Not out of the Mediterranean: Atlantic populations of the gorgonian Paramuricea clavata are a separate sister species under further lineage diversification

Abstract

The accurate delimitation of species boundaries in nonbilaterian marine taxa is notoriously difficult, with consequences for many studies in ecology and evolution. Anthozoans are a diverse group of key structural organisms worldwide, but the lack of reliable morphological characters and informative genetic markers hampers our ability to understand species diversification. We investigated population differentiation and species limits in Atlantic (Iberian Peninsula) and Mediterranean lineages of the octocoral genus Paramuricea previously identified as P. clavata . We used a diverse set of molecular markers (microsatellites, RNA‐seq derived single‐copy orthologues [SCO] and mt‐mutS [mitochondrial barcode]) at 49 locations. Clear segregation of Atlantic and Mediterranean lineages was found with all markers. Species‐tree estimations based on SCO strongly supported these two clades as distinct, recently diverged sister species with incomplete lineage sorting, P. cf. grayi and P. clavata , respectively. Furthermore, a second putative (or ongoing) speciation event was detected in the Atlantic between two P. cf. grayi color morphotypes (yellow and purple) using SCO and supported by microsatellites. While segregating P. cf. grayi lineages showed considerable geographic structure, dominating circalittoral communities in southern (yellow) and western (purple) Portugal, their occurrence in sympatry at some localities suggests a degree of reproductive isolation. Overall, our results show that previous molecular and morphological studies have underestimated species diversity in Paramuricea occurring in the Iberian Peninsula, which has important implications for conservation planning. Finally, our findings validate the usefulness of phylotranscriptomics for resolving evolutionary relationships in octocorals.

Differential apicomplexan presence predicts thermal stress mortality in the Mediterranean coral Paramuricea clavata

“…The water and food microbiome samples were taxonomically distinct from the coral microbiome samples in this study (Figure S2). The population originally sampled from Sagres, Portugal exhibited a distinct microbiome from the other P. clavata populations (Figure 1) and was later determined to be a different species based on genomic work (Coelho et al, 2023). It was hence removed from further analysis.…”

Apicomplexans predict thermal stress mortality in the Mediterranean coralParamuricea clavata

“…Their differential abundance within P. clavata across different thermal susceptibility categories highlights the necessity of studying the role of parasitism in the nutritional dynamics of marine holobionts, especially in the face of stressors. Hudson et al 2006 noted that a healthy system may be one that is rich in parasitic species due to the impact of parasite-mediated effects on population dynamics, interspecific competition, and energy flow [43]. Applying this perspective to coral holobionts may help us better understand the higher thermal tolerance of P. clavata rich in potential parasites such as the corallicolids or Syndiniales.…”

Symbiotic status does not preclude hybridisation in Mediterranean octocorals

“…Species are indeed hypotheses to be tested, if possible through the integration of independent criteria, and independent molecular markers (Pante et al, 2015b). Sound species delimitation and identification is useful, among others, to better estimatespecies range and biodiversity patterns (Coelho et al, 2023;Muir et al, 2022), to avoid biases in connectivity studies (Pante et al, 2015b), and adaptive abilities (Brener-Raffalli et al, 2022). Species delimitation can be problematic in the context of the grey zone of speciation, where different delimitation criteria may bring contradictory conclusions (De Queiroz, 2007).…”