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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Walter Federle, Zoology

Brief summary: 
This project will study what mechanisms determine the specificity of Macaranga ant-plant associations
Importance of the area of research concerned: 
Mechanical factors are fundamental to insect-plant relationships, and can lead to reciprocal adaptations with complex ecological and evolutionary consequences. This project will focus on the Macaranga ant-plant mutualism in SE Asia, which consists of 30 Macaranga tree and 12 Camponotus or Crematogaster ant species. In this fascinating interaction, plants provide food and hollow stems as shelter for ants, and the ants in return protect the plant from herbivory and overgrowth. While neither plants nor ants can survive without their partner, each Macaranga species can be colonised by 1-4 ant species, and each ant species can colonise 1-7 Macaranga species. The mechanisms underlying this complex pattern of associations are still unclear, but a key role is played by a mechanical factor, the slippery waxy stems that can only be climbed by some ant species. Several further plant and ant traits may promote specificity, including nutritional factors, chemical signals, the ants' competitiveness and colonization ability, and innate or learned preferences. The study of Macaranga-ant associations provides a unique opportunity to understand the evolution of specificity in a mutualism.
Project summary : 
The project aims to clarify the biomechanics of "wax barriers" and "wax-running", and to investigate what ant/plant traits and mechanisms underlie the observed specificity of Macaranga-ant associations. The following questions will be studied: 1. When and why are Macaranga stem surfaces slippery, and what morphological, biomechanical and behavioural adaptations are involved in the specialist ants' wax-running ability? To what extent is wax-running based on learning? 2. How do ant colonies develop when transplanted onto Macaranga species they normally avoid? To what extent is host specificity based on wax barriers, chemical signals, innate or learned preference, nutritional factors, or the ants' competitiveness and colonization ability? How have relevant ant and plant adaptations developed during evolution?
What will the student do?: 
The project will include fieldwork at natural sites in West-Malaysia and Brunei (Borneo) and laboratory/greenhouse work in Cambridge on selected Macaranga-ant associations. The approach can be tailored to the student's specific interests. Laboratory work: The biomechanics of wax-running will be studied by comparing the climbing locomotion of wax-runners and non-waxrunners using high-speed video, in addition to ablation experiments, manipulations of the wax layer, cryo-SEM, and whole-body or single-leg force measurements. Field (and greenhouse) work: To study the mechanisms of host plant specificity, partner ant colonies will be transplanted between selected Macaranga host species. Transplanted colonies will be checked for survival, growth rate, climbing performance and host plant preference. The ants’ level of self-defence and aggressiveness will be quantified, and nutritional factors tested using feeding trials with food bodies from other Macaranga species. The evolutionary development of identified traits and adaptations will be mapped onto available phylogenies of both ants and plants.
References - references should provide further reading about the project: 
Federle, W., Maschwitz, U., Fiala, B., Riederer, M. & Hölldobler, B. 1997. Slippery ant-plants and skilful climbers: Selection and protection of specific ant partners by epicuticular wax blooms in Macaranga (Euphorbiaceae). Oecologia 112: 217-224.
Federle, W. & Rheindt, F. 2005. Macaranga ant-plants hide food from intruders: correlation of food presentation and presence of wax barriers analysed using phylogenetically independent contrasts. Biological Journal of the Linnean Society 84: 177-193. DOI: 10.1111/j.1095-8312.2005.000423.x
Feldhaar, H., Fiala, B., Gadau, J., Mohamed, M. & Maschwitz, U. 2003. Molecular phylogeny of Crematogaster subgenus Decacrema ants (Hymenoptera: Formicidae) and the colonization of Macaranga (Euphorbiaceae) trees. Molecular Phylogenetics and Evolution 27: 441-452. DOI: 10.1016/s1055-7903(02)00449-9
You can find out about applying for this project on the Department of Zoology page.
Dr Walter Federle
Department of Zoology Graduate Administrator