Experimental evolution of parasitoid infectivity on symbiont-protected hosts leads to the emergence of genotype-specificity

Host-parasitoid interactions may lead to strong reciprocal selection for traits involved in host defense and parasitoid counter-defense. In aphids, individuals harboring the facultative bacterial endosymbiont Hamiltonella defensa exhibit enhanced resistance to parasitoid wasps. We used an experimental evolution approach to investigate the ability of the parasitoid wasp Lysiphlebus fabarum to adapt to the presence of H. defensa in its aphid host Aphis fabae. Sexual populations of the parasitoid were exposed for eleven generations to a single clone of A. fabae, either free of H. defensa or harboring artificial infections with three different isolates of H. defensa. Parasitoids adapted rapidly to the presence of H. defensa in their hosts, but this adaptation was in part specific to the symbiont isolate they were evolving against and did not result in an improved infectivity on all symbiont-protected hosts. Comparisons of life history traits among the evolved lines of parasitoids did not re...