A Shark Divide

 A recent Forbes article, titled "Three Sharks, Three Fates: The Genetic Divide Of Great Whites" by marine scientist and science communicator Melissa Cristina Marquez covers new research published by scientific journal Current Biology. Researchers Isabel Wagner, Irina Smolina, Martina E.L. Koop, etc. took genetic samples of 89 different Great White Sharks, then categorized the sharks by genetic similarity.

It turns out that Great White Sharks are genetically divided into three lineages: North Atlantic, North Pacific, and Indo-Pacific. These lines rarely mix due to habitat isolation. Specifically, ocean currents keep these groups of sharks apart in different ocean basins. Yet, interbreeding is still possible. The researchers also bring into question the possibility of sharks inheriting roaming behavior, a possible reason why different shark lineages may also stay on their respective areas.

This divide, however, presents a problem for the species in that depletion of one group could not be replenished by another. Marquez mentions that the genetic divide puts the Great White Shark in real danger of extinction, especially combined with other threats, such as pollution or poaching.

Could the three different lineages of the Great White Sharks evolve into completely new species, with their own separate niches? It is possible, but unlikely that we would see it anytime soon. Or, could there only be one lineage that survives? As of now, the possibilities for where this genetic division might go are practically endless. What may be be most likely (and most cynical to reason) is that human-caused habitat destruction and poaching may result in all three lineage's deaths. Evolution is happening now, all around us, and with us. It's hard to tell what direction it may go.

Pondering aside, I would like to do more research on each type of lineage. Different lineages concentrated in each area might indicate differences in each type of shark. That could mean differences in diet, physical appearance, or it could just be genetic differences. Either way, I would like to know.

ARTICLES:

https://www.forbes.com/sites/melissacristinamarquez/2024/11/08/three-sharks-three-fates-the-genetic-divide-of-great-whites/

https://www.sciencedirect.com/science/article/pii/S0960982224008601?dgcid=coauthor

https://www.britannica.com/science/ocean-basin

https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Map%3A_Raven_Biology_12th_Edition/22%3A_The_Origin_of_Species/22.01%3A_The_Nature_of_Species_and_the_Biological_Species_Concept/22.1.02%3A_Formation_of_New_Species/22.1.2.2%3A_Reproductive_Isolation#:~:text=In%20some%20cases%2C%20populations%20of,now%20reproductively%20and%20genetically%20independent.

Fatter is Better for Marine Mammals

     For land mammals, we typically see weight gain as a negative thing; it slows us down, it makes us use more energy to get to the same place, and its not too attractive. However, it is found that in northern elephant seals (mirounga angustirostris), the opposite is true.

     Plumping up for the elephant seals is how they remain a better swimmer, and more buoyant. Diving down takes the mammals a considerable amount of energy, but the more buoyant they are, the easier it is for them to come up. This makes it easy for them to dive down deep and can travel far away from their breeding grounds, nearly 4000 km away. A fully plumped female takes half as many strokes per meter and have a much easier time ascending after a dive, another study has shown.
     I think this was interesting how marine mammals differ so much from land mammals even though they are both mammals. Thinned out marine mammals can't swim far, can't hunt deep down, and are overall less able to survive, which is the polar opposite of how weight gain would be detrimental to a human.