In natural populations, epidemics provide opportunities to look for intense natural selection on genes coding for life history and immune or other physiological traits. If the populations being considered are of management or conservation concern, then identifying the traits under selection (or ‘markers’) might provide insights into possible intervention strategies during epidemics. We assessed potential for selection on multiple immune and life history traits of Arctic breeding common eiders (Somateria mollissima) during annual avian cholera outbreaks (summers of 2006, 2007 & 2008). We measured prelaying body condition, immune traits, and subsequent reproductive investment (i.e., clutch size) and survival of female common eiders and whether they were infected with Pasteurella multocida, the causative agent of avian cholera. We found no clear and consistent evidence of directional selection on immune traits; however, infected birds had higher levels of haptoglobin than uninfected birds. Also, females that laid larger clutches had slightly lower immune responses during the prelaying period reflecting possible downregulation of the immune system to support higher costs of reproduction. This supports a recent study indicating that birds investing in larger clutches were more likely to die from avian cholera and points to a possible management option to maximize female survival during outbreaks.

dataDryadPCRData with information on the carrier status of Pasteurella multocida labelled "PCR CARRIER STATUS" and several immune traits of Common eidersdataDryadIFData on measured immune traits of Common eiders during the pre-breeding and incubation stagesdataDryad15052014Dataset used to test for directional selection on immune traits. Body size and mass measurements are provided as well as data for the 8 immune traits. The LIVEDEAD column provides information on the fate of individuals (1 is dead, 0 alive). BLEEDING.TIME is in min.