Analyzing the laterality of superficial facial neuromasts in Astyanax mexicanus

Abstract

Astyanax mexicanus are a species of fish that populate northeastern Mexico with both river-dwelling surface populations and cave populations. The cave fish have no eyes or pigmentation, and a variety of other altered behavioral traits, which allow them to adapt to the extreme darkness of the cave environment. Cave fish have also independently evolved enhanced lateral line systems to compensate for their lack of sight. This project aimed to determine if three populations of cave fish (Molino, Pachon, and Tinaja) differ from surface fish regarding the number of superficial neuromasts found in the suborbital 3 (SO3) region, and whether there are different degrees of asymmetry of neuromasts in the left vs. right side. An ImageJ code was used to outline the SO3 region on each side of a fish, and the number of neuromasts was also recorded. Using R programming, the average number of neuromasts on the right and left side, along with the total number of neuromasts for each population, was calculated. The absolute difference in neuromasts between each side for each fish was also analyzed. It was found that all cave fish populations contained more neuromasts when separately comparing the left and right sides, and when combined, than surface fish. Pachon and Tinaja populations also contained greater differences in the neuromast asymmetry than their surface counterparts. This gives more insight into mechanisms that drive the evolutionary selection of traits, and utility of asymmetry within the lateral line system in A.mexicanus populations.