WHEN SHOULD A FEMALE AVOID ADDING EGGS TO THE CLUTCH OF ANOTHER FEMALE - A SIMULTANEOUS OVIPOSITION AND SEX ALLOCATION GAME

Avoidance of double oviposition (ADO) is the strategy not to oviposit on food patches where another female has oviposited before. If two fem ales oviposit on the same patch, competitive and mating interactions w ithin and between broods may lead to both a clutch size game and a sex allocation game between the two visitors. Though the two games intera ct, they are usually considered separately, Here, the ESS conditions f or ADO are investigated in an analysis that combines the two games int o one. The analysis strengthens the notion that it is really ADO that needs to be explained, because role-dependent net pay-off from an addi tional egg is most likely to favour double oviposition (DO). To a firs t female, the net pay off includes the effect on the eggs already pres ent, whereas to a second female only the egg's gross pay-off matters, ADO is the evolutionary stable strategy (ESS) if there are enough patc hes still without eggs and either (1) the fitness of an additional egg is so low that the first female would not lay it even in the absence of detrimental effects on earlier offspring, so neither would a second female, or (2) differences in either the survival probability of the offspring or their reproductive success are sufficient to counterbalan ce the differential interest in the eggs already present. The first co ndition requires that eggs are relatively large, because then the decr ease in pay-off between two successive eggs can be large. The second c ondition may be met when there is a time interval between ovipositions of subsequent females. The resulting developmental lag of the second clutch will (1) diminish its ability to compete for food and (2) lower its reproductive success when there is local mate competition and son s are too late to mate with daughters of the first female, If sons of first and second females compete on equal terms, however, ADO is unlik ely, Male migration between patches reduces the influence of sex alloc ation strategies on clutch size decisions; the same holds for small cl utch sizes. To illustrate the importance of considering sex allocation and clutch size decisions in an integrated way, oviposition strategie s of plant-inhabiting predatory mites (Acari: Phytoseiidae) are discus sed.