PARENT-OFFSPRING CONFLICT OVER SEX-RATIO .2. OFFSPRING RESPONSE TO PARENTAL MANIPULATION

A long-term selection, three-locus diploid model is developed in order to analyze the joint evolution of the primary sex ratio among offspring, parental manipulation, and offspring response to parental manipulation when the cost of rearing a male offspring is different from the cost of rearing a female offspring. It is shown that, when the mother has enough information about the potential offspring response to manipulation, natural selection operates to increase offspring intolerance to sex conversion up to a level at which a mother will have either no power of manipulation (if the cost of losing an offspring is high) or only limited power of manipulation through, for example, selective abortion or neglect of male offspring (ff the cost of losing an offspring is not too high). Quite paradoxically, when the information available to mothers on offspring tolerance of manipulation is limited, long-term natural selection operates to minimize the conflict up to the stage of full maternal control of the sex ratio.