Karyotypic Differentiation in the Phytophagous Ladybird Beetles Epilachna vigintioctomaculata Complex and Its Possible Relevance to the Reproductive Isolation, with a Note on Supernumerary Y Chromosomes Found in E. pustulosa

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Chromosomes of phytophagous ladybird beetles belonging to the Epilachna vigintioctomaculata complex (Coccinellidae) were investigated in 18 populations. All the populations basically showed a diploid number of 20 with Xyp sex chromosome associations in male meiosis. Detailed comparison of karyotypes using cluster and principal component analyses revealed a considerable divergence between the two groups of this species complex, the group A containing E. vigintioctomaculata and the group B including three other ''species'', E. pustulosa, E. niponica, and E. yasutomii. The divergence comes mainly from the addition of a large amount of heterochromatic segments on short arms of chromosomes Nos. 3 to 9 in karyotypes of the group B. This change in chromosomal structure confers the so-called diphasic state, which stands for a condition of chromosomes with one arm euchromatic and the other heterochromatic, in karyotypes of the group B species. The chromosome configurations observed suggested the late replication of heterochromatic arms in those diphasics. A new hypothetical model that accounts for the postmating reproductive isolation between the groups A and B is proposed on the basis of the karyotypic difference between the groups. Karyotypic differentiation within each group is also briefly mentioned. Significant differences were found among karyotypes of three populations of E. vigintioctomaculata, each of which represents one of three different geographic forms. Karyotypes of populations belonging to E. yasutomii deviated slightly from other species of the group B. Supernumerary Y chromosomes were found in males of some populations of E. pustulosa with considerable frequencies.
社団法人日本動物学会の論文
1993-12-15

Karyotypic Differentiation in the Phytophagous Ladybird Beetles Epilachna vigintioctomaculata Complex and Its Possible Relevance to the Reproductive Isolation, with a Note on Supernumerary Y Chromosomes Found in E. pustulosa

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