Abstract
Individual reproductive success largely depends on the ability to optimize behaviour, immune function and the physiological stress response. We have investigated correlations between behaviour, faecal steroid metabolites, immune parameters, parasite excretion patterns and reproductive output in a critically endangered avian species, the Northern Bald Ibis (Geronticus eremita). In particular, we related haematocrit, heterophil/lymphocyte ratio, excreted immune-reactive corticosterone metabolites and social behaviour with parasite excretion and two individual fitness parameters, namely, number of eggs laid and number of fledglings. We found that the frequency of excretion of parasites’ oocysts and eggs tended to increase with ambient temperature. Paired individuals excreted significantly more samples containing nematode eggs than unpaired ones. The excretion of nematode eggs was also significantly more frequent in females than in males. Individuals with a high proportion of droppings containing coccidian oocysts were more often preened by their partners than individuals with lower excretion rates. We observed that the more eggs an individual incubated and the fewer offspring fledged, the higher the rates of excreted samples containing coccidian oocysts. Our results confirm that social behaviour, physiology and parasite burden are linked in a complex and context-dependent manner. They also contribute background information supporting future conservation programmes dealing with this critically endangered species.
Highlights
Individual lifetime reproductive success largely depends on the ability to optimize the trade-off relationships between behaviour, immune function and other physiological parameters over the life history of that individual (Sheldon and Verhulst 1996; Barnard et al 1998)
Spring 2010 Individuals producing a high number of faeces containing coccidian oocysts received more allopreening (ZIGLMM1: estimate ± standard error (SE) 0.007 ± 0.002, z = -2.611, p = 0.009; Fig. 1; unless stated otherwise, all data for and related to ZigLMMs and generalized linear mixed models (GLMMs) in the Results section are given as the estimate ± SE) and won more agonistic interactions than individuals excreting fewer samples containing coccidian oocysts (ZIGLMM1: -0.687 ± 0.301, z = -2.281, p = 0.022; intercept: -1.894 ± 0.288, z = -6.563, p \ 0.001)
Excretion of samples containing nematode eggs was negatively related to the frequency of aggressive encounters won (ZIGLMM2: -0.63 ± 0.297, z = -2.121, p = 0.033) and to the frequency of aggressive interactions lost (ZIGLMM2: -1.837 ± 0.492, z = -3.733, p \ 0.001; intercept: 4.554 ± 0.736, z = 6.182, p \ 0.001; Table 2)
Summary
Individual lifetime reproductive success largely depends on the ability to optimize the trade-off relationships between behaviour, immune function and other physiological parameters over the life history of that individual (Sheldon and Verhulst 1996; Barnard et al 1998). Social context is among the most potent stressors in groupliving individuals (von Holst 1998; Klein and Nelson 1999; de Vries et al 2003; Wascher et al 2008a, b) Activation of both the acute and chronic physiological stress responses is adaptive in nature, contingent on specific ecological and habitat pressures (Wingfield et al 1998; Boonstra 2013). The physiological stress response appears to link immune functions with parasite burden Both of the latter are known to co-vary with season (Bakuza and Nkwengulila 2009), sex (Zuk and McKean 1996; Tschirren et al 2003), age (Hayward et al 2009), personality (Barber and Dingemanse 2010; Koprivnikar et al 2012), hierarchy (Zuk et al 1997; Ungerfeld and Correa 2007; Muehlenbein and Watts 2010), crowding (Raouf et al 2006) and reproductive effort (Klein and Nelson 1999)
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