Combined effects of cold exposure and sub-lethal intestinal parasites on host morphology and physiology

Multiple, simultaneous demands elicit physiological and morphological respo nses that may jeopardize an animal's ability to respond to future challenge s, especially when resources are limited. Laboratory mice (Mus musculus) ex perimentally infected with an intestinal nematode (Heligmosomoides polygyru s) and then exposed to cold showed phenotypic plasticity of morphological a nd physiological responses. The parasitized mice maintained a similar body mass to the unparasitized mice but had less body fat and showed changes in some organ masses, a greater resting metabolic rate (RMR) and a diminished glucose uptake capacity both at the site of infection and in regions of the small intestine not occupied hy parasites. Cold-exposed mice had a greater RMR, less body fiat, a greater glucose transport capacity and showed chang es in organ masses compared with mice maintained at room temperature, The r esponses to cold exposure were not affected by parasitism for any dependent variable. The costs of having parasites during simultaneous cold exposure included decreased energy reserves and greater maintenance requirements, wh ich may then decrease the energy available for future expenditures, such as reproduction.