Egg maturation, egg resorption and the costliness of transient egg limitation in insects

Although there is widespread agreement that the cost of oviposition underli es selective oviposition in insects, there is no consensus regarding which factors mediate the cost of oviposition. Models have suggested that egg cos ts are often paramount in those insects that do not continue to mature eggs during the adult stage (pro-ovigenic insects). Here we address tho hypothe sis that egg costs are generally less significant in synovigenic insects, w hich can replenish oocyte supplies through continuous egg maturation. A dyn amic optimation model based on the biology of a highly synovigenic parasito id, Aphytis aonidiae, suggests that the maximum rate of egg maturation is i nsufficient to balance the depletion of eggs when opportunities to oviposit are abundant. Transient egg limitation therefore occurs, which imposes opp ortunity costs on reproducing females. Thus, whereas the most fundamental c onstraint acting on the lifetime reproductive success of pro-ovigenic speci es is the fixed total number of eggs that they carry at eclosion, the most fundamental constraint acting on a synovigenic species is the maximum rate of oocyte maturation. Furthermore, the ability of synovigenic species to re verse the flow of nutrients from the soma to oocytcs (i.e. egg resorption) has a dramatic influence on the cost of oviposition. Whereas females in hos t-rich environments may experience oviposition-mediated egg limitation, fem ales in host-poor environments may experience oosorption-mediated egg limit ation. Both forms of egg limitation are costly. Contrary to initial expecta tions, the flexibility of resource allocation that typifies synovigenic rep roduction actually appears to broaden the range of conditions under which c ostly egg limitation occurs. Egg costs appear to be fundamental in mediatin g the trade-off between current and future reproduction, and therefore are an important factor favouring selective insect oviposition.