by Many large mammals have lost genetic diversity, often thanks to the actions of humans who are reducing their populations. The implications can be serious, because a population without genetic diversity has no ‘genetic database’ to fall back on to adapt to environmental changes.
The Iberian lynx (Lynx pardinus) is no stranger to this reduction in diversity.
Human activity has driven populations to dangerously low numbers, leaving them with an ever-shrinking genetic pool. This loss threatens the lynx’s ability to adapt to changing environments, jeopardizing their survival.
Our team’s research shows how the Iberian lynx interbred with its cousin, the Eurasian lynx (Lynx-lynx) of the past few thousand years.
This mixing may have increased the genetic diversity of the Iberian lynx. This is a crucial factor for its survival, especially as the species faces an uncertain future.
Low genetic diversity can lead to “inbreeding depression,” where closely related animals reproduce and produce offspring that are less fit to survive. In extreme cases, this can push entire populations, or even species, to the brink of extinction.
To increase the genetic diversity of populations on the brink, conservationists sometimes turn to “genetic rescue.” This involves introducing individuals from different populations in the hope that they will breed with the local animals, reducing inbreeding and increasing genetic diversity.
While this strategy can be effective, it is not without risks.
Introducing animals that are too genetically different can disrupt or dilute beneficial traits, potentially harming the population’s ability to survive and reproduce. It’s a phenomenon known as ‘outbreeding depression’.
Despite these risks, genetic rescue remains a valuable conservation tool, even if it is often approached with caution.
One of the most serious cases of reduced genetic diversity is the Iberian lynx, once the most endangered cat species in the world. The species is mainly found in parts of Spain and Portugal.
Rescue and recovery
Today, the Iberian lynx is recovering from near extinction. More than 400 reproductive females were reported in the 2023 census.
This is a huge increase from just 25 in 2002. This turnaround is largely due to an ambitious conservation program over the past twenty years, involving coordinated breeding programs and reintroductions.
Part of this success is due to the ‘genetic rescue effect’, where mixing the two remaining genetically distinct populations has helped increase the genetic diversity of the species.
Despite this progress, the Iberian lynx still faces significant challenges.
The population is far from reaching the minimum of 1,100 reproductive females needed to be considered genetically viable. Genetic diversity therefore remains one of the lowest ever measured.
Further genetic rescue could be a solution to increase diversity. But there’s a catch: no other Iberian lynx populations exist in the world that could serve as a source of new genetic material.
Ancient DNA can be extracted from historical remains or from subfossil samples (animals that are not old enough to be considered true fossils, but are also not considered modern).
By studying these, scientists can gain valuable insights into the genetic past of species, providing a sharp comparison with their current counterparts.
In 2015, our colleague Maria Lucena-Perez first visited the laboratory of another colleague, Michael Hofreiter, in Germany to generate the first-ever whole genome data from ancient Iberian lynx bones.
Extracting ancient DNA from bones is a highly specialized process that requires special cleanroom facilities to avoid contamination by modern DNA.
Working together, our team successfully extracted nuclear DNA from three ancient specimens of the Iberian lynx.
Two of these were about 2,500 years old. The third dated from more than 4,000 years ago.
This was the first time nuclear DNA had ever been recovered from the ancient Iberian lynx. Maria’s achievement has significantly increased our understanding of how the genetic makeup of the Iberian lynx has evolved over thousands of years.
Our team analyzed and compared the DNA with that of the modern Iberian lynx. To our surprise, ancient lynx showed even lower genetic diversity than their modern descendants.
Given the sharp decline in their population over the past few centuries, this finding was both unexpected and confusing.
Types of Crosses
The missing piece of the puzzle came with the discovery that modern Iberian lynx populations share more genetic variants with the closely related Eurasian lynx than their ancient counterparts.
This suggests that the two species have successfully reproduced over the past 2,500 years, increasing the genetic diversity of today’s Iberian lynx.
These findings are consistent with extensive genomic evidence of ancient gene flow from the Eurasian lynx to the Iberian lynx genome. Although the two species do not share the same habitats today, they once coexisted on the Iberian Peninsula, and possibly in southern France and northern Italy.
This situation would have offered sufficient opportunities for crossing.
The potential for these two species to naturally meet and reproduce is growing again as their range continues to expand. This could open up new possibilities for genetic diversity in the future.
The advent of complete nuclear genome analysis over the past thirty years has revealed numerous cases of interbreeding between species, such as between polar bears and brown bears. This suggests that the case of the lynx is not that unusual.
But the Iberian lynx stands out as the first documented example where interspecies breeding significantly increases genetic diversity across the species.
We still don’t fully understand the exact effect of this genetic boost, especially whether it has improved population fitness and survival. One intriguing possibility is that the Iberian lynx has managed to persist despite its extremely low genetic diversity, thanks to repeated genetic rescues by the Eurasian lynx.
While there is still more to learn, our research provides an unexpected but important case study for the broader discussion of genetic rescue.
If we can better predict the chances of inbreeding and outbreeding depression when interbreeding occurs, we can more effectively use genetic rescue as a conservation tool in the ongoing biodiversity crisis.
Johanna LA Paijmans, postdoctoral researcher in zoology, University of Cambridge; Axel Barlow, lecturer in zoology, Bangor University, and José A. Godoy, researcher Genómica de la Conservación, Estación Biológica de Doñana (EBD-CSIC)
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