- Predation is a major evolutionary force driving speciation. Identifying the stimuli prompting anti-predator responses is essential for unravelling the proximate mechanisms of anti-predator adaptations and for understanding how predation impacts species diversification.
- Here, we explore for the first time the divergence in the use of cues of predation risk by different incipient species of mosquitoes within the Anopheles gambiae complex. We examined the anti-predator responses to various predation cues by the aquatic larvae of Anopheles arabiensis and the two molecular forms, M and S, of Anopheles gambiae s.s. sampled from wild populations in Burkina Faso naturally exposed to different predator densities.
- The larvae altered their behaviour in response to various predation cues, shifting from the surface of the water to a less exposed location on the walls of the experimental arena. There were important differences in the use of predation cues between populations sharing the same larval development sites and, within the M form, related to predation pressure at their site of origin. Anopheles arabiensis larvae, which develop in small temporary waterbodies, relied only on physical cues signalling the presence of a predator to mount a vigilance response, whereas the sympatric larvae of the M and S forms of An. gambiae used both physical and chemical cues to fine-tune their response. M-form larvae, developing in permanent aquatic habitats with high densities of predators, responded chiefly to chemical stimuli ensuing from acute predation.
- Our results suggest that predation might play a role as a disruptive selective force promoting ecological divergence within the An. gambiae complex and, more recently, between the M and S molecular forms. Notably, beyond interspecific differences in the use of predation cues, our study also documented phenotypic differences within the M form based on predation pressure at their site of origin, suggesting that a process of ecological divergence is generating species ‘forerunners’ within the An. gambiae complex in the wild.
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