Seasonal Redistribution of Immune Function in a Migrant Shorebird: Annual‐Cycle Effects Override Adjustments to Thermal Regime

Abstract

Throughout the annual cycle, demands on competing physiological systems change, and animals must allocate resources to maximize fitness. Immune function is one such system and is important for survival. Yet detailed empirical data tracking immune function over the entire annual cycle are lacking for most wild animals. We measured constitutive immune indices once a month for a year on captive red knots (Calidris canutus). We also examined temperature as an environmental contributor to immune variation by manipulating ambient temperature to vary energy expenditure. To identify relationships among immune indices, we performed principal-component analysis. We found significant repeatability in immune indices over the annual cycle and covariation of immune indices within and among individuals. This covariation suggests immune strategies as individual traits among individuals and the use of different immune strategies during different annual-cycle stages within individuals. Over the annual cycle, both higher-cost phagocyte-based immunity and lower-cost lymphocyte-based immunity were high during mass change, but there was a clear shift toward lower-cost lymphocyte-based immunity during peak molt. Experimental manipulation of temperature had little effect on annual variation in immune function. This suggests that other environmental factors, such as food availability and disease, should also be examined in the future.

Identifying crucial gaps in our knowledge of the life-history of avian influenza viruses—an Australian perspective

“…Second, the intensity of population congregations of migratory birds often reaches its annual peak during migration or shortly after arrival on the wintering grounds, most notably in waterbirds. Finally, events within the annual cycle of birds may alter the susceptibility of individual hosts, such as changes in immune defences resulting from energetic trade-offs with moult, breeding or long-distance migration (Hasselquist 2007;Buehler et al 2008;Martin II et al 2008). Marked differences in viral prevalence have also been found between years (e.g.…”

No evidence for melatonin-linked immunoenhancement over the annual cycle of an avian species

“…Therefore, these birds experienced natural photoperiodic and temperature conditions of the northern Netherlands. The birds used to study seasonal rhythms of immune function (n = 12) were part a larger study examining the eVect of ambient temperature on immune function over the annual cycle (Buehler et al 2008a). For the discussion presented in this paper we included only birds in the control group (variable treatment), since the conditions experienced by these birds matched those experienced by the birds used to study melatonin.…”

“…The birds used to study seasonal rhythms of immune function were sampled monthly from March 2005 to March 2006 between 10:30 and 11:00 am (mean § SD = 10:44 § 5 min) and always within 20 min of entering an aviary (Buehler et al 2008a). A previous study has veriWed that none of the indices of immune function used by Buehler et al (2008a) are impacted by handling stress if blood is taken within 30 min of entry into the aviaries (Buehler et al 2008b).…”

“…A previous study has veriWed that none of the indices of immune function used by Buehler et al (2008a) are impacted by handling stress if blood is taken within 30 min of entry into the aviaries (Buehler et al 2008b). We refer the reader to Buehler et al (2008a) for further details on sampling and methodologies for the immune assays.…”

“…Red knots are long-distance migrant shorebirds with distinct phenotype annual cycles that are maintained even in captivity (Cadée et al 1996;Piersma 2007;Buehler et al 2008a). We then examine these data in conjunction with a yearlong dataset of immune function measured monthly (Buehler et al 2008a) to test the winter immunoenhancement hypothesis.…”