Subterranean Fishes of the World

3216

2013

AIM 2013

When an animal colonizes an extreme environment, numerous regressive and constructive morphological traits undergo rapid evolution. Blind Mexican cavefish, which reside in total darkness, have evolved a spectrum of defects in the craniofacial skeleton including fragmentation, reduced bony area, and dermal bone fusion. These traits remain difficult to categorize as obviously regressive or constructive. Modifications to the cavefish cranial structure, which deviate from the normal morphology of surfacedwelling fish, were first reported in the 1940s. The genetic and developmental bases of these cranial bone alterations, however, remain only partially understood. In this study, we investigated a number of osteological traits in the context of a large F2 mapping pedigree of surface x cave hybrids (n=227). We subjected each individual to an exhaustive set of craniofacial measurements, including area, count and fusion assessment within the circumorbital bone series and nasal region. In addition, we also assessed a variety of other well-characterized traits that segregated in this cross (e.g., eye size, albinism). We discovered a previously unappreciated asymmetry in suborbital bone fragmentation, as well as frequent fusion of bones. Consistent with prior studies, our preliminary results do not indicate these craniofacial abnormalities are strictly predicted by visual system regression. Here, we present results of additional correlation studies testing the participation of other morphological traits (e.g., nasal region area) on the incidence of fragmentation. Further, we investigated the presence of QTL mediating both left and right sides of the craniofacial skeleton to determine if identical genetic loci actuate the asymmetric presence of fragmentation and fusion. Significant QTL were discovered exclusively on the right side for both fragmentation and fusion, suggesting that there may be a genetic basis for asymmetrical development. For example, pleiotropic interactions between genes selected in the cave environment for constructive traits, such as cranial neuromast expansion, may interfere with normal patterns of bone ossification.

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