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Title: Complexity in mutualisms: indirect interactions with multiple parties
Abstract: Ant-plants provide ants with rewards such as housing and food in exchange for protection from herbivores. These protection mutualisms are complex webs of both direct interactions, such as ants feeding on host plant extrafloral nectar, and indirect interactions mediated by ‘third party’ species, such as ants consuming exudates from hemipterans feeding on the host plant. While some indirect interactions are well understood, in many cases our understanding is hindered by an incomplete picture of the relevant third-party species.
In this dissertation, I explore third-party interactions of three obligately phytoecious ant species on the African ant-plant Vachellia drepanolobium (formerly Acacia drepanolobium) – Crematogaster mimosae, C. nigriceps and Tetraponera penzigi.
First, I examine relationships between ants and fungi. I show behavioral differences towards fungi among the three ant species, and then use multiplexed amplicon sequencing to characterize their associated fungal communities. Each ant species harbors its own distinctive fungal community, and these communities are similar for each species even at two field sites separated by 200 kilometers. The ants may vector fungi when they colonize new host trees. T. penzigi most likely uses fungi as a food source, and fungi may also have nutritional or other growth implications for the host plant.
Second, I investigate relationships between ants and ‘myrmecophiles’ – i.e. ‘ant loving’ arthropods that live alongside ants in the domatia. I show that myrmecophile communities differ among the three ant species, but are also highly context dependent, differing strongly between locations and sampling periods. Surprisingly, several species of myrmecophilous Lepidoptera are herbivorous, but are more commonly associated with the ‘better’ ant mutualists, C. mimosae, whose workers defend more effectively against browsing mammalian herbivores.
My results show that plant ants shape both fungal communities and myrmecophile communities in domatia of their V. drepanolobium host plants. These third-party species may be viewed as ‘extended phenotypes’ of the ants, and are essential elements whose effects need to be incorporated into our understanding of the ant-plant protection mutualism.