Cooperative colony foundation in Crematogaster scutellaris (Hymenoptera:Formicidae) 1
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Masoni A. , Teseo S. , Mattioli M. , Frizzi F. , Turillazzi S. , Santini G. 1
Dipartimento di Biologia, via Madonna del Piano 6, 50019, Sesto Fno, Firenze, Italy
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Laboratoire Evolution, Génomes et Spéciation, CNRS-UPR 9034, France
INTRODUCTION In several ant species, during the colony foundation phase, foundresses independent queen could form aggregation that usually persist after the foundation phase with the creation of a polyginic colony. In some species moreover, this cooperation ends when the first workers born and the queens fights each other until only one queen survive (Pleometrosis). Because no sexual are produce in incipient colonies, the surviving queen will monopolize the future reproductive success of the colony. This kind of foundation is believed to be advantageous especially in highly competitive environments. Crematogaster scutellaris, is a dominant tree-nesting ant species widely distributed throughout the Mediterranean basin. This specie usually adopts an Independent Colony Foundation (ICF), after a cloistral hibernation of single founder queens (Fig.1), usually in cynipid or aphid gall, and its colony are monoginic. We found out that some gall (12% of occupied gall ) could contain more than one queen (maximum 5) so in this study we investigate the nature of this association.
Fig.1 Crematogaster queen on her brood
MATERIALS AND METHODS After an hibernation period, we put 26 natural couple, and 15 single queen, housed in a Petri dish(Fig.2) in a thermostatic chamber at the same condition of temperature (20°-25°C) and in the dark until the first workers completed development. The behaviour of ants was observed during the following months for a maximum of 28 days after worker emergence, assessing the onset of aggressive interactions in the couple, the survival probability of queens (independent vs group foundresses) and counting the number of eggs, larvae, pupae and worker in each foundation. To understand the degree of relatedness between the associated queen we carried out a kinship analyses using microsatellite DNA. Fig.2 cynipid and artificial plastic galls
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Larvae Eggs
Fig.3 Two associated queen during a fight.
Larvae
Pupae
Worker
Fig.4 Queen survival during the test. The green line is the time of the first worker’s birth.
RESULTS AND DISCUSSION Genetic analyses is currently in progress so we have only preliminary results. Our data show that from the beginning of the experiment to the birth of the first worker, the associated queens are not very aggressive and they usually stay in opposite parts of the plastic gall and rear her own brood. When workers born the queens start to be aggressive and they fight together till one queen died. The workers take care of both queens independently and do not take part in the fight.
Number of Workers 8 7
Queens that found alone have an higher survival probability (Fig.4) and produce more larvae and workers (Fig 6).
Workers
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We could affirm that queens associations are not cooperative and that there isn’t any type of Pleometrotic foundation. Fig.5 Number of eggs, larvae and Pupae produced by queens during the test.
Contact:
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Single queen Associated queen
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Fig.6 Number of Workers produced by queens during the test.
