Physiological mechanisms underlying male Culex quinquefasciatus acoustic mating behaviour

Abstract

In this thesis, I describe for the first time a stereotypical acoustic behaviour by male mosquitoes in response to female flight tones. This male-specific free-flight behaviour consists of phonotactic flight coincident with an increase in wing-beat frequency (WBF) followed by rapid frequency modulation (RFM) of the WBF, before eventual contact with the sound source. Male RFM behaviour is highly robust and can be elicited without acoustic feedback, from either an artificial sound source, or the physical presence of a female. The auditory Johnston’s organ at the base of the male’s sound-capturing flagellum detects the WBF of the female. This elaborate nonlinear sound receiver is not acutely tuned to the female WBF per se but to the difference between his own WBF and the female’s WBF. In this thesis, I propose that the male’s own flight tone mixes nonlinearly with the flight tone of a female to generate so-called distortion products (DP) in the antennae, which are detected by the Johnston’s organ. The prominent DP in mosquitoes is f2-f1 where f1 represents the WBF of the female and f2, the WBF of the male. This implies that male mosquitoes rely on their own flight tones to locate and orientate towards flying females. To test this distortion product hypothesis I used the temperature dependence of WBF and JO tuning and the ability of a masking tone to interfere and supress the distortion product. Changes in temperature influence the generation of distortion products and impact phonotactic RFM behaviour of males. This thesis is the first to report on the significance of these effects of temperature on both the physiological responses to sound and free-flight behaviour. These findings highlight the importance of matching the temperature in which biological systems operate with the experimental temperature. In addition, the temperaturedependant changes in WBF and JO tuning are closely coupled which suggests that mosquitoes are well adapted to cope with global warming. The RFM of male mosquitoes to acoustic stimulation is also masked most strongly by tones centred on female flight-tones. Masking frequencies above 600 Hz do not suppress RFM behaviour, suggesting that males that fly together in a swarm do not interfere with their ability to detect a female. Masking tones can suppress RFM behaviour by being competitively more attractive than the stimulus tone. Behavioural and electrophysiological measurements reported here indicate that acoustic masking of RFM behaviour is caused through suppression of difference-tone distortion

Date of Award	2017
Original language	English
Awarding Institution	University of Brighton
Supervisor	Ian Russell (Supervisor)