Heterogeneous selective pressures on egg‐hatching time and the maintenance of its genetic variance in a Tetraneura gall‐forming aphid

Abstract

1. The performance of gall‐forming aphids is largely dependent on the timing of egg hatch relative to host budburst. This study examined the mode of natural selection acting on egg‐hatching time and the extent of its genetic variance in a Tetraneura aphid.2. The budburst time of the primary host of the aphid varied greatly among individual trees. Egg hatch on a host tree was often asynchronous with host budburst.3. Transplant experiments indicated that egg‐hatching time was subject to heterogeneous selective pressures in heterogeneous host environments.4. Hatching time was compared between half‐sib families. Small nymphs in a half‐sib family tended to hatch later, and this resulted in large within‐family variance in hatching time.5. Small nymphs that hatched late were likely to be selected out during the galling process. Thus, these nymphs may be produced not as bet‐hedging but due to maternal effects. When such maladapted nymphs were not included in analysis, a significant amount of additive genetic variance was detected in hatching time.6. Heterogeneous selection, coupled with density‐dependent regulation of population on respective host trees, probably maintains additive genetic variance in this trait.