  Immunity is hypothesized to share limited resources with other physiological
functions and may mediate life history trade-offs, for example between
reproduction and survival. However, vertebrate immune defense is a complex
system that consists of three components. To date, no study has assessed all of
these components for the same animal model and within a given situation.
Previous studies have determined that the acquired immunity of common eiders
(Somateria mollissima) is suppressed during incubation. The present paper aims
to assess the innate immune response in fasting eiders in relation to their
initial body condition. Innate immunity was assessed by measuring plasma nitric
oxide (NO) levels, prior to and after injection of lipopolysaccharides (LPS), a
method which is easily applicable to many wild animals. Body condition index
and corticosterone levels were subsequently determined as indicators of body
condition and stress level prior to LPS injection. The innate immune response
in eiders did not vary significantly throughout the incubation period. The
innate immune response of eiders did not vary significantly in relation to
their initial body condition but decreased significantly when corticosterone
levels increased. However, NO levels after LPS injection were significantly and
positively related to initial body condition, while there was a significant
negative relationship with plasma corticosterone levels. Our study suggests
that female eiders preserve an effective innate immune response during
incubation and this response might be partially determined by the initial body
condition.
