Genetic diversity and differentiation between the two remaining populations of the critically endangered Mediterranean monk seal

Abstract

The Mediterranean monk seal Monachus monachus, is a critically-endangered species of which only two populations, separated by c. 4000 km, remain: the eastern Mediterranean (150-300 individuals) and the Atlantic/western Sahara populations (100-130 individuals). We measured current levels of nuclear genetic variation at 24 microsatellite loci in 12 seals from the eastern Mediterranean and 98 seals from the western Sahara population and assessed differences between them. In both populations, genetic variation was found to be low, with mean allelic richness for the loci polymorphic in the species of 2.09 and 1.96, respectively. For most loci, the observed allele frequency distributions in both populations were discontinuous and the size ranges similar. The eastern Mediterranean population had 14 private alleles and the western Sahara had 18, but with a much larger sample size. Highly significant differences in allele frequencies between the two populations were found for 14 out of 17 loci. F ST between the two populations was 0.578 and the estimated number of migrants per generation was 0.046, both clearly indicating substantial genetic differentiation. From a conservation perspective, these results suggest that each population may act as a source for introducing additional genetic variation into the other population.

The Mediterranean monk seal Monachus monachus: status, biology, threats, and conservation priorities

“…Genetic analyses of mitochondrial and nuclear DNA (Pastor et al. , , Karamanlidis et al. ) have shown that, as a consequence of severe population bottlenecks and population fragmentation, all monk seal subpopulations exhibit low levels of genetic diversity.…”

Genetic status of an endemic marine mammal, the Australian fur seal, following historical harvesting

“…Allen et al, 1995;Robertson & Gemmell, 2005;Pastor et al, 2007). To be cautious, this locus was removed from all further analyses.…”

Prehistoric and historic distributions of the critically endangered Mediterranean monk seal (Monachus monachus) in the eastern Atlantic

“…Comparative genetic studies among populations, using mtDNA and nuclear microsatellite loci, showed two genetically differentiated populations: one from the eastern Mediterranean and one from the Atlantic/Western Sahara (Stanley and Harwood , Pastor et al . ). The geographic separation of the populations has led to the suggestion of a taxonomic separation of this species based on the differences in skull morphologies between the Mediterranean monk seals in the eastern Mediterranean, and those from the Atlantic and western Mediterranean (van Bree ).…”

“…However, these studies showed that the genetic differences are most likely due to reproductive isolation of the two populations, and are not sufficient to permit a significant taxonomic differentiation of two distinct subspecies (Stanley and Harwood , Pastor et al . ).…”

“…Genetic studies suggest that, originally, there was a single, large population with gene flow extending from the Atlantic to the Mediterranean Sea (Pastor et al . ), and that the Atlantic monk seal populations most likely experienced a genetic bottleneck in the 18th century that lasted 10 generations or more (Pastor et al . ).…”