Courtship diversification and the evolution of reproductive isolation in Timema walking-sticks

The evolution of premating isolation through changes in mating behaviour is central to the process of speciation. Timema walking sticks display intermediate reproductive isolation between ecologically divergent individuals within species, and almost complete isolation between species. I characterized courtship and behavioural isolation in Timema to examine the role of courtship in isolation, and the evolution of reproductive isolation in this genus. I found that courtship apparently plays no role in current mate discrimination within or among species, and that separate traits underlie within-species mate choice and species-recognition. However, the evolutionary history of courtship diversification implicates it in the initiation of reproductive isolation, though strengthening of isolation selects for discrimination to occur earlier as divergence progresses. Overall, I conclude that courtship currently plays little role in reproductive isolation in Timema, and that stages of replacement or accumulation of reproductive barriers, rather than a continuous process, characterize the evolution of reproductive isolation.