An ant social parasite in-between two chemical disparate host species

Host-parasite coevolution shapes the structure of communities and simultaneously the traits of the interacting species. Social parasites developed sophisticated chemical integration strategies to circumvent host defences. Here, we show that the two Leptothorax host species of the obligate social parasite Harpagoxenus sublaevis exhibit extremely divergent chemical profiles, making it nearly impossible for this parasite to closely adapt to both hosts at once. Our cuticular hydrocarbon analyses demonstrate that H. sublaevis acquires some host chemicals passively, but additionally, actively biosyntheses some host hydrocarbons. The parasite adjusts thereby more closely to its smaller host, L. muscorum, because it actively produces two of its cuticular substances and also more easily acquires the short-chained hydrocarbons of this host. Community composition analyses indicate that the social parasite overexploits this chemical closer host species and, albeit costly for the parasite, frequently enslaves workers of the second host concurrently.