Female adaptation to developmental plasticity in male calling behavior

The katydid Neoconocephalus triops exhibits in North America substantial developmental plasticity of male mating calls. The AM rate of the summer calls is significantly faster than that of the winter calls at the same temperature. In the tropics, where N. triops originated, males express only the fast summer-call phenotype. We tested two alternative hypotheses: (1) call plasticity in the population from North America evolved in response to selection by female preference after N. triops colonized North America, or (2) call plasticity evolved before N. triops expanded into North America and its expression in the novel environment led to adaptive change of female preferences. First, we tested whether call plasticity was present in tropical populations of N. triops. Tropical males expressed the winter-call phenotype when reared under winter conditions, indicating that call plasticity did not evolve in response to temperate climates. Second, we compared female preferences among temperate and tropical populations. We found that the temperature dependence of preferred AM rate was significantly steeper in temperate N. triops than in a tropical population of N. triops. Third, we compared temperature dependence of female preference of the N. triops populations to three Neoconocephalus species without call plasticity. Only temperate N. triops had significantly steeper temperature dependence than the other species. This steeper temperature dependence matched female preference to the fast summer call at high temperatures and to the slow winter call at low temperatures in temperate populations. These results support the hypothesis that female preference changed in N. triops in North America to compensate for the plasticity of male calls.