Environmental determination of the male morph in the ant Cardiocondyla obscurior (Hymenoptera: Formicidae)

Cardiocondyla is one of the few ant genera in which winged dispersing males coexist with wingless fighter males, which predominantly mate inside their maternal nests. Male polymorphism is not genetically determined but induced by environmental conditions (e.g., a decrease in temperature). The factors leading to the production of winged males were studied-in more detail by exposing colonies of C. obscurior to a specific set of rearing conditions. A stressful environmental condition (rearing temperature lowered on average by 5 degrees C) experienced for at least two days, the decrease of temperature by a minimum of 3 degrees C, and the addition of protein-rich food triggered the development of winged males. In contrast, a smaller decrease in temperature, starvation, encounters with workers from other species, and encounters with alien, conspecific winged males did not induce the production of winged males. Colonies differed strongly in their reaction to changing environmental conditions, which might indicate a difference in their threshold sensitivity. The results are discussed and compared with data from other dimorphic insect species.