A morphometric analysis of polymorphism in the pharyngeal dentition of Cichlasoma minckleyi (Teleostei: Cichlidae)

Dental polymorphism in teleost fishes often involves production of a robust dentition, or “molarization”, in one morph. The lower pharyngeals of a sample of wild-caught individuals of the polymorphic Cuatro Cienegas cichlid, Cichlasoma minckleyi (Kornfield and Taylor) (Proc. Biol. Soc. Wash. 96 (1983) 253), were measured to investigate morphological changes associated with molarization. Principal components analysis demonstrates that dental variability in this species increases in larger fish, and that only the molariform morph contributes to this increase. Reduced major axis regression analyses between pairs of variables indicate that the papilliform morph increases both tooth measures and numbers, whereas the molariform morph maintains a relatively constant number of teeth as it produces teeth of progressively larger size. In the papilliform morph, negative allometric scaling between tooth size and dentigerous area is compensated for by addition of teeth. Tooth size variables are isometric in the molariform morph, and tooth numbers are nearly static. These results are consistent with those reported for other polymorphic cichlid species. Further study is required to elucidate the mechanisms whereby tooth form in polyphyodont species may respond to environmental factors (like food hardness), but possibilities include direct mechanical influences or transmission of signals via nerves to developing replacement teeth.