HAWAIIAN MONK SEAL GENETICS

Tavishi

During the 19th century, the Hawaiian monk seal was hunted to near extinction, just as most pinnipeds in the time. As a whole, most pinniped species very successfully recovered, like the Antarctic fur seal and the ever abundant California sea lion.

While most species recovered, the unlucky Caribbean monk seal and Japanese sea lion were hunted to extinction in the 20th century. Both species have had unconfirmed sightings in the past few decades, but its highly unlikely either of them are still present in the wild.

Some species, to this day, haven't fully recovered from past exploitation, and continue to suffer at the hands of humans. Chiefly among these are the critically endangered Hawaiian and Mediterranean monk seals, of which both species experienced significant population bottlenecks.

A population bottleneck is the narrowing of a population because of a threat to the population like hunting, bycatch, natural disaster, infection, or anything else; similar to how the neck of a bottle narrows. In 2004, only about 150 individuals were found in the wild.

The population has grown steadily to about 1,500, and the number only increases. But before that 150, numbers were even fewer. At which point, in order for populations to grow, quite a bit of consanguinity (science-y word for inbreeding) had to occur. While the seals were not left with Hapsburg-esque chins, there are certain genetic markers indicative of quite a bit of inbreeding within the population.

Consanguinity is genetically dangerous because it narrows the gene pool, reducing genetic diversity. As a result, there is less resistance to disease and other things. A variety of genotypes within a population allows for greater genetic resistance.

One of the indicative features of consanguinity within a population is a reduction in heterozygosity. Inbreeding causes a shift away from a middle ground.

Take an example. Two parents, one homozygous recessive and another homozygous dominant, breed and produce two heterozygous children. Now, if those two heterozygous children breed, their children are more likely to be homozygous recessive and dominant than their progenitors. As the population continues to grow, less and less children will end up being heterozygous in the long run, causing a shift towards two extremes. At some point, there were only about 23 individuals contributing to the Hawaiian monk seal gene pool.... not good...

The most prominent gene affected by low heterozygosity is MHC class II- VERY NOT GOOD! MHC class II genes are critical for immune system function. MHC stands for major histocompatibility complex, and these proteins present antigens on the surface of cells like B cells. This is essential for the initiation of the innate response.

The Hawaiian monk seal is known for extremely low genetic diversity, which isn't exactly promising for the future of the species, and resistance to disease. And so, increased involvement from groups like the Marine Mammal Center has been a potential and helpful solution. For example, vaccination of monk seals in the wild for parvovirus has been an attempt to not excessively burden the species with yet another threat to population.