The challenge hypothesis (Wingfield et al. 1990, American Naturalist, 136, 829–846) predicts varying androgen responses to mating, breeding or territorial behaviour in avian males. At the interspecific level, the highest androgen responsiveness has been observed in males from monogamous species with paternal incubation, and the lowest in males from promiscuous, nonpaternal species. Studies of a...

In New World primates, mixed-species troops have been reported. Here, we analysed the performance of affiliative and agonistic behaviours of Callithrix jacchus and Callithrix penicillata living in mixed groups. For this purpose, we recorded the interaction of the individuals from two groups located in Bauru city, in the state of São Paulo (Brazil). Our data show that in both groups, affiliative...

One mechanism to resolve conflict among group members is third party intervention, for which several functions, such as kin protection, alliance formation, and the promotion of group cohesion have been proposed. Still, empirical research on the function of intervention behaviour is rare. We studied 40 cases of intervention behaviour in a field study on 13 semi-wild bachelor horses (Equus ferus ...

Many arthropods possess filiform hair sensilla (termed trichobothria in arachnids), which are extremely sensitive detectors of medium particle displacement. Electrophysiological evidence in some taxa suggests that these sensilla can detect air particle displacements resulting from intraspecific communication signals. However, it has not yet been shown for any species that the air particle displ...

The forces responsible for maintaining genetic polymorphisms within populations are often unclear. Male pygmy swordtails are polymorphic at a single Y-linked locus that regulates body colour. The visually conspicuous, sex-limited polymorphism suggests that sexual selection is important for maintaining genetic variation for these conspicuous phenotypes. We performed a series of behavioural exper...