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Title: Omnivore diet composition alters parasite resistance and host condition

item BLUBAUGH, CARMEN - University Of Illinois
item JONES, CAMI - Washington State University
item JOSEFSON, CHLOE - University Of Idaho
item OWEN, JEB - Washington State University
item Scoles, Glen
item SNYDER, WILLIAM - University Of Illinois

Submitted to: Journal of Animal Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2023
Publication Date: 9/15/2023
Citation: Blubaugh, C.K., Jones, C.R., Josefson, C., Owen, J.P., Scoles, G.A., Snyder, W.E. 2023. Omnivore diet composition alters parasite resistance and host condition. Journal of Animal Ecology.

Interpretive Summary: Host defensive responses to parasites fall into broad categories of resistance and tolerance. Resistance traits decrease parasite burden and tolerance traits limit damage caused by the parasite. Defenses require energetic investment and laboratory models have shown that properties of the host’s diet influence the expression of resistance and tolerance traits. We tested if diet influenced resistance and tolerance in a natural host-ectoparasite system involving the deer mouse (Peromyscus maniculatus) and Rocky Mountain wood tick (RMWT; Dermacentor andersoni). Deer mice are omnivorous rodents that feed on seeds and insects. Larval RMWTs commonly use deer mice as hosts in the wild. We maintained groups of deer mice on diets that varied in the balance of seeds versus insects. The mice were infested twice with larval RMWTs and we measured resistance (number of blood-fed ticks) and tolerance (maintenance of body mass) responses of the hosts. Mice were able to produce resistance and tolerance responses together when parasitized by larval ticks. This underscores that resistance and tolerance traits are not mutually exclusive and can be co-expressed. However, we observed that dietary resources affected only tolerance responses of infested mice, and all mice, regardless of diet, were able to acquire resistance to ticks. Our data provide clues into how dietary shifts in hosts may alter resistance and tolerance against parasites, but more work is needed to fully elucidate the defense mechanisms. Exploring these interactions in the field would provide a better understanding of how environmental conditions may influence disease transmission dynamics and effects of parasitism on host ecology.

Technical Abstract: 1.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. 2.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). 3.In two repeated experiments, deer mice fed for 4'weeks on controlled diets that varied in proportions of seeds and insects were then challenged with 50 tick larvae in two sequential infestations. 4.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. 5.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. 6.While mounting/maintaining an immune response may be energetically demanding, mice may compensate for parasitism with fat and carbohydrate-rich diets. 7.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.