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.