Possibility of sperm competition in spermathecae of ants

由于CAP-PCRDNA指纹法在分析蚂蚁亲缘关系方面具有以下优点：1)所需DNA含量低至50 ng，即使是非常微小的昆虫也能获得；2)谱带变异较大，只需少量个体或群体即可进行亲缘关系分析。3)同一样品的带型几乎总是相同的，因此重复性很高。因此，大多数蚂蚁物种的蚁后都是一夫多妻制的，只有少数物种表现为一夫多妻。也就是说，不同雄性的精子很少共存于女王的受精囊中。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)在分布于中南美洲的Attini族中，社会高级属如Atta、Acromymex和Sericmyrmex是多性的，而较低的属如Cyphomrmex和Myrmiypypta则表现为单性生殖。这表明，一夫多妻制有助于有效的多妻制和庞大的群居昆虫社会的进化。2)正如理论预测的那样，在单性物种中，性别比被扭曲为雌性，而在多雄物种中，雌性比例下降。在阿塔，性别比例显然被扭曲为男性，原因不明。3)真菌是幼虫和蜂王的主食，而不是成年工蜂的主食，这与已提出的四种假说的预测不同，这些假说解释了Attini的真菌吞噬进化。这意味着，在真菌吞噬是为熔岩进化的条件下，必须考虑另一种假设。

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.