ǧ����Ƶ

It’s hard to imagine a life more awful than a barnacle’s.

For half the day you’re battered by salty, cold water. For the other half, you bake in the hot sun. All the while, you still have to gather food, keep yourself safe from predators, and find a mate. Somehow, these strange crustaceans thrive in this environment. , a Whitman Center scientist at the Marine Biological Laboratory (MBL), wants to understand how they do it.

Rohner, a developmental biologist at the , has spent much of his career studying animals that make themselves at home in extreme environments. He visited the ǧ����Ƶ this summer with the intention of returning next year to expand his research towards marine animals, specifically barnacles. 

The animals that Rohner studies are characterized by a “feast or famine” lifestyle. They oscillate between periods of intense starvation and having a profound wealth of food, and they must capitalize on the latter to survive the former. Being able to switch between modes requires enormously flexible physiology, which fascinates Rohner.

The first species that Rohner studied is a fish named Astyanax mexicanus, or the Mexican tetra. This fish species consists of two distinct populations. One group lives in creeks and pools throughout southern Texas and northern Mexico and looks like any other small, silvery fish. The second group, meanwhile, is blind, colorless, and lives deep in caves. These caves are so dark that no plants grow within them; the fishes’ only food comes in the summer months, when flooding pushes debris into their subterranean pools. During this time, the fish must eat fast to consume enough food to get through the rest of the year. 

“A lot of food comes in, they eat a lot, get really fat, and then starve for a very long time,” Rohner said. It is one of the most extreme feast-or-famine lifestyles of any animal on the planet. 

Rohner has identified a whole suite of adaptations that help cave populations of Astyanax mexicanus survive in this dramatically fluctuating environment. Their melanocortin 4 cell-surface receptors, for instance, are mutated both to increase appetite and resist starvation. They are also resistant to insulin so their blood sugar can rise more than would otherwise be possible, and they retain more fat than their river-dwelling populations. All of these physiological adaptations allow them to survive in the extreme environments of the Mexican caves.