Studies on the Embryogenesis of Aulocara elliotti (Orthoptera; Acrididae). Iii. Influence of Maternal Environment and Aging on Development of the Progeny1,2

Abstract

Sibling embryos of the grasshopper Aulocara elliotti (Thomas) obtained from single pairs of adults from 3 geographically isolated wild populations were incubated to 30 days of age at 25°C. The developmental rates of these sibling embryos were found to vary according to the time in the imaginal ontogeny when the eggs were laid. A nearly linear regression was observed when the mean stages or lengths of embryos from each pod from the population from Townsend, Montana, in 1965, were plotted against the maternal age at the date the pod was laid. The rate of filial embryonic development declined slightly in the progeny from longer-lived mothers after reaching a maximum. Graphs of the frequency distribution of morphological stages of embryos from each of the populations showed significant differences. Embryos from the population from Townsend had a mean stage of development of 8. The frequency distribution and mean stages of embryos obtained from adults from Decker, Montana, in 1966, reared under varying densities at 2 different daylengths, indi-cated that these factors in the parental generation may be cumulative in their effects upon the rate of embryonic development. The mean stages of embryos obtained from adults from Decker, 1966, reared under 4 environmental regimens were stages 8.6, 9.5, 10, and 11. Embryos from adults reared under long days in single pairs developed most slowly, while those from adults reared with 2 pairs per cage under short daylengths developed most rapidly. Fecundity was found to be inversely proportional to density. The number of progeny from females reared under heat stress or in cages with multiple males was greatly reduced. Likewise, the rate of embryonic development of the offspring appeared to be reduced. It is concluded that viability and rate of embryonic development in A. elliotti are determined largely by the physiological state of the mother rather than hy the genotypes of the embryos themselves. The possible importance of maternal factors upon the population dynamics of this species is discussed.