Chronicle of an extinction foretold: genetic properties of an extremely small population of Iberolacerta monticola

Abstract

The fragmentation and destruction of natural habitats by human intervention is producing a continuous and inexorable reduction of the size of populations in multitude of species all over the world. Small and isolated populations face higher extinction risks, due to demographic and environmental stochasticity, and also because of several genetic threats, among which inbreeding is considered the most important one. For many of these species, the extinction of a population is an irreversible event, so that determining the immediate importance of these risk factors and understanding their interactions is crucial for conservation plans. Iberolacerta monticola is a small lacertid endemic to the northwestern Iberian Peninsula, distributed mainly across moderate/high altitude mountainous regions. Some populations are found nearly at sea-level, though, in fluvial valleys with relict Atlantic forests, in the severely fragmented western part of its range. One of them has been dramatically reduced over the last 30 years, and presently is on the brink of extinction. Using microsatellite nuclear markers, we obtained different measures of genetic variation at this site, together with demographic and breeding data. Both the level of heterozygosity and the number of alleles per locus indicate that the level of variation in this population is comparatively high, and the average inbreeding coefficient is very low. Individuals appear healthy and long-lived, and are related by a few different lines of descent. These findings are discussed in the context of current theories and experimental evidence of associative overdominance and purging of the genetic load of populations, with special emphasis on the evolutionary potential of recovery of small evolutionary units.