ONTOGENY OF GENE-EXPRESSION IN POMOXIS (PISCES, CENTRARCHIDAE)

The regulation of gene expression during embryogenesis was investigate d in white and black crappie (Pomoxis spp.) and their reciprocal inter specific F-1 hybrids. The schedule of morphological development and th e timing of isozyme expression were compared among the two species and both reciprocal maternal half-sibling F-1 hybrids. Although absolute rates of morphological development differed in response to incubation temperature, relative rates of morphological development (normalized t o the onset of retinal pigment deposition) were similar among all cros ses. Furthermore, these relative rates were similar to those previousl y documented for other centrarchid species. To assess differences in o ntogenetic patterns of gene expression among the crosses, we examined expression for 39 enzyme-encoding loci. Expression was not detected in the embryos for 16 loci due to low or nonexistent activity. Enzymatic activity from eight other loci were continuously detected throughout embryogenesis as a result of maternal enzyme in the egg. However, 15 l oci initiated expression during the early development period investiga ted (fertilization through yolk sac absorption). We observed temporal variability in expression of these 15 loci among the crosses, either i n the form of differential expression between parental species or as d isturbances in the ontogeny of expression in interspecific hybrids. Su ch variability in expression suggests that some of the gene regulating mechanisms have diverged since Pomoxis species shared a common ancest ral genome. (C) 1994 Wiley-Liss, Inc.