Subterranean Fishes of the World

3269

2017

AIM 2017

Jumandi cave is home to Ecuador’s most charismatic troglobite, the catfish Astroblepus pholeter. It was defined as “essentially unpigmented” and published photos show yellow-white specimens. However, specimens we collected in 2016 do show pigmentation throughout the body, unlike the previously published photos. It is unknown if previous authors took photos with high contrast to create an enhanced image, collected a particularly unpigmented specimen, or if there has been introgression from surface fish. Since A. pholeter is not albino, we sequenced the MC1R gene. In mammals, MC1R variants result in red hair with light skin color due to low concentrations of eumelanin. Two mutations were found in ultra-conserved regions. Interestingly, the first locus has been discussed in the literature regarding pigmentation in felids, suggesting a functional consequence for the A. pholeter mutation. MC1R has also been the target of mutations in the regressive evolution of Astyanax cavefish. We propose convergent regressive evolution of the MC1R gene across cavefish species. The species was also portrayed with an unusual mechanosensory cave adaptation. The authors reported an increase in number of mechanosensory skin denticles along the dorsal surface of the head and trunk that could detect the direction of water flow and the proximity to the substrate by changes in fluid velocity. However, comparisons to the local surface loricarioid catfish show that A. pholeter actually has fewer denticles throughout its head and body than the local surface species. Behaviorally, A. pholeter can detect light and presents nyctophilia, a preference for darkness. Histology of the eye showed that despite reduction in overall size and the eye being embedded under the skin, A. pholeter has conserved all of the major components of the eye; lens, optic nerve, and all retinal layers. While dermal layers may blur images, the eyes are most likely functional.

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