Kristel Wautier

A quantitative analysis of pharyngeal tooth shape in the zebrafish (Danio rerio, Teleostei, Cyprinidae)

To test whether successive replacement cycles in the pharyngeal dentition of the zebrafish, a polyphyodont vertebrate model organism, entail overall shape changes in the teeth, a qualitative and quantitative analysis was made of size and shape variables in the five ventral teeth. The following measurements were defined: tooth length, tooth height, neck-crown angle, cusp depth, and crown curvature. Ontogenetic changes in fish, ranging between 6 and 29 mm standard length (SL), were analysed by linear regressions on to SL. The teeth became significantly larger with growth of the fish, through successive replacements and cusp depth also increased over time. Neck--crown angle and crown curvature did not change over time. Position-dependent differences were analysed by Friedman ANOVA and Kendall concordance tests. Measurements differed significantly according to tooth position in the pharyngeal jaws. Tooth 1V was always the smallest, 3V the largest. The neck--crown angle and curvature of the crown increased from 1V to 5V. Cusp depth increased from 1V to 3V, and then decreased again. These results indicate that successive replacement cycles entail a size increase accompanied by shape changes apparently restricted to the crown. These quantitative data lay the basis for further descriptive and experimental studies of tooth shape in this model-species.

Tooth succession in the zebrafish (Danio rerio)

To test whether the formation of replacement teeth in arbitrarily chosen zebrafish follows the same pattern as described for larval and young zebrafish of known age, dentitions of more than 90 animals of different ages and standard lengths were observed under the stereomicroscope. Only the teeth of the ventral tooth row (1V-5V) were considered. Statistical results (G-tests) suggested that tooth replacement does not occur randomly. The most common order of replacement can be represented as the formula 5V-2V-3V-1V-4V and counts for approximately 70% of the observed patterns. Initiation of replacement teeth at positions 4V and 5V is separated by a larger time interval than between any other combination. It is hypothesized that in older juveniles and adults, replacement teeth may be formed during three odontogenic waves.

Fish dentitions as paradigms for odontogenic questions

Bony fish, and in particular teleosts, represent a morphologically extremely diverse group of vertebrates, well suited to study certain problems in odontogenesis. In this article we address some questions that can benefit much from the use of fish dentitions as paradigms, such as endodermal participation in tooth formation and epithelial primacy in initiation events. Next, we highlight some results recently obtained in our laboratory with respect to two models, the zebrafish (Cyprinidae), and selected species of cichlids (Cichlidae). Finally, we pinpoint some questions that lend themselves admirably to be examined using fish models, such as the factors that control renewed initiation of teeth, and the relationship (or absence thereof) between Hox genes and tooth formation.

Tooth Shape Differences Analyzed by Biometric and Morphometric Approaches: A Case Study on Two Morphologically Very Similar Lacustrine Cichlid Species

Tooth shape is generally considered to be under strong genetic control, and highly species specific. It is therefore widely used for taxonomic studies. The tooth shape-based morphological classification of the Eretmodini (a tribe of closely related cichlids endemic to Lake Tanganyika), has, however, been shown to be in conflict with recent molecular data, which suggests the occurrence of parallel evolution. A detailed biometric and morphometric analysis of tooth shape has been undertaken for two genetic lineages of the taxon Eretmodus cyanostictus . The use of both landmark-based measurements and elliptic Fourier analysis reveals differences between both lineages and supports the molecular phylogeny. These differences further endorse the interpretation of parallel evolution. In addition, we here present a powerful tool for the analysis of tooth shape.

Construction and testing of a replica of Einstein’s “little machine”

Einstein developed his “little machine” to measure small electrical charges, but there are no publications that describe measurements done with this apparatus. We report on our construction of a replica of the little machine and on our tests of its performance.