Selective Pressures on Clutch Size in the Gall Maker Asteromyia Carbonifera
1983
Weis, Arthur E. | Price, Peter W. | Lynch, Michael
The insect Asteromyia carbonifera (Diptera; Cecidomyiidae) has a life history that entails larval development in a gall with several sibs, maturation of a single batch of gametes during pupal development, and an ephemeral adult existence that includes many ovipositional events, each of which results in formation of a gall. Ecological factors acting on both the adult and larval stages were evaluated to determine the selective pressure they exert on the number of eggs deposited per ovipositional site (i.e., clutch size). Optimal clutch size is determined by a balance between the fitness per offspring, which is dependent on clutch size, and the number of clutches mothers can deposit in their brief life—span. As clutch size increased, so did sibling competition, with the result of smaller size and lower fecundity for larvae developing in large clutches. Larval survivorship was lower in small clutches because of differential attack by parasitoids. From the offspring's viewpoint, benefits of small clutch size out—weighed the deficits, since those deposited in clutches of one enjoyed the greatest potential fitness. A model was constructed indicating that when mothers experience no risk of mortality, optimal clutch size from their viewpoint is also one. However as the risk of mortality between ovipositional events increases, females are unlikely to survive to deposit all their eggs. When fewer clutches can be formed, females will be selected to deposit several eggs per clutch, since this results in the development of many moderately fecund offspring whose aggregate fitness is greater than that of the few highly fecund offspring that would result if one egg were deposited per site.
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