Conference Paper
The evolution of scleral ossification in the Mexican Cavefish (Astyanax mexicanus)
O'Quin, K.E., Doshi, P., Lyon, A., Hoenemeyer, E., Yoshizawa, M. and Jeffery, W.R.
Record Number:
3902
Year:
2016
Abstract:
The sclera is the tough outer covering of the eye. In some fishes, reptiles, and birds, the sclera is reinforced with a ring of hyaline cartilage or bone that forms from scleral ossicles. Currently, the evolutionary and genetic basis of scleral ossification is poorly understood, especially in teleost fishes. We assessed scleral ossification among the eyed (surface) and eyeless (cave) morphs of the Mexican tetra (Astyanax mexicanus). Although surface fish have bony sclera similar to other teleosts, the ossicles of cavefish generally do not form. We assessed scleral ossification in cavefish from multiple populations and used ancestral character state reconstructions to determine how many times scleral ossification has been lost. We then confirmed this result by assessing complementation of scleral ossification among the F1 hybrid progeny of two cavefish populations. Finally, we quantified the number of scleral ossicles present among surface x cave F2 hybrids and used this information to identify quantitative trait loci (QTL) responsible for scleral ossification. We found that the loss of scleral ossification is common – but not ubiquitous – among Astyanax cavefish, and that this trait has been convergently lost at least three times, which is confirmed by the presence of wild-type, ossified sclera among the progeny of our complementation cross. We observed a strongly skewed distribution of scleral ossicles among the surface x cave F2, suggesting that scleral ossification is a threshold trait with a complex genetic basis. Quantitative genetic mapping identified a single QTL for scleral ossification on Astyanax linkage group 1. We estimate that the threshold for this trait is likely determined by at least three genetic factors which may control the severity and onset of lens degeneration in cavefish. We conclude that complex evolutionary and genetic patterns underlie the loss of scleral ossification in Astyanax
Times Cited:
1
Conference Name:
23rd International Conference on Subterranean Biology
Conference Year:
2016
Conference Location:
2016
Conference Location:
2016
Relevent Species: