Architecture and evolution of gene regulatory networks underlying environmental responses in butterflies

This project investigates how African butterflies tune their morphology, behaviour and lifecycle to varying environmental conditions. This phenomenon is called phenotypic plasticity and is accomplished via tightly regulated developmental and regulatory cascades. It has evolved in many organisms across the globe as almost all environments show variability, in particular between seasons.

While we have a good understanding of the ecological relevance, we only have a rudimentary mechanistic understanding of plasticity. What are the genes and pathways that sense the environment and produce a different phenotype when the environment changes? How do these genes interact in gene regulatory networks (GRNs)? How have these GRNs evolved when species invade new habitats or are faced with environmental changes? How does plasticity affect future adaptation, for instance to climate changes?

To fill this gap, we use an established system that combines ecological relevance, experimental tractability and genomic resources-African Bicyclus butterflies. These species have repeatedly evolved plasticity in wing pattern, behaviour and life cycle upon invasions of seasonal savannahs from forests. Laboratory experiments have revealed Ecdysteroid hormone signalling as a key switch between developmental pathways leading to alternative adult phenotypes. However, the mechanistic relationship between this switch and environment-sensitive GRNs is unknown, as are the
evolutionary origin and dynamics of these GRNs.

With lab experiments and computational analyses of sequence data from wild populations of various Bicyclus species, we will study the development, evolution and genomics of plasticity. Specifically, we will (i) test the role of ecdysteroid hormone, juvenile hormone and insulin signalling in tissue and stage-specificity of plasticity, (ii) identify and characterise different genes and GRNs associated with developmental plasticity and compare these across species to find the origin of plasticity, and (iii) infer the repeated evolution and convergent genomic changes of plasticity GRNs by comparisons with conserved processes in non-plastic ancestor species.

Different species of Bicyclus butterflies will be collected from wild populations in Africa ( Kenya, Cameroon, South Africa and Ghana) and will be lab-reared in controlled conditions spanning the range of seasonal environments to produce seasonal phenotypes including dry season, wet season and intermediate forms. These data along with stage-specific (larva and pupa) hormone titration experiments (involving ecdysteroid hormone, juvenile hormone and insulin) on different seasonal conditions will correlate the environmental cues associated with the phenotype and the hormone signalling. Further, stage-specific hormone level manipulation experiments will decipher their roles in developmental plasticity. Comparative RNA seq transcriptome analysis of these lab-reared (controlled condition and hormone manipulated) individuals will identify the genes and regulatory pathways correlated with the hormone signalling. These data along with whole-genome sequencing data of different Bicyclus species will be used in phylogenomic approaches to form an ancestral state reconstruction and identify convergent genomic changes associated with the origin and evolution of plasticity.