Diversity is a key to survival for mammals

Mammals most at risk of extinction have low genetic diversity in some regions of DNA, according to a new genomic analysis.

An international team led by Kerstin Lindblad-Toh from the Broad Institute, US, compared the genomes of 240 mammals, creating the largest dataset to date.

Their analysis spanned 80% of mammalian families and 110 million years of evolution, revealing how important genetic diversity is for survival.

Diversity refers to the difference in the DNA sequences between members of the same species. Differences naturally occur through mutation of DNA over generations, which then gets shared through the population as mammals breed.

When a population shrinks in size there is less choice of a mate, which leads to inbreeding.

The point at which this inbreeding becomes a problem depends on the genetic diversity in a species. Problems from inbreeding happen more quickly in a population that has low diversity, and these populations are often at higher risk of extinction.

This is because animals that have the same set of genes will be equally affected by a threat, making them vulnerable to changes in the environment. For example, if the group is small and inbred, a new disease could threaten them all because their genes are “weaker”.

The new study found that the species with the most notably low diversity were the social tuco-tuco – a small rodent that came from a lab population that started with only 12 founders – and the eastern vole, which had fallen in numbers due to pest control.

However, it was difficult to determine what exactly is causing this low diversity without in-depth analysis of single species, which is why more genomes need to be sequenced to test this pattern.

“Should this pattern prove robust across more species, diversity metrics from a single reference genome could help to identify populations that are at risk – even when few species-level phenotypes are documented – and to prioritise species for follow-up at the population level,” the researchers write in a paper in Nature.

However, large-scale comparative genomic projects like this can still provide a genetic basis for new technologies that target these vulnerable species.

“The reference genomes themselves support the development of technologies such as using gene drives to control invasive species or pursuing ‘de-extinction’ through cloning and genetic engineering,” they say.

Thankfully, they catalogued this genetic data so others can use it to design cost-effective, efficient DNA tests for further conservation efforts.

“Preserving, rather than merely recording, the biodiversity of the Earth must be a priority,” the authors write. “Through global scientific collaborations, and by making genomic resources available and accessible to all research communities, we can ensure that the legacy of genomics is not a digital archive of lost species.”

Interestingly, this wasn’t what they set out to discover.

“The core idea for the project was to develop and use this data to help human geneticists figure out which mutations cause disease,” says Lindblad-Toh.

They did identify some genes that could potentially harbour insights about protection from cancer in large mammals and how venom developed in some mammals, and potential SARS-Cov-2 animal hosts, but these were explored further in other papers. Of course, this is the core philosophy of their project – their data can be used by everyone.