Improving the utility of Drosophila melanogaster for neurodegenerative disease research by modelling courtship behaviour patterns

A problem presented at the UK MMSG Cambridge 2014.

Presented by:
Dr Birgit Brüggemeier (University of Oxford)
A Bianchi, B Brüggemeier, X Cai, N Jenkins, S Lynch, H Pavlou, C Schusterreiter

Problem Description

Courtship in Drosophila is used already to screen genes linked to memory-deficiency and neurodegeneration in humans. However the research community does not understand the mechanism which gives rise to courtship patterns. When a male fly encounters a female fly, he starts to follow her, licks her genitalia, sings a courtship song and eventually bends his abdomen to reach her genitalia. Male courtship in Drosophila is overt, easily quantifiable, and occurs without any prior experience.

Despite being innate, courtship is complex in that the sequence of behaviours shown, does not necessarily appear in a precise order as suggested above. Rather there is a probabilistic component to behavioural switches which we believe originates from non-linear dynamics. Our problem is to model courtship patterns as a network of neurons and muscles. This will give the biological community an understanding of possible mechanisms disturbing courtship and will help in establishing fly courtship as an alternative to other animal models of human disease.

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Study Group Report

We have developed three models of fly courtship to study potential mechanisms underlying this complex behaviour. We have found that dynamics of fly courtship behaviour can be modelled reasonably well as a markovian stochastic pro- cess.

A stochastic model may help to account for males’ interaction with females: the male reacts to female cues and his behaviour is partially driven by them. The female might influence courtship choices in the male by sexually motivating him, as Margaret Bastock suggested in her model of male courtship. In Bastock’s theory, sexual motivation deter- mines courtship choices: when sexual motivation exceeds a threshold, the male courts. Each courtship behaviour requires a different level of sexual motivation. We apply Bastock’s theory in two neuronal models. We modelled sexual motivation as firing frequency of model neurons. Our preliminary results suggest that our neuronal models can also simulate courtship dynamics.

In our neuron model approach, we model impaired processing of sexual cues in the male by reduced fir- ing rates of neurons. When firing rates are sufficiently high the whole behavioural space is traversed. We will test how the path through the behavioural space changes when we assume low firing rates. We expect that the path becomes highly cyclical – only behaviours with low excitatory thresholds are shown repeatedly. We are the first to test markovian properties of courtship dynamics and to implement Bastock’s ethological model of courtship to mathematical models. We believe that finding the appropriate model parameters for the modelling of fly courtship, might give valuable information on the state of the male fly: is the male capable of taking all states in the behavioural space or is he dwelling in few of them only?

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