Examining effects of persistent retroviral infection on fitness and pathogen susceptibility in a natural feline host

Many animal populations carry endemic (i.e., permanently present) viruses but few studies have assessed the demographic consequences of these infections under natural conditions. We examined the effects of chronic infection with FIV _Pco, a feline retrovirus, on the fitness and pathogen susceptibility of its natural host, the cougar (Puma concolor (L., 1771)), in the wild. Based on data obtained through intensive monitoring of 160 cougars from two populations, we estimated survival and different measures of host fecundity of infected and uninfected individuals. In addition, we used serological data collected from 207 cougars to test whether FIV _Pco predisposes individuals to a higher probability of infection with other pathogens. We found no evidence for an overall reduction in survival due to FIV _Pco when accounting for other sources of demographic variation (age, sex, and population). There was a consistent but nonsignificant trend towards poorer reproductive performance in FIV _Pco-infected females. We found no serological evidence for a higher probability of secondary infections associated with FIV _Pco. Overall, these results support the premise that chronic FIV _Pco infection is asymptomatic in its natural cougar host, probably because of a long evolutionary association between virus and host. However, results of stochastic simulations indicate that only larger reductions in annual survival (>20%) can be excluded with confidence. Also, the possibility of a so far unrecognized cost of FIV _Pco infection on cougar fecundity remains.