Testing the local mate competition rule in a quasi-gregarious parasitoid with facultative superparasitism

<p><span>As </span><span>an </span><span>important </span><span>domain</span><span> of evolutionary ecology, sex allocation theory well explains the evolution of investment into female versus male offspring. Local mate competition (LMC) is </span><span>a </span><span>good predictor of sex allocation, where</span> <span>the optimal sex ratio becomes less female-biased</span><span> and asymptotically approaches 0.5 as </span><span>the</span><span> number</span><span> of foundresses</span><span> increases.</span> <span>Parasitoid wasps, with </span><span>haplodiploid sex determination</span><span>, </span><span>offer</span><span> excellent opportunities to test how organisms manipulate their offspring sex ratio in response to environmental variation, and many species have been </span><span>proven</span><span> to allocate sex according to predictions under LMC. When hosts are spatially clustered, as in gregarious species, the mating systems of quasi-gregarious parasitoids meet the essential assumptions (female </span><span>mating</span><span> before dispersal</span><span>) of LMC. </span><span>However, inconsistent with predictions, </span><span>i</span><span>n the </span><span>quasi-gregarious species </span><span><em>Anastatus disparis</em> </span><span>(Hymenoptera: Eupelmidae)</span><span>,</span><span> a</span> <span>strongly female-biased </span><span>eclosion</span><span> sex ratio (</span><span>0.156</span><span>±0.018 to 0.185±0.016) </span><span>was observed </span><span>as the number of females laying eggs in a patch increased.</span> <span>Superparasitism, </span><span>in which</span> <span>44.7</span><span>%</span><span> of parasitized hosts contained more than one egg</span><span> but only one adult </span><span>emerged</span><span> from each host, </span><span>was </span><span>common in <em>A. disparis</em>.</span><span> However, </span><span>the egg sex ratio was </span><span>determined by microsatellites and</span><span> likely fit the predictions of LMC theory. Male-biased offspring mortality arising from</span><span> s</span><span>uperparasitism</span><span> during development likely contributes to the shift from the primary sex ratio predicted under LMC to the observed female-biased eclosion sex ratio.</span> <span>Inconsistent with results in gregarious parasitoids, t</span><span>he role of superparasitism in driving sex ratio shifts in </span><span>quasi-gregarious parasitoids</span><span> should be incorporated into </span><span>LMC-based predictions of sex ratio</span><span>s.</span></p>