Highway to the danger zone: exposure-dependent costs of immunity in a vertebrate ectotherm

Parasite exposure often causes innate immune activation, resulting in tradeoffs among physiological processes and strong selection on the parasite. Costs of immune activation vary widely among and within host populations though, likely dependent on the evolutionary history of host-parasite interactions and the environments in which they occur. For hosts, degree of exposure may drive the magnitude of costs incurred, and subsequently whether hosts resist or tolerate infections.

If costs increase concomitantly with exposure, a threshold may exist where the expense of parasite resistance becomes prohibitive and parasite tolerance becomes favorable. Here, we characterized exposure-dependent costs of an innate immune response in brown anoles (Anolis sagrei) by tracking allocation of an isotopically-labelled essential amino acid (13C-leucine), to the liver and gonads. To elicit immune responses, we used lipopolysaccharide (LPS), a strongly immunogenic molecule from Salmonella spp.

We fou...