Resource tracking in aphids: programmed reproductive strategies anticipate seasonal trends in habitat quality.

摘要

Most aphids show cyclical parthenogenesis, have short generation times and complete several generations each season. Two hypotheses have been proposed to account for the adaptive seasonal trends observed in the reproductive strategies of aphids. Firstly, individuals of each generation modify their reproductive strategy in direct response to the conditions they experience during their development. Secondly, the reproductive strategies of the different generations are, to a large extent, programmed and anticipate seasonal trends in habitat quality. These hypotheses were tested by rearing individuals of three generations of the host-alternating willow-carrot aphid, Cavariella aegopodii, on both willow (Salix sp.) and carrot. This revealed that the way this aphid allocates resources to gonads and lipid reserves is independent of weight and the food plant on which it is reared. In addition, each generation shows a specific relationship between offspring size and adult size, which tends to keep the absolute investment in individual offspring relatively constant from generation to generation, in spite of the big differences in adult size between generations. That is, through programmed allometric engineering, aphids anticipate the predictable seasonaltrends in habitat quality and so more closely track their resources, investing relatively more in gonads when food quality is high and relatively more in lipid reserves when food quality is poor.