چکیده :

In scramble competition mating systems, individual behaviours related to maleemale competition are

expected to be plastic across sociosexual environments. However, the evolutionary forces that shape

individual differences in behavioural plasticity remain poorly understood. We measured behaviour

associated with scramble competition in male water striders, Tenagogerris euphrosyne, in two social

contexts. Male T. euphrosyne tend to mount other individuals or pairs indiscriminately and then

dismount if their target is either another male or a mating pair. We measured the speed with which a

focal male dismounted (i.e. his sensitivity to having made an inappropriate mounting) in each of these

contexts. We quantified temporal consistency of dismount speed within each context, as well as individual

variation in behavioural plasticity across contexts. We then estimated the effect of the behaviour

and of plasticity on individual fitness in different sex ratio conditions. We found that individuals differed

in their recognition sensitivity traits, and also in how plastic their sensitivity (i.e. dismount speed) was to

context (mating status or sex). When we measured the mating success of each male within experimental

groups kept at four different sex ratios, recognition sensitivity traits in both contexts interacted to

influence mating success, and there were significant differences in linear selection on sensitivity traits

between sex ratio treatments. We discuss how insensitive males evolve, and how individual variation in

behavioural plasticity could be maintained by selection or environmental variability.