SCHMIDT, K. *; STARCK, J.M.; Ludwig-Maximilians-University of Munich; Ludwig-Maximilians-University of Munich: Developmental plasticity vs. phylotypic constraints during early embryogenesis of zebra fish, Danio rerio

During the phylotypic stage vertebrate embryos pass through a period of morphological similarity. In zebra fish, Danio rerio, multiple correlations among characters stabilize morphology during the phylotypic stage, but a considerable degree of phenotypic variability can still be observed (coefficient of variation for morphometric measurements > 4 %.) Here, we studied zebra fish embryogenesis under different experimental conditions to see if besides the morphological similarity, developmental plasticity is limited during the early developmental period. Eggs of zebra fish were raised at different temperatures (24°C, 27°C, 30°C) and different salinities (10mosmol/200mosmol). The size development of the maximum diameter of the eye, the length of the embryo, the size of somites, the inclination of somites, the size of otic vesicle, the maximum diameter of the yolk sac of individual embryos were documented at 12 , 15, 18 and 24 hours post fertilization. Embryos grew faster at higher temperatures, but were smaller in overall size and somite size at the same developmental stage. The size of eye, otic vesicle, and the inclination of somites were not affected by temperature or salinity. Only the yolk sac decreased in higher salinity. This effect can most likely be associated with the reduced osmotic pressure. Analysis of variance (one-way ANOVA) showed that internal constraints are effective for most of the observed characters. Limited plasticity was only detected in the overall size of the embryo and the somites, but not in other organs. We conclude that developmental plasticity is also reduced during the phylotypic stage.