The effects of inbreeding on condition-dependent survival and innate immunity in a translocated robin population.

Abstract

It is well known that inbreeding leads to reductions in fitness traits of inbred individuals. These negative effects of inbreeding are a key consideration for conservation when the number of species become reduced or only small numbers of individuals have been translocated. If inbreeding reduces the fitness of individuals then the persistence of these populations and species may be threatened. Studying the effects of inbreeding is important for the future management of potentially inbred populations. The Ulva Island population of Stewart Island robins (Petroica australis rakiura) provides an ideal opportunity to study the effects of inbreeding. This re-introduced population was founded between 2000 and 2001 from only 12 genetic founders and through regular monitoring, a population pedigree has been created. To date there has been no attempt to investigate the relationships between inbreeding, condition and overall survival within one population and few studies have assessed the effects of inbreeding on innate immunity. The current study aimed to fill these research gaps by first testing whether the negative effect that inbreeding is frequently found to have on the survival of individuals is due to a reduction in body condition (energy reserves) (also caused by inbreeding). Secondly, in order to provide another explanation for the reduced survival of inbred individuals, the effects of inbreeding on innate immunity were tested.

The links between inbreeding, condition and survival were not supported and inbreeding was only found to have a weak negative effect on the control of two microbe species and two blood cell frequencies. The inability to detect a strong negative effect of inbreeding on body condition and innate immunity was unexpected and may represent the influence of environmental variables and age as well as low statistical power (for some immunity measures). The Stewart Island robin species may not exhibit inbreeding depression in immunity due to an historical bottleneck or the low pathogen pressure experienced by island populations/species, resulting in low over all immune function. The results of the current study highlight a number of factors that may require consideration for future studies of the effects of inbreeding on fitness traits. Firstly, the detection of inbreeding may be dependent on age due to developmental and selection pressure differences. Secondly, inbreeding depression may not be detectable in populations or species that are historically bottlenecked or inbred.