PHENOTYPIC PLASTICITY IN THE LOWER PHARYNGEAL JAW DENTITION OF ASTATOREOCHROMIS-ALLUAUDI (TELEOSTEI, CICHLIDAE)

The potentially molluscivorons cichlid fish Astatoreochromis alluaudi is known to exhibit a pronounced phenotypic plasticity in its pharynge al jaw apparatus. Two phenotypes (wild-caught snail-eating specimens a nd specimens raised on soft food) were examined for differences in the number, size, shape, spacing and wear of functional teeth on the lowe r pharyngeal jaw. During growth, snail-eating specimens maintain tooth numbers but invest in teeth of a larger size (width and depth). In co ntrast, specimens fed a soft diet invest in more teeth, their size rem aining unchanged except for the central, most posterior teeth. All cha nges in the dentition must be achieved through successive tooth genera tions. Serial microradiographs in the caudal area of the lower pharyng eal jaw, a region that is most significant in food processing, indicat ed that functional teeth in hard-food specimens more often show a succ essor below. This may be due to more time needed for larger replacemen t teeth to form and possibly to a shorter replacement cycle linked to the greater wear of the functional teeth. It is hypothesized that main tenance of tooth numbers and increase of tooth size in hard-food speci mens is achieved by a one-for-one replacement and expansion of the too th-bearing region and possibly by closer spacing of the teeth. Increas e of tooth numbers in the soft-food specimens is probably achieved thr ough the establishment of new tooth loci at the margins of the dentige rous area in addition to a one-for-one replacement.