The global drivers of shifts in mutualistic dependence

Overview

Background: Mutualisms – cooperation between species – are ubiquitous and linked to major transitions in the history of life, such as the evolution of eukaryotes or the conquest of the land by plants [1]. They have allowed the diversification of new lineages, permitted species to access otherwise inaccessible resources and radically modified Earth’s geochemical cycles. Yet, understanding the origins and evolutionary trajectories of mutualistic dependences remains a major challenge. What macroecological drivers explain the macroevolutionary patterns of mutualistic dependence? Are they convergent or divergent in major plant/insect mutualisms, namely defence against herbivores, seed dispersal, and pollination? The student will test whether climatic factors, plant habit and density-dependence predict the gain, maintenance or loss of mutualistic dependence, using large-scale phylogenetic comparative approaches.

Aims: The student will conduct comparative conduct comparative phylogenetic analyses using the largest plant phylogenies available (e.g. Zanne et al. 2014 Nature [2]) and large plant mutualism databases assembled by the PI for pollination, seed dispersal, plant defense as well as already available mycorrhizal fungus. The student will perform a number of analyses to test potential drivers of the global macroecological patterns such as climatic variables, plant traits. The student will then design comparative tools adapt trait evolution (e.g. Brownian Motion, Orstein-Ulhenbeck) and biogeographic models (e.g. DEC) that explicitly model mutualistic interactions. The student will then select groups for which well-sampled phylogenies are available (e.g. some plant/pollinator or ant/plant interactions) and test several hypotheses regarding of how mutualisms impact macroevolution namely (i) that mutualisms constrain clade biogeography in horizontally transmitted mutualisms as a function of the level of specialization and dependence of the mutualism (Chomicki et al. 2019 TREE) or (ii) that specialized mutualism reduce the pace of interaction-related trait evolution via stabilizing selection (Chomicki and Renner, 2017 PNAS [3]).

Methodology

This project will use (i) a wide range of large-scale phylogenetic comparative methods, (ii) spatial linear analyses to tests for spatial correlates of mutualism and climate; (iii) simulation-based inference techniques, such as Approximate Bayesian Computation (ABC), to fit the model of trait and range evolution.

Project Timeline

Year 1

Clean databases, perform large scale comparative analyses.

Year 2

Finish comparative analyses of the large datasets, perform mapping and spatial linear analyses. Develop new phylogenetic comparative tools and select groups to test them.

Year 3

Test the new tools developed, finish all analyses.

Year 3.5

Write-up thesis and papers.

Training
& Skills

The student will receive training in (1) phylogenetic comparative methods; (2) trait-based macro ecological analyses (including spatial analyses); (3) development of new phylogenetic comparative tools using simulation-based inference techniques, such as Approximate Bayesian Computation (ABC).

References & further reading

1. Chomicki et al. (2019). TREE 34: 698-711. 2. Zanne et al. (2014). Nature 506 : 89-92. 3. Chomicki G. & Renner S.S. (2017). PNAS 114: 3951-3956.

Further Information

guillaume.chomicki@durham.ac.uk
+44 (0) 191 33 41238

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