Parental Optimism and Progeny Choice: When is Screening for Offspring Quality Affordable.

Three general classes of fitness incentives have been proposed for parental overproduction of offspring: (1) tracking environmental variation; (2) developmental facilitation; and (3) replacements for failed or defective members of the core brood. In one version of this last category, called the progeny choice hypothesis, parents are seen as creating an enlarged array of offspring from which a genetically superior subset is chosen for full investment. In the selection process, parents may eliminate the victims either through personal effort (filial infanticide) or by proxy (by allowing or even encouraging fatal sibling rivalry). Because the culling process is non-random, it can elevate average offspring quality. Progeny choice, however, is only cost-effective if the expenses of early overproduction (including elevated levels of sibling competition) do not outweigh the eventual upgrade in offspring quality. A fair competition within the offspring "arena" offers the greatest potential for discriminating on the basis of intrinsic quality, but may be overwhelmed by high costs of sibling rivalry. Conversely, while parentally managed competition (conferring handicaps to some and advantages to others) can discount those rivalry costs, it simultaneously diminishes the system's capacity for distinguishing good offspring from bad. Ceteris paribus, one would expect to find progeny choice mechanisms in species with cheap sibling rivalry, large cohorts of evenly matched offspring, and exaggerated variation in offspring genetic quality. Conversely, this class of incentives of parental overproduction seems least suited to taxa in which parents dole out marked advantages or handicaps to various concurrent offspring (e.g. asynchronously hatching birds).Copyright 1998 Academic Press Limited