Animal mating systems are often studied with the goal of understanding why species, populations, or groups vary from one another in the system they display. Although these differences are often treated as basically stable, it is also known that these systems may shift over time (e.g. from one breeding season to the next). There has been some study of how ecological factors correlate with these changes; however, few, if any, studies have investigated how the phenotypic composition of a group governs the timing and probability of system transitions. Groups of stream water striders (Aquarius remegis) can demonstrate quick and flexible transitions in mating system dynamics, with many groups eventually transitioning to a system in which a single, large male monopolizes mating opportunities. We asked if variation in individual- and group-level traits associated with morphology and behavior (e.g. size of the largest individual, variance in activity behavioral types, and average social plasticity) could partially explain the variability in how rapidly groups make this transition, if they make it all. Our results show that the average social plasticity of males in a group has important effects on the emergence timing of mating systems dominated by a single male.