Hemmerter Stéphane, Slapeta Jan, van den Hurk Andrew F, Cooper Robert D, Whelan Peter I, Russell Richard C, Johansen Cheryl A, Beebe Nigel W
Institute for the Biotechnology of Infectious Diseases, University of Technology, Sydney, New South Wales, Australia.
BMC Evol Biol. 2007 Jun 29;7:100. doi: 10.1186/1471-2148-7-100.
The mosquito Culex annulirostris Skuse (Diptera: Culicidae) is the major vector of endemic arboviruses in Australia and is also responsible for the establishment of the Japanese encephalitis virus (JEV) in southern Papua New Guinea (PNG) as well as its incursions into northern Australia. Papua New Guinea and mainland Australia are separated by a small stretch of water, the Torres Strait, and its islands. While there has been regular JEV activity on these islands, JEV has not established on mainland Australia despite an abundance of Cx. annulirostris and porcine amplifying hosts. Despite the public health significance of this mosquito and the fact that its adults show overlapping morphology with close relative Cx. palpalis Taylor, its evolution and genetic structure remain undetermined. We address a hypothesis that there is significant genetic diversity in Cx. annulirostris and that the identification of this diversity will shed light on the paradox that JEV can cycle on an island 70 km from mainland Australia while not establishing in Australia itself.
We sequenced 538 bp of the mitochondrial DNA cytochrome oxidase I gene from 273 individuals collected from 43 localities in Australia and the southwest Pacific region to describe the phylogeography of Cx. annulirostris and its sister species Cx. palpalis. Maximum Likelihood and Bayesian analyses reveal supporting evidence for multiple divergent lineages that display geographic restriction. Culex palpalis contained three divergent lineages geographically restricted to southern Australia, northern Australia and Papua New Guinea (PNG). Culex annulirostris contained five geographically restricted divergent lineages, with one lineage restricted to the Solomon Islands and two identified mainly within Australia while two other lineages showed distributions in PNG and the Torres Strait Islands with a southern limit at the top of Australia's Cape York Peninsula.
The existence of divergent mitochondrial lineages within Cx. annulirostris and Cx. palpalis helps explain the difficulty of using adult morphology to identify Cx. annulirostris and its ecological diversity. Notably, the southern limit of the PNG lineages of Cx. annulirostris coincides exactly with the current southern limit of JEV activity in Australasia suggesting that variation in these COI lineages may be the key to why JEV has not yet established yet on mainland Australia.
环喙库蚊（Culex annulirostris Skuse，双翅目：蚊科）是澳大利亚地方性虫媒病毒的主要传播媒介，也是日本脑炎病毒（JEV）在巴布亚新几内亚南部（PNG）传播以及侵入澳大利亚北部的罪魁祸首。巴布亚新几内亚和澳大利亚大陆被一小片水域——托雷斯海峡及其岛屿隔开。尽管这些岛屿上经常有日本脑炎病毒活动，但尽管有大量的环喙库蚊和猪作为扩增宿主，日本脑炎病毒仍未在澳大利亚大陆传播开来。尽管这种蚊子具有重要的公共卫生意义，且其成虫形态与近缘种泰勒库蚊（Cx. palpalis Taylor）有重叠，但它的进化和遗传结构仍未确定。我们提出一个假设，即环喙库蚊存在显著的遗传多样性，对这种多样性的识别将有助于解释一个矛盾现象：日本脑炎病毒能在距离澳大利亚大陆70公里的岛屿上循环传播，却无法在澳大利亚本土传播。
我们对从澳大利亚和西南太平洋地区43个地点采集的273只个体的线粒体DNA细胞色素氧化酶I基因的538个碱基对进行了测序，以描述环喙库蚊及其姊妹种泰勒库蚊的系统地理学。最大似然法和贝叶斯分析揭示了多个显示地理限制的不同谱系的支持证据。泰勒库蚊包含三个在地理上分别局限于澳大利亚南部、澳大利亚北部和巴布亚新几内亚（PNG）的不同谱系。环喙库蚊包含五个在地理上受限的不同谱系，其中一个谱系局限于所罗门群岛，两个主要在澳大利亚境内被识别出来，而另外两个谱系分布在巴布亚新几内亚和托雷斯海峡群岛，其南界位于澳大利亚约克角半岛顶端。
环喙库蚊和泰勒库蚊中不同线粒体谱系的存在有助于解释利用成虫形态识别环喙库蚊及其生态多样性的困难。值得注意的是，环喙库蚊在巴布亚新几内亚谱系的南界与目前日本脑炎病毒在澳大拉西亚活动的南界恰好重合，这表明这些细胞色素氧化酶I谱系的变异可能是日本脑炎病毒尚未在澳大利亚大陆传播开来的关键原因。
