Leucocyte counts variation and measures of male fitness in the lekking Black Grouse

Abstract

Differences in the ability to sustain chronic stress can underlie the variation in individuals' fitness directly or indirectly by impairing the expression of condition-dependent signals used in female mate choice. Therefore, understanding the effect of the stress response on individuals' fitness is key to identifying the mechanism of sexual selection. We tested the hypothesis that an indicator of stress-the heterophil/lymphocyte ratio (H/L ratio)-is related to several major components of male fitness in the lekking Black Grouse (Tetrao tetrix), a species with intense male-male competition. The H/L ratio accurately measured the stress response, as it increased within a few hours of trapping and during the months prior to the mating season. The H/L ratio was positively related to the expression of morphological traits, suggesting that males of higher ''quality'' might be able to express elaborated ornaments and better cope with stressful conditions or with changes in health status. However, in Black Grouse, ornaments are (partly) independent of behavioural display and are under only weak selective pressure. Therefore, the H/L ratio was not significantly related to male mating success and survival to the following year. Under natural conditions, observed levels of the H/L ratio might not be associated with strongly deleterious effects because of behavioural adjustments. Mechanisms other than the stress response may mediate the observed variance in male mating success.

Life-History Differences in Age-Dependent Expressions of Multiple Ornaments and Behaviors in a Lekking Bird

“…Morphological data were collected on lek sites annually during January-March by catching black grouse with oatbaited walk-in traps (for methods, see Lebigre et al 2012). Each bird captured for the first time was marked for future identification with a unique combination of an aluminum tarsus ring (with an individual serial number) and three colored plastic tarsus rings.…”

Social and environmental factors modulate leucocyte profiles in free-living Greylag geese (Anser anser)

“…In birds, heterophils are rather indicative of changes in the environment (Gross & Siegel, 1983; Maxwell & Robertson, 1998). As lymphocyte numbers decrease while heterophil numbers increase in response to stressful conditions, the ratio of heterophils/lymphocytes (H/L ratio) is used as an indicator of physiological stress (e.g., Gross & Siegel, 1983; Gross & Siegel, 1986; McFarlane & Curtis, 1989; Maxwell, 1993; Vleck et al, 2000; Lebigre et al, 2012). Finally, monocytes are long-lived phagocytic cells associated, together with other leukocyte types (e.g., eosinophils, basophils), with defence against infections and bacteria (Davis, Maney & Maerz, 2008).…”

Simultaneous age‐dependent and age‐independent sexual selection in the lekking black grouse (Lyrurus tetrix)

“…; Lebigre et al . ). Each captured individual was aged as yearling or older according to plumage characteristics and individually ringed for future identification with an aluminium tarsus ring with a unique serial number and three coloured tarsus rings.…”

“…; Lebigre et al . ). Male behaviour was scan sampled at regular intervals and categorized as rookooing, hissing (the two main vocal displays), fighting or inactive (methods and behaviours are described in detail in Höglund, Johansson & Pelabon ).…”