New Insights into the Phylogeny of the Genus Ovis.

Sheep are thought to have been one of the first livestock to be domesticated in the Near East, thus playing an important role in human history. The current whole mitochondrial genome phylogeny for the genus Ovis is based on: the five main domestic haplogroups occurring among sheep (O. aries), along with molecular data from two wild European mouflons, three urials, and one argali. With the aim to shed some further light on the phylogenetic relationship within this genus, the first complete mitochondrial genome sequence of a Cypriot mouflon (O. gmelini ophion) is here reported. Phylogenetic analyses were performed using a dataset of whole Ovis mitogenomes as well as D-loop sequences. The concatenated sequence of 28 mitochondrial genes of one Cypriot mouflon, and the D-loop sequence of three Cypriot mouflons were compared to sequences obtained from samples representatives of the five domestic sheep haplogroups along with samples of the extant wild and feral sheep. The sample included also individuals from the Mediterranean islands of Sardinia and Corsica hosting remnants of the first wave of domestication that likely went then back to feral life. The divergence time between branches in the phylogenetic tree has been calculated using seven different calibration points by means of Bayesian and Maximum Likelihood inferences. Results suggest that urial (O. vignei) and argali (O. ammon) diverged from domestic sheep about 0.89 and 1.11 million years ago (MYA), respectively; and dates the earliest radiation of domestic sheep common ancestor at around 0.3 MYA. Additionally, our data suggest that the rise of the modern sheep haplogroups happened in the span of time between six and 32 thousand years ago (KYA). A close phylogenetic relationship between the Cypriot and the Anatolian mouflon carrying the X haplotype was detected. The genetic distance between this group and the other ovine haplogroups supports the hypothesis that it may be a new haplogroup never described before. Furthermore, the updated phylogenetic tree presented in this study determines a finer classification of ovine species and may help to classify more accurately new mitogenomes within the established haplogroups so far identified.

Patterns of spatial genetic variation in Patella ulyssiponensis: insights from the western Mediterranean marine ecoregion

Patterns of genetic variation in marine species reflect the interplay of species-specific traits, oceanographic features, historical processes and selection. In the Atlantic–Mediterranean regions, Patella ulyssiponensis (Mollusca: Gastropoda) was previously used as a model to investigate these patterns. Our study gained insight into the genetic patterns of P. ulyssiponensis in the western Mediterranean marine ecoregion (WME), by means of ISSRs and COI. We evaluated the genetic structure of the WME with respect to the Atlantic and eastern Mediterranean, as well as the occurrence of further structuring within this ecoregion. Both population- and individual-based analysis evidenced that WME does not appear to be sharply isolated from the adjacent regions. Within the WME, P. ulyssiponensis displays a pattern of genetic structure that may reflect a chaotic patchiness scenario: structuring is neither related to coastal distance nor to other factors that may constrain dispersal. Compared to the congener P. ferruginea, P. ulyssiponensis shows weaker spatial genetic structure, which may reflect a higher dispersal potential coupled with greater population effective size. Whilst other processes that may have influenced the genetic pattern in the WME remain to be cleared, a recent range expansion coupled with species-specific traits favouring larval dispersal may have contributed to the genetic structuring.

Molecular support for morphology‐based family‐rank taxa: The contrasting cases of two families of Proseriata (Platyhelminthes)

Representatives of the Meidiamidae and Otomesostomidae (Platyhelminthes: Proseriata) are seldom encountered, and the monophyly and phylogenetic relationships of these families have never been assessed on molecular basis. Here, we present the first exhaustive molecular study of Proseriata at the family level, including species belonging to the genera Meidiama and Yorknia (Meidiamidae), and Otomesostoma auditivum (Otomesostomidae), using 18S and 28S genes as markers. We performed phylogenetic analyses (Maximum Likelihood [ML] and Bayesian Inference [BI] methods) and species delimitation methods (Single/Multiple Threshold‐Generalized Mixed Yule Coalescent [ST/MT‐GMYC] and Poisson Tree Processes [PTP/bPTP]). The taxon Meidiamidae was not supported, since the type species (Meidiama lutheri) and Meidiama etrusca sp. n. are nested within the Archimonocelididae, formerly restricted to specialized cnidarian feeders. Species belonging to the genus Yorknia resulted genetically well separated from species of Meidiama and from the rest of Archimonocelididae. The new family‐level taxon Yorkniidae fam. n. is thus here introduced, to include the type species of Yorknia (Yorknia aprostatica), and six new species, five of which are formally described here. Otomesostoma auditivum, representative of Otomesostomidae, the only exclusively freshwater taxon of the Proseriata, is the sister taxon of the predominantly marine Apingospermata. This result is not conflictual with the family level attributed to Otomesostomidae on morphological grounds, but it raises speculations on the marine versus freshwater origin of Apingospermata.

Fistularia commersonii (Teleostea: Fistulariidae): walking through the Lessepsian paradox of mitochondrial DNA

Abstract The Mediterranean Lessepsian migrations excite the interest of biologists who are devoted to inferring the effects of selection on the genetic structure of immigrants. The bluespotted cornetfish Fistularia commersonii is an Indo-Pacific species that was first recorded in the Levantine cost of Mediterranean, and within a few years, it rapidly expanded throughout the entire basin. Studies on its genetic variability, performed via mitochondrial sequencing of the Mediterranean specimens, suggest that a limited number of mitochondrial lineages passed through the Suez Canal. However, nuclear markers provide a scenario, with a high genetic variability among the Mediterranean F. commersonii migrants, along with the occurrence of haplotype sharing between the Mediterranean and the Red Sea. The aim of this study was to enlarge the number of Mediterranean sites in order to evaluate if the rapid expansion and different patterns of spread of F. commersonii in the basin could have led to a genetic structuring. The analysis was carried out by sequencing mitochondrial D-loop I in individuals from Sardinia, Sicily, Tunisia, Lampedusa, Libya and Lebanon. Sequences available from previous studies were included in the data set, allowing us to obtain a data set that likely represents the entire distribution range of the species. Results suggest the possible occurrence of two mitochondrial lineages involved in the Mediterranean invasion of F. commersonii, a bottleneck may have caused a loss in the genetic variation, leading to the fixation of specific lineages as an adaptive response to the new environmental conditions.