Mating behaviour and sexual selection in the African ball-rolling scarabKhepher platynotus(Bates) (Coleoptera: Scarabaeidae)

Spider dung beetles: coordinated cooperative transport without a predefined destination

Cooperative transport allows for the transportation of items too large for the capacity of a single individual. Beyond humans, it is regularly employed by ants and social spiders where two or more individuals, with more or less coordinated movements, transport food to a known destination. In contrast to this, pairs of male and female dung beetles successfully transport brood balls to a location unknown to either party at the start of their common journey. We found that, when forced to overcome a series of obstacles in their path, transport efficiency of pairs of beetles was higher than of solo males. To climb tall obstacles with their common ball of dung, the female assisted the leading male in lifting the ball by steadying and pushing it upwards in a 'headstand' position during the climb initiation. Finally, we show that pairs were faster than single beetles in climbing obstacles of different heights. Our results suggest that pairs of Sisyphus beetles cooperate in the transportation of brood balls with coordinated movements, where the male steers and the female primarily assists in lifting the ball. Taken together, this is to our knowledge, the first quantitative study of cooperative food transport without a known goal to aim for.

Contests over reproductive resources in female roller beetles: Outcome predictors and sharing as an option

Fights among females are frequent, although less attention has been placed on them than on male fights. They arise when females compete for food, oviposition, mates, brooding sites, or access to resources which increase offspring survival. It has been shown that the outcome of female fights may be less predictable by asymmetries in resource holding power, than in male fights. Male roller beetles fight over food resources, food balls, needed for mating and nesting, and it has been show in some species that asymmetries in reproductive experience and resource holding power in terms of size predict fight outcome, including ties in which contenders cut and split the food ball. In this study, we tested the influence of asymmetries in reproductive status (experience) and body size on female fight outcome in the carrion roller beetle Canthon cyanellus cyanellus. As predicted, and as previously found for males of the same species, female reproductive status of both contenders and relative size predict fight outcome. Larger and reproductively experienced contenders have a higher probability of winning. Furthermore, ties are more likely in fights involving opposing asymmetries (vgr. Large reproductively naïve owner versus small reproductively experienced intruder). Also as predicted, food ball splitting is more likely to be started by the predicted loser. This mode of resource sharing may be the result of a fighting strategy in which the costs of continuing to fight are greater than the benefits of not splitting, if a fraction of the disputed resource is more than the minimum needed for the present reproductive needs, and reduces costs associated to a longer fight.