The importance of direct fitness for helpers in advanced insect societies

• Applicant: Professor Dr. Jürgen Heinze
• Subject Area: Evolution, Anthropology
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 283883031

The evolution of cooperation and altruistic behavior among selfish individuals has long puzzled biologists. Hamilton s theory of inclusive fitness explains that helpers can gain indirect fitness benefits when they assist a breeding relative and through their help increase the number of its offspring. In addition, helpers in group-living mammals and birds can gain direct fitness through taking over the breeding position in the nest or territory or through improving their brood care skills, which later benefits their own offspring. But are such direct fitness benefits also important in advanced eusocial societies, such as ants? The behavior of workers suggests that they are. Workers of many ant species can produce males from unfertilized eggs, but usually refrain from doing so in the presence of the queen. After the death of the queen, however, workers establish social and reproductive rank orders and only the top-ranking workers lay eggs. Furthermore, socially dominant workers refrain from costly tasks, such as foraging and colony defense. This suggests that workers aim to retain the option of obtaining direct fitness, but whether selfishness pays off has never been quantified. In this project we will fill this important gap in our understanding of eusociality by for the first time estimating worker direct fitness in a wild social insect population. To do so we will determine the abundance of worker reproduction in colonies of Temnothorax crassispinus ants by censuses in the field and by genetic analyses of the maternity of males. In addition, we will determine whether worker-and queen-produced males differ in fitness traits through controlled breeding experiments and measuring sperm quantity and viability. Finally, through manipulation of colony composition we will examine whether worker selfishness has a cost for colony cohesiveness and productivity. The project builds on extensive pilot studies in T. crassispinus. It receives additional actuality from the ongoing heated discussion about the value of inclusive fitness and kin selection and will lead to a more complete understanding of the maintenance of eusociality in advanced social insects.

• DFG Programme: Research Grants