Genetic Variability of mitochondrial DNA in Ascidians, genus Halocynthia.

根据其繁殖行为、产卵季节和日产卵时间，将罗氏盐爪鱼分为三类。实验表明，这三种类型的杂交均获得成功，并产生了正常的幼胚，但F2胚胎尚未发育。有一种可能性，这三种类型的Halocynthia roretzi显示一个同域物种形成的例子。为了估计这些类型的遗传分化，对每种类型的25个个体进行了限制性内切酶片段谱和限制性内切酶位点分析，并根据共有限制性内切酶片段和限制性内切酶位点的比例（Nei & Li '79）估计了遗传分化程度。由此估算出陆津湾3个类型内的遗传分化（d）为4.4-6.2 × 10 ~（-1）<-4>，且各分化点的标准差在3个类型间重叠。有趣的是，在相同的分析中估计了与罗氏盐萼花相同的遗传分化。本研究还对盐萼属4个种间的遗传距离进行了研究。罗雷茨和橙黄之间的（d）值为6.5 * 10^<-2>，希尔根多菲和硬毛之间的（d）值为4.5 * 10 <-2>^，聚类结果为9.0 *10^<-2>。在盐辛西娅属中，上述物种可能在600万至300万年前分为四个。地理隔离或生殖隔离与遗传分化的关系尚待进一步研究。

Halocynthia roretzi is classified into three types on account of their reproductive behavior ; spawning season and daily spawning time. Experimentally, the cross fertilization among these three types was succeeded and the resulting embryos gave rise to normal young adults, but F2 embryo has not been developed. There is a possibility that these three types of Halocynthia roretzi show an example of sympatric speciation. To estimate the genetic divergence of these types, 25 individuals of each type were examined by restriction-fragment pattern and by restriction site analysis of mtDNA.The degree of genetic differentiation was estimated by the proportion of shared restriction fragment and restriction site (Nei & Li '79). According to these estimates, the genetic divergence (d) within three types of Mutsu Bay was 4.4-6.2*10^<-4>, and these standard deviations at each diverging point were over lapped among three types. Interestingly, the equal genetic differentiation as Halocynthia roretzi was estimated in same analysis of Halocynthia aurantium. In this study, the genetic distance (d) between the four species in genus Halocynthia was also investigated. The (d) value between H.roretzi and H.aurantium was 6.5 * 10^<-2> and that of between H.hilgendorfi and H.hispada was 4.5 * 10^<-2> and these cluster was jointed at 9.0 *10^<-2>.According these results, it seems that the genetic differentiation among these types is not significant. In the genus Halocynthia, above-mentioned species might be divided into four the range 6 to 3 million years ago. The relation between the geographic isolation or the reproductive isolation and the genetic differentiation were still under investigation.