Maternal effects as a mechanism for manipulating male care and resolving sexual conflict over care

Abstract

Understanding how sexual conflict influences male and female parental decisions is a longstanding problem in behavioral ecology. Until now, most research on sexual conflict over parental care has focused on behavioral mechanisms mediating the resolution of this conflict through negotiation between parents. Here, we review evidence suggesting that maternal effects that alter offspring phenotypes may provide females with a mechanism for manipulating male care. We show that empirical studies on the role of maternal androgens in birds with biparental care provide no support for female manipulation of male care. However, we argue that it would be premature to conclude that maternal androgens play no role in female manipulation of male care given methodological problems in previous work. We then identify a number of additional mechanisms by which females may manipulate male care, including egg components other than androgens, egg size and egg coloration. We show that there is good evidence that egg coloration affects male care, suggesting that this mechanism warrants further research. We also highlight that current evidence is derived from studies using experimental design that target specific candidate mechanisms, such as maternal androgens. Given the multitude of candidate mechanisms, we discuss an alternative approach based on targeting ecologically relevant pre-natal conditions, such as food availability, and monitoring subsequent effects on candidate mechanisms, offspring phenotypes, and male and female care. Finally, we argue that it is timely to extend this work beyond birds with biparental care to include other taxa and species with uniparental male care and cooperative breeding.

Females manipulate behavior of caring males via prenatal maternal effects

“…This species is ideal for studying female manipulation of male behavior because it allows us to address all five challenges listed above. First, we used a new experimental approach in which we targeted prenatal environmental conditions expected to influence female decisions on maternal effects and then monitored downstream consequences for offspring size at hatching, male and female care, and male, female, and offspring fitness (9). Here we targeted a prenatal environmental condition that is essential for female manipulation of males: the presence or absence of the male during egg laying.…”

“…Our current understanding of the resolution of sexual conflict suggest that males and females use the same behavioral strategies for resolving conflict (e.g., negotiation) (9). However, given that females produce the eggs, they might use their control over egg production as a mechanism for biasing conflict resolution in their favor.…”

“…However, given that females produce the eggs, they might use their control over egg production as a mechanism for biasing conflict resolution in their favor. In many species, females deposit hormones and/or nutrients into the eggs that alter the offspring's behavior or development (9)(10)(11), thereby providing a potential tool for manipulating the behavior of caring males. For example, by producing smaller eggs, females could redirect the costs of parental care from the prenatal period, when they pay the full costs of egg production, toward the postnatal period, when the costs of rearing young are shared with the male (9).…”

“…In many species, females deposit hormones and/or nutrients into the eggs that alter the offspring's behavior or development (9)(10)(11), thereby providing a potential tool for manipulating the behavior of caring males. For example, by producing smaller eggs, females could redirect the costs of parental care from the prenatal period, when they pay the full costs of egg production, toward the postnatal period, when the costs of rearing young are shared with the male (9). Alternatively, females may deposit yolk androgens that modulate offspring begging behavior in a way that alters the male's perception of offspring need, thereby increasing male contributions to care (9)(10)(11).…”

“…For example, by producing smaller eggs, females could redirect the costs of parental care from the prenatal period, when they pay the full costs of egg production, toward the postnatal period, when the costs of rearing young are shared with the male (9). Alternatively, females may deposit yolk androgens that modulate offspring begging behavior in a way that alters the male's perception of offspring need, thereby increasing male contributions to care (9)(10)(11). Thus, if prenatal maternal effects influence the resolution of sexual conflict over care, this would introduce an asymmetry of power between the two sexes, with the female gaining the upper hand.…”