Extremely female-biased sex ratios of parasitoid wasps in multiple-foundress groups challenges evolutionary theory which predicts diminishing bias as foundress numbers increase. Recent theory based on foundress cooperation has achieved qualitative rather than quantitative success in explaining bias among parasitoids in the genus Sclerodermus. Here, we develop an explanation, expanding the theory of local mate competition, based on the observation that male production seems dominated by some foundresses within groups. Two sex ratio effects arise from such reproductive dominance: an immediate effect via suppression of male production, and a long-term evolutionary response to reproductive skew. We analyze the outcome of these effects at the individual and group level, the latter being more readily observable. Three model scenarios are analyzed: (1) random killing of developing sons in a group by all foundresses, without reproductive skew, (2) the development of reproductive dominance by some foundresses after sex allocation decisions by all foundresses have been implemented, and (3) reproductive dominance within foundress groups before sex allocation decisions are implemented. The 3 scenarios have subtly different implications for sex ratio evolution, with Models 2 and 3 being novel additions to theory, showing how reproductive dominance can alter the outcome of sex ratio evolution. All models match observations in their outcomes better than other recently proposed theory, but Models 2 and 3 are closest to observations in their underlying assumptions. Further, Model 2 shows that differential offspring mortality after parental investment can influence the primary sex ratio even when random with respect to parental and offspring characters, but targeted at entire clutches. The novel models are solved for both diploid and haplodiploid genetic systems, and confirmed with simulations. Overall, these models provide a feasible explanation for the extremely female-biased sex ratios produced by multi-foundress groups and expand the scope of local mate competition theory to consider reproductive dominance.
All authors declare that there is no conflict of interest or financial interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
Under the experimental condition, the hyperspectral reflectance spectra of the mixed pixel of lotus and water body were acquired using the multi-angles dichotic reflex platform and ASD spectrum instrument. The reflectance spectral morphological character index variation of the hyperspectral mixed pixel at different component proportion was analyzed. The conclusions are as follows: the correlation between these morphological indexes was obvious, and the best morphological index was chosen by removing the index whose R2 was greater than 0.5 (R is correlation coefficient); the variation of different morphological index was obvious; the cluster analysis shows that there was a critical value in the progress of the transformation from the pure pixel (water) to mixed pixel. If the proportion was less than the critical value, the reflectance spectra reflected the reflection characteristics of pure pixel; otherwise, it was the reflection of characteristics of mixed pixel.
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