Nagaraju G P C, Borst D W
Department of Biology, University of Central Florida, Orlando, FL 32816, USA.
J Exp Biol. 2008 Sep;211(Pt 17):2773-8. doi: 10.1242/jeb.019133.
Carcinus maenas males have two major color phases. Green-phase males molt frequently and tend to live in brackish estuaries during the summer. After becoming red-phase males, they molt infrequently, have higher mating success, and live in cooler, deeper water. We found profound differences between these two phases in the way salinity and temperature affect hemolymph levels of methyl farnesoate (MF), a hormone that affects crustacean reproduction. Few green-phase males (<10%) had detectable MF in 33 ppt seawater (SW) at 11 or 18 degrees C. By contrast, about 30% of the red-phase males had detectable MF at either temperature. After transfer to 5 ppt SW, none of the green-phase males had detectable MF at 11 degrees C whereas 100% of green-phase males did at 18 degrees C. By contrast, 100% of the red-phase males had detectable MF in 5 ppt SW at either temperature. At 11 degrees C, green-phase males had detectable MF after eyestalk ablation (ESA), showing that they can produce MF. There was no additional increase in MF levels when ESA animals of either color phase were transferred to 5 ppt SW, suggesting that the eyestalk is the primary regulator of the MF response to low salinity. MF levels of green-phase males were increased by injecting MF, by ESA, or by exposure to 5 ppt SW at 18 degrees C. The testicular index of these treated animals nearly doubled after two weeks. Our results strongly suggest that environmental conditions such as temperature and salinity, affect testicular development in this crab by changing its MF levels.
绿青蟹雄性有两种主要的颜色阶段。绿色阶段的雄性频繁蜕皮，夏季往往生活在微咸的河口。变成红色阶段的雄性后，它们很少蜕皮，交配成功率更高，生活在更凉爽、更深的水中。我们发现，在盐度和温度影响法尼酸甲酯（MF）血淋巴水平的方式上，这两个阶段存在显著差异，MF是一种影响甲壳类动物繁殖的激素。在11摄氏度或18摄氏度的33ppt海水中，很少有绿色阶段的雄性（<10%）能检测到MF。相比之下，在这两个温度下，约30%的红色阶段雄性能检测到MF。转移到5ppt的海水中后，在11摄氏度时，没有绿色阶段的雄性能检测到MF，而在18摄氏度时，100%的绿色阶段雄性能检测到。相比之下，在这两个温度下，100%的红色阶段雄性在5ppt海水中都能检测到MF。在11摄氏度时，绿色阶段的雄性在眼柄切除（ESA）后能检测到MF，这表明它们可以产生MF。当将任何一个颜色阶段的ESA动物转移到5ppt海水中时，MF水平没有进一步增加，这表明眼柄是MF对低盐度反应的主要调节因子。通过注射MF、进行ESA或在18摄氏度下暴露于5ppt海水中，绿色阶段雄性的MF水平会升高。两周后，这些经过处理的动物的睾丸指数几乎翻了一番。我们的结果有力地表明，温度和盐度等环境条件通过改变其MF水平来影响这种螃蟹的睾丸发育。
