Constitutive Immune Function Responds More Slowly to Handling Stress than Corticosterone in a Shorebird

Abstract

Ecological immunologists are interested in how immune function changes during different seasons and under different environmental conditions. However, an obstacle to answering such questions is discerning the effects of biological factors of interest and investigation artifacts such as handling stress. Here we examined handling stress and its effects on constitutive (noninduced) immune function via two protocols on captive red knots (Calidris canutus). We investigated how constitutive immunity responds to handling stress, how quickly these changes take place, and the practical implications for researchers interested in sampling baseline immune levels. We found that Staphylococcus aureus and Candida albicans killing increased with handling stress while total leukocyte and lymphocyte concentrations decreased. However, although corticosterone increased significantly and rapidly in response to handling stress, none of the 10 measures of constitutive immunity that we tested differed significantly from baseline within 20 or 30 min of capture. Thus, researchers interested in baseline immune function should sample animals as soon as possible after capture, but studies in species not easily sampled in less than 3 min (such as red knots) could still yield useful results.

Leukocyte profiles indicate nutritional, but not moulting stress in a migratory shorebird, the Common Snipe (Gallinago gallinago)

“…The handling time of sampled birds (including transport from walk-in traps) was less than 1 h and in most cases less than 45 min. Although it has been reported that avian heterophil or lymphocyte counts can occasionally change within 60 min of capture (Cīrule et al 2012), studies on shorebirds (Buehler et al 2008;D'Amico et al 2017) and some passerines (Davis 2005) indicated that H/L ratio is relatively stable within the first hour after capture. Consequently, we assumed that the measurements of shorebird leukocyte profiles were unlikely to be affected by handling stress under our sampling protocol.…”

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

“…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.…”

Common measures of immune function vary with time of day and sampling protocol in five passerine species

“…While measuring immune function in an ecological context has yielded many insights, scientists continue to struggle with understanding what particular immune measurements indicate about the overall immune function of an individual (Boughton et al, 2011). One basic obstacle to interpreting field immune data is separating variation in immune function that is related to factors of biological interest from measurement artifacts, such as variation associated with handling stress (Buehler et al, 2008). This issue is compounded by the fact that field-collected blood samples are typically obtained opportunistically over the course of the day as individuals are captured, and that some amount of time elapses between capture of an individual and taking of a blood sample (handling time).…”

“…30 min, 60 min or even 2.5 h after capture). Several of these studies reported a discernible difference in immune function between individuals sampled within 3 min of capture versus those sampled 30 min or more after capture, especially in the case of bactericidal activity (Buehler et al, 2008;Davis, 2005;Fratto et al, 2014;Matson et al, 2006;Millet et al, 2007). It remains unknown whether measures of innate immune function in wild birds vary with capture stress over shorter time intervals; however, it is variation over these shorter time intervals that is likely to be the most relevant for field studies using mist nets or walk-in traps, given that welfare considerations dictate individuals be processed expeditiously post-capture, with the result that blood samples are more likely to be collected within minutes rather than hours of capture.…”