Abstract
Because there are basic sexual differences in reproductive potential, and the cost of parental care is assumed to be high, biparental care is viewed as a constant tug-of-war between the partners. This raises the question of the system’s evolutionary stability. Several models have been proposed to resolve this problem but none has received unequivocal support. Here, I propose a framework that not only integrates the earlier theoretical ideas (sealed bids, negotiation) but also considers the importance of the environment (frequently neglected in previous models) and views the cost of parental care from a different perspective (costly in terms of parent’s survival only when performed close to the boundary of parental capacity). The framework suggests that sexual conflict may not be such a significant factor mediating parental care as commonly assumed, and that a parent trying to shift the parental burden onto the partner – assumed to be the winner in the tug-of-war interplay – is actually more likely to be a loser, as doing so may put the success of the current breeding attempt in jeopardy, thereby reducing overall fitness of the parent. Once it is realized that the importance of sexual conflict is actually much less than it seems, it becomes clear that the stability of the biparental care system no longer seems to be such a puzzling issue.
Highlights
Biparental care is a rather rare form of rearing the offspring across animal kingdom (Lack, 1968; Clutton-Brock and Vincent, 1991; Bennett and Owens, 2002; Reynolds et al, 2002), it has repetitively evolved in birds, mammals, amphibians, fishes and insects (Balshine, 2012; Trumbo, 2012)
In more favorable conditions, when a single parent is potentially capable of successfully raising offspring, the unpredictability of the environment during the breeding attempt may still keep both parents engaged; even if conditions happen to be favorable at the onset of the breeding season, they may deteriorate over the time
The only situation, when leaving the partner may be profitable in some way, is when two conditions are met simultaneously: 1) environmental conditions are sufficiently favorable/predictable that a single parent can successfully raise its offspring, and 2) the chance of the leaving individual for a successful breeding attempt with another partner are high
Summary
Biparental care is a rather rare form of rearing the offspring across animal kingdom (Lack, 1968; Clutton-Brock and Vincent, 1991; Bennett and Owens, 2002; Reynolds et al, 2002), it has repetitively evolved in birds, mammals, amphibians, fishes and insects (Balshine, 2012; Trumbo, 2012). If we translate this into the costs of parental care (in the sense of the reduced survival and/or fecundity of the parent), the higher costs would incur the higher risk of brood failure when care is being performed beyond the optimal range of parental capacity It is worth considering the parents’ certainty of success in the current breeding attempt. In the least favorable conditions, there must be an equal division of labor between the partners, otherwise they may both experience breeding failure In such a case there is a very little parental flexibility, no room for negotiations between the partners, no chance of any compensation of potential shortcomings/indisposition on the part of one, as under these conditions the parental care incurs extra costs because the parenting individual is operating at the edge of its optimal parental capacity (Figures 1, 2; Supplementary Materials 1 – https://kasiawojczulanis-jakubas.shinyapps.io/biparental_care_ gametheory/). The cost of parental care (in the sense of reduced parental survival and/or fecundity) very much depends on the species’ environment and social situation (Figures 1, 2;Supplementary Materials 1 – https://kasiawojczulanis-jakubas.shinyapps.io/biparental_care_ gametheory/)
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