Evolvability of Tooth Location in Teleost Fishes

Abstract

The form and distribution of teeth in vertebrates are closely related to feeding mode, but the pattern of dental diversification may differ substantially among related taxa. Whether these differences are the result of differences in ecological opportunities or in the evolvability of such taxa is rarely distinguished. The orders Cypriniformes (carps, loaches, minnows, and relatives) and Characiformes (tetras, piranhas, and relatives) are dominant elements of the freshwater fish fauna, with over 4200 and 2300 species, respectively. Both groups exhibit a diversity of feeding modes, ranging from detritivory to herbivory to carnivory, but differ significantly in the location of dentition. Teeth in cypriniforms are restricted to the posterior ventral pharynx, while in characiforms they are variably present on the dorsal as well as ventral pharynx, the oral jaw margins, and bones of the palate. The dentition of both groups represents reduction from the ancestral condition of teleost (modern ray‐finned) fishes, in which teeth were present on virtually all of the bones lining the oral and pharyngeal cavities. We hypothesized that differences in tooth location in the groups may reflect differences in the retention of ancestral developmental potential for dentition, a form of evolvability. To test this hypothesis, we ubiquitously and continuously expressed a tooth initiation signal, the ectodysplasin ligand, in the cypriniform zebrafish (Danio rerio) and found that potential for ectopic dentition was limited to the upper pharynx. In contrast, similar expression of ectodysplasin in the characiform Mexican tetra (Astyanax mexicanus) resulted in ectopic teeth widely distributed in the oral and pharyngeal cavities. Included among the bones bearing ectopic teeth were the ectopterygoids and endopterygoids, palatal bones on which teeth are variably present in characiforms. To investigate whether the retained potential for dentition has been utilized in the diversification of characiforms, we mapped palatal tooth characters on previously‐published phylogenies of the group and found evidence for the evolutionary reappearance of teeth on both the ectopterygoids and endopterygoids. Taken together, our results suggest that the evolvability of tooth location differs among teleost fish lineages and that such differences may have led to differences in patterns of dental diversification.Support or Funding InformationThis study was supported by NSF grants IOS‐0446720, IOS‐1121855, and NIH grant R03 DE016328‐01.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.