Tuesday, September 1, 2015

Genetic diversity in threatened vertebrates

Threatened or endangered populations are identified and ranked by varying methods across states, countries and organizations, but criteria typically are based on demographics.

The International Union for Conservation of Nature (IUCN), for example, identifies species of conservation concern based on the number of mature adults in a population, range size and evidence of population decline. Animal species on IUCN's Red List, the most comprehensive record of threatened species worldwide, are ranked by estimates of how close to extinction they are. However, the criteria currently used to identify at risk species are not correlated with genetic diversity. This suggests that some threatened species could be overlooked because populations with low genetic diversity may not be able to adapt to challenges such as changing environmental conditions, shrinking habitats or new diseases, which could put them at risk of disappearing. 

A new study presents a novel approach for identifying vertebrate populations at risk of extinction by estimating the rate of genetic diversity loss, a measurement that could help researchers and conservationists better identify and rank species that are threatened or endangered.

Genetic diversity is a key component to the long-term survival of a population.The approach we developed identifies populations with limited genetic diversity that isn't going to be enough to allow the population to persist over time. We found that this method performs significantly better than current methods for identifying species in need of conservation efforts.

The colleagues conducted a review of vertebrate genetic data published since 1990 to investigate the relationship between genetic diversity and the at-risk status of animal species. The team used microsatellite datasets from 5,285 studies spanning 17,988 loci to estimate genetic diversity (heterozygosity and allelic richness) across wild populations of birds, fish, reptiles, amphibians and mammals. They found that threatened species had reduced genetic variation, likely due to inbreeding and the random loss of variation that occurs when population sizes are small.

Unless a population with poor genetic diversity has undergone a dramatic decrease in size, it could be overlooked with our current methodology. We should consider genetic diversity in conservation rankings so a species doesn't go extinct simply because it wasn't on our radar.

The team then examined IUCN's criteria for classifying threatened species to determine how effective the criteria were at identifying genetically poor species. If genetic diversity estimates correlated with the Red List criteria, then IUCN would be systematically selecting for populations or species that have declining diversity, the researchers reasoned. However, they found that IUCN's criteria were not closely linked to genetic diversity.

The criteria of many conservation organizations were formulated before the availability of genetic data we have today. But genetic methodology has advanced so rapidly that factoring in genetic diversity is now pretty straightforward. Therefore, we propose that IUCN incorporates an additional criterion that addresses effective population size and genetic diversity for the use in ranking conservation priorities.

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