IMMUNITY OF LEAFCUTTER ANTS AND ITS ROLE IN HOST-PARAITOID INTERACTIONS

ELIZALDE LUCIANA; HUGHES WILLIAM; TREANOR DAVID; PAMMINGER TOBIAS

Congreso; XXIII Simposio de Mirmecologia; 2017

Parasites are one of the most important components in ecological communities because of their high diversity and the strong selection pressure that they exert on their hosts. Factors generating and constraining host-parasite interactions in a community context (i.e. involving all species interacting) are still poorly known. One such factor is the host immune response which may influence the number of host species that a parasite uses as resource (i.e. its host-range). Host species with strong immune defences may suffer from lower parasitism; however, the investment in immune function seems to be related to the natural selection pressure imposed by parasites, leading to a stronger immune defence in hosts suffering from higher parasite load. Comparative studies quantifying the immune responses of potential hosts of parasites in a community are rare. Thus, there seems to be a need for more studies quantifying the relationship between host immune defences and parasite load at an interspecific level. We studied the immune response of 6 leafcutter ants present in a community where their interaction with phorid fly parasitoids is well-known, to test whether ant immunity correlates with parasitoid load (number of species and abundance) and their host specialization. For 3 colonies of each ant species, we measured the following immune variables: i) the encapsulation to standard challenge, ii) PhenolOxydase (PO) and proPO levels, and iii) the number of haemocytes. Ant species differed in their encapsulation response, PO, and number of haemocytes; however, no difference was detected for proPO. There was high intra and intercolony variation in immunity. We found that there was a positive correlation between the strength of immune response (except for PO) with parasitoid load and specificity variables. After taking into account ant species phylogenetic relatedness, correlations were not significant although remain positive. Our results suggest that immunity is an important factor accounting for leafcutter ant-phorid parasitoid interactions, but that other factors, such as evolutionary history, play a role too. Since leafcutter ants are important agricultural pests in the Neotropic, our results might help in finding alternative ways to control their populations, as well as answering basic questions in host?parasite community ecology. (PICT 2014-N°1206, CONCIET)