The influence of subterranean habitats in the sensorial and brain morphology of hypogean and epigean Copionodontinae catfish (Siluriformes, Trichomycteridae)

Brazilian cavefishes are among the richest troglobitic ichthyofauna worldwide including 13 genera. Most cavefish in the Neotropical region belong to Siluriformes. Trichomycteridae are highly diverse siluriforms, and the subfamily Copionodontinae are notably primitive in body shape, showing unique specializations to cave life. We studied the sensorial morphology referring to perception of the environment and processing of this information in four species Copionodon pecten , C. lianae , Glaphyropoma spinosum , and G. rodriguesi , of which G. spinosum is the only hypogean species, involved in perception of presenting some classical troglomorphisms such as reduction of eyes and body pigmentation, in addition to brain morphometry. Previous studies have demonstrated that troglobitic copionodontines are highly agonistic; therefore we measured the barbels, eyes and counted pores of the lateral canal system on the head. A PERMANOVA was performed to test for statistically significant differences in these morphological traits among the species groups. These similarities were significant among both genera and epigean and hypogean populations in terms of external morphometric/meristic and morphometry of the brain. G. spinosum has a longer telencephalon than the other studied species, a region related to olfaction, spatial memory and species-specific behavior such as social interactions and reproductive behavior, a region typically wider in the studied hypogean fishes. We detected troglomorphisms (character states related to isolation in subterranean habitats) in the laterosensory cephalic system of the whole group, such as the reduction of anterior canal segments in relation to other trichomyterids, indicating that all four species have exaptations to inhabit hypogean habitats. Although we could not confirm the existence of morphological differences between the two genera, the hypogean and epigean populations of these endemic Chapada Diamantina cave catfishes may exhibit morphological similarities.