Figure 1. Three geographically-distinct populations of cavefish exhibit bone fragmentation and an increase in the number of SO3 superficial neuromasts.

The species Astyanax mexicanus includes surface-dwelling morphs inhabiting river systems throughout Mexico and cave-dwelling morphs found in caves throughout the El Abra mountain range (A). Fragmentation, as defined by the number of separate suborbital #3 (SO3) bony elements, was assessed for surface fish and three populations of cavefish (B; Chica, Tinaja and Pachón). The number of superficial neuromasts within the SO3 bony region were scored for each population (C). Pairwise t-tests were performed and populations were grouped by statistical significance (a-d). White scale bar set to 3mm. Map adapted from Mitchell et al. (1977).