Abstract
Dispersal is a key life-history trait governing the response of individuals, populations and species to changing environmentalconditions. In the context of global change, it is therefore essential to better understand the respective role ofcondition-, phenotype- and genetic-dependent drivers of dispersal behaviour. Although the importance of immune functionand pathogen infestation in determining patterns of dispersal is increasingly recognised, no study to our knowledgehas yet investigated the influence of immune gene variability on dispersal behaviour. Here, we filled this knowledge gapby assessing whether individual heterozygosity at five immune gene loci (one from the Major histocompatibility complexand four from encoding Toll-like receptors) influences roe deer natal dispersal. We found that dispersal propensity wasaffected by immune gene diversity, suggesting potential pathogen-mediated selection through over-dominance. However,the direction of this effect differed between high and low quality individuals, suggesting that dispersal propensity is drivenby two different mechanisms. In support of the condition-dependent dispersal hypothesis, dispersal propensity increasedwith increasing body mass and, among high quality individuals only (standardized body mass 18 kg), with increasingimmune gene diversity. However, among poor quality individuals, we observed the opposite pattern such that dispersalpropensity was higher for individuals with lower immune gene diversity. We suggest that these poor quality individualsexpressed an emergency dispersal tactic in an attempt to escape a heavily infested environment associated with poor fitnessprospects. Our results have potentially important consequences in terms of population genetics and demography, as wellas host–pathogen evolution.