Differences in chemosensory response between eyed and eyeless Astyanax mexicanus of the Rio Subterráneo cave

TLDR

Blind cave-dwelling Astyanax mexicanus have evolved morphological and behavioral shifts, including modifications of the lateral line and taste buds, and it has been hypothesized that their olfactory system may have also adapted to aid food searching in darkness. During a March 2013 expedition to the Sierra de El Abra region, researchers tested the chemosensory abilities of the Rio Subterráneo cave population, which contains a hybrid mix of troglomorphic and epigean phenotypes. In situ behavioral tests revealed that eyeless fish were more attracted to food extracts and had larger naris openings than eyed counterparts, indicating that chemosensory capabilities and naris size may have evolved adaptively in cave-dwelling populations.

Abstract

Abstract Background In blind cave-dwelling populations of Astyanax mexicanus , several morphological and behavioral shifts occurred during evolution in caves characterized by total and permanent darkness. Previous studies have shown that sensory systems such as the lateral line (mechanosensory) and taste buds (chemosensory) are modified in cavefish. It has long been hypothesized that another chemosensory modality, the olfactory system, might have evolved as well to provide an additional mechanism for food-searching in troglomorphic Astyanax populations. Findings During a March 2013 cave expedition to the Sierra de El Abra region of San Luís Potosi, Mexico, we tested chemosensory capabilities of the Astyanax mexicanus of the Rio Subterráneo cave. This cave hosts a hybrid population presenting a wide range of troglomorphic and epigean mixed phenotypes. During a behavioral test performed in situ in the cave, a striking correlation was observed between the absence of eyes and an increased attraction to food extract. In addition, eyeless troglomorphic fish possessed significantly larger naris size than their eyed, nontroglomorphic counterparts. Conclusions Our findings suggest that chemosensory capabilities might have evolved in cave-dwelling Astyanax mexicanus and that modulation of naris size might at least partially underlie this likely adaptive change.