Meeting Abstract
The Mexican tetra, Astyanax mexicanus, has evolved a number of regressive (pigmentation and eye loss) and constructive (enhanced lateral line and gustatory systems) phenotypes. Craniofacial anomalies, such as bone fragmentation and cranial bending, however escape simple classification. Prior work demonstrated that cavefish have more superficial neuromasts (SN) atop their fragmented facial bones, and this trait may facilitate certain cavefish behaviors facilitating food finding (e.g., vibration attraction). To understand how sensory and skeletal traits may interact with one another, we co-analyzed a number of phenotypes in surface fish and three cavefish populations, including: degree of fragmentation, third suborbital bone (SO3) size, severity of bend, eye orbit diameter, sixth suborbital bone (SO6) presence, and superficial neuromast (SN) and canal neuromast (CN) numbers. We found that fragmentation severity varied, with Pachón fish having the most elements followed by Tinaja and Chica. Fragmentation increased the surface area (SA) and volume (V) of the SO3. All cave populations had more SNs and higher SN density compared to the surface morph. CN number and placement was symmetric in surface fish, but varied greatly in all three cave populations. The presence of a ninth CN was perfectly associated with presence of the SO6 bone. Further, individuals lacking an SO6 had a smaller eye orbit. Compared to highly symmetric surface fish, Pachón and Tinaja cavefish exhibited a leftward dorso-cranial bend, while Chica cavefish exhibited moderate bends without a directional bias. This study represents the first comprehensive co-analysis of the sensory and skeletal systems in Astyanax mexicanus, and illustrates how craniofacial anomalies and sensory enhancement may interact to enable adaptation in the extreme cave environment.
