Development of microsatellite markers for a hard-shelled mussel, Mytilus coruscus, and cross-species transfer

Development of polymorphic microsatellites for genetic studies of white scar oyster (Crassostrea belcheri) using paired-end shotgun sequencing

White scar oyster Crassostrea belcheri is a commercially important bivalve species in Thailand. Appropriate genetic markers are needed for effective management to elevate its production efficiency. Type II microsatellites of C. belcheri were identified and characterized using an Illumina paired-end shotgun sequencing. A total of 14,743,710 reads were generated for which 198,849 reads containing microsatellites and 217,998 microsatellite loci were found. Twenty out of 60 microsatellite loci (33.33%) were polymorphic and these microsatellites were further tested against DNA bulks (N = 10 each) originating from 7 different geographic locations in Thai waters. Results indicated that newly developed microsatellites can be used for genetic diversity analysis of C. belcheri. Genotyping of C. belcheri collected from Surat Thani (Gulf of Thailand; N = 50) were performed. The number of alleles per locus ranged from 2 to 12 (average = 4.95). Observed and expected heterozygosities ranged from 0.0000 to 0.9400 (average = 0.3419) and 0.1139 to 0.8190 (average = 0.5844), respectively. Genome information and 20 newly isolated microsatellites will facilitate further studies in population genetics, stock management, and genetic improvement of C. belcheri in Thailand.

Development of 26 highly polymorphic microsatellite markers for the highly endangered fan mussel Pinna nobilis and cross-species amplification

The fan mussel, Pinna nobilis is a highly endangered bivalve species endemic to the Mediterranean Sea. During the last few decades, populations have been greatly reduced due to anthropic impacts and they are now under strict protection in most Mediterranean countries. Today, the species is facing a major crisis following the introduction of an haplosporidan parasite which is driving mass mortality in almost all P. nobilis populations throughout the Mediterranean Sea. Gathering additional knowledge regarding dynamics and connectivity patterns of P. nobilis populations is now more than ever critical. Here, we describe the development of 26 highly polymorphic microsatellite markers. Average allelic diversity of 10.9 alleles per locus was reported and heterozygosity ranged from 0.0294 to 0.9737. We tested cross-species amplification in four Pinna species for the new markers together with 10 already published markers, and analysed its success according to the genetic distances among species. Cross-species transferability success ranged from 3 to 38% and had a negative relationship with the genetic distance between the target species and the tested species. The establishment of this new set of high-resolution markers provides a useful tool to understand processes driving gene flow and genetic diversity in P. nobilis populations and the closest congeneric species.