Population structure, biochemical adaptation and systematics in temperate marine fishes of the genera Arripis and Chrysophrys (Pisces: Perciformes)

Abstract

Electrophoretic and heat stability data have been obtained from 22 enzymatic proteins to assess the amount and distribution of genetic variation in fishes of the temperate percoid genera Arripis and Chrysophrys. Available biological and life history data have been reviewed, and indicate that Arripis species are mobile, migratory, pelagic fishes, with planktonic larvae and a comparatively short life span (up to 9 years), while Chrysophrys species are comparatively sedentary and demersal, have benthic larvae, and are long-lived (up to 60 years). The electrophoretic and heat stability data have been used to test the hypothesis that species with different life history characteristics exhibit different distribution patterns of genetic variation, and that these differences are the result of different adaptive strategies adopted by the organisms to cope with contrasting environmental regimes. The results generally agreed with predictions, although some alternative explanations for observed gene distributions could not be eliminated. Electrophoretic data were also analysed using kinship and genetic distance techniques to provide information on the structure of snapper (C. Auratus) and western salmon (Arripis sp) populations in Australian waters. The results indicate that western salmon consist of a single breeding population extending across the southern Australian coastline, while at least five geographically distinct snapper populations were detected. Enzyme kinetic studies were carried out on snapper isocitrate dehydrogenase (IDH) and salmon malic enzyme (ME) allozymes to determine whether or not functional differences existed in response to temperature fluctuation. It was found that differences did exist between IDH allozymes, but that the functional variation was correlated with heat stability variants rather than electrophoretic variants. The geographical distribution of snapper IDH variation was re-examined in the light of this result, and the relative contributions of random and selective processes to observed patterns were discussed. No functional differences in response to temperature fluctuations were detected for salmon ME electrophoretic or heat stability allozymes. The observed functional characteristics of snapper IDH and salmon ME allozymes over known biological temperature ranges of the species were compared as indicators of biochemical adaptive strategies in organisms with different ecological requirements. The observed results agree with expectations based on the known biology of snapper and salmon, but further enzymes need to be assayed to confirm this pattern. Taxonomy and evolutionary relationships within the genera Arripis and Chrysophrys have been examined using genetic distance and time-since-divergence estimates based on the electrophoretic data. Attempts have been made to reconstruct the evolutionary history of each genus on the basis of the genetic data, the current distribution of taxa, and information about past geomorphological events in key areas, such as Bass Strait.