Intra-specific variation of sperm length in the malaria vector Anopheles gambiae: males with shorter sperm have higher reproductive success

<p>Abstract</p> <p>Background</p> <p>Intra-specific variation in sperm length influences male reproductive success in several species of insects. In males of the malaria vector <it>Anopheles gambiae</it>, sperm length is highly variable but the significance of this variation is unknown. Understanding what determines the reproductive success of male mosquitoes is critical for controlling malaria, and in particular for replacing natural populations with transgenic, malaria-resistant mosquitoes.</p> <p>Methods</p> <p>A laboratory population of <it>A. gambiae </it>males was tested for intra-specific variation in sperm length. A full-sib quantitative genetic design was used to test for a genetic component of sperm length in <it>A. gambiae </it>males and estimate its heritability. This study also tested for a relationship between sperm length and male reproductive success in <it>A. gambiae</it>. Male reproductive success was measured as the proportions of inseminated and ovipositing females.</p> <p>Results</p> <p>There was intra-specific variation of sperm length in <it>A. gambiae</it>. There was no significant genetic variation in sperm length and its heritability was low (h²= 0.18) compared to other insects. Sperm length was correlated with male body size (measured as wing length). Males with short sperm had significantly higher reproductive success than males with long sperm and this was independent of body size.</p> <p>Conclusion</p> <p>This is the first study to demonstrate intra-specific variation in sperm length in <it>A. gambiae </it>and that males with short sperm have higher reproductive success. That sperm length influences female oviposition is important for any strategy considering the release of transgenic males.</p

Disruptive coloration and background pattern matching

Effective camouflage renders a target indistinguishable from irrelevant background objects. Two interrelated but logically distinct mechanisms for this are background pattern matching (crypsis1,2) and disruptive coloration: in the former, the animal's colours are a random sample of the background; in the latter, bold contrasting colours on the animal's periphery break up its outline. The latter has long been proposed as an explanation for some apparently conspicuous coloration in animals, and is standard textbook material. Surprisingly, only one quantitative test of the theory exists, and one experimental test of its effectiveness against non-human predators. Here we test two key predictions: that patterns on the body's outline should be particularly effective in promoting concealment and that highly contrasting colours should enhance this disruptive effect Artificial moth-like targets were exposed to bird predation in the field, with the experimental colour patterns on the 'wings' and a dead mealworm as the edible 'body'. Survival analysis supported the predictions, indicating that disruptive coloration is an effective means of camouflage, above and beyond background pattern matching