Studies on differential fitness of PGI genotypes with regard to temperature in Gammarus insensibilis (Crustacea: Amphipoda)

Abstract

This paper deals with an experimental study of survival, combined with estimates of biochemical activity, of different genotypes at the PGI (phosphoglucose isomerase) locus in Gammarus insensibilis, in relation to temperature. Samples were collected in the lagoon of Venice during 1987. No mortality occurred at 10°C whereas at 27°C, where mortality reached the value of 50%, heterozygotes exhibited significantly higher survival than homozygotes. Experiments conducted in order to evaluate the PGI biochemical activity of homo- and heterozygote genotypes at three different temperatures (4°, 20° and 37°C) showed in all genotypes an increased activity from 4° to 20°C and a fall of activity from 20° to 37°C. Heterozygotes exhibited higher activity at all temperatures tested. The difference between homo- and heterozygotes became more obvious at 37°C. Our results suggest that in G. insensibilis the PGI locus, as already shown in other organisms, may be subject to selection and that the heterozygous genotypes possess superior fitness. The biochemical bases of the observed differences between genotypes are briefly discussed.