Differential allocation and compensation: who deserves the silver spoon?

Abstract

It is well known that being given ‘‘silver spoons’’ can be beneficial to offspring, in the sense that conditions experienced early in life can have long-lasting consequences (Lindstrom 1999; Qvarnstrom and Price 2001). Traits expressed by parents often form a large part of the offspring environment. Life-history theory predicts that parents should adjust their current reproductive investment according to both the expected pay-off from the current attempt and the expected future reproductive events (Stearns 1992). Thus, for selection to favor increased investment, the cost of decreased survival or future reproductive success for the parent should be compensated by higher survival or reproductive success of the current offspring. Because offspring of diploid species have a mother as well as a father, a parent of either sex might benefit by adjusting its investment based on the phenotypic or genetic traits of its mate. Since Burley’s (1986) first formulation, this idea has been called differential allocation (DA). Burley’s early studies focused on a particular aspect of the interaction between costs and benefits experienced by the mother and the father: In her hypothesis that an individual could benefit by increasing effort when mated to an attractive member of the opposite sex because this might enhance the ability to maintain the pairbond with this mate now or in future breeding attempts (Burley 1986, 1988). The discrepancy between early work that focused on pair-bond maintenance and current much broader definitions is probably a healthy sign of progress in a field. Even so, in this paper, we would like to point out that the field is still plagued by differences between researchers in what they consider DA and in which direction they predict allocation of resources to vary. Particularly, the ‘‘compensation hypothesis’’ has recently been proposed as a mechanism that appears to make opposite predictions to the DA hypothesis, but as we shall show, there is much clarification needed before we can reach a stage where the core ideas are crisply stated and the relationships between various hypotheses are properly evaluated. We will show that similar clarifying work needs to occur in the development of theory as well as in empirical studies.