Diversity of interactions among leaf-cutting ants and their phorid parasitoids: a community approach

ELIZALDE LUCIANA; FOLGARAIT, PATRICIA JULIA

Simposio; XX Symposium de Myrmecologia; 2011

Host-parasitoid interactions can be shaped by diverse factors, depending both on hosts and parasitoids. Ecological and evolutionary similarities among species of leaf-cutting ant hosts suggest that they should share several phorid parasitoid species, accordingly most phorids might be generalists. On the other hand, since an abundant resource availability may promote specialization on the resource, variation in colony size among ant species may select for parasitoids narrowing their range to use ant species with big colony sizes. Here, we studied the interactions among leaf-cutting ants and their phorid parasitoids using a community ecology framework, i.e. including all leaf-cutting ant hosts from a community. In addition, we determined the potential for indirect effects among host species by shared phorid parasitoids. Finally, we evaluated whether host colony size, as a measure of resource abundance, influence the specialization, richness and abundance of phorids. To record host-parasitoid interactions, we sampled in 14 localities along a host species richness gradient. Then, we sampled the interactions seasonally in two localities, one with highest ant richness. We collected 18 species of parasitoids over 11 ant species. More than half of the parasitoid species turn out to be specialists, a number higher than expected by chance. Acromyrmex and Atta did not share phorid species. Many Acromyrmex species share parasitoids, thus we investigated the potential for indirect interactions mediated through parasitoids. In the richest community only Ac. lobicornis acted as source of parasitoids for Ac. fracticornis. Thus, although not general, this mechanism could be important for Ac. fracticornis given that Ac. lobicornis is also present. Host species with small colonies showed very few interactions with phorids. All phorid species using these ants were generalists. Meanwhile, many phorids attacking Acromyrmex hosts with medium colonies were specialists. Most parasitoids attacking Atta with big colonies were specialists. Atta species had higher phorid richness and abundance, followed by Acromyrmex species with medium colonies. Thus, we found a broad variation in host range of these phorids, with generalist species probably due to similarities among host species. On the other hand, we presented evidence that host colony size, as a measure of resource abundance, explained part of host specialization in some phorid species.