Some close relatives can be hard to distinguish. Take the extensive Anopheles family of mosquitoes: until recently, Anopheles coluzzii and A. gambiae mosquitoes were thought to be members of the same species because they are almost perfectly identical. Yet, despite sharing much of the same geographical range, they rarely, if ever, interbreed – even when mingling in the same habitat. Somehow, members of the two species manage to select out the correct mates despite their similarities. Patricio Simões from the University of Brighton, UK, wondered whether A. coluzzii and A. gambiae suitors fine tune their elaborate courtship displays to distinguish themselves from each other in the ears of their intendeds.
When a male Anopheles mosquito picks up the distinctive tone of an approaching female, he begins to serenade by speeding up his wing beats before rapidly increasing and decreasing the wing beat frequency (known as rapid frequency modulation) to produce a whining refrain that woos the lady. Would Simões and his colleagues Gabriella Gibson and Ian Russell find differences between the species’ melodies that could help the females select the right suitor? Playing the seductive tone of an approaching female to individual males in an enclosure, the trio recorded the males’ responses. However, the trio found that the love songs from males of the two species were essentially indistinguishable. In both cases, the males accelerated their wing beat frequencies at rates in excess of 1250 Hz s−1 before warbling up and down ∼12 times per second and maintaining the solo for up to 2 s; so A. coluzzii and A. gambiae females cannot rely on the males’ serenades to select suitors of the correct species.
Referring to a previous study of the mating manoeuvres of more distantly related Culex quinquefasciatus mosquitoes, the trio suggests that this courtship behaviour may have evolved over 200 Ma, before the Culcinae and Anophelinae families separated, and they say: ‘Rapid frequency modulation might be found throughout all of the Culicidae [mosquito] family’. They also hope that traps based on the male's mating melody could be used to ensnare voracious females to reduce the spread of mosquito-borne diseases.
