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


Eggs from 25 parental pairs were reared at sustained temperatures from 200C to 340C, or were changed from 200C to 300C or vice versa at various development stages. Crowding, mechanical shock, 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 9 groups, with nadirs varying from 240C to 320C; in 2 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.

Publication Title

Canadian Journal of Zoology