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Host-plant adaptation drives the parallel evolution of reproductive isolation


Parallel evolution of similar traits in independent populations that inhabit ecologically similar environments strongly implicates natural selection as the cause of evolution1. Parallel speciation is a special form of parallel evolution where traits that determine reproductive isolation evolve repeatedly, in closely related populations, as by-products of adaptation to ecological conditions1,2. The outcome of such parallel evolution is that ecologically divergent pairs of populations exhibit greater levels of reproductive isolation than ecologically similar pairs of populations of a similar or younger age2,3,4. The parallel evolution of reproductive isolation provides strong evidence for natural selection in the process of speciation1, but only one conclusive example from nature is known2. Populations of the walking-stick insect Timema cristinae that use different host-plant species have diverged in body size and shape, host preference, behaviour and the relative frequency of two highly cryptic colour-pattern morphs5,6. Here we report that divergent selection for host adaptation, and not genetic drift, has promoted the parallel evolution of sexual isolation in this species. Our findings represent a clear demonstration that host-plant adaptation can play a crucial and repeatable role in the early stages of speciation.

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Figure 1: Copulation frequencies were higher for ecologically similar pairs of T. cristinae walking-stick insects than for ecologically divergent pairs, where divergence refers to differences in host-plant use (P < 0.001, logistic regression).


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We thank T. E. Reimchen, H. Rundle, A. Mooers, F. Breden, J. Endler, R. Vos, C. Parent, J. Joy, S. Springer and especially D. Schluter for discussion and comments on the manuscript. M. Fulton, D. McLaren, B. Mickelson, M. Vankoeveringe and T. Luchin provided field and technical assistance. E. Rolàn-Alvarez provided software and statistical advice. J. Endler provided laboratory space for all the mating experiments. Financial support was provided by the Natural Science and Engineering Research Council of Canada.

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Correspondence to Patrik Nosil.

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Nosil, P., Crespi, B. & Sandoval, C. Host-plant adaptation drives the parallel evolution of reproductive isolation. Nature 417, 440–443 (2002).

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