“…The "rare male effect" so very often observed in experiments in which females are offered a choice between two different male genotypes or phenotypes will almost inevitably occur when females have specific mating preferences: rare males are preferred by a relatively greater proportion of females than common males; the selection is negatively frequency-dependent, becoming weaker as the preferred males become more common. This "rare male effect" has been observed very commonly in Drosophila (Ehrman, 1967;1970;1972;Spiess, 1968; 1969; Spiess and Ehrman, 1978), in a parasitic wasp Mormoniella vitripennis (Grant, Snyder and Glessner, 1974), in the guppy (Farr, 1977) and in the Two-spot Ladybird (Muggleton, 1979;O'Donald and Muggleton, 1979; O'Donald and Weir, l982a).…”