Subterranean Fishes of the World

3904

2016

The blind Mexican Cavefish, Astyanax mexicanus, has undergone extensive morphological changes, such as eye loss and pigmentation regression, following colonization of numerous caves in northeastern Mexico. Extant surface-dwelling forms of this species provide powerful comparisons between ancestral and derived morphologies. Several populations of cavefish are completely eyeless, which has had a dramatic effect on the shape and positioning of cranial bones. Further, cavefish harbor dramatic lateral asymmetries in their skull, such as premature bony fusions present on one side of the face and not the other. Using geometric morphometrics to capture shape variation, we performed a global shape analysis of the chondrocranium and osteocranium in juveniles and adults across surface fish, cave x surface hybrids and two geographically and phylogenetically distinct cavefish populations (Pachón and Tinaja). In juveniles, each population segregated into significantly distinct groups with respect to cartilaginous skull shape (p<0.05). Intra-individual shape asymmetry was found at the level of individual bones in adults, such as the opercle bone in hybrids (p=0.0015). We also found segregation of shape by performing an inter-individual analysis across adult surface fish, cavefish, F1 hybrids and F2 hybrids. By removing the landmarks outlining the eye, we found that the shape of the eye orbit is not the only factor that differs between the surface and cavefish skull (p<0.0001). This result may highlight other shape changes, such snout shape and jaw width, which evolved as a foraging mechanism in the dark caves. This work reveals dynamic changes to the craniofacial skeleton, over the course of life history, which likely arose in response to the extreme environmental pressures of the cave environment.

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23rd International Conference on Subterranean Biology

2016

2016

2016