Electronic Journal of Biology

Perspective

Natural selection is fuelled by genetic variation. It's a source of inheritable character differences that can help populations adapt to changing surroundings. The greater a population's genetic variety, the more likely some individuals in that population will be able to adapt to new environmental conditions. As a result, the population will not become extinct as a result of any changes. Small populations have little genetic diversity, while large populations have tremendous genetic diversity. When a species' population size plummets as a result of natural calamities, human irresponsibility, or anthropogenic actions, its genetic diversity suffers, resulting in a genetic bottleneck. When this happens, the population is not only stripped of its ability to survive, but it is also subject to inbreeding. Inbreeding is more likely to occur in small groups where genetically related individuals are more likely to mate with one another [1].

Inbreeding depression, a condition in which genetic variations with deleterious mutations accumulate over time, affects such populations. Cheetahs are a famous illustration of how inbreeding depression can push a species to extinction, despite substantial conservation efforts such as captive breeding programmes. A series of genetic tests were conducted to determine why captive breeding efforts in cheetahs were failing. Cheetahs were shown to be extremely inbred as a result of the combined effects of past natural disasters and indiscriminate human killing, according to these findings. Cheetahs became vulnerable to diseases as a result of inbreeding, which resulted in poor fertility and high infant mortality rates [2].

The genetic diversity of cheetahs was so severely reduced that a critical immune-related gene complex, which is normally quite polymorphic in most species, was monomorphic (lacks genetic variation) in cheetahs. This resulted in the abolition of over 80% of a captive breeding population of cheetahs in the United States due to feline infectious peritonitis, a common viral disease that kills 1% of domestic cats. Conservationists have attempted "genetic rescues" in captive and protected populations of various endangered species (Mexican red wolves, Puerto Rican crested toads, and African lions, to mention a few). To improve genetic diversity, genetic rescues are carried out by introducing new individuals (who can provide more genetic variance) into inbred communities [3].

However, in some species, such as the Ibex and Arabian oryx, such attempts can backfire, as they suffer from 'outbreeding depression.' Because such animals' populations are insular, with minimal immigration and emigration, gene flow between populations is typically negligible; as a result, each population seems genetically inbred. This, on the other hand, is beneficial to the population since it has evolved 'local adaptation' and preserves a specific combination of gene variants that enable better survival in local settings. Breeding programmes match individuals from other populations in a misguided attempt at genetic rescue by reversing local inbreeding to'recover' genetic diversity in such systems. Typically, the results of these attempts are dismal. Such couplings frequently produce offspring with genetic combinations that make them unable to live in either of the two local environments. Nubian ibex, for example, were brought into the Tatra highlands in an attempt to genetically save the Alpine ibex. Unfortunately, introduced ibex acclimated to warmer climates rutted in the autumn and gave birth to hybrid offspring in February, the coldest month of the year. These children, obviously, did not survive [4].

References

1. Lacy RC (1997). Importance of genetic variation to the viability of mammalian populations. J mamm. 78:320-35.
2. Latch EK (2020). Integrating genomics into conservation management. Mol Ecol Res. 20:1455-7.
3. Frankham R (1994). Conservation of genetic diversity for animal improvement. In Proceedings of the 5th World Congress on Genetics Applied to Livestock Production XI. 385-392.
4. Snyder NF, Derrickson SR, Beissinger SR, et al.(1996). Limitations of captive breeding in endangered species recovery. Cons Biol.10:338-48.