NORTH-AMERICAN MOSQUITOFISH, GAMBUSIA-AFFINIS - UNIQUE CASE IN SEX-CHROMOSOME EVOLUTION
NORTH-AMERICAN MOSQUITOFISH, GAMBUSIA-AFFINIS - UNIQUE CASE IN SEX-CHROMOSOME EVOLUTION
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DOI：
10.2307/1443231
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发表时间：
1979-01-01
期刊：
影响因子：
2.6
通讯作者：
HOWELL, WM
中科院分区：
文献类型：
--
作者：
BLACK, DA;HOWELL, WM
蚊鱼 G. affinis 的两个亚种早已被古典系统学家所认识：G. a. affinis 发现于密西西比河流域以及墨西哥湾北部从德克萨斯州到密西西比州 [美国] 的支流，以及 G. a.霍尔布鲁克沿着美国东海岸从新泽西州到佛罗里达州分布，并穿过乔治亚州南部流入佛罗里达州北部墨西哥湾的支流。 2 ssp 的范围。阿拉巴马州南部和佛罗里达州西北部重叠，形成一个融合区。染色体研究表明，G. a. 所有种群的雌性。 affinis 拥有较大的异形性染色体对 (WZ)，但 G. a.霍尔布鲁克缺少WZ。这两个亚种的雄性都没有异形性染色体对。在融合区内，无论有或没有WZ，女性的融合都是预期的，但事实并非如此。所有女性跨年级者都缺乏 WZ。这种令人费解的现象可以通过实验室杂交来解释。当G.a. affinis 雌性（带有 WZ）与 G. a. 的雄性交配。 holbrooki（不是WZ），所有后代出生时都严重畸形并早逝。互十字，G. a. holbrooki 女性（无 WZ）.times。 G.a. affinis 雄性（无 WZ），产生了健康且可育的 F1 后代。自然界中不会发生与 WZ 的交联，正如实际情况一样。自从 G. a. 雌性中 WZ 机制的独立进化以来。由于 affinis 会阻止一个方向的成功交配，但不会阻止另一个方向的成功交配，因此提出了如何从分类学角度对待这些种群的问题。这些种群既不符合当前物种的定义，也不符合亚种的定义，因为它们表现出两个类群的一些特征，并被归类为半种。
Two subspecies of the mosquitofish, G. affinis, have long been recognized by classical systematists: G. a. affinis found in the Mississippi River basin and tributaries to the northern Gulf of Mexico from Texas to Mississippi [USA], and G. a. holbrooki distributed along the eastern coast of the US from New Jersey to Florida and across southern Georgia into tributaries to the Gulf of Mexico in northern Florida. The ranges of the 2 ssp. overlap on southern Alabama and northwestern Florida producing an intergradation zone. Chromosome studies showed that females from all populations of G. a. affinis possessed a large heteromorphic sex chromosome pair (WZ) but those of G. a. holbrooki lacked the WZ. No males of either subspecies had heteromorphic sex chromosome pairs. Within the zone of intergradation, female intergrades both with and without the WZ were expected, but this was not the case. All female intergrades lacked the WZ. This puzzling phenomenon was explained by performing laboratory crosses. When G. a. affinis females (with WZ) were mated with males of G. a. holbrooki (no WZ), all offspring were born severely deformed and died early. The reciprocal cross, G. a. holbrooki females (no WZ) .times. G. a. affinis males (no WZ), yielded healthy and fertile F1 offspring. No intergrades with the WZ would be expected to occur in nature, as was the case. Since the independent evolution of the WZ mechanism in females of G. a. affinis prevents successful mating in one direction, but not the other, a problem is presented as to how to treat these populations from a taxonomic viewpoint. These populations fit neither the current definition of species nor subspecies since they exhibit some of the characteristics of both taxa and were classified as semispecies.