Helping behaviour, reproductive value, and the future component of indirect fitness

Abstract

The indirect component of an individual's inclusive fitness incorporates the effects of the individual's behaviour on the survival and reproductive success of non-descendent kin. Indirect fitness benefits may be particularly important in species in which helpers assist in the reproductive activities of close relatives. Although helpers can influence both present and future reproduction of recipients, future effects have received relatively little attention. In this paper a general method is developed for estimating the future component of indirect fitness in which activities of helpers in the present influence residual reproductive value and future reproduction by recipients. The future component of indirect fitness is the sum of these effects weighted by genetic relatedness between the helper and each recipient breeder and between each recipient and its offspring. This approach is illustrated by estimating the relative contributions of present and future components to total indirect fitness gained by non-breeding helpers in three species of cooperatively breeding birds, the Florida scrub jay, Aphelocoma coerulescens, pied kingfisher, Ceryle rudis, and splendid fairy-wren, Malurus splendens. The results of this study, along with those available for other species, suggest that the future component of indirect fitness may comprise 29–49% of the total gain in indirect fitness accruing to helpers. The effect of helping and other forms of aidgiving behaviour on the survival and future reproduction of recipients thus should be given considerably more emphasis in analyses of the selective costs and benefits of such behaviour.