The cavefish, Astyanax mexicanus, is an exciting model organism that provides us with a clear ecological adaptation scenario, the adaptation to the subterranean cave environment. The model is perfect to study the combination of environment and the resulting variation, given the direction of evolution and adaptation is known (from surface to cave) and the environment of the cave provides reasonably well defined environmental parameters such as the lack of light, the scarcity of food, and the absence of predators. Most importantly the ancestral surface form remains interfertile with the cave populations, allowing for genetic (e.g. Quantitative Trait Loci - QTL) and developmental studies.
Our current main focus in the lab is to study the genetic basis of metabolic adaptation. Among the biggest challenges for animals in a cave environment is the scarcity of food. Since caves are completely dark, no primary photosynthetic producers can survive in this extreme environment. Therefore, cavefish depend from food sources outside of the caves, mostly input from bats and seasonal flooding. Given the unpredictability of such food sources, cavefish have adapted to long starvation periods and optimized their metabolism accordingly.
For example, cavefish have increased their appetite, enlarged fat reservoirs, and altered fat and lipid deposition. Despite these impressive changes to their metabolism, cavefish remain healthy, fertile and do not show any sign of distress, even when fed high fat diets.
In a recent study we found that cavefish are showing phenotypes that are usually associated with diabetes patients, such as high blood sugar, glucose intolerance and insulin resistance. But in contrast to humans, cavefish are using these phenotypes to grow faster and and gain more weight. As such they presumably have found strategies to circumvent the typically negative consequences associated with these phenotypes. As a matter of fact we found common markers of diabetes such as inflammation and glycation end products to be reduced in cavefish.
Check out our latest paper on insulin resistance in cavefish
We are aiming to study the genetic basis of these physiological alterations in order to understand adaptation to nutrient poor environments with the ultimate goal of finding ways to counteract our own health problems which arise as a consequence of living under conditions we are not adapted to.
Recently we have become interested in the interface of the immune system and inflammation and the metabolic changes we observe in cavefish.
Distribution of the 29 known cavefish populations in Mexico (white circles).
C, D show some exemplary habitats of the ones we are currently studying (F-H).
Stowers Aquatics Core cavefish facility located next to the Rohner Lab.
Our custom built state-of-the-art Pentair systems (10 racks) are individually monitored and controlled to ensure the best health, growth and breeding success of several thousand cavefish.
Surface fish and cavefish of the same species, Astyanax mexicanus
Cavefish display many phenotypes usually associated with metabolic syndrome, such as larger amount of visceral fat and insulin resistance as part of their strategy to survive under limited nutrient availability in the cave environment. Interestingly, these phenotypes, however, do not lead to health problems in cavefish.