Inoda Toshio, Härdling Roger, Kubota Souichirou
Conservation Laboratory of Rare Water Insects, Shibamata 5-17-10, Katsushika, Tokyo 125-0052, Japan.
Zoolog Sci. 2012 Aug;29(8):505-9. doi: 10.2108/zsj.29.505.
Many species of Dytiscus diving beetles exhibit intrasexual dimorphism, e.g., the elytra is smooth in some females and grooved in others. However, the expression of the grooves and whether they are a product of heredity or the environment remain unknown. One Japanese species, Dytiscus sharpi sharpi Wehncke, 1875 , also shows female dimorphism, with grooved and smooth morphs, while D. sharpi validus Régimbart, 1899, only has a single morph (the grooved type). A hybrid of the two species should therefore provide a means of sorting out how the grooves are inherited. We found two independent wetlands of D. sharpi sharpi in Chiba Prefecture, Japan. One was a place where a high proportion of grooved females lived, and the others had high proportions of smooth females. After five to eight generations of beetles from two populations with different proportions of grooved females were reared under aquarium conditions constituting a common garden design, i.e., water temperature, water depth, and presence of a plant for oviposition, the differences remained. We mated smooth virgin females of D. sharpi sharpi with males of D. sharpi validus to obtain hybrid offspring. The elytral traits of the hybrid females produced only grooved forms. These results suggested that the female dimorphism is determined by genetics, and that the grooved morph was dominant over the smooth one, independent of environmental factors. In addition, the hybrid insects did not differ from the two subspecies insects in larval survivorship, pupation success, or sex ratio. They also showed neither morphological abnormality nor reduced survival.
许多龙虱科潜水甲虫物种表现出种内二态性，例如，一些雌性的鞘翅是光滑的，而另一些则有沟槽。然而，沟槽的表现形式以及它们是遗传产物还是环境产物仍然未知。一种日本物种，即1875年的夏普龙虱Dytiscus sharpi sharpi Wehncke，也表现出雌性二态性，有带沟槽和光滑的形态，而1899年的有效夏普龙虱D. sharpi validus Régimbart只有单一形态（带沟槽类型）。因此，这两个物种的杂交种应该能提供一种方法来理清沟槽是如何遗传的。我们在日本千叶县发现了两个独立的夏普龙虱栖息地。一个地方生活着高比例的带沟槽雌性，另一个地方则有高比例的光滑雌性。在水族箱条件下（构成一个共同花园设计，即水温、水深和有用于产卵的植物）饲养来自两个带沟槽雌性比例不同的种群的甲虫五到八代后，差异仍然存在。我们将夏普龙虱的光滑处女雌虫与有效夏普龙虱的雄虫交配，以获得杂交后代。杂交雌性的鞘翅特征只产生带沟槽的形态。这些结果表明，雌性二态性是由基因决定的，并且带沟槽形态对光滑形态是显性的，与环境因素无关。此外，杂交昆虫在幼虫存活率、化蛹成功率或性别比例方面与两个亚种昆虫没有差异。它们也没有表现出形态异常或存活率降低。
