Phenotypic plasticity of mate recognition systems prevents sexual interference between two sympatric leaf beetle species

Maladaptive sexual interactions among heterospecific individuals (sexual interference) can prevent the coexistence of animal species. Thus, the avoidance of sexual interference by divergence of mate recognition systems is crucial for a stable coexistence in sympatry. Mate recognition systems are thought to be under tight genetic control. However, we demonstrate that mate recognition systems of two closely related sympatric leaf beetle species show a high level of host-induced phenotypic plasticity. Mate choice in the mustard leaf beetles, Phaedon cochleariae and P. armoraciae, is mediated by cuticular hydrocarbons (CHCs). Divergent host plant use causes a divergence of CHC phenotypes, whereas similar host use leads to their convergence. Consequently, both species exhibit significant behavioral isolation when they feed on alternative host species, but mate randomly when using a common host. Thus, sexual interference between these syntopic leaf beetles is prevented by host-induced phenotypic plasticity rather than by genotypic divergence of mate recognition systems.

异种个体间的适应不良性互动（性干扰，sexual interference）会阻碍动物物种的共存。因此，通过配偶识别系统（mate recognition systems）的分化来规避性干扰，对于同域分布（sympatry）物种的稳定共存至关重要。既往研究表明，配偶识别系统受到严格的遗传调控（genetic control）。然而，本研究证实，两种近缘同域分布的叶甲的配偶识别系统呈现出极高水平的宿主诱导表型可塑性（host-induced phenotypic plasticity）。芥菜叶甲属的两个物种——Phaedon cochleariae与P. armoraciae——的配偶选择由表皮碳氢化合物（cuticular hydrocarbons, CHCs）介导：宿主植物利用模式的分化会导致其表皮碳氢化合物表型产生分化，而相似的宿主利用模式则会使表型趋于一致。因此，当两种叶甲取食非原生宿主植物时，二者会表现出显著的行为隔离（behavioral isolation）；而当它们共享同一宿主时，则会随机交配。综上，这两种同域分布的叶甲之间的性干扰并非通过配偶识别系统的基因型分化（genotypic divergence）得以避免，而是依托宿主诱导的表型可塑性实现的。