Genetic and Social Transmission of Parental Sex Roles in Zebra Finch Families

Parental care plays a central, reinforcing role in the evolution of sex roles and its development is often reported to be driven by genetic, rather than environmental effects. Based on these studies, however, genetic inheritance does not account fully for the often-significant phenotypic variability observed within species, a variation that we hypothesized may be explained by social effects from parents. Following a full cross-fostering design, here we aimed at disentangling genetic and social parental effects in the ontogeny of parental behaviours. Clutches of eggs were swapped, and we monitored parental behaviours in two consecutive generations of a captive population of the socially monogamous, biparental zebra finch (Taeniopygia guttata). Using nest box cameras, parental behaviour was recorded for 3 h in two reproductive stages: on day 8 of incubation and day 10 post-hatching. These fostered birds, after becoming fully matured, received a pair randomly and we observed parental care of this second generation too, following the same protocol. We then compared various parental behaviours (such as time spent incubating, or number of nest attendances during offspring provisioning) in the second generation to those of their genetic and social parents. Based on the results of our experiment, both genetic and social effects can contribute to intergenerational transmission of specific parental behaviours, with various weights. However, the strongest and most consistent effect that we found is that of the current mate; a social effect that can manifest both in negative and positive directions, depending on the behavioural trait. Our study suggests context-specific and sexually different genetic, social and non-social environmental effects in the ontogeny of parental sex roles and outline the importance of parental negotiation in explaining individual variation of parental behaviour in biparental species.

Negotiations over parental care: a test of alternative hypotheses in the clown anemonefish

In species with biparental care, conflict arises over how much each parent provides to their offspring because both parents benefit from shifting the burden of care to the other. Here, we tested alternative hypotheses for how parents will negotiate offspring care using a wild population of clownfish (Amphiprion percula). We experimentally handicapped parents by fin-clipping the female in 23 groups, the male in 23 groups, and neither parent in 23 groups and measured changes in indicators of female, male, and pair effort in response to handicapping. First, we found that handicapping resulted in a decrease in the number of eggs laid by fin-clipped females and a decrease in the amount of parental care by fin-clipped males. Second, contrary to predictions, female effort did not change in response to the male being handicapped, or vice versa. Finally, the number of embryos that matured to hatching, an indicator of pair effort, was not influenced by the manipulation, suggesting that although the handicap was effective, clownfish do not face the predicted “cost to conflict” when one parent is handicapped. Together, these results test the generality of theoretical predictions and uncover novel questions about whether and how negotiations operate in systems where interests are aligned.

Power and punishment influence negotiations over parental care

Asymmetries in power (the ability to influence the outcome of conflict) are ubiquitous in social interactions because interacting individuals are rarely identical. It is well documented that asymmetries in power influence the outcome of reproductive conflict in social groups. Yet power asymmetries have received little attention in the context of negotiations between caring parents, which is surprising given that parents are often markedly different in size. Here we built on an existing negotiation model to examine how power and punishment influence negotiations over care. We incorporated power asymmetry by allowing the more-powerful parent, rank 1, to inflict punishment on the less-powerful parent, rank 2. We then determined when punishment will be favored by selection and how it would affect the negotiated behavioral response of each parent. We found that with power and punishment, a reduction in one parent’s effort results in partial compensation by the other parent. However, the degree of compensation is asymmetric: the rank 2 compensates more than the rank 1. As a result, the fitness of rank 1 increases and the fitness of rank 2 decreases, relative to the original negotiation model. Furthermore, because power and punishment enable one parent to extract greater effort from the other, offspring can do better, that is, receive more total effort, when there is power and punishment involved in negotiations over care. These results reveal how power and punishment alter the outcome of conflict between parents and affect offspring, providing insights into the evolutionary consequences of exerting power in negotiations.