What shapes leaves? The interaction of physiology, defence and escape in passionflower leaf optimisation.

The project investigates the relative contribution of biotic and abiotic factors in shaping leaf morphology in plants. Specifically, the project will focus on Passiflora-Astrophea plants, which are a classic example of co-evolution with herbivorous butterflies (Heliconius genus). The Passiflora-Heliconius system offers a unique potential to address yet unanswered questions on the evolution of plant-insect interactions and the evolution of leaves against ecological and biological pressures.

Whilst we understand that particular leaf traits are adaptions to the biotic and abiotic environment, we know very little of the interplay between selective forces on these. Recent studies have highlighted the existence of trade-offs between plant growth and plant defences, but detailed and direct evidence of trade-offs in leaf traits evolving under environmental and biological pressures is still scarce.

There are two leading and opposing (but not exclusive) hypotheses on what drives leaf trait variation in plants:

(1)One hypothesis suggest that leaf trait diversity has evolved to maximise photosynthetic function and minimise the cost of supporting ineffective leaf types. (2)An alternative hypothesis suggests that leaf traits are driven by interactions with insect herbivores.

The project specifically focuses on Astrophea group within the passionflowers as these represents an ideal group for investigating leaf surface evolution and associated defensive and ecophysiological traits given its small number of species (~60), diverse leaf morphology at intra- and interspecific levels, and the highly specialized interactions the plants have with a small clade of butterflies in the Heliconius sara/sapho complex (~15 species).

The research project will be conducted within an interdisciplinary framework, integrating morphometrics, metabolomics, phylogenetics, taxonomy, and comparative biology at multiple evolutionary scale. I would expect to find stronger effect of biotic factors in driving leaf morphology and chemistry in the Andean Passiflora plant species compared to Brazilian Passiflora species which occur in more eco-physiologically stressful ecosystems.

This research will help us to understand the processes that maintain and generate our planet's biodiversity. With a particular focus on plants and herbivores as they constitute to more than half of the macroscopic diversity on Earth and whose interactions play a fundamental role in biodiversity and ecosystem function.