Abstract
Populations of Egyptian spiny mice (Acomys cahirinus dimidiatus) in a fragmented montane wadi system in the Sinai showed significant differences in the abundance of gut helminths. Differences in parasite load between populations were positively associated with measures of androgen activity but showed no significant relationship with glucocorticoid activity. Social discrimination tests with adult males from different wadis showed that those from sites with greater helminth abundance were less likely to investigate odours from other males and were less aggressive when subsequently interacting with the odour donors. Subjects showed markedly more investigation towards the odours of males from distant wadis compared with those from their own or immediately neighbouring wadi, but were less aggressive when confronted with odour donors from distant wadis. Despite this, there was a positive relationship between the amount of investigation towards distant male odour and subsequent aggression towards the male. While aggressiveness was positively associated with measures of androgen and glucocorticoid activity, no significant relationship emerged with individual helminth infection. Thus aggressiveness appeared to relate to overall local population levels of infection rather than individual challenge.
Highlights
The idea that susceptibility to infection, and the prevalence and intensity of disease in host populations, reflects adaptive variation in investment in the immune system (so-called ‘ecological immunology’ (Sheldon & Verhulst, 1996)) has gained considerable support in recent years (Behnke et al, 1992; Folstad & Karter, 1992; Sheldon & Verhulst, 1996; Barnard & Behnke, 2001)
We have tested whether males of the Egyptian spiny mouse (Acomys cahirinus dimidiatus), show associations between parasite burden, steroid hormone activity and aggressive behaviour that are consistent with the adaptive immunity modulation
Since the lengths of the left and right feet showed a significant unsigned asymmetry when compared with measurement error, and hind foot asymmetry has been shown to be associated with local population differences in parasite burdens and behaviour in other rodent species (Barnard et al, 2002), we included hind foot asymmetry in the Principal components analysis (PCA)
Summary
The idea that susceptibility to infection, and the prevalence and intensity of disease in host populations, reflects adaptive variation in investment in the immune system (so-called ‘ecological immunology’ (Sheldon & Verhulst, 1996)) has gained considerable support in recent years (Behnke et al, 1992; Folstad & Karter, 1992; Sheldon & Verhulst, 1996; Barnard & Behnke, 2001) Evidence from both field and laboratory studies suggests that immunity may be traded off against other components of life history, or, constrain investment in other components, and that, in birds and mammals, steroid hormones play an important mediating role (Grossman, 1985; Alexander & Stimson, 1988; Folstad & Karter, 1992; Wedekind & Folstad, 1994; Wilckens & de Rijk, 1997). We have tested whether males of the Egyptian spiny mouse (Acomys cahirinus dimidiatus), show associations between parasite burden, steroid hormone (androgen and glucocorticoid) activity and aggressive behaviour that are consistent with the adaptive immunity modulation
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