Evidence of genetic isolation between two Mediterranean morphotypes of Parazoanthus axinellae

Coralligenous assemblages are among the most species-rich and vulnerable habitats of the Mediterranean Sea. Nevertheless, data on connectivity patterns on species inhabiting these habitats, crucial to define management and protection priorities, are largely lacking. Moreover, unreliable species-level taxonomy can confound ecological studies and mislead management strategies. In the northwestern Mediterranean two Parazoanthus axinellae morphotypes differing in size, color and preferred substrate are found in sympatry. In this study, we used COI and ITS sequence polymorphism to assess (1) the genetic divergence between the two morphotypes, (2) their connectivity patterns and (3) their phylogenetic position within the Parazoanthidae. Specimens of P. axinellae were sampled in 11 locations along the northwestern Mediterranean; in 6 locations, samples of the two morphotypes were collected in sympatry. Small genetic diversity and structure were found within morphotypes, while marked and consistent differentiation was detected between them. Moreover, the less widespread morphotype appeared to be closer to Pacific species as P. juanfernandezii and P. elongatus. Our findings confirmed the limited knowledge on Parazoanthus species complex, and how this gap can have important implication for the conservation strategies of this widespread and valuable genus in the Mediterranean Sea

Population genomics in Mediterranean vulnerable ecosystems: the case of the black coral Antipathella subpinnata

Mediterranean seamounts and canyons represent one of the most important and less studied deep vulnerable marine ecosystems (VMEs). Marine forests of the black coral Antipathella subpinnata (Ellis & Solander, 1786) characterize these ecosystems creating complex three-dimensional habitats, hosting a rich associated fauna and attracting numerous species of commercial interest. However, these corals are particularly vulnerable to direct damages (e.g., commercial fishing activities), mostly because of their arborescent morphology and low growth rate. Quantify the level of genetic variability of populations inhabiting different seamounts and their levels of connectivity with deep coastal populations is a crucial step for an effective policymaking and resource management. In fact, populations found on seamounts if are not connected with coastal populations could be more isolated, became smaller and therefore more susceptible to natural and anthropic perturbation. Recently developed techniques allow genome-wide identification of genetic markers for a better understanding of the population structure in species with limited genome information as the case of A. subpinnata. Here, for the first time, using restriction-site associated DNA analysis (2bRAD), we successfully genotyped individuals from one Ligurian seamount, one Tyrrhenian canyon and four deep coastal populations (Liguria and Calabria) to detect current genetic diversity and to identify barriers to gene flow. Data have been integrated with the environmental features and reproductive behaviour of the species to understand their influence on the observed genetic pattern. The genomic approach should be used to implement conservation and management decision and to achieve Good Environmental Status of Mediterranean deep vulnerable marine ecosystem

Gene correlation networks reveal the transcriptomic response to elevated nitrogen in a photosynthetic sponge

Nutrient levels in coastal environments have been increasing globally due to elevated inputs of sewage and terrigenous sediments carrying fertilizers. Yet, despite their immense filtering capacities, marine sponges appear to be less affected by elevated nutrients than sympatric benthic organisms, such as corals. While the molecular-level stress response of sponges to elevated seawater temperatures and other toxicants has been defined, this study represents the first global gene expression analysis of how sponges respond to elevated nitrogen. Gene correlation network analysis revealed that sponge gene modules, coded by colours, became either highly upregulated (Blue) or downregulated (Turquoise, Black, Brown) as nitrogen treatment levels increased. Gene Ontology enrichment analysis of the different modules revealed genes involved in cell signalling, immune response and flagella motility were affected by increasing nitrogen levels. Notably, a decrease in the regulation of NF-kappaB signalling and an increase in protein degradation was identified, which is comparable to metabolic pathways associated with the sponge thermal stress response. These results highlight that Cymbastela stipitata can rapidly respond to changes in the external environment and identifies pathways that probably contribute to the ability of C. stipitata to tolerate short-term nutrient pulses

Genome-wide SNPs data provides new insights into the population structure of the Atlantic-Mediterranean gold coral Savalia savaglia (Zoantharia: Parazoanthidae)

Savalia savaglia is an Atlantic-Mediterranean zoantharian species with a patchy geographic and bathymetric distribution. Due to its longevity, S. savaglia may form large-sized colonies which play a crucial role in the ecosystem as habitat formers. Despite its ecological importance, little is known about the population structure and intraspecific genetic diversity of this species. Using ddRAD-Seq genotyping, we obtained genome-wide single nucleotide polymorphisms (SNPs) from 50 S. savaglia individuals collected at different depths (8–60 m) and localities across the Mediterranean Sea (Marseille, Sardinia, Puglia and Montenegro) and eastern Atlantic (Portugal). Our molecular observations were discussed with the reproductive behaviour of the species to understand the observed patterns of connectivity and gene flow. These results highlight the presence of three main genetic clusters (Marseille; Sardinia; and Montenegro + Portugal + Puglia), with some of the Mediterranean individuals being genetically closer to the Atlantic population rather than to other Mediterranean populations. The strong linkage disequilibrium recorded across loci and the detection of clonal individuals in the shallow populations suggest that asexual reproduction seems to be the dominant reproductive strategy among the S. savaglia populations sampled at lower depths. Our work highlights the potential of genome-wide SNP data to study the reproductive behaviour in species such as S. savaglia that are difficult to investigate in the field. The genetic connectivity data obtained in this study can be used in the future to better guide the development of effective management and conservation plans

Genome-wide SNPs data provides new insights into the population structure of the Atlantic-Mediterranean gold coral Savalia savaglia (Zoantharia: Parazoanthidae)

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2bRAD reveals fine-scale genetic structuring among populations within the Mediterranean zoanthid Parazoanthus axinellae (Schmidt, 1862)

The zoanthid Parazoanthus axinellae (Schmidt, 1862) is a widespread coral species in the Mediterranean coralligenous assemblages where two morphotypes are found: Slender and Stocky, differing in size, color, and preferred substrate. Due to these marked differences, Slender and Stocky morphotypes were hypothesized to be two species. Here, we used 2bRAD to obtain genome-wide genotyped single nucleotide polymorphisms (SNPs) to investigate the genetic differentiation between Slender and Stocky morphs, as well as their population structure. A total of 101 specimens of P. axinellae were sampled and genotyped from eight locations along the Italian coastline. In four locations, samples of the two morphotypes were collected in sympatry. 2bRAD genome-wide SNPs were used to assess the genetic divergence between the two morphotypes (1319 SNPs), and population connectivity patterns within Slender (1926 SNPs) and Stocky (1871 SNPs) morphotypes. Marked and consistent differentiation was detected between Slender and Stocky morphotypes. The widely distributed Slender morphotype showed higher population mixing patterns, while populations of the Stocky morphotype exhibited a stronger genetic structure at a regional scale. The strong genetic differentiation observed between P. axinellae Slender and Stocky morphotypes provides additional evidence that these morphs could be attributed to different species, although further morphological and ecological studies are required to validate this hypothesis. Our study highlights the importance of resolving phylogenetic and taxonomic disparities within taxonomically problematic groups, such as the P. axinellae species complex, when performing genetic connectivity studies for management and conservation purposes.[GRAPHICS