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.

Fine with heat, problems with water: microclimate alters water loss in a thermally adapted insular lizard

“…This can lead to inbreeding depression, which further decreases fitness and resilience (Eldridge et al 1999, Frankham et al 2002. Isolated populations may therefore be vulnerable not only due to their small size, but also because the resulting genetic impoverishment undermines their capacity for evolutionary responses to environmental change (Willi et al 2006, Remon et al 2011. Island species represent typical examples of such isolated populations.…”

Causes and Evolutionary Consequences of Population Subdivision of an Iberian Mountain Lizard, Iberolacerta monticola

“…Second, small isolates of I. monticola show no evidence of overall excess of homozygotes, not even Lambre, a very small population that may have gone extinct by now [19], although inbreeding should be, in principle, much more intense in them than in large populations. This could be due, at least in part, to transient associative overdominance, produced either by local genetic linkage to the target loci of selection [109] or genomic effects on fitness [110].…”

“…Western populations, however, can be found at downright lowland areas, most of them associated to patches of Atlantic forests in shady fluvial gorges of Galicia [16]. Besides, whereas the species extends with no apparent discontinuities over vast areas of suitable habitat throughout the Cantabrian Mountains, it appears severely fragmented elsewhere, with evidences of ongoing range contraction and local population extinction [17]–[19]. On the other hand, glacial dynamics in the NW of the Iberian Peninsula [20], [21] indicate that large parts of the current range of I. monticola at middle high altitude (in principle, most sites >700–1,000 m asl, meters above sea level) must have been unsuitable for the species during the last ice age, a situation that most likely took place repeatedly during the cyclical climate changes of the Pleistocene [22].…”

Alone on an island: The reassessment of an enigmatic species of Handmaiden Moth (Lepidoptera, Erebidae) endemic to Mauritius

“…Thus, we can imagine that even 100 years ago the species was more abundant than now and that this situation can soon deteriorate. Decreasing population sizes and ranges can lead to other possible threats, such as bottleneck effects, leading to the loss of genetic variation and inbreeding (Remón et al., 2012). We have no knowledge of genetic variation in D. florida and thus cannot evaluate potential effects of loss of such variation.…”