Abstract:
Parasites deplete the resources of their host and can consequently affect the investment in competing traits (e.g.
reproduction and immune defence). The immunocompetence handicap hypothesis posits that testosterone (T) mediates
trade-offs between parasite defence and reproductive investment by suppressing immune function in male vertebrates
while more recently a role for glucocorticoids (e.g. cortisol (C)) in resource allocation has been suggested. These hypotheses
however, have not always found support in wild animals, possibly because most studies focus on a single parasite species,
whereas infections with multiple parasites are the rule in nature. We measured body mass, T- and C-levels of wild male
highveld mole-rats (Cryptomys hottentotus pretoriae) naturally uninfected or infected with a cestode (Mathevotaenia sp.)
right after capture. Subsequently, we injected animals subcutaneously with a lipopolysaccharide (LPS) to simulate a bacterial
infection and recorded changes in body mass, food intake, haematological parameters and hormone levels. As a control,
animals were injected with saline. Natural infection neither affected initial body mass nor C-levels, whereas infected males
had significantly reduced T-levels. We observed significant reductions in food intake, body mass and T in response to LPS
but not saline while C increased. However, this response did not vary with infection status. In contrast, final body mass and
some haematological parameters were significantly lowered in infected males. Our results suggest that naturally infected
males are able to compensate for resource depletion by physiological adjustments. However, this leaves them less tolerant
to the challenges of a secondary infection.
