Effects of behavioural type, social skill and the social environment on male mating success in water striders

• More active and aggressive male water striders tended to have higher mating success.
• More active–aggressive males also tended to become hyperaggressive.
• Individual male mating success was reduced by time spent with a hyperaggressive male.
• Being hyperaggressive is a poor social skill, as it reduces a male's mating success.
• More active–aggressive males were more socially plastic.

We examined the relative importance of individual differences in personality (activity and aggressiveness), social skill and the social environment (average activity and aggressiveness of the group, presence of hyperaggressive males) in determining the behaviour and mating success of males of the stream water strider, Aquarius remigis. Males that had a consistently more active–aggressive behavioural type had, on average, higher mating success largely because they spent more time active in microhabitats associated with acquiring mates. Some active–aggressive males, however, showed hyperaggressive behaviour, apparently attempting to mate forcibly with other males, or forcibly separate pairs, which was rarely successful. A higher tendency to be hyperaggressive was associated with reduced mating success (i.e. being hyperaggressive represents low social skill). The overall effect was thus stabilizing sexual selection on male activity and aggression. The social environment also had large effects on male behaviour and mating success. In particular, the presence of a keystone hyperaggressive male had strong negative effects on the mating success and general activity of other males in the pool. Notably, males with a more active–aggressive behavioural type maintained higher mating success than less active–aggressive males in the presence of a hyperaggressive male. Social plasticity (change in behaviour in response to changing social conditions) also depended on the male's behavioural type; males with a more active–aggressive behavioural type were more plastic.