Kawamura K, Hosoya K
National Research Institute of Aquaculture, Watarai, Mie, Japan.
J Hered. 2000 Nov-Dec;91(6):464-73. doi: 10.1093/jhered/91.6.464.
The sex ratio of bitterling hybrids (subfamily: Acheilognathinae) is often likely to be biased toward males. Artificial hybridization was carried out in 10 species of bitterlings (three genera) in order to elucidate the masculinization mechanism of hybrids. Tanakia himantegus never produced viable F1 hybrids with other species, while hybrids of most other species were viable. In terms of sex ratio and fertility, hybrids were clearly divided into two groups: congeneric Tanakia hybrids and others. Both male and female congeneric Tanakia hybrids were fertile. The sex ratio was nearly 1:1 in all groups of Tanakia hybrids. Except for the congeneric Tanakia hybrids, sterile males appeared predominantly in groups of hybrids in which females were very rare but remained fertile. Sterile intersexes were also observed in five hybrid groups: T. lanceolata (female) x Acheilognathus cyanostigma (male), Rhodeus uyekii (female) x T. lanceolata (male), A. rhombeus (female) x T. lanceolata (male), A. rhombeus (female) x T. limbata (male), and A. tabira tabira (female) x A. cyanostigma (male). In the development of male-predominant hybrids, although hybrid and control (parental species) hatching and survival rates do not differ, no females appeared in hybrids, contrary to the controls. Taking the female heterogametic sex-determining system (ZW) and the phylogenetic relationship of bitterlings into consideration, the masculinization mechanism of hybrids in bitterlings can be explained by the interaction of two sex chromosomes, derived from each parental species. The basic genetic sex in bitterlings is male (ZZ) and the derivative is female (ZW). When parental species are related, the sex phenotype of hybrids coincides with the genetic sex. However, when the parental species differ, the sex phenotype of the ZW genotype is reversed to become male by an abnormal interaction between the Z and W chromosomes. The rare appearance of females and intersexes in male-predominant hybrids might be due to complete or partial functional expression of the W chromosome.
苦𬶋杂交种（亚科：𬶋亚科）的性别比例通常可能偏向雄性。为了阐明杂交种的雄性化机制，对10种苦𬶋（3个属）进行了人工杂交。高体鳑鲏从未与其他物种产生过可存活的F1杂交种，而大多数其他物种的杂交种是可存活的。在性别比例和育性方面，杂交种明显分为两组：同属鳑鲏杂交种和其他杂交种。同属鳑鲏杂交种的雄性和雌性都可育。所有鳑鲏杂交种群体的性别比例接近1:1。除了同属鳑鲏杂交种外，不育雄性在雌性非常罕见但仍可育的杂交种群体中占主导地位。在五个杂交组中也观察到了不育雌雄同体：高体鳑鲏（雌性）×蓝斑副𬶋（雄性）、须鳑鲏（雌性）×高体鳑鲏（雄性）、方氏副𬶋（雌性）×高体鳑鲏（雄性）、方氏副𬶋（雌性）×长身鳑鲏（雄性）以及条纹副𬶋（雌性）×蓝斑副𬶋（雄性）。在雄性占主导的杂交种发育过程中，尽管杂交种和对照（亲本物种）的孵化率和存活率没有差异，但与对照相反，杂交种中没有出现雌性。考虑到雌性异配性别决定系统（ZW）和苦𬶋的系统发育关系，苦𬶋杂交种的雄性化机制可以用来自每个亲本物种的两条性染色体的相互作用来解释。苦𬶋的基本遗传性别为雄性（ZZ），衍生性别为雌性（ZW）。当亲本物种亲缘关系较近时，杂交种的性别表型与遗传性别一致。然而，当亲本物种不同时，ZW基因型的性别表型会因Z和W染色体之间的异常相互作用而逆转成为雄性。雄性占主导的杂交种中雌性和雌雄同体的罕见出现可能是由于W染色体的完全或部分功能表达。
