Urbanelli S, Silvestrini F, Reisen W K, De Vito E, Bullini L
Department of Genetics and Molecular Biology, University of Rome La Sapienza, Italy.
J Med Entomol. 1997 Mar;34(2):116-27. doi: 10.1093/jmedent/34.2.116.
Phallosome morphology (DV/D ratio) and allozyme variation were used to reexamine the transition from Culex pipiens pipiens L. to Cx. p. quinquefasciatus Say, detected in California from the northern Central Valley to the Mexican border of the United States of America. Significant deficiency of heterozygotes was observed at the diagnostic locus Mdhp-2 in populations from the central part of the hybrid zone. Long tails of introgression were detected: populations from both north and south ends of the transect were not genetically pure Cx. p. pipiens or Cx. p. quinquefasciatus, respectively, as previously considered, but included approximately 5% introgressed individuals. A narrow reversed cline from the Delta area into the Sacramento Valley, characterized by increasing frequencies of Cx. p. quinquefasciatus alleles proceeding to the north, was confirmed. Both these cline appear to be related mainly to temperature gradients. Over the last 50 yr, an increase in the proportion of Cx. p. pipiens DV/D phenotypes was detected proceeding north to south along the main latitudinal cline, as well as in the narrow reversed cline. Accordingly, the center of the main latitudinal hybrid zone has apparently moved approximately 100 km to the south. This phenomenon is only partially paralleled by the differentiated locus Pgm of the 3 for which comparison was possible. Similarities to and differences from previous studies are discussed, also in relation with comparable data from another hybrid zone between Cx. p. pipiens and Cx. p. quinquefasciatus recently detected in Madagascar. Hybrid index scores based on differentiated allozymes and the diagnostic locus Mdhp-2 prove to be better descriptors than the DV/D ratio of hybridization and introgression occurring between Cx. p. pipiens and Cx. p. quinquefasciatus. This seems to be caused mainly by the influence of temperature on male genitalia development, and the weaker association found between genetic markers and DV/D phenotypes in hybrid populations.
阴茎形态（DV/D比率）和等位酶变异被用于重新审视在加利福尼亚州从中央谷地北部到美利坚合众国墨西哥边境所检测到的尖音库蚊指名亚种（Culex pipiens pipiens L.）向致倦库蚊（Cx. p. quinquefasciatus Say）的转变。在杂交区中部的种群中，诊断位点Mdhp - 2处观察到杂合子显著不足。检测到渗入的长尾现象：样带南北两端的种群并非如先前认为的那样分别是基因纯合的尖音库蚊指名亚种或致倦库蚊，而是各自包含约5%的渗入个体。从三角洲地区到萨克拉门托山谷确认存在一条狭窄的反向渐变群，其特征是向北致倦库蚊等位基因频率增加。这两条渐变群似乎都主要与温度梯度有关。在过去50年里，沿着主要纬度渐变群以及狭窄的反向渐变群，从北向南检测到尖音库蚊指名亚种DV/D表型的比例增加。因此，主要纬度杂交区的中心显然已向南移动了约100公里。对于可以进行比较的3个位点中的分化位点Pgm，这种现象只是部分相似。还讨论了与先前研究的异同，以及与最近在马达加斯加检测到的尖音库蚊指名亚种和致倦库蚊之间另一个杂交区的可比数据的关系。基于分化等位酶和诊断位点Mdhp - 2的杂交指数得分被证明比尖音库蚊指名亚种和致倦库蚊之间杂交和渗入的DV/D比率更能描述情况。这似乎主要是由温度对雄性生殖器发育的影响以及在杂交种群中遗传标记与DV/D表型之间发现的较弱关联所导致的。
