The benefits of genetic diversity outweigh those of kin association in a territorial animal

Abstract

The theories of kin selection and heterogeneous advantage have been central to studies of altruistic behaviour and the evolution of sex over the last 35 years. Yet they predict diametrically opposite e¡ects of genetic diversity on population density. Close relatives gain inclusive ¢tness advantages by preferentially associating with and behaving altruistically towards one another. However, heterogeneous advantage, which predicts competition to be highest when genetic diversity is low, suggests that bene¢ts will be greater for individuals in groups of non-kin. Here we test how these two processes balance and a¡ect the productivity of populations of animals in natural habitats. We report from a study of juvenile Atlantic salmon in the wild that heterogeneous advantage outweighs the bene¢ts of kin-biased behaviour, resulting in a 1.8-fold higher population biomass and signi¢cantly better condition of individual ¢sh.

Intraspecific genetic variation and competition interact to influence niche expansion

“…However, genetic variation may also directly alter the strength of selection: genetically dissimilar individuals may compete less than genetically similar individuals (Dempster 1955;Lewontin & Matsuo 1963;Maynard Smith 1978). Although evidence favouring this hypothesis is equivocal, experiments with plants (Allard & Adams 1969;Cheplick & Kane 2004;Reusch et al 2005;Boyden et al 2008), Drosophila (Pérez-Tomé & Toro 1982;Fowler & Partridge 1986;Martin et al 1988; López-Suárez et al 1993), territorial salmon (Griffiths & Armstrong 2001) and fire-bellied toads (Jasienski 1988) show that genetically heterogeneous groups of individuals have greater productivity than genetically similar groups, potentially due to more efficient niche partitioning within genetically diverse groups. Consequently, at a given population density genetically diverse populations may be subject to weaker selection for niche diversification compared with less diverse populations.…”

Changes in the fish community of Loch Leven: untangling anthropogenic pressures

“…Despite this potential limitation of recruitment on production, densities of trout were high in Loch Leven streams compared with other populations and at least as high as those determined by Thorpe (1974a). Presence of the remnants of yolk sacs and a wide range of lengths in samples collected in May/June were consistent with the occurrence of a wide range of spawning times and may facilitate high levels of production through heterogeneous advantage (Griffiths & Armstrong, 2001) due to young fish of different sizes using different local niches and therefore competing little with one another. Further examination of the streams would be enhanced by trapping of trout migrating to and from the loch to measure production of smolts and migrant fry directly, to assess the numbers of spawners, and to derive indices of stock size.…”

The effect of kinship on intraspecific competition in larvae of the poison frog Ameerega bassleri (Anura, Dendrobatidae)

“…In tadpoles, mechanisms for cooperation may include competitive restraint (reducing exploitative competition), decreased interference with competitors (thereby increasing time available for foraging), or beneficial behaviors such as stirring up more periphyton than they can consume (Waldman 1991, Hokit andBlaustein 1997). However, these beneficial behaviors may be counteracted by genetic similarities between kin that increase the potential for exploitative competition, potentially canceling out effects of cooperation (Griffiths and Armstrong 2001). Since the effects of kin selection and heterogeneous advantage are thought to oppose each other, this may provide some explanation as to why we failed to detect significant differences in growth between the two treatments.…”

“…The theories of kin selection and heterogeneous advantage produce opposing predictions about how relatedness affects intraspecific competition (Hamilton 1964), and both have received empirical support in certain taxa (Griffiths and Armstrong 2001). On one hand, kin selection theory predicts that groups of closely related individuals should compete less intensely than unrelated individuals.…”