No selection on immunological markers in response to a highly virulent pathogen in an Arctic breeding bird.

Pierre Legagneux,Oliver P Love,Lisha L Berzins,Mark Forbes,Sophie Bourgeon,H G Gilchrist,Jeffrey T Foster,Naomi Jane Harms,Sébastien Descamps,Gary Burness,Catherine Soos,Holly L Hennin,Joël Bêty

doi:10.1111/eva.12180

Abstract

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.

Highlights

In natural populations, unpredictable environmental perturbations can occur from changing climatic conditions, habitat degradation, and introduction of predators or epidemics
Even when a given immune trait predicted the probability of mortality (i.e., H:L ratio), relationships were associated with large standard errors or depended on outliers (Fig. 1 and Figure S1)
Our results revealed no stabilizing or directional selection on any of the immune traits measured in the presence of a highly virulent disease in a population of Arctic breeding birds

Summary

Introduction

Unpredictable environmental perturbations can occur from changing climatic conditions, habitat degradation, and introduction of predators or epidemics Such occurrences can offer useful, quasi-experimental opportunities to explore and potentially uncover intense natural selection on morphological (Brown and Brown 1998; Grant and Grant 2002), physiological (Wilcoxen et al 2010), or other fitness-related traits (Carroll et al 2007). Timing of reproduction and breeding effort are expected to be direct drivers of an individual’s fitness, but can affect subsequent survival and/or future reproduction (Faaborg et al 2010) Measuring these types of tradeoffs is challenging, and they are often only revealed through experimental manipulation (Gustafsson et al 1996; Sheldon and Verhulst 1996). To our knowledge, no studies have yet investigated trade-offs between immune traits, reproductive investment and survival during a disease outbreak, when they are most likely to be detected

Methods

Results

Conclusion