Possibility of sperm competition in spermathecae of ants

采用CAP-PCR DNA指纹法估算蚁王的授精频率，因为该方法在分析亲缘关系方面具有以下优点：1)所需的DNA量小至50 ng，即使是非常微小的昆虫也可以获得。2)带型变异大，亲缘关系分析只需要少量的个体或菌落。3)来自同一样品的波段模式几乎总是相同的；因此，重现性非常高。因此，大多数蚁王都是一妻多夫制，只有少数蚁王表现为一妻多夫制。也就是说，不同雄性的精子细胞很少共存于一个女王的精子囊中。可能正因为如此，我在目前的研究中找不到任何精子竞争的证据。尽管如此，本研究还是获得了一些重要的社会生物学结果：1)在分布于南美洲和中美洲的Attini部落中，Atta、Acromymex和Sericomyrmex等社会高级属为一妻多夫制，而Cyphomyrmex和Myrmicocrypta等社会低级属为一妻多夫制。这表明，一妻多夫制有助于有效的多工制和庞大的群居昆虫社会的进化。(2)正如理论预测的那样，雌雄比例在单雄物种中被扭曲，而在多雄物种中，雌性比例下降。在阿塔，由于未知的原因，性别比例明显向男性倾斜。3)真菌是幼虫和蜂后的主要食物，而不是幼虫工蜂的主要食物，这与为解释阿蒂尼的真菌吞噬进化而提出的四种假设的预测不同。这就意味着，必须考虑另一种假设，即在真菌为寄生而进化的情况下。

CAP-PCR DNA Fingerprinting method was used for estimating the insemination frequency of ant queens, because this method had the following advantages for analyzing kin relatedness : 1) The required amount of DNA was as small as 50 ng, which is available even from very tiny insects. 2) The variation of band pattern was large and only a few individuals or colonies were required for the analysis of kin relatedness. 3) Band patterns from the same sample were almost always identical ; thus, the reproducibility was very high. Accordingly, queens of most ant species were monandrous and only a few species showed polyandry. That is, sperm cells of different males rarely coexist in a spermatheca of a queen. Probably because of this, I could not find any evidence of sperm competition in the present study.Nonetheless, some sociobiologically important results were obtained in this study : 1) In the tribe Attini which is distributed in South and Central America, such socially higher genera as Atta, Acromymex and Sericomyrmex were polyandrous, while lower genera such as Cyphomyrmex and Myrmicocrypta showed monandry. This suggests that the polyandry contributes to the evolution of effective polyethism and huge societies of social insects. 2) As theoretically predicted, the sex ratio was distorted to females in the monandrous species, though the ratio of the females decreased in the polyandrous species. In Atta the sex ratio was obviously distorted to males for unknown reasons. 3) Fungi were the staple food of larvae and queens but not of abult workers, unlike the prediction of four hypotheses which have been proposed to account for the evolution of mycophagy in Attini. This means that another hypothesis have to be considered under the condition that the mycophagy evolved for lavae.