Personality, hormonal correlates and parasite load in the eastern rock elephant shrew

Abstract

Inter-individual variation in behaviour, or as it has now come to be known, personality, has been shown to affect many different components of fitness in animals. A concept that used to be thought of as background ‘noise’ has come to explain much of the variation we observe within populations and between individuals. The personality of an animal can affect how an animal utilises its environment. In a heterogeneous environment this may increase the potential to find limiting resources, such as mates. However, it may also result in different risks experienced by the animal, such as the number of parasites in may be exposed to. To date, links between personality and parasites have rarely been studied although it is a commonly held concept that more exploratory, bolder individuals should have greater parasite loads. As with individual differences in behaviour, individuals may differ in their circulating hormone profiles. Hence it has been proposed that personality can potentially be shaped by these circulating hormone concentrations with shyer individuals having higher corticosteroid (i.e. cortisol and corticosterone) concentrations while bolder ones may have higher testosterone levels. However, corticosteroids may also be elevated by stressors such as parasites. Similarly, animals that produce more testosterone may have reduced immune-abilities as suggested by the immunocompetence handicap hypothesis. These animals would also protect larger territories and fight rather than flee from potential conspecifics. Consequently, correlations between personality with both parasitic infestation and hormone concentrations have been suggested. In the current study we examined this relationship in the eastern rock sengi (Elephantulus myurus) or elephant shrew that is endemic to southern Africa. They are monogamous, sexually monomorphic and both sexes maintain and defend home ranges year-round. In the wild these animals also have large diversity of ectoparasites with two tick, one mite and one louse species being the most important. Burdens of these varied seasonally but not with sex. Personality was highly correlated across time and contexts suggesting a behavioural syndrome with reactive (more exploratory, bold and aggressive) and reactive (less exploratory, shy and submissive) types for E. myurus. In addition, personality was repeatable within individuals captured over a long term period. Personality scores suggested increasing reactivity with increasing body condition. At the same time only one of the four main ectoparasite species was affected by personality with burdens increasing with increasing reactivity. This suggests that correlations between personality and parasites may depend on the parasite species and that more studies should be done with multiple parasites when evaluating this relationship. We found consistently high levels of urinary C and low T throughout the study with no correlations of either hormone with our personality measures. The former may in part be due to the large abundances of ectoparasites while the monogamous mating system and year-round territorial defense by both sexes could account for low T. Consequently, the current study does not support some of the frequently assumed links between personality and other traits but highlights the need to explicitly consider mating system and multiple parasite species when addressing similar questions.