One worm, two minds: Investigating divergent neuronal architecture associated with the evolution of a polyphenic behavioural trait.

• Applicant: James Lightfoot, Ph.D.
• Subject Area: Cognitive, Systems and Behavioural Neurobiology ; Sensory and Behavioural Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 533395631

Phenotypic plasticity describes the capacity of a single genotype to exhibit a multitude of different phenotypes dependent on environmental inputs. Furthermore, when a phenotypically plastic trait results in discrete phenotypes rather than continuous features it is known as a polyphenism. Importantly, while there is growing recognition for the importance of phenotypic plasticity for the evolution of morphological traits, little is known regarding its contribution to behavioural adaptations. Therefore, in this proposal we will investigate the neuronal architecture associated with a polyphenism controlling two distinct behaviours in the nematode species Pristionchus pacificus. In P. pacificus a polyphenic feeding trait results in the formation of one of two possible irreversible morphs. Under certain environmental conditions animals form a single toothed morph which feeds solely on microbes while other conditions result in animals acquiring an alternative omnivorous morph with two teeth which facilitates predation on the larvae of other nematodes. Importantly, while in this highly genetic and molecularly tractable organism much is known of the gene regulatory network determining morph fate, behavioural regulation is unknown. Using RNA-seq experiments we will initially identify genetic components associated with differences in neuronal expression patterns between the morphs. These will be investigated further using transgenes and CRIPSR/Cas9 to identify potential functional contributions associated with the morph specific behavioural divergence. Furthermore, as P. pacificus has a small nervous system consisting of an estimated 300 neurons it is highly conducive to connectomic approaches. As such, we will concurrently generate comparative head connectomes between morphs to determine the potential contribution of the neuronal architecture to the distinct behaviours. Thus, this work will examine the evolutionary specialisation and adaptability of shared core circuits and investigate functional-level conservation and divergence between both genetic components as well as neuronal circuit operations in a polyphenic species for the first time.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2205: Evolutionary Optimisation of Neuronal Processing
• Co-Investigator: Professor Kevin Briggman, Ph.D.