Tobias Otte Livres

Speciation in herbivorous insects may be influenced by their specialization on host plants, with plasticity in host preferences potentially fostering sympatric speciation through effects on mating signals and assortative mating. This thesis investigates the causes and consequences of phenotypic plasticity in mating recognition systems among herbivorous insects, focusing on the leaf beetles Phaedon cochleariae and P. armoraciae, which share a common host plant range but prefer different species at the same site. Their sexual behavior relies on cuticular hydrocarbon (CHC) profiles, which serve as contact pheromones for mate and species recognition. The study employs behavioral bioassays and chemical analyses to determine if host plant species influence the beetles' CHC patterns and mate recognition. Findings indicate that males prefer females feeding on the same host plant over those on alternative plants, and sexual isolation between species diminishes when both feed on the same host. Discriminant analysis shows that CHC profiles vary significantly based on sex, host plant, and species, yet become more similar when feeding on the same plant. These results suggest that plant-induced phenotypic divergence in mate recognition cues may serve as an early barrier to gene flow between insect populations on different host species, potentially leading to ecological speciation.