Over thousands of years, blind cavefish evolved in cave ponds in northeastern Mexico, losing their vision in the process. They are pale pink and translucent compared to their silvery counterparts in surface rivers and streams. Some cavefish also developed an unusually high number of taste buds on their head and chin. However, the genetic and developmental processes behind this trait were not well understood until a recent study conducted by scientists at the University of Cincinnati, supported by the National Science Foundation.
The study focused on determining when the extra taste buds appear in blind cavefish beyond the oral cavity. The researchers looked at two cavefish populations in Mexico known for having additional taste buds. They found that the number of taste buds in cavefish is similar to surface fish from birth to around 5 months of age. However, after this initial period, the taste buds begin to increase in number and appear on the head and chin, continuing to do so well into adulthood, around 18 months and beyond.
The research team discovered that despite the similarities in the timing of taste bud appearance, there were differences in density and expansion timing between the two cavefish populations. Additionally, the genetic architecture of this trait revealed that the presence of more taste buds on the head is primarily controlled by only two regions of the genome. This suggests a level of complexity in the genetic regulation of this unique trait in blind cavefish.
The increase in taste buds in cavefish correlates with a shift in their diet from live foods to other food sources such as bat guano. This suggests that the expansion of taste buds may be an adaptive trait that aids in the detection of different flavors, contributing to their survival in their cave environments. The research team is now conducting studies focusing on exposing the cavefish to different flavors like sour, sweet, and bitter to better understand the functional and adaptive relevance of their augmented taste system.
Overall, this study sheds light on the evolutionary and developmental processes that have led to blind cavefish developing an excess of taste buds on their head and chin. By uncovering the genetic architecture and timing of taste bud appearance, researchers are gaining insight into how these cave-dwelling vertebrates have adapted to their unique environments. Further research into the adaptive significance of this trait may provide valuable information on the sensory capabilities and ecological strategies of blind cavefish.