Neural Representations of Acoustic Communication and its Evolution in Drosophila

Abstract

Acoustic communication is widespread in the animal kingdom, and most species coexist in elaborate, noisy ecosystems. Successful reproduction of an acoustically communicating individual is contingent on preferentially responsive (tuned) behaviors and auditory neural pathways to conspecific acoustic signals. Flies of the genus Drosophila communicate acoustically in courtship and are useful model organisms in neuroethological investigations that connect behavior to underlying neural circuitry. Two closely related, sympatrically occurring Drosophila species, melanogaster and simulans, have known differences in the parameters of their courtship song; one such parameter is the timing of pulse song elements, the inter-pulse-interval (IPI). The differences in song elements have been quantified, but corresponding tuning of auditory circuits to IPI has yet to be compared between species. Tuning to pulses of conspecific IPI has been demonstrated in melanogaster females. However, this finding preceded the discovery of two discrete pulse types, Pfast and Pslow, and it is not yet known how the two types of pulses are differentially processed. This thesis seeks to elucidate the potential neural correlates of audition in both simulans and melanogaster by investigating the extent of conspecific tuning of females’ neural activity and behavior in response to male pulse song elements Pfast and Pslow. Auditory neural responses were measured using two-photon calcium imaging, and a playback assay was used to quantify behavior. In sexually dimorphic fru+ auditory neurons in the anterior ventrolateral protocerebrum (aVLP), both melanogaster and simulans females had significantly different tuning patterns to inter-pulse-interval (IPI) for Pfast and Pslow pulse types, but the divergence in auditory processing between the two species is still far from being understood. The question remains as to precisely what role audition plays in reproductive isolation of the two species.