Spatial distribution and male mating success of Anopheles gambiae swarms

Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland 20852, USA.
BMC Evolutionary Biology (Impact Factor: 3.37). 06/2011; 11(1):184. DOI: 10.1186/1471-2148-11-184
Source: PubMed


Anopheles gambiae mates in flight at particular mating sites over specific landmarks known as swarm markers. The swarms are composed of males; females typically approach a swarm, and leave in copula. This mating aggregation looks like a lek, but appears to lack the component of female choice. To investigate the possible mechanisms promoting the evolution of swarming in this mosquito species, we looked at the variation in mating success between swarms and discussed the factors that structure it in light of the three major lekking models, known as the female preference model, the hotspot model, and the hotshot model.
We found substantial variation in swarm size and in mating success between swarms. A strong correlation between swarm size and mating success was observed, and consistent with the hotspot model of lek formation, the per capita mating success of individual males did not increase with swarm size. For the spatial distribution of swarms, our results revealed that some display sites were more attractive to both males and females and that females were more attracted to large swarms. While the swarm markers we recognize help us in localizing swarms, they did not account for the variation in swarm size or in the swarm mating success, suggesting that mosquitoes probably are attracted to these markers, but also perceive and respond to other aspects of the swarming site.
Characterizing the mating system of a species helps understand how this species has evolved and how selective pressures operate on male and female traits. The current study looked at male mating success of An. gambiae and discussed possible factors that account for its variation. We found that swarms of An. gambiae conform to the hotspot model of lek formation. But because swarms may lack the female choice component, we propose that the An. gambiae mating system is a lek-like system that incorporates characteristics pertaining to other mating systems such as scramble mating competition.

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    • "Mating in An. gambiae occurs in male swarms, which await and then compete for, arriving females. Such swarms apparently lack a female-choice component, placing more emphasis on male competition [33]. It has also been suggested that slower development of transgenic mosquito larvae can delay the onset of male sexual maturity [12]. "
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    • "In natural populations males await females in male-dominated swarms thereby creating conditions in which male competition for females is high and reproductive success may largely be driven by female choice [57]. This type of conditions, which bear analogies with leks, typically leads to very skewed distributions of male reproductive success with males of higher phenotypic quality securing most copula [57,58]. The 50:50 sex ratio artificially created by combining distinct cohorts of freshly hatched female and male imagoes in small laboratory cages results in starkly different selection pressures on males. "
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    • "With this fact in mind, significant effort has been dedicated to understanding the compensating benefits that grouping behavior provides [9]. Many such benefits of grouping behavior have been proposed, for example, swarming may improve mating success [10] [11], increase foraging efficiency [12], or enable the group to solve problems that would be impossible to solve individually [1]. Furthermore , swarming behaviors are hypothesized to protect group members from predators in several ways. "
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