Federica Costantini

Genetic structuring of the temperate gorgonian coral (Corallium rubrum) across the western Mediterranean Sea revealed by microsatellites and nuclear sequences

In the past decades, anthropogenic disturbance has increased in marine costal habitats, leading to dramatic shifts in population size structure of various marine species. In the temperate region, the gorgonian coral (Corallium rubrum) is one of the major disturbed species, mostly owing to the exploitation of its red skeleton for jewellery purposes. Red coral is a gonocoric species inhabiting subtidal rocky habitats in the Mediterranean and neighbouring Atlantic coasts. In order to investigate the spatial genetic structuring of C. rubrum, five microsatellite markers and the ribosomal internal transcribed spacer 1 (ITS‐1) sequences were analysed in 11 samples from the northwestern Mediterranean Sea. Phylogenetic reconstructions obtained from ITS‐1 sequences analysis showed that samples from Minorca and Sardinia islands were the most divergent while the three samples from the Tuscan archipelago (Argentario, Giannutri and Elba) appeared genetically homogeneous. Both markers revealed a strong structuring over large spatial scales (though to a different extent) with no isolation by distance pattern. Microsatellite‐based FST estimates appeared much smaller than ITS‐based estimates and not significantly correlated, likely due to microsatellite allele size homoplasy typical of these highly polymorphic loci. Our study shows that the absence of clear patterns of genetic structuring over large spatial scales together with strong genetic structuring should be interpreted with caution because such patterns may hide underlying small‐scale genetic structuring. Our results further confirm that effective larval dispersal in red coral is highly restricted in the northwestern Mediterranean Sea, suggesting that an increase of anthropogenic disturbance could aggravate the disappearance of red coral, not only along the Mediterranean coasts but also, and with more intensity, in the main Mediterranean islands.

Phylogeography of the common ragworm Hediste diversicolor (Polychaeta: Nereididae) reveals cryptic diversity and multiple colonization events across its distribution

Previous studies on the common ragworm Hediste diversicolor (Polychaeta: Nereididae) revealed a marked genetic fragmentation across its distribution and the occurrence of sibling taxa in the Baltic Sea. These results suggested that the phylogeographic patterns of H. diversicolor could reflect interactions between cryptic differentiation and multiple colonization events. This study aims to describe the large‐scale genetic structuring of H. diversicolor and to trace the phylogeographic origins of the genetic types described in the Baltic Sea. Samples of H. diversicolor (2 < n < 28) were collected at 16 locations across the NE Atlantic coasts of Europe and Morocco and in the Mediterranean, Black and Caspian Seas and sequenced at two mitochondrial gene fragments (COI and cytb, 345 and 290 bp, respectively). Bayesian analyses revealed deep phylogeographic splits yielding three main clades corresponding to populations (i) from the NE Atlantic coasts (from Germany to Morocco) and from part of the Western Mediterranean, (ii) from the Mediterranean Sea, and (iii) from the Black and Caspian Seas. These clades are further divided in well‐supported subclades including populations from different regions of NE Atlantic and Mediterranean (i.e. Portugal/Morocco, Western Mediterranean, Adriatic Sea). The Baltic Sea comprises three sympatric lineages sharing a common evolutionary history with populations from NE Atlantic, Western Mediterranean and Black/Caspian Seas, respectively. Hence, the current patterns of genetic structuring of H. diversicolor appear as the result of allopatric isolation, multiple colonization events and possible adaptation to local environmental conditions.

Quantifying spatial genetic structuring in mesophotic populations of the precious coral Corallium rubrum.

While shallow water red coral populations have been overharvested in the past, nowadays, commercial harvesting shifted its pressure on mesophotic organisms. An understanding of red coral population structure, particularly larval dispersal patterns and connectivity among harvested populations is paramount to the viability of the species. In order to determine patterns of genetic spatial structuring of deep water Corallium rubrum populations, for the first time, colonies found between 58–118 m depth within the Tyrrhenian Sea were collected and analyzed. Ten microsatellite loci and two regions of mitochondrial DNA (mtMSH and mtC) were used to quantify patterns of genetic diversity within populations and to define population structuring at spatial scales from tens of metres to hundreds of kilometres. Microsatellites showed heterozygote deficiencies in all populations. Significant levels of genetic differentiation were observed at all investigated spatial scales, suggesting that populations are likely to be isolated. This differentiation may by the results of biological interactions, occurring within a small spatial scale and/or abiotic factors acting at a larger scale. Mitochondrial markers revealed significant genetic structuring at spatial scales greater then 100 km showing the occurrence of a barrier to gene flow between northern and southern Tyrrhenian populations. These findings provide support for the establishment of marine protected areas in the deep sea and off-shore reefs, in order to effectively maintain genetic diversity of mesophotic red coral populations.

Inter- and Intraspecific Variability of Nitrogenated Compounds in Gorgonian Corals via Application of a Fast One-Step Analytical Protocol

Gorgonian corals play a structural role in temperate and tropical biogenic reefs, forming animal forests and creating biodiversity hot spots. In the Mediterranean Sea, slow‐growing and long‐lived gorgonian species are threatened by human disturbances and global environmental changes and concern about their conservation is rising. Alkaloid metabolites have proven to be essential in protecting these species from environmental stressors. Traditional profiling methodologies to detect these metabolites require a large quantity of living tissue. Here, the chemodiversity of gorgonian alkaloids was investigated by applying a fast and effective protocol combining extraction and derivatization using small‐scale tissue samples and GC/MS analysis. The method was effective in identifying and quantifying alkaloids and guanine‐based compounds. Eight N‐heterocyclic compounds were found in six Mediterranean gorgonians differing for types and quantity. The metabolomic profile was conservative in species of the Eunicella genus, with three species sharing the same pattern. Conversely, Paramuricea clavata displayed a noticeable spatial pattern of variation among colonies collected in different locations. The analytical approach presented here proved to be effective, allowing rare, endangered, and small‐sized species to be screened rapidly for detection of new compounds in order to explore their biological and ecological functions.

Genetic Connectivity and Conservation of Temperate and Cold-Water Habitat-Forming Corals

Recent explorations of rocky habitats from 40 to about 6,000 m depth disclosed the role of gorgonian and scleractinian corals as habitat formers in tropical, temperate, and polar deep waters. Deep biogenic habitats host high species richness and complexity and their conservation requires a profound understanding of biological and ecological features of sessile species inhabiting them, such as the habitat-forming corals. In sessile species, earliest life history stages and larval processes (e.g., reproduction mode, larval development, behavior, and feeding mode) ensure the exchange of individuals within and among subpopulations, supporting species and habitat resistance and resilience. Genetic studies allow investigating larval processes when direct observations cannot be used. Parameters such as genetic connectivity, gene flow, and levels of genetic diversity are essential to monitor health and resilience of populations under current and future scenarios of anthropogenic environmental changes. In this chapter a review of studies on genetic connectivity of temperate and cold-water habitat-forming corals and associated invertebrate species will be presented. Among them, two case studies, Desmophyllum dianthus, a deep-sea worldwide-distributed scleractinian, and Corallium rubrum, a harvested Mediterranean and Eastern Atlantic alcyonacean with a wide bathymetric distribution, will be discussed in detail. This chapter will also show how these studies contributed to develop, implement, and recommend future conservation strategies and management plans. Existing gaps in literature on genetic connectivity of habitat-forming corals and other invertebrates have been also stressed and discussed. Finally, a conceptual framework for optimizing and planning effective studies on genetic connectivity is provided, including general recommendations on sampling design, key species and new molecular markers to use with a special emphasis on the “nextgeneration” DNA sequencing technologies.