Queen-size dimorphism in the ant Ectatomma tuberculatum (Hymenoptera : Formicidae : Ponerinae)

摘要

Queen dimorphism is known in different ant subfamilies and corresponds to the co-occurrence of several queen morphs within the same species. It is frequently associated with different colony-founding and dispersion strategies. We studied the queen-size dimorphism in the Ponerinae ant, Ectatomma tuberculatum from field colonies collected at Apazapan (Veracruz, Mexico). Microgynes were present in half the colonies collected and their production among the female sexuals prevailed over that of macrogynes. Colonies possessed one or several gynes, up to 8 for macrogynes and 11 for microgynes. From the data basis on nest excavation, worker size population was correlated neither with the number of dealate gynes nor with the number of microgynes, and it seemed that microgynes were as productive as macrogynes. Both gynes were morphologically similar but their distribution was clearly bimodal without overlapping, the microgynes being not completely separated from the workers. Microgynes fell on a continuous regression line with the macrogynes and represented the isometric reduction of normal queens. The ovarian morphology differed among the three female groups: macrogynes had the most numerous ovarioles on average but produced as many oocytes as microgynes. Contrary to the workers, all gynes possessed a developed spermatheca and had the potential ability to lay fertilized eggs. Such queen dimorphism was not previously observed in this species and only found in the Apazapan site. It may constitute an alternative reproductive strategy leading to a functional facultative polygyny, as already reported in E. ruidum (Schatz et al. 1996, Lachaud et al. 1999a, b), or a case of a social intraspecific parasitism. Further investigations are being conducted to better understand the reproductive biology of this species.