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Studies of maternal age as a source of variation in two insect species Mackay, Patricia Ann


Differences in progeny characteristics arising from differences in maternal age at time of birth are discussed as a possible source of ecologically important variation. The literature on effects of maternal age on progeny guality is reviewed. Experiments designed to document any effects of maternal age on two biological processes are described. The processes selected were production of alatae by an aphid, ASiSiioSiEiiOS. £isum , and incidence of diapause in a sawfly, Eriocamoa ovata . Maternal-age effects influenced the production of alatae by the aphid. Early-born progeny of wingless aphids were more likely to respond to a standard crowding stimulus by producing alatae than were late-born progeny. Early-born alata-producers also produced higher numbers of alatae than late-born ones. Maternal age affected the progeny of winged aphids, but in the opposite manner. Early-born progeny of this morph usually did not produce alatae at all, whereas late-born progeny did. The inhibition of alata-prcduction in the lineage of an alate aphid was satisfactorily explained by maternal age effects alone. A timing mechanism such as the "interval timer" proposed by Lees (1966) did not apply. Ho significant effects of maternal age on the incidence of diapause in the sawfly could be found. However, diapause was shown to be influenced by at least two factors. More animals diapaused at low humidities. Seven-instar larvae diapaused more frequently than did six-instar larvae. Larval developmental times varied with the number of instars, the occurrence of diapause, and the date of egg-laying. Length of the cccocn stage of ncn-diapausing individuals varied with the date of egg-laying. It is concluded that maternal age effects, although not universal, are a common biological phenomenon, and probably of ecological significance as a source of variation.

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