Omnivore diet composition effects on parasite load and host weight

Diet composition modulates animals’ ability to resist parasites and
recover from stress. Broader diet breadths enable omnivores to mount
dynamic responses to parasite attack, but little is known about how
plant/prey mixing might influence responses to infection. Using omnivorous
deer mice (Peromyscus maniculatus) as a model, we examine how varying
plant and prey concentrations in blended diets influence resistance and
body condition following infestation by Rocky Mountain wood ticks
(Dermacentor andersoni). In two repeated experiments, deer mice fed for
four weeks on controlled diets that varied in proportions of seeds and
insects, were then challenged with 50 tick larvae in two sequential
infestations. The numbers of ticks successfully feeding on mice declined
by 25% and 66% after the first infestation (in the first and second
experiments, respectively), reflecting a pattern of acquired resistance,
and resistance was strongest when plant/prey ratios were more equally
balanced in mouse diets, relative to seed-dominated diets. Diet also
dramatically impacted the capacity of mice to cope with tick infestations.
Mice fed insect-rich diets lost 15% of their body weight when parasitized
by ticks, while mice fed seed-rich diets lost no weight at all. While
mounting/maintaining an immune response may be energetically demanding,
mice may compensate for parasitism with fat and carbohydrate-rich diets.
Altogether, these results suggest that a diverse nutritional landscape may
be key in enabling omnivores’ resistance and resilience to infection and
immune stressors in their environments.