Figure 1.

Occurrence and putative independent origins of inquiline social parasites. (a) Area of each slice is proportional to the number of species of known inquiline social parasites within the subfamily. The number in parentheses reports the minimum number of independent origins of inquilinism, as evaluated from the literature ([12,13,15,16,26–29], see electronic supplementary material, table S1). Where data were not available, the number of genera showing at least one case of the inquiline social parasites is reported, under the assumption that origins of inquiline social parasitism occurred independently in different genera. Thus, the figure provides a conservative estimate of the independent origins of social parasitism. (b–d) Exemplary representatives of obligate inquiline social parasites in: (b) bumblebees (Bombus rupestris, right, and its host Bombus lapidarius, photo by Luca Franzini); (c) Pogonomyrmex anergismus, left, and its host Pogonomyrmex barbatus (photo by Elizabeth Cash); (d) Polistes sulcifer, left, and its host Polistes dominula (photo by Rita Cervo). (Online version in colour.)