Different underlying mechanisms drive associations between multiple parasites and the same sexual signal

Associations between parasite loads and sexual signal expression have long been the focus of research. However, our understanding how selection operates in context multiple infections within same host is still quite limited. We examined plumage coloration, which sexually selected North American barn swallows, Hirundo rustica erythrogaster, tail streamer length, other swallow subspecies, eight different infections. found that two parasites, nest mites Plasmodium, were associated with colour expression, but opposite directions. Attractive males less likely to their nests, more be infected Plasmodium. underlying mechanisms generating links these parasites signal. Males invested survive when suggesting a physiological mechanism linking Plasmodium we no clear cost examining mites, primarily infect offspring. Instead, using experimental mite manipulations, provide evidence for behavioural mechanism, where territorial behaviour male–male competition drive association did not find associations length this divergent signals may flexible. These results suggest evolution single can shaped by several, even opposing,