Immune variability in tuco-tucos: genetic influence, fitness benefits and energetic costs.

CUTRERA ANA PAULA, ZENUTO ROXANA R. LUNA FACUNDOO ANTENUCCI DANIELL

Mendoza, Argentina

Conferencia; 10th International Mammalogical Conference; 2009

International Mammalogical Society

Parasites and pathogens are expected to exert strong selection pressures on their hosts by affecting variables intimately linked to host fitness. Because hosts exhibiting less efficient defenses should be selected against, it is intriguing that hosts vary so markedly in the strength and efficiency of their antiparasite strategies. Two main explanations have been proposed to account for this variation. First, parasite resistance is under genetic control, with negative frequency-dependent parasite-mediated selection on Major Histocompatibility Complex (MHC) genes acting to maintain variability in immune response. However, few studies that have demonstrated diversifying selection on MHC genes in free-living mammals have also explored the functional consequences of such variation. Interpopulation comparisons of levels of MHC variability in Ctenomys talarum revealed that heterozygosity and diversifying selection at MHC genes were consistently greater for the more pathogen-challenged population. To assess the functional consequences of this difference in polymorphism, we examined whether MHC variability is associated with levels of parasite resistance in this species. Second, because the immune response may entail substantial costs, variability in this response can arise from differential allocation of resources to immunity vs. other costly physiological processes. Among mammals, studies of immune response costs have focused on surface-dwelling rodents with often contradictory results. Studies on tucos – with lower mass-specific metabolic rates and a slower «pace of life» than surface rodents – will give insights into the factors that influence investment on immunity. Our studies of C. talarum indicated that mounting an immune response was associated with a significant increase in energy expenditure, suggesting that pathogens can impact the energy budget of tucos, creating the opportunity for trade-offs. Together, these lines of research involving Ctenomys are contributing to understanding the bases for variation in immune defense in natural populations of mammals.Ctenomys talarum revealed that heterozygosity and diversifying selection at MHC genes were consistently greater for the more pathogen-challenged population. To assess the functional consequences of this difference in polymorphism, we examined whether MHC variability is associated with levels of parasite resistance in this species. Second, because the immune response may entail substantial costs, variability in this response can arise from differential allocation of resources to immunity vs. other costly physiological processes. Among mammals, studies of immune response costs have focused on surface-dwelling rodents with often contradictory results. Studies on tucos – with lower mass-specific metabolic rates and a slower «pace of life» than surface rodents – will give insights into the factors that influence investment on immunity. Our studies of C. talarum indicated that mounting an immune response was associated with a significant increase in energy expenditure, suggesting that pathogens can impact the energy budget of tucos, creating the opportunity for trade-offs. Together, these lines of research involving Ctenomys are contributing to understanding the bases for variation in immune defense in natural populations of mammals.