The Means of Signal Divergence Early in a Host Shift

AbstractWe used a "quasi-natural" selection experiment and subsequent reciprocal transplants to assess the means of divergence in mating signals early in a host shift. We worked with a member of the <i>Enchenopa binotata</i> complex of treehoppers (Hemiptera: Membracidae), where speciation results from host plant shifts and involves remarkable signal-preference codivergence. We shifted treehoppers from a natural population on one host plant to three different novel host species under conditions of allopatry and sympatry. After five generations, we conducted reciprocal transplants that manipulated oviposition and development hosts. We found tentative evidence of signal divergence fueled by standing genetic variation and strong evidence of signal divergence through overall plasticity and evolution in the form of plasticity, resulting in signal differences between treehoppers on novel and ancestral hosts. These results suggest that signal divergence (and consequently assortative mating) may arise early in a host shift from multiple means. Together with a prior analysis of the adaptive consequences of these experimental host shifts, our findings indicate that adaptation/specialization and divergence in sexual traits may originate independently and in parallel or with divergence in sexual traits leading. Thus, ecological specialization may be facilitated by sexual divergence rather than being the initiating factor.