Rahman Sk Mustafizur, Uehara Tsuyoshi
Graduate School of Science and Engineering, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan.
Comp Biochem Physiol A Mol Integr Physiol. 2004 Dec;139(4):469-78. doi: 10.1016/j.cbpb.2004.10.005.
Interspecific and intraspecific morphological and fertilization variations were studied in three sibling species of Echinometra (known as sp. B, C and D) found off the coast of Okinawa, Japan. Eggs from C and D were readily fertilized by sperm from all three color morphs of B when the sperm concentrations were high, but no fertilization was observed when sperm of the former were mixed with eggs from the latter. Under limiting sperm concentrations, however, both C and D were incapable to fertilize reciprocally with B. In contrast, crossing between C and D produced fertilization membrane at high and limiting sperm concentrations in both directions. Interspecific crosses between B vs. C and B vs. D clearly showed that these combinations were reproductively isolated in contrast to that observed for crossing between C and D. Interestingly, intraspecific fertilization of B showed considerable morphological variation in addition to variability in fertilization success. Intraspecific fertilization and morphological variations may occur due to a number of genetic and/or non-genetic factors. While the underlying cause(s) remain to be elucidated, the results of the present study suggest that B is now speciating very slowly.
在日本冲绳海岸发现的三种刺冠海胆姐妹种（称为B、C和D种）中，研究了种间和种内的形态学及受精差异。当精子浓度较高时，C和D的卵子很容易被B的所有三种颜色形态的精子受精，但当前者的精子与后者的卵子混合时，未观察到受精现象。然而，在精子浓度有限的情况下，C和D都无法与B相互受精。相比之下，C和D之间的杂交在高精子浓度和有限精子浓度下双向都产生了受精膜。B与C以及B与D之间的种间杂交清楚地表明，与C和D之间的杂交情况相比，这些组合在生殖上是隔离的。有趣的是，B的种内受精除了受精成功率存在差异外，还表现出相当大的形态学变异。种内受精和形态学变异可能是由多种遗传和/或非遗传因素引起的。虽然潜在原因仍有待阐明，但本研究结果表明，B现在正在非常缓慢地形成新物种。
