“Differential allocation revisited: When should mate quality affect parental investment?”

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Thomas R. Haaland, Jonathan Wright, Bram Kuijper, and Irja I. Ratikainen

When should parental investment depend on mate quality? Models shed new light on the differential allocation hypothesis

Should you invest more resources in producing offspring when you are with an attractive, high-quality mate?

Differential allocation was first studied in zebra finches, when Nancy Burley (Burley 1986, 1988) discovered that the birds with a “sexy” red leg ring received more help from their partner with feeding the chicks, while birds with “unsexy” green rings received less help. Haaland et al. (2017) have now created theoretical models explaining the logic behind the birds’ behavior.
(Credit: Thomas R. Haaland)

Thomas Haaland and colleagues at the Norwegian University of Science and Technology and the University of Exeter have combined several different modelling approaches to investigate the phenomenon known as differential allocation: adjusting parental investment according to the quality or attractiveness of the current mate.

Since its discovery in the late ’80’s, this surprising finding has attracted a lot of research attention in animal behavior circles. Experiments on organisms as diverse as penguins, peacocks, antelopes, frogs, and beetles have shown how egg size, clutch size, feeding rates, and other reproductive decisions vary with mate quality. However, results from different studies have often shown confusing and contradictory results, and a lack of theory underlying the differential allocation hypothesis makes interpretations difficult. For example, females in some species show increased investment in offspring when paired with good-quality males, while in a closely related species it is the young of poor-quality males who receive extra investment. In other studies, no relationship is seen at all. In order to understand which mechanisms drive this variation, a theoretical explanation of the logic is necessary.

Haaland and colleagues show how female investment should differ when male quality affects either the offspring fitness or the female’s reproductive costs in various ways. The benefits of mating with a good-quality male will therefore depend on the details of the species’ mating system and biology, and using these new models, researchers will be able to generate predictions for their experiments and interpret their results to better understand why the animals behave the way they do. In a wider context, this better understanding of differential allocation will also aid research concerning sexual selection and the evolution of parental care. Read the Article