Each year, thousands of southern elephant seals (Mirounga leonina) haul themselves onto land to breed. For the males, this means fighting off rivals. While this may seem difficult, female elephant seals have it harder. After they give birth, they have to remain on land while their pups need milk, meaning that they don't get to eat for almost a month. And once the pups are weaned, they too must fast for weeks while their mothers go off to find themselves something to eat in the ocean. But maybe this hardship is preparing the young seals for their life ahead. Soon, they'll need to leave the beach and spend months at sea, potentially diving down over 2000 m to find food. Could this period of fasting help prepare them for what's to come? Laura Charlanne of the Université de Strasbourg, CNRS, ANR HYPO 2, France, along with a team of other French researchers headed to the Kerguelen Archipelago in late October 2022 to see whether young elephant seals were getting prepped for their life at sea, or whether they're born ready to dive.
After arriving on the island to the north of Antarctica, Charlanne and the team had to deal with the blustery wind and frigid temperatures while taking samples of muscle and blood from mother seals and their pups. The team were interested in whether the seals’ mitochondria – structures in the cell that use oxygen to make energy – were different when they were adults and had experience going long periods without oxygen during dives. Surprisingly, the mitochondria of the mother seals worked almost the same as they did in the young seals. The researchers knew from earlier studies that the mitochondria of seals at sea work differently from normal, helping the seals dive without running out of energy. This means that their mitochondria can switch between life on land and life at sea. If the mitochondria aren't working differently in the mothers and the pups, maybe the seals’ muscles are different after they've spent a good deal of time away from shore?
After checking the kinds of muscle fibers the seals had, the scientists didn't see any differences between the mothers and the pups. So, the team turned to the blood samples instead. They found that the mothers expressed higher levels of antioxidant genes which keep them protected from toxins that the mitochondria produce while making energy. The mothers also expressed higher levels of genes that help them deal with low oxygen levels. Charlanne and colleagues suggest that this is probably because the mother seals have already experienced these low oxygen levels during dives while the pups have not.
So, what helps the young seals prepare for life at sea? The team believe that it's a combination of things, not just the practice dives they do while learning how to swim. First, the fact that their mitochondria can switch so easily from life on land to life at sea helps the young seals, but also the time that they spend practicing swimming but not being able to eat seems to be important in priming their bodies to go on these deep dives to forage for food. Although there is still work to be done, Charlanne and colleagues are confident that the short time the seals spend hungry helps them to feast later.
