Recently, Pinna nobilis pen shells population in Mediterranean Sea has plummeted due to a Mass Mortality Event caused by an haplosporidian parasite. In consequence, this bivalve species has been included in the IUCN Red List as “Critically Endangered”. On the other hand, the sibling species Pinna rudis remains unaffected. Therefore, correct identification of both species and potential hybrids is extremely important to assess the existence of survivors of P. nobilis.

This study used morphological characteristics and molecular analysis to identify putative P. nobilis-P. rudis hybrids.

The obtained results show that putative hybrids showed shell morphology and mantle coloration intermingled exhibiting both P. nobilis and P. rudis traits. Hybrids also showed parental diagnostic alleles and intermediate positions regarding the multilocus genotypes.

This is the first study evidencing the existence of hybrids of both species, providing molecular methodology for a proper identification of new hybrids. The authors suggest that further studies testing systematically all parasite-resisting isolated P. nobilis should be undertaken to determine if the resistance is resulting from introgression of P. rudis into P. nobilis genome and identifying aspects related to resistance.

Vázquez-Luis et al. (2021) Natural hybridization between pen shell species: Pinna rudis and the critically endangered Pinna nobilis may explain parasite resistance in P. nobilis. Molecular Biology Reports 48: 997-1004.