Evolution of trophobiosis between Acropyga ants and scale insects

Ants practice two distinct types of agriculture: fungus farming and herding of scale insects and aphids. While fungus-farming ants have been relatively well studied, rather few studies have addressed herder ants. The study of herder ants provides the opportunity to investigate the evolution and maintenance of an animal-to-animal mutualistic symbiosis (trophobiosis). Acropyga ants practice a unique form of herding where unmated alate Acropyga queens vertically transmit trophobionts by taking an individual with them on their mating flights. Trophophoresy is a method of trophobiont transmission that spans across generations and provides the strong possibility that codiversification has occurred between the partners. The results of robust phylogenies of both the ants and scale insects will be discussed in the context of trophobiosis. Acropyga trophobionts are from two main scale insect families: Rhizoecidae and Xenococcidae. The xenococcids are the original trophobionts of Acropyga, having evolved with the ants around 30 million years ago. The addition of rhizoecids, is more recent and has multiple independent origins. Using phylogenies of both groups the transition from xenococcids to rhizoecids among New World Acropyga species will be discussed, along with the implications for morphological coevolution between both partners.