Heritable and temperature-induced meristic variation in the medaka, Oryzias latipes

Abstract

Eggs from 25 parental pairs were reared at sustained temperatures from 20C to 34C, or were changed from 20C to 30C or vice versa al various developmental stages. Crowding, mechanical shoes, container type, amount of aeration, and malachite green prophylaxis did not alter numbers of vertebrae, and pectoral or dorsal rays; nor did these numbers vary between eggs laid on different days by the same parents. Numbers of anal and caudal rays were significantly different between sibling egg batches, and were decreased by crowded rearing conditions. Mechanical shock increased anal ray counts. Caudal rays were sometimes decreased by lack of aeration. Response of vertebrae to different sustained temperatures was U-shaped in nine groups, with nadirs varying from 24C to 32C; in two groups, vertebrae were progressively fewer at higher temperatures. Pectoral ray counts usually were progressively lower at higher temperatures. Dorsal ray counts of most formed arched curves. In all series, heritable variation at one temperature roughly equalled phenotypic variability between temperatures. Inherited differences in response patterns of different meristic series are largely independent of each other, and of mortality and of hatching time. Temperature breaks produced an overcompensation in vertebrae if applied early, or a paradoxical reaction if applied late.