Dispersal as a means of inbreeding avoidance in a wild bird population

Abstract

The long-term study of animal populations facilitates detailed analysis of processes otherwise difficult to measure, and whose significance may appear only when a large sample size from many years is available for analysis. For example, inbreeding is a rare event in most natural populations, and therefore many years of data are needed to estimate its effect on fitness. A key behaviour hypothesized to play an important role in avoiding inbreeding is natal dispersal. However, the functional significance of natal dispersal with respect to inbreeding has been much debated but subject to very few empirical tests. We analysed 44 years of data from a wild great tit Parus major population involving over 5000 natal dispersal events within Wytham Woods, UK. Individuals breeding with a relative dispersed over several-fold shorter distances than those outbreeding; within the class of inbreeding birds, increased inbreeding was associated with reduced dispersal distance, for both males and females. This led to a 3.4-fold increase (2.3-5, 95% CI) in the likelihood of close ( fZ0.25) inbreeding relative to the population average when individuals dispersed less than 200 m. In the light of our results, and published evidence showing little support for active inbreeding avoidance in vertebrates, we suggest that dispersal should be considered as a mechanism of prime importance for inbreeding avoidance in wild populations.

Dispersal in an extensive continuous forest habitat: Marsh Tit Poecile palustris in the Białowieża National Park

“…Furthermore, because of the extreme site fidelity of adults (see above), this automatically excluded the possibility of incestuous mating between parents and their offspring (no such cases observed in BNP). The Marsh Tit results are thus consistent with data for other forest species (Greenwood et al 1978;Schiegg et al 2006;Szulkin and Sheldon 2008), which suggest that dispersal could serve as a primary mechanism of inbreeding avoidance. It remains to be seen, though, whether inbreeding avoidance has played a major role in shaping the evolution of dispersal in Marsh Tits, or whether it is simply an advantageous by-product of other selective pressures, such as avoidance of intra-specific competition between kin (Nilsson 1989).…”

Natal Dispersal, Mating Patterns, and Inbreeding in the AntFormica exsecta

“…Earlier evidence for sex-biased dispersal as an inbreeding avoidance mechanism in the wild is indeed mixed, being apparently effective in some species (e.g. black grouse, Lebigre et al 2010, and the great tit, Szulkin and Sheldon 2008), but less so in others (Seychelles warbler, Eikenaar et al 2008). …”

Condition, innate immunity and disease mortality of inbred crows

“…In particular, scant information is available regarding the proximate factors that might predispose inbred individuals to disease in wild populations. A more complete picture of the causes and consequences of disease-mediated inbreeding depression in wild populations would contribute to our understanding of the evolution and maintenance of behaviours such as sex-biased dispersal (Charlesworth & Charlesworth 1987;Szulkin & Sheldon 2008), gregariousness (Jog & Watve 2005) and avoidance of kin matings (Koenig & Haydock 2004). Detailed knowledge about the factors that influence disease-mediated inbreeding depression, and ways in which the impacts of disease can be mitigated, is also critically important for the conservation of small, inbred populations (Keller & Waller 2002).…”