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Inbreeding can actually be beneficial for some species in the long run

The Svalbard reindeer, among all reindeer subspecies, stands out for its high level of inbreeding and notably low genetic diversity.

Around 7,000 to 8,000 years ago, the first reindeers made their journey to Svalbard, likely traversing from Russia via Novaya Zemlya and the islands of Franz Josef Land. Starting perhaps with just a handful, their arrival on the Arctic archipelago might seem a precarious foundation based on evolutionary theory.

High inbreeding rates can lead to an accumulation of damaging genetic mutations which can cause disease and decrease survival rates.

Adapting rapidly to extreme environments

Nicolas Dussex, a postdoctoral researcher from the Norwegian University of Science and Technology’s (NTNU) Department of Natural History, studied this phenomenon more closely. Dussex noted that despite these initial challenges, the Svalbard reindeer has not only survived but thrived. Their population now exceeds 20,000 animals.

Dussex highlights their remarkable evolution to adapt to the extreme Arctic conditions. Compared to other northern reindeer and caribou subspecies, they are smaller, have shorter legs, can digest mosses in the absence of lichens, and can adjust their circadian rhythm to suit the drastic seasonal changes of Svalbard.

A collaborative research initiative involving NTNU and other institutions has delved deeper into the genetic makeup of the Svalbard reindeer. By examining genetic samples from 91 reindeer, the study aimed to uncover differences between them and their mainland relatives.

Professor Michael D. Martin, from NTNU’s Department of Natural History, remarked on the valuable insights that can be gleaned from studying such isolated populations, especially considering the Svalbard reindeer’s history of near extinction in the early 1900s due to excessive hunting.

Staving off extinction by inbreeding

This near brush with extinction, resulting in only a few survivors, is termed as a ‘bottleneck’ in population biology. Such a scenario typically spells doom for a species due to increased inbreeding.

However, this inbreeding might have a silver lining. Known as ‘purging’, this process can potentially help eliminate harmful mutations. As harmful mutations manifest more rapidly in inbred populations, affected offspring tend to reproduce less, ensuring these damaging genes are less likely to be passed on. Dussex pointed out the paradox that, in the long run, inbreeding can have positive effects.

Parallels found in other animal species

The research also drew parallels with New Zealand’s Kakapo parrots, which, after a long period of isolation and inbreeding, showed signs of harmful genetic variants being eradicated from their population.

Brage Bremset Hansen, a senior researcher at NTNU and the Norwegian Institute for Nature Research, emphasized the significance of these findings for population management and broader genetic studies. He cited the good genetic health of the Svalbard reindeer, despite the potential harmful mutations.

However, Dussex shared that there remain unanswered questions regarding the speed at which these mutations are counteracted, either over short spans of centuries or over millennia. This is a research area they’re keen to expand upon, utilizing DNA samples from ancient bone remains and antlers.

Moreover, the team is also invested in understanding the beneficial mutations that have allowed the reindeer to thrive in Svalbard’s unique environment. Researcher Mathilde Le Moullec has been instrumental in this, gathering most of the bone samples from across Svalbard.

Overcoming speed of climate change

A looming threat to these reindeers, however, is the accelerating pace of climate change. As Svalbard faces some of the fastest climate change rates worldwide, there’s uncertainty over the reindeer’s adaptability to the altered conditions. The rapid transformations in snow cover and vegetation could pose significant challenges.

Hansen warned that the adaptability the reindeers showcased after initially colonizing the islands might not extend to the current fast-paced warming. Their diminished genetic variation could be a stumbling block.

This situation could reflect the struggles of many terrestrial animals limited in mobility, as they grapple with the swift and disruptive changes caused by global warming. Yet, Martin remains hopeful, suggesting that this research lays a foundation for a deeper understanding of species adaptation capabilities in ever-shifting environments.

The full study was published at iScience.

More about inbreeding

Inbreeding, the mating of close relatives, is a phenomenon observed throughout the animal kingdom. It profoundly influences species’ genetic diversity and evolutionary trajectory.

Inbreeding acts as a double-edged sword. It can both accentuate detrimental mutations and, paradoxically, can lead to the purging of these harmful alleles from the gene pool. This then enhances a species’ adaptation and survival.

Biodiversity Crisis

Inbreeding typically occurs when populations become isolated or decrease in size, leading to reduced genetic diversity. It increases homozygosity, whereby offspring inherit identical alleles from both parents.

This genetic similarity often brings recessive, harmful mutations to the forefront, causing a range of genetic disorders and decreasing overall fitness and survival rates.

Many species, including the cheetah and the giant panda, are witnessing the detrimental impacts of inbreeding. This is due to their shrinking, isolated populations, and habitat loss. Reduced genetic diversity makes these species more susceptible to diseases and decreases their ability to adapt to environmental changes.

Purging and beneficial mutations

Conversely, inbreeding can also be a mechanism for genetic refinement. As harmful mutations become more pronounced, individuals carrying these mutations are less likely to reproduce, gradually eliminating these deleterious alleles from the population.

As mentioned previously, this process is known as ‘purging’ and can theoretically lead to more robust populations in the long run. Instances of inbreeding, such as seen in the Svalbard reindeer, illustrate how isolated populations can survive and even thrive despite high levels of inbreeding. They owe their survival to the elimination of harmful genetic variants over time.

Adaptive evolution

Inbreeding may also expedite the fixation of beneficial mutations within a population, thereby fostering adaptive evolution.

When beneficial alleles arise, inbreeding can help spread these favorable traits quickly throughout the population. This allows the species to adapt more rapidly to their environment.

This is particularly significant in isolated or newly established populations, where rapid adaptation can be crucial for survival.

Inbreeding management

Recognizing the complex impacts of inbreeding is vital for conservation efforts and biodiversity management. Scientists actively study inbreeding patterns and their consequences to devise strategies for maintaining genetic diversity within endangered populations.

In many cases, interventions like translocations are utilized to introduce new genetic material into inbred populations. This process enhances their genetic health and adaptive potential.

Zoos and wildlife conservation programs often employ careful breeding strategies to prevent inbreeding depression and maintain the genetic vigor of endangered species.

In summary, inbreeding plays a complex, dual role in the animal kingdom. While it often leads to a decline in genetic diversity and can bring harmful mutations to the forefront, it also provides a pathway for the elimination of these deleterious alleles and the amplification of beneficial ones, fostering adaptive evolution.

A nuanced understanding of inbreeding and its impacts is crucial for the effective conservation and management of biodiversity in a rapidly changing world.

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