Immune systems have repeatedly diversified in response to parasite diversity. Many animals have outsourced part of their immune defence to defensive symbionts, which should be affected by similar evolutionary pressures as the host’s own immune system. Protective symbionts provide efficient and specific protection and respond to changing selection pressure by parasites. Here, we use the aphid Aphis fabae, its protective symbiont Hamiltonella defensa and its parasitoid Lysiphlebus fabarum to test whether parasite diversity can maintain diversity in protective symbionts. We exposed aphid populations with the same initial symbiont composition to parasitoid populations that differed in their diversity. As expected, single parasitoid genotypes mostly favoured a single symbiont that was most protective against that particular parasitoid, while multiple symbionts persisted in aphids exposed to more diverse parasitoid populations, which in turn affected aphid population density and rates of parasitism. Parasite diversity may be crucial to maintaining symbiont diversity in nature.

For an exact description of the methods used to obtain the data herein, please refer to the associated article.

basic.txt: Data collected during aphid transfer in every generation. See methods for exact procedured to obtain each meassurement.

mol.txt: Information on the presence and absence of H. defensa and the identity of the H. defensa strain present. This data was obtained by diagnostic PCRs on aphids collected during transfer in generation 2, 6, and 10 and subsequent sequencing if H. defensa was present (see methods for more details). Data for generation 0 was known because of the strain each aphid belonged to during set up.

See readme.txt for a description of column names used in the data sets.