Dr Guillaume Chomicki

Evolution and ecology of mutualisms
Why do mutualistic partnerships evolve, and what causes them to breakdown? My research uses field experiments, comparative genomics and transcriptomics, CT-scanning based 3D imaging and phylogenetic comparative methods to investigate how mutualisms evolve across the tree of life. We explore the formation, stabilization, and breakdown of mutualism in a species-rich clade of plants forming nutritional and defensive symbioses with ants as well as using large-scale trait datasets and phylogenies in multiple mutualisms across vascular plants. Recent insights include the finding that specialized parasites did not evolve from mutualistic ancestors (Proceedings B 2015), that generalist and facultative mutualisms break down more easily than obligate ones (PNAS 2017, Annu. Rev. Ecol. Evol. Syst 2020), their interaction-related traits are under less stabilizing selection (PNAS 2017, TREE 2019); obligate mutualisms are also more efficient (New Phytol 2019), and offer greater rewards to their partners (New Phytol 2016).

Origins and evolution of agriculture in insects and humans
The gradual shift from hunting and gathering to plant cultivation and animal husbandry started globally at the boundary between the end of the Pleistocene and the beginning of the Holocene some 12,000-11,000 years ago, and is one of the most important transition in human history, allowing the development of our modern cultures. But agriculture has evolved much earlier in several lineages across the tree of life. ‘Primitive’ farming mutualisms are found in amoeba, fungus or deep-sea crab that cultivate bacteria, and damselfish, or sloth farming algae. The most sophisticated agricultures, sharing a number of aspects with our human agriculture includes fungiculture by ants, termites and ambrosia beetles. I discovered the first obligate agriculture of plants by ants (Nature Plants 2016). I am interested in the convergences between human and non-human agriculture and work specifically in two areas: the origin and domestication of the watermelon and related crops in the Cucurbitaceae genus Citrullus, and plant farming by ants, including generalist ant-gardens and obligate, highly specialised Fijian farming symbioses involving the ant Philidris nagasau that farm Squamellaria. We use taxonomy, ancient DNA analysis and phylogenomics to decipher the origin and domestication of crops in Citrullus, and field ecology, phylogenies, metabolomics, and transcriptomics and comparative genomics to dissect the evolution and functioning of ant/plant farming mutualism. Recently, I discovered that Fijian ant farmers have evolved strategies to optimize crop yield and mitigate tradeoffs between different crop requirements (PNAS 2020).

Evolution of plant functional morphology
Morphology is often uncorrelated to relatedness with related species sometimes looking entirely different and species far apart looking the same. While the genetic basis of morphological novelty is becoming increasingly well understood, the rules governing morphological change at a macroevolutionary level are not well characterised. My work has shown that shifts in mutualism strategies, such as specialisation or breakdown, are important drivers of morphology in interaction-related traits (PNAS 2017). My work on the evolution of morphology is threefold. First, I am interested in the evolution of plant morphology, and in particular plant architecture, notably in the context of crop domestication and (past) climate change. Second, I am interested to develop a coherent framework to understand morphological evolution at a macroevolutionary level. Third, I collaborate with physicists, engineers and mathematicians to understand the function of plant structure in a symbiotic context, notably in the context of temperature regulation in plant domatia housing symbiotic ants. This involves a mix of morphological and anatomical work, functional morphology, CT-scanning, architectural analysis, modelling, together with phylogenetic comparative methods.

Selected ongoing projects:
• ‘The drivers of major transitions in mutualistic dependence’. NERC (2019-2024)
• ‘Deciphering the 3-million year old ‘air conditioning’ mechanism in a Fijian obligate ant/plant farming mutualism’. National Geographics (2017-2021)
• ‘The evolution and domestication of multiple crop species in the watermelon genus Citrullus’. DFG (2018-2021)