Mangrove killifish
The mangrove killifish is one of only two vertebrates known to fertilize its own eggs for reproduction.
Actually, the peculiar fish is full of surprises. It can be happy in freshwater or water twice as salty as the ocean. It can even live on land for up to eight weeks while breathing through its skin before flinging itself back into the water with a series of acrobatic 180-degree flips.
Still though, the fish’s propensity for sustaining self-love is what has piqued the interest of scientists at Washington State University.
A recent study conducted in part by Luana Lins, a postdoctoral researcher in the WSU School of Biological Science, found that despite their insular breeding habits, mangrove killifish are able to maintain a surprisingly diverse gene pool.
The study notes that “selfing,” the term given to solo-reproduction, has numerous benefits. First and foremost it allows singular fish to instantaneously begin reproduction once they find themselves in a suitable situation. However, the practice results in the replication of only one set of DNA, which deprives it of the diversity typically required to handle rapidly changing environments. Additionally, limited genetic diversity can increase the odds of dangerous mutations taking hold in a population.
Still, killifish have proven their ability to adapt to a vast array of inhospitable conditions in slippery defiance of the normal laws of nature. The proof is hidden deep within a genome known as the mangrove rivulus, Kryptolebias marmoratus, or “Kmar,” for short.
Working with genome scientist Joanna Kelley and other colleagues, Lins’ study was able to identify unusual activity in the Kmar genome sequence. A report published in the journal Genome described how they compared 15 different lineages of the species and discovered a surprising amount of genetic diversity. However, because of their singular genetic genesis, one generation of offspring is essentially identical to the next, much like clones.
Despite those familial similarities, the overall population of killifish displayed a notable lack of DNA uniformity.
“We found way more areas that were heterogeneous, heterozygous, than we expected if you just followed the logic of something that has been mating with itself for a long time,” said Lins in a news release from WSU. “That opens up a can of worms. How is that happening?”
Killifish populations include a small percentage of males, and scientists have speculated that some of their sperm is sometimes able to fertilize a small percentage of eggs belonging to other fish.
Another wrinkle to the sexual behavior of killifish may be contributing to their ability to maintain genetic diversity within their species. Separate studies have observed that when hermaphrodite killish are exposed to fish from different lineages, they are more likely to lay extra eggs than they would in the presence of a fish from the same lineage. A news release from WSU compared the phenomenon to the archetypal narrative of the “stranger in town,” noting that when fertile specimens see a stranger they are quick to attempt to capture the newly available DNA.
While Lins has reported that killifish can be trained to a feeding schedule, learning to wake up for feeding time, she admits that the prospect of a fish recognizing a new DNA opportunity is a sort of perception that is unlikely for most creatures.
“How they know how different the other individual is, we don’t know,” said Lins, in the release. “There are a lot of unknowns, and I think that’s the fun of science. We’re all trying to figure out what is going on with these fishes.”
