Genetic aspects for the management of the stocks of the spiny spider crab "Maja brachydactyla"heteroplasmy and multipaternity

Resumo

The spiny spider crab Maja brachydactyla is a decapod of high commercial interest. Despite the large number of studies conducted on this species, genetic research is still scarce. This doctoral thesis was focused on studying genetic aspects of the biology of M. brachydactyla relevant for a sustainable exploitation of stocks. As these studies require high-quality DNA, the first step consisted of performing methodological improvements of DNA extraction process, from choosing an adequate starting tissue to selecting the most effective protocol, both for adults and eggs. These improvements for DNA extraction facilitated the analysis of nuclear and mitochondrial markers. The analysis of microsatellites revealed multipaternity, although the prevalence differed between populations with different exploitation levels, probably due to the selective fishing focused on large males promoted by some fishing regulations. The analysis of mitochondrial genes disclosed heteroplasmy, likely caused by hybridisation with the congeneric species Maja squinado. Multipaternity and heteroplasmy, together with the high connectivity of the stocks, are probably responsible for the typical sperm limitation and genetic diversity loss of highly exploited populations not being detectable in this crab yet. However, if intense fishing continues, spider crab stocks will reach an unbridgeable bottleneck. For this reason, it is urgent to review the management measures that promotes male-selective fishing in M. brachydactyla.