Heritable basis for choice of group size in a colonial bird

Abstract

Sizes of most kinds of animal groups vary considerably within a population, with group size often causing direct effects on the fitness of group members. Although the consequences of varying group size have been well studied, the causes of variation in group size remain poorly known for most animals. Groups might vary in size because different individuals perform better in differently sized groups and thus have genetic predispositions to choose large or small groups. We examined whether heritable variation for choice of group size exists in the cliff swallow (Petrochelidon pyrrhonota), a colonial bird that nests in colonies ranging from 2 to 3,700 nests. Parent-offspring regressions showed significant heritabilities for choice of colony size under natural conditions. Partial cross-fostering experiments showed that individuals reared in colonies of sizes different from those of their birth returned to breed the next year in colonies that matched their birth colony in size and actively avoided those similar to their rearing colony, suggesting that choice of colony size is genetically based. Common environmental effects, maternal effects, and philopatry did not explain these results. Variation in group size probably results in part from a polymorphism in genetic preferences within the population, and the range in colony sizes is maintained by natural selection on the type of bird occupying each site.

Opposing selective pressures may act on the colony size in a waterbird species

“…Higher physiological quality of control and foster broods raised in the smaller colonies suggests that all measured components of offspring quality were not inherited, but reflected more favourable developmental conditions prevailing in nesting aggregations of smaller size. This also seems to contradict previous reports on a strong heritable component to colony size choice based on individual ability to withstand parasites (Brown and Brown 2000), which is consistent with the results of the recent simulation study by Danchin et al (2014).…”

“…In order to confirm whether any potential differences in offspring condition were not genetic, but could be directly attributed to different rearing conditions experienced in the colonies of varying size, a cross-fostering experiment was also conducted. So far, only few studies cross-fostered nestlings between colonies of different size, suggesting a heritable basis for choice of group size (Brown and Brown 2000;Møller 2002;Roche et al 2011; but see Danchin et al 2014). We are not aware of any cross-fostering experiments investigating the effects of colony size on physiological condition and stress in birds.…”

Developmental perspectives on personality: implications for ecological and evolutionary studies of individual differences

“…preferences for habitats and social environments will, if those dispersers have a choice of areas in which to settle, lead to systematic variation among dispersers in the conditions they experience for a period of time after that dispersal event. Several authors have reported broad-sense heritable variation in preferences for habitat features (Leibold et al 1994;Barker & Starmer 1999), and social group sizes (Brown & Brown 2000;Serrano & Tella 2007), supporting the notion that animals with different genotypes and any PEFs associated with those genotypes may, at a given age or life stage, prefer different types of environments, potentially leading to rGE (Plomin et al 1977). Similarly, individuals may, by their own behaviour, modify the social or physical environment in which they develop (niche-construction).…”

Steroid Hormone Levels Are Related to Choice of Colony Size in Cliff Swallows

“…What causes variation in group size is poorly understood, however, with explanations often involving extrinsic constraints such as the amount of available breeding space at a given site (Lack 1968, Wittenberger 1981, Brown and Brown 1996. More recently, a few studies on birds have suggested a possible genetic basis to an individual's choice of colony size (Brown and Brown 2000, Møller 2002, with, for example, cross-fostered birds later settling to breed in colonies more similar in size or density to those of their birth than those where they were reared. Presumably, in such cases, there are inherent differences among individuals that make them more or less successful in groups of different sizes, and their performance in these different social settings has selected for their sensitivity to group size in making settlement decisions (Brown and Brown 2000).…”

“…More recently, a few studies on birds have suggested a possible genetic basis to an individual's choice of colony size (Brown and Brown 2000, Møller 2002, with, for example, cross-fostered birds later settling to breed in colonies more similar in size or density to those of their birth than those where they were reared. Presumably, in such cases, there are inherent differences among individuals that make them more or less successful in groups of different sizes, and their performance in these different social settings has selected for their sensitivity to group size in making settlement decisions (Brown and Brown 2000). No studies to date have identified the nature of the differences among individuals that might influence choice of colony size, and we know essentially nothing about the phenotypic characteristics that promote success in large vs. small groups.…”