Abstract
BackgroundBlood parameters such as haematocrit or leucocyte counts are indicators of immune status and health, which can be affected, in a complex way, by exogenous as well as endogenous factors. Additionally, social context is known to be among the most potent stressors in group living individuals, therefore potentially influencing haematological parameters. However, with few exceptions, this potential causal relationship received only moderate scientific attention.MethodsIn a free-living and individually marked population of the highly social and long-lived Greylag goose, Anser anser, we relate variation in haematocrit (HCT), heterophils to lymphocytes ratio (H/L) and blood leucocyte counts to the following factors: intrinsic (sex, age, raising condition, i.e. goose- or hand-raised), social (pair-bond status, pair-bond duration and parental experience) and environmental (biologically relevant periods, ambient temperature) factors. Blood samples were collected repeatedly from a total of 105 focal birds during three biologically relevant seasons (winter flock, mating season, summer).ResultsWe found significant relationships between haematological parameters and social as well as environmental factors. During the mating season, unpaired individuals had higher HCT compared to paired and family individuals and this pattern reversed in fall. Similarly, H/L ratio was positively related to pair-bond status in a seasonally dependent way, with highest values during mating and successful pairs had higher H/L ratio than unsuccessful ones. Also, absolute number of leucocytes tended to vary depending on raising condition in a seasonally dependent way.DiscussionHaematology bears a great potential in ecological and behavioural studies on wild vertebrates. In sum, we found that HTC, H/L ratio and absolute number of leucocytes are modulated by social factors and conclude that they may be considered valid indicators of individual stress load.
Highlights
Our results show that social and environmental factors interact with individual physiology in a complex way
We found that in the free-living greylag geese investigated, haematocrit (HCT) and differential leucocyte counts are seemingly contingent with a suite of endogenous, social and environmental factors
Pair-bond status showed a seasonal dependent relationship with several haematological parameters: unpaired individuals had the highest HCT during the mating season and heterophils to lymphocytes ratio (H/L) ratio was significantly higher in individuals who successfully raised young as compared to individuals which failed to fledge offspring that year
Summary
Haematocrit (HCT) and differential leucocyte count are important diagnostic tools in gaining information about an animal’s condition and health and may be regarded as indicators of individual responses to environmental and social conditions (Cooper, 1975; Gavett & Wakeley, 1986; Hellgren, Vaughan & Kirkpatrick, 1989; Averbeck, 1992; Saino et al, 1997; Ots, Murumägi & Hõrak, 1998; Bortolotti et al, 2009; Vinkler et al, 2010). The flock re-unites in August after moulting, when androgens reach a second peak in unpaired males, while in paired individuals the second peak is reached later in fall (Hirschenhauser, Moestl & Kotrschal, 1999a; Hirschenhauser, Moestl & Kotrschal, 1999b) This hints at the close interplay between physiology and social status in greylag geese, as suggested by further studies (e.g., stress response and social allies: Sachser, Duerschlag & Hirzel, 1998; heart rate in the context of sociality: Aureli, Preston & De Waal, 1999; steroid hormones and social status: Wingfield, Hegner & Lewis, 1991; Goymann, Villavicencio & Apfelbeck, 2015). As handraised individuals generally differ from parent-raised conspecifics in glucocorticoid stress reactivity (Hemetsberger et al, 2010), we predict that hand-raised geese will show higher values of both haematological parameters during socially challenging periods than parent-raised ones
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