The evolution of host plant feeding is critical for understanding insect evolution and in particular the responses of populations to a changing climate. For example, UK butterfly species that have done well in response to a warming climate have typically also expanded or altered their patterns of host plant use, while those that have suffered typically have a narrow host plant range. Here we will explore how butterflies can alter their biochemical responses to allow the exploitation of different host plants. This is a form of phenotypic plasticity, where a single genotype can produce alternative phenotypes under different environmental conditions. Plasticity is an important adaptation that can allow organisms to survive variable and heterogeneous environments and promote longer term divergence and diversification. Plant-feeding insects have to deal with toxic plant chemistry, but in some cases such toxins can also provide an important source of defensive chemicals for the insects. Tropical Heliconius butterflies can either obtain cyanogenic toxins from their Passiflora hosts, or can synthesise their own compounds. We have demonstrated that these butterflies can switch between these two strategies dependent on host chemical composition. When the larval diet lacks toxins that can be sequestered, Heliconius respond by increasing biosynthesis of their own defences. This permits use of a wider range of Passiflora species while maintaining their chemical defences. We can readily distinguish toxins derived from the host plant from those that are made by the butterflies, making this an easily quantifiable form of phenotypic plasticity. However, the genetic and biochemical basis of this plasticity remains unknown, as well as it's ecological importance for niche partitioning. We will first address the ecological context, using targeted metabolomics to track the chemical composition of Heliconius erato across seasons at sites with well characterised host plant use in Brazil and Panama. Next, we will explore the fitness trade-offs between different strategies, addressing the reasons for switching between strategies in a plastic species, Heliconius erato. We will compare growth rate and other life history traits of individuals raised on different diets. We will also compare efficiency of sequestration in a derived specialist species, which obtains its toxins only from a specific host plant. Increased efficiency in the derived lineage is predicted by the 'plasticity first' hypothesis. The other major axis of variation for defensive compounds is their influence on predation, and we will measure toxicity and distastefulness of host-plant derived and synthesised toxins. Third, we will explore how plasticity controlled genetically, testing two alternative hypotheses for the molecular control of plasticity. Using transcriptomics we will estimate changes in gene expression in response to larval diet (presence and absence of host-plant derived toxins), and also test whether plasticity is controlled at the level of protein regulation. Finally, we will explore the evolutionary history of cyanogen biosynthesis across the Heliconiines, using molecular evolutionary approaches across a large data of whole genome sequences. We will study the gain and loss of genes involved in cyanogen uptake and synthesis, comparing generalist with those where cyanogen biosynthesis has been lost. In summary, this integrative study will explore the ecological context, fitness consequences, genetic control and long-term evolutionary trajectory of plasticity in the use of defensive toxins across a diverse group of insects. We will exploit a readily quantifiable and experimentally tractable system in order to understand how butterflies respond metabolically to variation in host plant chemistry. This will have general relevance to understanding how species can respond to a changing climate.

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At least 50% of earth's plant and animal species is found in tropical rainforests, but this rich biodiversity is under threat from deforestation and climate change. Ecologists are interested in understanding why these habitats are so diverse, and how their diversity will change in the future. One leading explanation for high plant biodiversity in tropical forests is the Janzen-Connell Effect. This theory suggests that pests such as plant-feeding insects and fungal diseases can help maintain tropical biodiversity if (1) they specialise on particular plant species, and (2) they cause 'density-dependent' mortality (i.e., they kill more seeds and seedlings where these are locally abundant). This pest pressure acts as a negative feedback mechanism, putting locally rare plant species at an advantage and preventing any one species from reaching high abundance. Recent research shows that this form of density-dependence from both insects and fungi plays a key role in the maintenance of plant diversity in the tropics. We now want to discover how this process changes under different climatic regimes. Wetter tropical forests have more plant species than drier forest, and we will test the theory that more intense density-dependent pest pressure in these places is a factor behind these differences. We will also investigate whether future changes to the climate (higher or lower rainfall) are likely to alter the strength of the Janzen-Connell Effect, and consequently plant diversity. Our work will take place in Panama, where we will take advantage of a steep gradient in rainfall and soil humidity from the dry (Pacific) coast to the humid (Atlantic) coast to test our hypotheses. We will carry our experiments in the field and in controlled nursery conditions that manipulate the density of seeds and seedlings and the presence of fungal pathogens and plant-feeding insects, and we will analyse long-term data and build mathematical models to explore whether and to what extent climate change will alter tropical plant diversity.

Human activity has led to an increase in pCO2 and methane levels from pre-industrial times to today. While the former increase is primarily due to fossil fuel burning, the increase in methane concentrations is more complex, reflecting not only direct human activity but also feedback mechanisms in the climate system related to temperature and hydrology-induced changes in methane emissions. To unravel these complex relationships, scientists are increasingly interrogating ancient climate systems. Similarly, one of the major challenges in palaeoclimate research is understanding the role of methane biogeochemistry in governing the climate of ice-free, high-pCO2 greenhouse worlds, such as during the early Paleogene (around 50Ma). The lack of proxies for methane concentrations is problematic, as methane emissions from wetlands are governed by precipitation and temperature, such that they could act as important positive or negative feedbacks on climate. In fact, the only estimates for past methane levels (pCH4) arise from our climate-biogeochemistry simulations wherein GCMs have driven the Sheffield dynamic vegetation model, from which methane fluxes have been derived. These suggest that Paleogene pCH4 could have been almost 6x modern pre-industrial levels, and such values would have had a radiative forcing effect nearly equivalent to a doubling of pCO2, an impact that could have been particularly dramatic during time intervals when CO2 levels were already much higher than today's. Thus, an improved understanding of Paleogene pCH4 is crucial to understanding both how biogeochemical processes operate on a warmer Earth and understanding the climate of this important interval in Earth history. We propose to improve, expand and interrogate those model results using improved soil biogeochemistry algorithms, conducting model sensitivity experiments and comparing our results to proxy records for methane cycling in ancient wetlands. The former will provide a better, process-orientated understanding of biogenic trace gas emissions, particularly the emissions of CH4, NOx and N2O. The sensitivity experiments will focus on varying pCO2 levels and manipulation of atmospheric parameters that dictate cloud formation; together, these experiments will constrain the uncertainty in our trace greenhouse gas estimates. To qualitatively test these models, we will quantify lipid biomarkers and determine their carbon isotopic compositions to estimate the size of past methanogenic and methanotrophic populations, and compare them to modern mires and Holocene peat. The final component of our project will be the determination of how these elevated methane (and other trace gas) concentrations served as a positive feedback on global warming. In combination our work will test the hypothesis that elevated pCO2, continental temperatures and precipitation during the Eocene greenhouse caused increased wetland GHG emissions and atmospheric concentrations with a significant feedback on climate, missing from most modelling studies to date. This work is crucial to our understanding of greenhouse climates but such an integrated approach is not being conducted anywhere else in the world; here, it is being led by international experts in organic geochemistry, climate, vegetation and atmospheric modelling, and palaeobotany and coal petrology. It will represent a major step forward in our understanding of ancient biogeochemical cycles as well as their potential response to future global warming.