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, 275 (1635), 703-11

Dispersal as a Means of Inbreeding Avoidance in a Wild Bird Population

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Dispersal as a Means of Inbreeding Avoidance in a Wild Bird Population

Marta Szulkin et al. Proc Biol Sci.

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 (f=0.25) inbreeding relative to the population average when individuals dispersed less than 200m. 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.

Figures

Figure 1
Figure 1
Natal dispersal distances (median and IQR) for male and female great tits (open and filled circles, respectively) with respect to six different inbreeding classes. Parent–offspring matings are excluded from this analysis. The values for males have been offset on the abscissa to facilitate presentation.
Figure 2
Figure 2
Frequency distributions of natal dispersal distances for (ad) males and (eh) females that either (a,e) outbred or were involved in close inbreeding of the following types: (b) fathers from father–daughter matings, (c) brothers from brother–sister matings, (d) sons from mother–son matings, (f) mothers from mother–son matings, (g) sisters from brother–sister matings and (h) daughters from father–daughter matings.
Figure 3
Figure 3
The likelihood of mating with kin decreases with respect to natal dispersal distance (m). The bold line shows the fitted values from a GLM with binomial errors where natal dispersal distance was fitted as a predictor to inbreeding (f≥0.03125); dashed lines show the 95% CI for the fit. The horizontal line represents the overall population average likelihood of inbreeding.

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