家幽灵蛛食物和性别特异性的生长策略

如果存在性二态，预计不同环境和性别之间的生长模式会有所不同，一般的观点是，雄性的生长策略主要是基于性选择，而雌性的生长策略是基于生殖。我们研究了食物对家幽灵蛛cellar spider Pholcus phalangioides性别特异性生长的影响，Pholcus phalangioides是一种性别二态蜘蛛，雄性比雌性大。在全因子设计中，39只交配过的雌性的1164只后代在两种喂养方式下饲养至性成熟。食物水平对蜘蛛一下2个方面有很强的正向影响 (1) 后代体型大小(雄性大于雌性)和 (2) 后代重量(雌性成熟重于雄性)，对(3)雄性发育时间有负面影响，但对雌性发育时间没有影响。在无限制的食物条件下，雄性比雌性先成熟。对整个个体发育的分析表明，直到最后一龄，两性都因食物限制而发育迟缓，雄性落后于雌性。在最后一龄，情况正好相反：雄性在高、低食物中的发育时间相当，而雌性在高食物中的发育时间极长，在低食物中的发育时间较短。我们的结论是，雌性的选择是为了增加重量并进而提高繁殖力，而性选择显然有利于体型较大的雄性，但同时也有利于较早的成熟(即雄先成熟)。只有在食物充足的情况下，才有可能做到这两点，而且发育时间和体型之间的遗传相关性很低，这就促进了这两个目标的实现。我们发现个体的大小、质量、发育时间和生长速度存在较高的遗传变异以及基因型-环境互作，因此具有较高的全同胞（兄弟姐妹）遗传力，但较低的亲子遗传力(仅大小)。食物胁迫下的遗传变异不大，但遗传协变较大。

原文: 

Growth patterns are expected to differ between environments and between the sexes if there is sexual dimorphism, the general view being that male growth strategies are primarily sexually selected whereas female growth strategies are fecundity selected. We investigated the effects of food on sex-specific growth in the cellar spider Pholcus phalangioides, a sexually dimorphic spider with larger males than females. In a full sib design, 1164 offspring of 39 once-mated females were reared to sexual maturity under two feeding regimes. Food level had strong positive effects on (1) offspring body size, with males growing larger than females, and (2) offspring mass, with females maturing heavier than males; it had negative effects on (3) development time for males but not females. Males matured before females under unlimited food conditions. Analysing the entire ontogeny revealed that until the last instar, both sexes were equally retarded in development by food limitation, males lagging behind females. During the last instar, the picture reversed: development time of males was equally long at high and low food, while females had extremely long development at high food and abbreviated development at low food. We conclude that females are selected to increase mass and hence fecundity, while sexual selection apparently favours larger males but at the same time earlier maturity (i.e. protandry). Achieving both was only possible when food was plentiful, and is facilitated by a low genetic correlation between development time and body size. We found high genetic variation, as well as genotype–environment interactions, for size, mass, development time and growth rate, and consequently high full-sib but lower parent–offspring (size only) heritabilities. Genetic variation was not greater under food stress but genetic covariation was.

文献来源

Uhl, G., Schmitt, S., Schafer, M.A., Blanckenhorn, W., 2004. Food and sex-specific growth strategies in a spider. Evolutionary Ecology Research 6, 523–540.

我对文中所说，雄性家幽灵蛛个体比雌性大表示质疑，但雌性成熟重量大于雌性应该是可以相信的，若如此，两性之间的大小差别并不是那么大？？目前，在实验室里看到的幽灵蛛尚不知是否是家幽灵蛛，按照分布来看，我想应该是的吧。