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Open Access Research article

Demographic costs of inbreeding revealed by sex-specific genetic rescue effects

Susanne RK Zajitschek12*, Felix Zajitschek12 and Robert C Brooks1

Author Affiliations

1 Evolution & Ecology Research Centre and School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia

2 Station d'Ecologie Expérimentale du CNRS à Moulis, USR 2936, 09200 Moulis, France

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BMC Evolutionary Biology 2009, 9:289  doi:10.1186/1471-2148-9-289

Published: 10 December 2009

Abstract

Background

Inbreeding can slow population growth and elevate extinction risk. A small number of unrelated immigrants to an inbred population can substantially reduce inbreeding and improve fitness, but little attention has been paid to the sex-specific effects of immigrants on such "genetic rescue". We conducted two subsequent experiments to investigate demographic consequences of inbreeding and genetic rescue in guppies.

Results

Populations established from pairs of full siblings that were descended either from two generations of full-sibling inbreeding or unrelated outbred guppies did not grow at different rates initially, but when the first generation offspring started breeding, outbred-founded populations grew more slowly than inbred-founded populations. In a second experiment, adding two outbred males to the inbred populations resulted in significantly faster population growth than in control populations where no immigrants were added. Adding females resulted in growth at a rate intermediate to the control and male-immigrant treatments.

Conclusion

The slower growth of the outbred-founded than inbred-founded populations is the opposite of what would be expected under inbreeding depression unless many deleterious recessive alleles had already been selectively purged in the inbreeding that preceded the start of the experiment, and that significant inbreeding depression occurred when the first generation offspring in outbred-founded populations started to inbreed. The second experiment revealed strong inbreeding depression in the inbred founded populations, despite the apparent lack thereof in these populations earlier on. Moreover, the fact that the addition of male immigrants resulted in the highest levels of population growth suggests that sex-specific genetic rescue may occur in promiscuous species, with male rescue resulting in higher levels of outbreeding than female rescue.