Response of host species to brood parasitism in dung beetles: importance of nest location by parasitic species

1. Brood parasitism is an interaction that negatively affects reproductive success of host species, some of which have evolved defences to reduce offspring mortality caused by the parasites. In this study, we analyse the responses to interspecific brood parasitism of a dung beetle species, Onthophagus merdarius , in which reproductive success is heavily affected by parasitic beetles. 2. We used a combination of field and laboratory experiments to approach this question. Manipulating the effect of the presence of brood parasites on host nesting showed that there were no differences between treatments in nest traits. This absence of responses of the host species might be related to how and when brood parasites localize host nests: brood parasites actively find host nests after the nests have been finished and the nest burrows sealed. 3. Although both the rate of parasitism and the mortality rate caused by parasites are very high on O. merdarius , the possibility of the host species to evolve defence strategies against brood parasites is probably constrained by resource limitation for nesting in the study area. Because brood parasitism and resource limitation act synergistically favouring small brood size and small brood-mass size, smaller individuals may be also favoured under these conditions in the study area.