The genetic basis of wing dimorphism in the sand cricket, gryllus firmus and its relevance to the evolution of wing dimorphisms in insects

Abstract

The sand cricket, Gryllus firmus is dimorphic with respect to wing length, some individuals being micropterous and others macropterous. The trait has a polygenic basis, micropterous parents producing a higher proportion of micropterous offspring than macropterous parents. The heritability of the trait, determined under a fixed photoperiod/temperature regime is 0·62 ±0-075 and 0·68 ±0·085 for males and females respectively. An alternate method of determining heritability based on a modified mid-parent on mean offspring regression is presented. This method is predicted to give an underestimate of heritability but permits an analysis of the separate influences of each parent. This analysis indicates the heritability in males and females to be 0·55 and that there are no maternal effects under the particular rearing conditions. A 5 hour shift in the photoperiod appears not to drastically change the heritability but a change in rearing temperature from 30°C to 25°C probably reduces it. Field observations suggest that at certain times of the year heritability may be relatively high whereas at others it could be very low. The adaptive significance of wing polymorphism and its evolution is discussed. © 1986 The Genetical Society of Great Britain.