Natural hybridization between pen shell species: Pinna rudis and the critically endangered Pinna nobilis may explain parasite resistance in P. nobilis.

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". In the current scenario, several works are in progress to protect P. nobilis from extinction, being identification of hybrids (P. nobilis x P. rudis) among survivors extremely important for the conservation of the species.Morphological characteristics and molecular analyses were used to identify putative hybrids. A total of 10 individuals of each species (P. nobilis and P. rudis) and 3 doubtful individuals were considered in this study. The putative hybrids showed shell morphology and mantle coloration intermingled exhibiting both P. nobilis and P. rudis traits. Moreover, the analyses of 1150 bp of the 28S gene showed 9 diagnostic sites between P. rudis and P. nobilis, whereas hybrids showed both parental diagnostic alleles at the diagnostic loci. Regarding the multilocus genotypes from the 8 microsatellite markers, the segregation of two Pinna species was clearly detected on the PCoA plot and the 3 hybrids showed intermediate positions.This is the first study evidencing the existence of hybrids P. nobilis x P. rudis, providing molecular methodology for a proper identification of new hybrids. 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.

Tracking a mass mortality outbreak of pen shell Pinna nobilis populations: A collaborative effort of scientists and citizens.

A mass mortality event is devastating the populations of the endemic bivalve Pinna nobilis in the Mediterranean Sea from early autumn 2016. A newly described Haplosporidian endoparasite (Haplosporidium pinnae) is the most probable cause of this ecological catastrophe placing one of the largest bivalves of the world on the brink of extinction. As a pivotal step towards Pinna nobilis conservation, this contribution combines scientists and citizens' data to address the fast- and vast-dispersion and prevalence outbreaks of the pathogen. Therefore, the potential role of currents on parasite expansion was addressed by means of drift simulations of virtual particles in a high-resolution regional currents model. A generalized additive model was implemented to test if environmental factors could modulate the infection of Pinna nobilis populations. The results strongly suggest that the parasite has probably dispersed regionally by surface currents, and that the disease expression seems to be closely related to temperatures above 13.5 °C and to a salinity range between 36.5-39.7 psu. The most likely spread of the disease along the Mediterranean basin associated with scattered survival spots and very few survivors (potentially resistant individuals), point to a challenging scenario for conservation of the emblematic Pinna nobilis, which will require fast and strategic management measures and should make use of the essential role citizen science projects can play.

Ultrastructural developmental cycle of Haplosporidium montforti (phylum Haplosporidia) in its farmed abalone host, Haliotis tuberculata (Gastropoda).

The sequential developmental cycle of Haplosporidium montforti, a recently described species from farmed abalone Haliotis tuberculata (Gastropoda), was studied. Ornamented and operculated mature spores were electron dense. The nucleus of the uninucleated free cell divided successively, giving rise to multinucleate plasmodia, containing up to 100-120 nuclei. Later, the plasmodia developed into sporonts inside sporocysts with irregular contours. Each of their nuclei gave rise to uninucleate sporoblasts. At the next phase of development, a very irregular membranous group of cisternae began to differentiate in the cytoplasm of each sporoblast, surrounding each nucleus and the adjacent cytoplasm. Each sporoblast differentiated into a spore. This process was characterized by the appearance of dense blisters of amorphous material at the periphery that gradually formed the prespore wall and pre-operculum. Simultaneously, in the endosporoplasm, the spherulosome and several haplosporosomes were formed. During the final phase of the maturation process, the spores became gradually denser, and the endosporoplasmic structures were barely visible.

Investigating the possible role of benthic macroinvertebrates and zooplankton in the life cycle of the haplosporidian Bonamia ostreae.

Bonamia ostreae is a protistan parasite of the European flat oyster, Ostrea edulis. Though direct transmission of the parasite can occur between oysters, it is unclear if this represents the complete life cycle of the parasite, and the role of a secondary or intermediate host or carrier species cannot be ruled out. In this preliminary study, benthic macroinvertebrates and zooplankton from a B. ostreae-endemic area were screened for the presence of parasite DNA, using polymerase chain reaction (PCR). Eight benthic macroinvertebrates and nineteen grouped zooplankton samples gave positive results. Certain species, found positive for the parasite DNA, were then used in laboratory transmission trials, to investigate if they could infect naïve oysters. Transmission of B. ostreae was effected to two naïve oysters cohabiting with the brittle star, Ophiothrix fragilis.