A biologist is investigating blind cavefish, a type of fish residing in cave ponds in Mexico. His research has revealed that these fish begin to grow extra taste buds on their heads and chins starting at five months of age, and this growth continues into adulthood.
Over the course of thousands of years, cavefish have adapted by losing their sight, which is why they are referred to as “blind cavefish.” Interestingly, some of these fish have also developed an unusually high number of taste buds on their heads and chins.
A recent study published in the journal Communications Biology by researchers at the University of Cincinnati has identified the timeline for when taste buds begin to form in areas beyond the mouth. This study received support from the National Science Foundation.
Blind cavefish are found in cave ponds in northeastern Mexico and are characterized by their pale pink, nearly transparent appearance, in contrast to their silvery surface counterparts. Although cavefish have faint outlines of eye sockets, surface fish possess large, round eyes that give them a constantly surprised look.
Despite these noticeable physical distinctions, both types of fish are classified as the same species.
According to Joshua Gross, professor and senior author of the article, “While the regression, such as loss of eyesight and pigmentation, is a well-documented process, the biological factors behind the development of new features are not as well understood.” His lab focuses on exploring the evolution and development of fish that live in caves.
Although populations of blind cavefish with additional taste buds on their heads and chins were discovered in the 1960s, the developmental and genetic mechanisms behind this unique trait had not been further explored, Gross notes.
To find out when these extra taste buds emerge, Gross and his team studied the species Astyanax mexicanus, specifically two distinct cavefish populations residing in the Pachón and Tinaja caves in northwestern Mexico known for their extra taste buds.
The team discovered that from birth to five months, the number of taste buds in cavefish is comparable to that of surface fish. After this period, however, the number of taste buds begins to rise, appearing on the head and chin in clusters, continuing well into adulthood around 18 months.
Cavefish can live significantly longer than 18 months in the wild and in captivity. The researchers suspect that additional taste buds may continue to develop as the fish get older.
While the timing of taste bud development was similar for both populations of cavefish, Gross observed some differences in the density and pattern of growth. Another unexpected finding was that, despite the complexity of this trait, “the increased number of taste buds on the head seems to be primarily controlled by just two regions of the genome,” he explains.
The increase in taste buds coincides with a shift in the cavefish’s diet as they stop eating live food and begin to seek alternative sources, such as bat droppings. It’s also intriguing that this taste bud expansion may take place in other cave habitats even without bat populations, Gross adds.
With the additional taste buds, cavefish develop a more acute sense of taste, which Gross suggests is likely an evolutionary adaptation.
“The specific functional and adaptive significance of this enhanced taste system is still uncertain,” says Gross, prompting the research team to initiate new studies focusing on taste by exposing the fish to various flavors, including sour, sweet, and bitter.
