Assessment of the applicability of COI and 16S gene regions for molecular genetic diagnostics of the species Bactrocera tryoni (Froggatt)

The Queensland fruit fly Bactrocera (Bactrocera) tryoni (Froggatt, 1897) is a member of the Tephritidae family and is a serious pest of a wide range of fruit and vegetable crops in Australia. The object of this study, Bactrocera tryoni, belongs to the complex of B. tryoni species, which, in addition to it, includes the species Bactrocera aquilonis (May, 1965), Bactrocera neohumeralis (Hardy, 1951), and Bactrocera melas (Perkins & May, 1949). Since these species are morphologically very similar and some may infect similar products, there is a need for molecular genetic diagnostic methods that will reliably distinguish these species from other species and among themselves. According to the obtained data on the COI gene generally in the sample matrix, there is a hiatus - a gap between intra- and interspecific distances. However, the species B. tryoni, B. aquilonis, and B. neohumeralis on the dendrogram form clades corresponding to the same species, therefore, it is impossible to distinguish them using the sequences of the COI gene region. However, based on this sequence, it is possible to narrow down the identification by molecular genetic methods to these three species, since they are well separated from other studied species. According to the graph of the distribution of pairwise genetic distances for the 16S gene, there is a lower variability than for the COI gene. On the dendrogram, the species B. tryoni, B. aquilonis, and B. neohumeralis form the one clade, but other species formed separate clades. It is necessary to increase the number of 16S gene sequences in the sample for each species. Thus, based on the COI gene sequence, it is possible to separate the species B. tryoni, B. aquilonis, and B. neohumeralis from other species of the genus Bactrocera studied by us. To study the relationships within the complex of B. tryoni species and search for a gene sequence by which it will be possible to reliably differentiate the B. tryoni species, another, possibly more rapidly evolving gene is required.昆士兰果实蝇（Bactrocera (Bactrocera) tryoni, Froggatt, 1897）隶属于实蝇科（Tephritidae），是澳大利亚境内危害多种果蔬作物的重大害虫。 本研究的目标物种——昆士兰果实蝇（B. tryoni）属于B. tryoni物种复合群，该复合群除本种外，还涵盖北澳果实蝇（Bactrocera aquilonis, May, 1965）、新肩实蝇（Bactrocera neohumeralis, Hardy, 1951）以及黑额实蝇（Bactrocera melas, Perkins & May, 1949）。鉴于上述物种形态相似度极高，且部分类群可侵染相同寄主产品，因此亟需开发分子遗传诊断方法，以实现这些物种与其他类群、以及彼此间的可靠区分。 基于样本矩阵中COI基因 (COI gene) 的现有测序数据，样本中存在一处遗传间隔——即种内与种间遗传距离之间存在显著缺口。然而，在系统发育树上，B. tryoni、B. aquilonis与B. neohumeralis各自形成对应物种的单系进化支，因此无法通过COI基因区域序列对这三个物种进行区分。不过，依托该基因序列，可将分子遗传鉴定的范围缩小至这三个物种，因为它们与本次研究涉及的其他物种均存在明显分化。 通过16S基因 (16S gene) 的成对遗传距离分布图谱可知，其变异水平低于COI基因。在系统发育树上，B. tryoni、B. aquilonis与B. neohumeralis共同构成一个单系进化支，而其余物种则各自形成独立进化支。因此，需扩充各物种对应的16S基因序列样本量。 综上，依托COI基因序列，可将B. tryoni、B. aquilonis与B. neohumeralis与本次研究涉及的其他果实蝇属（Bactrocera）物种进行有效区分。若要深入解析B. tryoni物种复合群内部的系统发育关系，并筛选出可稳定区分该复合群内各物种的基因序列，则需借助另一种进化速率可能更快的基因标记。