Original Article

Crematogaster abstinens and Crematogaster pygmaea (Hymenoptera: Formicidae: Myrmicinae): from monogyny and monodomy to polygyny and polydomy

Martins Segundo, G.B., De Biseau, J.-C., Feitosa, R.M., Carlos, J.E.V., Sá, L.R., Fontenelle, M.T.M.B. & Quinet, Y.

Abstract: Polygyny and polydomy are key features in the nesting biology of many ants, raising important questions in social insect biology, in particular about the ecological determinants of such derived traits. One relevant way to investigate those questions is the comparative study of closely related species with contrasting colony structure. In our study, we investigated and compared morphological (morphology of queens, workers and males), chemical (cuticular hydrocarbon profiles), behavioral (attractiveness of queens and substrates chemically marked by queens, colony foundation, mating behavior), and colony-structure (nest architecture, queen number, nest number) traits in Crematogaster abstinens Forel, 1899 and C. pygmaea Forel, 1904, two related Neotropical species. Our aim was to provide evidence of close evolutionary relationship between the two species and to give new insight into the ecological significance of the polygynous and polydomous system found in C. pygmaea. We first showed that the two species share important traits supporting a close evolutionary relationship: same basic morphology in workers and queens, with high queen / worker dimorphism, and ground-dwelling habit with almost identical nest architecture. The two species also share a significant part of their cuticular hydrocarbon (CHC) profiles, which possibly explains the observed attractiveness of substrates marked by queens of one species to workers of the other species. However, the two species completely differ in colony structure: highly polygynous and polydomous colonies in C. pygmaea; small, monogynous and monodomous colonies in C. abstinens. They also show, in addition to the shared compounds, significant differences in their Chc profiles and differ in mating and colony foundation behavior. In previous studies, the probable existence of a dual dispersal strategy in C. pygmaea was shown: a long-range dispersal strategy followed by independent colony foundation and a short-range dispersal strategy through budding events associated with seasonal polygyny and polydomy. We hypothesize that in C. pygmaea, polygyny and polydomy could represent a combined evolutionary response to efficiently explore and rapidly saturate patchily distributed habitats that are unstable and subject to a strong seasonality. We also speculate that the polygynous and polydomous colony structure observed in C. pygmaea is a derived condition from the monogyny and monodomy observed in C. abstinens.