Temperature-induced meristic variation among three homozygous genotypes (clones) of the self-fertilizing fish Rivulus marmoratus

Abstract

Embryos of clones DS, NA, and M were reared at sustained temperatures of 19, 25, and 31 °C. Diverse evidence indicates a closer genetic affinity between DS and NA than between either and M. DS and NA converged and M diverged regarding thermal responses of vertebrae, and anal and pelvic rays; DS and M converged and NA diverged regarding responses of pectoral, caudal, and dorsal rays. For vertebrae and pectoral rays, response curves were declivous; for caudal rays, inverted-V shaped; for anal rays, upright-V shaped (NA), inverted-V shaped (DS), declivous (M); for dorsal rays, declivous (NA), upright-V shaped (DS and M); for pelvic rays, subhorizontal (DS and NA), inverted-V shaped (M). The vertebral response curves of DS and NA diverged at 25 °C, converging at 19 and 31 °C. Caudal counts increased between 31 and 25 °C, caudal and precaudal, between 25 and 19 °C. Vertebral differences (as percentage of the midpoint count) exceeded any of previous experiments on species other than R. marmoratus. At 19 and 31 °C pelvic fins are often lacking, but never in outbreeding R. cylindraceus. Response curves except vertebral ones differed qualitatively between these species. Many kinds of variations, and proportions of phenotypic differences due to genotypic and environmental differences and their interactions are compared.