Abstract
In socially monogamous species, pair-bonded males often continue to provide care to all offspring in their nests despite some degree of paternity loss due to female extra-pair copulation. Previous theoretical models suggested that females can use their within-pair offspring as ‘hostages' to blackmail their social mates, so that they continue to provide care to the brood at low levels of cuckoldry. These models, however, rely on the assumption of sufficiently accurate male detection of cuckoldry and the reduction of parental effort in case of suspicion. Therefore, they cannot explain the abundant cases where cuckolded males continue to provide extensive care to the brood. Here we use an analytical population genetics model and an individual-based simulation model to explore the coevolution of female fidelity and male help in populations with two genetically determined alternative reproductive tactics (ARTs): sneakers that achieve paternity solely via extra-pair copulations and bourgeois that form a mating pair and spend some efforts in brood care. We show that when the efficiency of mate guarding is intermediate, the bourgeois males can evolve to ‘specialize' in providing care by spending more than 90% of time in helping their females while guarding them as much as possible, despite frequent cuckoldry by the sneakers. We also show that when sneakers have tactic-specific adaptations and thus are more competitive than the bourgeois in gaining extra-pair fertilizations, the frequency of sneakers and the degrees of female fidelity and male help can fluctuate in evolutionary cycles. Our theoretical predictions highlight the need for further empirical tests in species with ARTs.
Highlights
Apart from a few exceptions [1,2,3,4], socially monogamous females and males often mate multiply and produce extra-pair offspring (EPO) [5,6]
We show that when sneakers have tactic-specific adaptations and are more competitive than the bourgeois in gaining extra-pair fertilizations, the frequency of sneakers and the degrees of female fidelity and male help can fluctuate in evolutionary cycles
Using a population genetics model and individual-based simulations, we studied the coevolutionary dynamics of female fidelity and male help in populations with two male alternative reproductive tactics (ARTs), and with EPO having higher or lower survival rates relative to within-pair offspprffiffiing (WPO)
Summary
Apart from a few exceptions [1,2,3,4], socially monogamous females and males often mate multiply and produce extra-pair offspring (EPO) [5,6]. The ESS approach used in these previous models, only predicts the overall levels of male help or guarding in the population, but remains silent about how these are realized through individual behavior Those models, implicitly assumed a monomorphic population of males where everyone uses the same tactic, despite the fact that male alternative reproductive tactics (ARTs) are widespread in nature [20]. We consider two male ARTs, namely, ‘sneakers’ that attempt to achieve paternity solely through EPCs, and ‘bourgeois’ that attempt to form social pairs with one female and spend some time caring for the brood (following the nomenclature in [30]). Using the above notions and assuming that within- and extra-pair matings are likely to fertilize an egg, the expected proportion of EPO females produce is E = (1 − u)(1 − δh). Denote u 1⁄4 P(1 À l)(1 À E) RS(h)=(FAA þ FAa þ Faa)(MAA þ MAa), the numbers of survived female WPO of each genotype are DwpFAA 1⁄4u
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