Selection for male weapons boosts female fecundity, eliminating sexual conflict in the bulb mite

Extreme differences between the sexes are usually explained by intense sexual selection on male weapons or ornaments. Sexually antagonistic genes, with a positive effect on male traits but a negative effect on female fitness, create a negative inter-sexual correlation for fitness (sexual conflict). However, such antagonism might not be apparent if sexually selected male traits are condition-dependent, and condition elevates female fitness. Here we reveal a surprising positive genetic correlation between male weaponry and female fecundity. Using mite lines that had previously been through 13 generations of selection on male weapons (fighting legs), we investigated correlated evolution in female fecundity. Females from lines under positive selection for weapons (up lines) evolved higher fecundity, despite evolving costly, thicker legs. This is likely because male mites have condition-dependent weaponry that increases our ability to indirectly select on male condition. Alleles with positive effects on condition in both sexes could have generated this correlation because: the up lines evolved a higher proportion of fighters and there were positive correlations between weapon size and the male morph and sex ratios of the offspring. This positive inter-sexual genetic correlation should boost the evolution of male weapons and extreme sex differences. Usage Notes This file has two tabs. The first one contains the fecundity data (number of eggs laid in 10 days) for females after 13 generations of artificial selection applied on the fighter legs of fighter males of the mite Rhizoglyphus echinopus. Each row contains information for one female mated to two scrambler males, and the columns contain information about (respectively from left to right): replicate selection line; selection direction (up for thicker legs and down for thinner legs); the ID of the line (replicate and direction combined); family ID (the family from which each female was derived in the previous generation); and the number of eggs laid by this female. The other tab has information about sex and morph ratio through the first 9 generations of selection. Each row has information on the offspring of selected sires in each generation, and the columns contain information about (respectively from left to right): generation (1 to 9); replicate selection line; selection direction (as described above); the ID of the line (as described above); the ID of the particular sire; number of fighter males in that sire's offspring, number of females in that sire's offspring, number of scrambler males in that sire's offspring, number of 'intermorph' males (rare males with one scrambler and one fighter leg — they are counted as males for 'sex ratio' but ignored in the information for 'morph ratio') in that sire's offspring; and then descriptive stats based on these numbers (total of adults, total of males, sex ratio and morph ratio).两性间的极端差异通常被解释为对雄性武器（male weapons）或装饰物（ornaments）的强烈性选择（sexual selection）所致。性拮抗基因（sexually antagonistic genes）对雄性性状具有正向效应，但对雌性适合度（fitness）产生负向效应，由此产生适合度的跨性别负相关，即性冲突（sexual conflict）。然而，若受性选择的雄性性状存在条件依赖（condition-dependent），且条件本身可提升雌性适合度，则这类拮抗作用可能并不显著。本研究揭示了雄性武器与雌性繁殖力（fecundity）间令人意外的正向遗传相关。我们利用此前经13代针对雄性武器（格斗足，fighting legs）的选择的螨类品系（mite lines），探究了雌性繁殖力的协同进化（correlated evolution）情况。结果显示，经针对武器的正向选择（positive selection）的品系（向上选择品系，up lines）的雌性，尽管演化出代价高昂的更粗壮的足，但其繁殖力却有所提升。这一现象大概率源于：螨类雄性的武器呈条件依赖，这增强了我们对雄性生理条件的间接选择能力。同时，对两性生理条件均具有正向效应的等位基因（alleles）可能促成了该相关：向上选择品系演化出更高比例的格斗型雄性，且武器大小与雄性形态型（male morph）、后代性比（sex ratio）间均存在正向相关性。这种正向跨性别遗传相关应会推动雄性武器及极端性别差异的演化。 使用说明 本文件包含两个工作表。第一个工作表包含对刺足根螨（Rhizoglyphus echinopus）格斗型雄性的格斗足实施13代人工选择（artificial selection）后，雌性个体的繁殖力数据，即10天内的产卵数。每一行对应一只与两只游荡型雄性（scrambler males）交配的雌性个体，各列依次包含以下信息：重复选择品系（replicate selection line）、选择方向（向上选择对应更粗壮的足，向下选择对应更纤细的足）、品系ID（重复选择品系与选择方向的组合）、家系ID（family ID，即该雌性在上一代所属的家系）、以及该雌性的产卵数。第二个工作表包含前9代选择过程中的性比与形态比（morph ratio）信息。每一行对应各世代中被选择的父本（sires）的后代，各列依次包含以下信息：世代（1至9）、重复选择品系、选择方向（同上）、品系ID（同上）、特定父本的ID、该父本后代中的格斗型雄性数量、该父本后代中的雌性个体数量、该父本后代中的游荡型雄性数量、该父本后代中的‘中间形态型（intermorph）’雄性数量（指同时具有一条游荡型与一条格斗型足的稀有雄性，在性比统计中计入雄性，但形态比统计中不予纳入）；随后是基于上述数值计算的描述性统计量（descriptive stats），包括成虫总数、雄性总数、性比与形态比。