Pre-copula acoustic behaviour of males in the malarial mosquitoes Anopheles coluzzii and Anopheles gambiae s.s. does not contribute to reproductive isolation

Abstract

We reveal that males of two members of the Anopheles gambiae s.l. species complex, Anopheles coluzzii and Anopheles gambiae s.s. (hereafter A. gambiae), which are both malaria vectors, perform a stereotypical acoustic behaviour in response to pure tones at frequencies that encompass the frequency range of the female's flight-tones. This behaviour resembles that described for Culex quinquefasciatus and consists of phonotactic flight initiated by a steep increase in wing-beat frequency (WBF) followed by rapid frequency modulation (RFM) of WBF when in close proximity to the sound source. RFM was elicited without acoustic feedback or the presence of a live female, but it appears to be a stereotypic behaviour in the immediate lead up to copula formation. RFM is an independent and different behavioural process from harmonic convergence interactions used by male-female pairs for mate recognition at earlier stages of mating. Acoustic threshold for RFM was used to plot behavioural audiograms from free-flying A. coluzzii and A. gambiae males. These audiograms were almost identical (minima ∼400 Hz) and encompassed the WBF ranges of A. coluzzii (378-601 Hz) and A. gambiae (373-590 Hz) females, indicating that males of the two species share similar frequency tuning and range. Furthermore, no differences were found between the two species in their WBFs, RFM behaviour or harmonic convergence ratios. These results indicate that assortative mating between A. coluzzii and A. gambiae is unlikely to be based on male-specific acoustic behaviours during RFM. The significance of these findings in relation to possible mechanisms for assortative mating is discussed.

Sex, Age, and Parental Harmonic Convergence Behavior Affect the Immune Performance ofAedes aegyptiOffspring

“…Further, observations suggest that female mate choice is important in determining male mating success, with females displaying a variety of active rejection behaviors (e.g., abdominal tilts, tarsal kicks, thrusts, and holds) toward undesired males (30)(31)(32)(33)(34) resulting in consistently low proportion of successful copulations when individual mating encounters are observed (30,32,33). Finally, male mosquitoes are strongly attracted to the sounds produced by the wingbeat of a female mosquito, allowing them to locate prospective mates in the aerial swarm (35)(36)(37)(38)(39).…”

Analysis of natural female post-mating responses of Anopheles gambiae and Anopheles coluzzii unravels similarities and differences in their reproductive ecology

“…Where the two species are sympatric, e.g. in Burkina Faso, spatial and temporal segregation of the swarms is significantly contributing to assortative mating 33 , 34 , while close-range mate recognition cues, such as species-specific flight tones and/or contact cuticular pheromones, are believed to reinforce pre-mating isolation 35 – 41 . Inter-specific mating couples have, however, been repeatedly collected in the field 42 , 43 , suggesting the co-occurrence of intrinsic and/or extrinsic post-mating isolation mechanisms.…”

Dissecting functional components of reproductive isolation among closely related sympatric species of theAnopheles gambiaecomplex

“…is imperfectly maintained in nature (Tripet et al., ) and periodically breaks down, resulting in extensive hybridization (Caputo et al., ; Costantini et al., ; Lee et al., ; Oliveira et al., ) and in detectable levels of introgression and current gene flow (Marsden et al., ; Reidenbach et al., ; Weetman, Wilding, Steen, Pinto, & Donnelly, ). Several premating behavioural mechanisms such as spatial segregation of mating swarms (Diabaté et al., ), complex short‐range acoustic recognition responses (Pennetier, Warren, Dabiré, Russell, & Gibson, ; Simões, Gibson, & Russell, ) and lags in circadian activity associated with reproductive behaviour (Sawadogo et al., ) might contribute to diminish heterospecific inseminations. It is plausible that reduced hybrid fitness mediated by extrinsic ecological factors, as opposed to intrinsic genetic incompatibilities, may further contribute to reproductive isolation, making these species another example of ecological speciation.…”