Mammalian host traits and bacterial disease risk

M.A. PREVITALI; OSTFELD, R.S.; F. KEESING

Congreso; 96th Ecological Society of America Annual Meeting; 2011

Ecological Society of America

Until recently, the role that species traits play in disease ecology has escaped notice.  The use of traits in disease ecology, could help in identifying reservoir species, understanding community resilience to disease, and detecting the mechanisms behind the patterns. The question is which traits are important determinants of the disease risk and transmission.  The answer to this question relies on a closer examination of the mechanisms behind the trait-disease association. In the case of Lyme disease, the species with high reservoir competence, also have high densities and smaller body sizes than species with lower reservoir competence. At the same time they range in from fast to slow in their pace of life. We hypothesized that this arrangement may be related to the immunological strategies that they use, with most competent reservoir species favoring cheap, broad immune defenses, and species with a low reservoir competence favoring specific but expensive immune defenses.  To assess immunological strategies we captured wild individuals of several mammalian host species, collected a blood sample, and measured bacterial killing capacity (BKC). Then, we tried to explain the variation in BKC by species and gender differences and the individual?s body condition. We looked for the best proxy for species differences by replacing it with body mass, life-history traits and correlates such as density. We found important differences between males and females, the direction of which depended on the species. We also found significant individual variation in BKC. These results suggest that trait-base disease ecology studies would benefit from incorporating measurements at a finer scale than the species level.  When we replaced the species id with their attributes, we found that body mass was better at explaining species differences than lifespan or densities. This is in agreement with the traditional view that body mass is the most important attribute of an animal and supports the wide use that it has received in trait-based studies. However, the predictive power of body mass was much lower than that of the species id, indicating that this trait is related to but not able to fully capture the mechanisms by which these species differ in their innate immune function. More studies should focus on understanding the connections between traits and the mechanisms linking them to disease risk and transmission, which is particularly limited for vertebrate hosts. Additionally, for many under-studied vertebrate species, the information on relevant traits is lacking, and measuring disease parameters may prove easier than measuring certain traits. In other more well-studied systems, trait-based disease ecology may be more useful as a means suggestive of potential mechanisms rather than as a predictive tool for identifying reservoir species.  On the other hand, we believe that studies that use large data bases looking at numerous species for which there is enough trait information are complimentary to studies conducted at a finer scale, on a reduced number of species, but with better measurements of important parameters in disease ecology.