Abstract
Differential allocation (DA) is the adaptive adjustment of reproductive investment (up or down) according to partner quality. A lack of theoretical treatments has led to some confusion in the interpretation of DA in the empirical literature. We present a formal framework for DA that highlights the nature of reproductive benefits versus costs for females mated to males of different quality. Contrary to popular belief, analytical and stochastic dynamic models both show that additive benefits of male quality on offspring fitness have no effect on optimal levels of female investment and thus cannot produce DA. Instead, if offspring fitness is affected multiplicatively by male quality, or male quality affects the female cost function, DA is expected because of changes in the marginal benefits or costs of extra investment. Additive male quality effects on the female cost function can cause a novel form of weak DA, because reduced costs can slightly favor current over future reproduction. Combinations of these distinct effects in more realistic model scenarios can explain various patterns of positive and negative DA reported for different species and mating systems. Our model therefore sheds new light on the diversity of empirical results by providing a strong conceptual framework for the DA hypothesis.
Highlights
Differential allocation (DA) is usually described as the strategy of a parent adjusting its investment in the current reproductive attempt according to the perceived attractiveness or general quality of its mate
This has become known as reproductive compensation (RC; Gowaty et al 2007; Gowaty 2008), but the more recent viewpoint has been that DA and RC represent the ends of a continuum of investment patterns across mate qualities (Harris and Uller 2009; Ratikainen and Kokko 2010; Kindsvater et al 2013)
A similar multiplicative relationship between male quality and female investment holds for the benefit-position scenario, and again we expect DA
Summary
Differential allocation (DA) is usually described as the strategy of a parent adjusting its investment in the current reproductive attempt according to the perceived attractiveness or general quality of its mate. DA has traditionally been considered to imply an increase in parental investment (PI) with increasing mate quality, but several studies have shown a decrease in PI with increasing mate quality (Bluhm and Gowaty 2004; Byers and Waits 2006; Bolund et al 2009), a pattern initially viewed as in direct conflict with DA This has become known as reproductive compensation (RC; Gowaty et al 2007; Gowaty 2008), but the more recent viewpoint has been that DA and RC represent the ends of a continuum of investment patterns across mate qualities (Harris and Uller 2009; Ratikainen and Kokko 2010; Kindsvater et al 2013). It is important to recognize that adaptive DA can be carried out by both male and female parents in various forms of parental and reproductive investments, for convenience we discuss the more common situation here of male mate quality effects on female reproductive investment, but most arguments can be turned around to understand how female quality should affect male reproductive investment
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