Many large mammals have lost their genetic diversity, often thanks to the actions of humans in reducing their populations. These consequences can be severe because without genetic diversity, a population does not have a “genetic database” to adapt to environmental changes.
Iberian lynx (Lynx leopard) is no stranger to this decrease in diversity.
Human activities have driven populations to dangerously low numbers, leaving them with a shrinking gene pool. This loss of lynxes’ ability to adapt to changing environments threatens their survival.
Our team’s research shows how the Iberian lynx interbred with its cousin, the Eurasian lynx (Lynx Lynx) in the last few thousand years.
This admixture may have enhanced the genetic diversity of the Iberian lynx. This is a critical factor for its survival, especially as the species faces such an uncertain future.
Low genetic diversity can lead to “inbreeding depression,” where closely related animals produce offspring that are unfit for survival. In extreme cases, this can push entire populations or even species to the brink of extinction.
To enhance the genetic diversity of endangered populations, conservationists sometimes resort to “genetic rescue.” This includes introducing individuals from different populations in the hope that they will breed with local animals, reducing inbreeding and increasing genetic diversity.
Although this strategy can be effective, it is not without risk.
Introducing animals that are genetically very different can disrupt or dilute beneficial traits, potentially harming a population’s ability to survive and reproduce. This is a phenomenon known as “outbreak depression”.
Despite these risks, genetic rescue remains a valuable tool in conservation, although it is often approached with caution.
One of the most severe cases is the decline in genetic diversity of the Iberian lynx, which was once the most threatened cat species in the world. It is mostly found in parts of Spain and Portugal.
Rescue and recovery
Today, the Iberian lynx is recovering from near extinction. More than 400 fertility women were reported in the 2023 census.
This is a huge increase from just 25 in 2002. This turnaround is largely thanks to an ambitious conservation program over the past two decades, including coordinated breeding and reintroduction programs.
Part of this success is due to the “genetic rescue” effect, where the mixing of two remaining genetically distinct populations helped to increase the genetic diversity of the species.
Despite this progress, the Iberian lynx still faces significant challenges.
The population is a long way from reaching the minimum of 1,100 reproductive cells required for genetic survival. Therefore, its genetic diversity is one of the lowest ever recorded.
More genetic rescue can be a solution to increase diversity. But there is a catch – there is no other Iberian lynx population in the world that can serve as a source of new genetic material.
Ancient DNA can be extracted from historical remains or subfossil samples (animals that are not old enough to be considered true fossils but are not considered modern either).
By studying these, scientists can gain valuable insights into the genetic past of species and provide clear comparisons with their modern-day counterparts.
In 2015, our colleague Maria Lucena-Perez visited the laboratory of another colleague, Michael Hofreiter, in Germany for the first time to generate the first complete genome data from ancient Iberian lynx bones.
Extracting ancient DNA from bones is a highly specialized process that requires dedicated clean room facilities to avoid modern DNA contamination.
Collaboratively, our team extracted nuclear DNA from three ancient Iberian lynx specimens.
Two of them were approximately 2,500 years old. The third date back to more than 4000 years ago.
This was the first time that nuclear DNA was recovered from the ancient Iberian lynx. Maria’s achievement has significantly advanced our understanding of how the Iberian lynx has been genetically structured over thousands of years.
Our team analyzed and compared DNA with the modern Iberian lynx. Surprisingly, ancient lynxes showed even less genetic diversity than their modern descendants.
This finding was both unexpected and puzzling, given their drastic population declines over the past few centuries.
Mixing species
The missing piece of the puzzle came with the discovery that modern Iberian lynx populations have more genetic diversity than their ancient Eurasian lynx counterparts.
This suggests that the two species interbred successfully over the past 2,500 years, boosting the genetic diversity of today’s Iberian lynx.
These findings are consistent with genome-wide evidence of ancient gene flow from the Eurasian lynx to the Iberian lynx genome. While the two species do not share the same habitats today, they once lived together in the Iberian Peninsula and possibly in southern France and northern Italy.
This situation provided many opportunities for mixing.
The potential for these two species to meet naturally and breed once again is increasing as their range continues to expand. This could open up new opportunities for genetic diversity in the future.
The advent of whole-genome nuclear analysis in the past 30 years has revealed numerous cases of hybridization between species, such as polar bears and brown bears. This shows that the lynx case is not that unusual.
But the Iberian lynx stands out as the first documented example where interbreeding significantly increases genetic diversity at the species level.
We do not yet fully understand the exact effect of this genetic enhancement, particularly whether it improves population fitness and survival. One interesting possibility is that the Iberian lynx managed to survive despite its very low genetic diversity thanks to frequent genetic rescues from the Eurasian lynx.
While there is much more to learn, our research provides an unexpected but important case study for the broader debate about genetic rescue.
If we can predict the chance of inbreeding and inbreeding depression when mating occurs, we can use genetic rescue as a conservation tool in the current biodiversity crisis.
Johanna LA Paijmans, Postdoctoral Researcher in Zoology, University of Cambridge. Axel Barlow, Lecturer in Zoology, Bangor University, and Jose A. Godoy, Conservation Genomics Researcher, Donna Biological Station (EBD-CSIC)
This article from The Conversation is republished under a Creative Commons license. Read the original article.
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