PhasE PolyPhenism Emergence and associated Risks – PEPPER

Locust species alternatively display harmless solitarious and gregarious phenotypes. The latter create migrating bands and swarms that are devastating for all types of agriculture. This plasticity, named phase polyphenism, has been hypothesized as an evolutionary response to cannibalism avoidance. Group movement was also proposed as an adaptation to predation risk. Alternatively, we propose that phase polyphenism could emerge as a response to variable conditions of resource, mainly vegetation. The hypothesis is that these environmental conditions change the trade-offs of costs and benefits of being in the group and interacting strongly with congeners. Group selection may occur on behaviors of grouping and/or collective movement as these could be considered as a form of cooperative behavior. Hence, a first objective of PEPPER will be to theoretically explore the trade-offs and environmental conditions leading to phase polyphenism emergence. Identifying the regimes of environmental variation of resources favorable to phase polyphenism evolution may help in identifying conditions of outbreaks. Further, the actual models tools to forecast the risk of outbreaks of desert locust are not integrative of the biological knowledge on this species. Modelling ecological processes at the individual level coupled with environmental drivers from satellite imagery will be a major step forward in forecasting locust outbreaks. Hence, the second objective of PEPPER will be to develop a forecasting model of locust population dynamics and validate it using field data from desert locust observations.
Agent-based models adapted from previous theoretical studies can be used to explore the conditions of emergence of phase polyphenism. However, these should represent the demographical processes as well as the genetic of heritable density-dependent reaction norms. Hence, demogenetic agent-based model should be used in the first objective. The second objective will also benefit from integrating the biological knowledge on desert locust within a mechanistic agent-based model that will consider remote-sensing imagery to represent environmental drivers. Pattern-oriented modelling will be applied to both objectives to select the processes to consider in the models and adjust them to real-world data. The two main limitations of both models are identical: the consideration of different spatial and temporal scales and the huge variations in population size of locusts. As the limitations need to be solved for both objectives, we will develop a core model that will consider technical solutions using a meta-individuals approach and high parallel computing. The different versions of models to use on both objectives will be adapted from this core model.
Cyril Piou is an ecological modeler with long experience on agent-based models. He works on locust ecology since 2010. He and his team are in a key position to conduct the PEPPER researches. They have all the necessary background to bring new understandings on phase polyphenism and an important simulation tool to forecast locust outbreaks. The work will be separated in three work-packages including seven main tasks and 20 sub-tasks. PEPPER will fund computer materials, a PhD and two master fellowships, travelling costs and a small part of needed outsourcing.
PEPPER will participate in the global objective of understanding how some key components of ecosystems may adapt to climate change. It will bring a forecasting tool that is an important asset in the global food security objective considering the importance of locust threats worldwide. At a local level, PEPPER will position C. Piou as a leader in demogenetic modelling, a new line of research of his research unit, CBGP. PEPPER will also foster the international visibility of the project team as a “force vive” in locust ecology and evolution research.