Shaw D D, Wilkinson P, Moran C
Chromosoma. 1979;75(3):333-51. doi: 10.1007/BF00293476.
A hydrid zone between the Moreton and Torresian taxa of the grasshopper Caledia captiva in S.E. Queensland has been characterised in terms of allozyme and chromosome variation within the same individuals.--On chromosomal criteria (pericentric rearrangements), the zone is asymmetrical with evidence of high levels of introgression of Torresian chromosomes into the Moreton taxon. This is apparent from the analysis of two independent transects across the hydrid zone. Major changes in chromosomal frequency occur over distances of less than 0.5 km. and the level of introgression differs between the two transects, with much higher levels in the northern Moreton populations, characterised by an acrocentric X-chromosome, when compared with the southern metacentric-X Moreton populations. Chromosome analysis of samples taken from the same transect over two years has revealed no major changes in the structure of the zone. Moreover, a Moreton population located only 0.5 km. from the null point was found to be stable over 6 generations with evidence for a new balanced genome having originated following the differential incorportation of Torresian chromosomes.--Contrary to the chromosomal situation, the same hybrid zone was found to be symmetrical with respect to allozyme variation with evidence of movement of diagnostic alleles in both directions across the zone. The alleles are independent and not tightly linked to any of the pericentric rearrangements. Thus these 5 alleles are acting as markers of the background genome and reveal the relatively free movement of genes which are located outside the pericentric rearrangements.--It is proposed that the hybrid zone in Caledia captiva is unstable and is moving slowly in a westerly direction into the Torresian territory. This is due to the ability of the Moreton taxon to incorporate more readily into its genome those Torresian chromosomes or chromosome segments which increase the fitness of the Moreton taxon. On chromosomal criteria, the Torresian taxon does not share the same capacity.--It is suggested that, so long as the two taxa retain their ability to hybridise with subsequent asymmetrical introgression, the zone will continue to move westwards and eventually lead to the selective incorporation of the Torresian genome into the Moreton taxon. This will result in a polymorphic situation with clinal variation in chromosomal frequencies. The structure of the zone is dependent upon a fine balance between genomic reorganisation in recombinant genotypes and the relative dispersal capacities of the two hydridising taxa.
在昆士兰东南部，蝗虫Caledia captiva的莫顿种群和托雷斯海峡种群之间的杂交区域已根据同一群体内的等位酶和染色体变异进行了特征描述。——根据染色体标准（臂间重排），该区域不对称，有证据表明托雷斯海峡染色体大量渗入莫顿分类单元。这从对杂交区域两条独立样带的分析中可以明显看出。染色体频率的主要变化发生在不到0.5公里的距离内。两条样带的渗入水平不同，与南部具中着丝粒X染色体的莫顿种群相比，北部以近端着丝粒X染色体为特征的莫顿种群的渗入水平要高得多。对同一两年内同一样带采集的样本进行的染色体分析表明，该区域的结构没有重大变化。此外，发现一个距离零位点仅0.5公里的莫顿种群在6代中保持稳定，有证据表明在差异纳入托雷斯海峡染色体后产生了一个新的平衡基因组。——与染色体情况相反，发现同一杂交区域在等位酶变异方面是对称的，有诊断等位基因在该区域双向移动的证据。这些等位基因是独立的，与任何臂间重排都没有紧密联系。因此，这5个等位基因作为背景基因组的标记，揭示了位于臂间重排之外的基因的相对自由移动。——有人提出，Caledia captiva的杂交区域不稳定，正在缓慢向西移动到托雷斯海峡区域。这是因为莫顿分类单元能够更容易地将那些增加莫顿分类单元适应性的托雷斯海峡染色体或染色体片段纳入其基因组。根据染色体标准，托雷斯海峡分类单元没有同样的能力。——有人认为，只要这两个分类单元保持杂交及随后不对称渗入的能力，该区域将继续向西移动，最终导致托雷斯海峡基因组被选择性地纳入莫顿分类单元。这将导致一种多态情况，染色体频率呈渐变。该区域的结构取决于重组基因型中基因组重组与两个杂交分类单元相对扩散能力之间的精细平衡。
