Ant-plant sociometry in the Azteca-Cecropia mutualism

Abstract

A holistic understanding of superorganism biology requires study of colony sociometry, or the quantitative relationships among growth, nest architecture, morphology, and behavior. For ant colonies that obligately nest within plant hosts, their sociometry is likely intertwined with the plant, which has implications for the evolution, strength, and stability of the mutualism. In the Azteca-Cecropia mutualism, plants provide ants with food rewards and hollow stems for nesting in return for protection from herbivores. Several interesting questions arise when considering ant-plant sociometry: are colony growth and plant growth synchronized? How do colonies distribute themselves within the stem of their host plant? How do plant traits influence worker morphology? How is collective personality related to tree structure, nest organization, and worker morphology? To address these questions, we investigated patterns within and relationships among five major sociometric categories of colonies in the field – plant traits, colony size, nest organization, worker morphology, and collective personality. We found that colony sociometry was intimately intertwined with host plant traits. Colony and plant growth rates were synchronized, suggesting that positive feedback between plant and colony growth stabilizes the mutualism. The colony’s distribution inside the host tree tended to follow leaf growth, with most workers, brood, and the queen in the top half of the tree. Worker morphology correlated with plant size instead of colony size or age, which suggests that plant traits influence worker development. Colony personality was independent of colony distribution and tree structure but may correlate with worker size such that colonies with smaller, less variable workers had more aggressive personalities. This study provides insights into how ant-plant structural relationships may contribute to plant protection and the strength of mutualisms.

Natural history notes on worker size, colony size, and nest structure of Azteca muelleri Emery, 1893 (Hymenoptera: Formicidae) in Cecropia glaziovii (Rosales: Urticaceae) from the Atlantic Forest

“…The spatial distribution of A. muelleri ants along the cavities in the trunk of C. glaziovii was similar to other Azteca species (see Longino 1989). In A. constructor Emery, 1896, registered in tropical rainforest in Panama, colonies are distributed according to leaf growth, and most workers and immatures, as well as the queen, are found in the upper half of the trunk (Marting et al 2018b). Colony distribution within cavities of the trunk of Cecropia spp.…”

“…Colony distribution within cavities of the trunk of Cecropia spp. is highly variable according to the Azteca species, which may be related to defense of the host plant (see Longino 1991a), resource foraging by workers, and colony size (Marting et al 2018b).…”

“…This could be related to (1) the number of plants analyzed in this study or (2) the immaturity of the colonies, which is suggested by absence of winged males and females (Longino 1991b). We selected plants of the same height because the number of entrances is positively correlated with plant growth rate (Marting et al 2018b), but it is possible that our results represent initial colony growth. In addition, the entrances were actively open which suggests that all of them were being used by workers to search for food resources and protect the tree against herbivores (Marting et al 2018a).…”

Azteca ants maintain unique microbiomes across functionally distinct nest chambers

“…Azteca ants live within Cecropia trees that have internally segmented chambers (in essence, rooms) to which the ants assign different functional roles (e.g. food storage, brood chamber, waste chamber [34][35][36]). The chamber walls have large porous cavities that act as absorptive surfaces that allow plants to gain nutrients from ant waste [37,38].…”

Herbivores just need a calm place to feed: Ants cannot help them

“…We have not yet seen quantitatively that this characteristic is more important for effective exclusion of herbivores than the total number of ants foraging per se. Besides that, once the colony personality can be independent of colony size or tree size, workers in younger colonies are capable to A B C (Marting et al 2018). So, we can observe plants with slightly smaller colonies but with very active and aggressive ants that expel enemies and protect trees effectively.…”