Abstract
BackgroundThe mosquito Anopheles irenicus, a member of the Anopheles punctulatus group, is geographically restricted to Guadalcanal in the Solomon Islands. It shows remarkable morphological similarities to one of its sibling species, An. farauti sensu stricto (An. farauti s.s.), but is dissimilar in host and habitat preferences. To infer the genetic variations between these two species, we have analyzed mitochondrial cytochrome oxidase subunit II (COII) and nuclear ribosomal internal transcribed spacer 2 (ITS2) sequences from Guadalcanal and from one of its nearest neighbours, Malaita, in the Solomon Islands.ResultsAn. farauti s.s. was collected mostly from brackish water and by the human bait method on both islands, whereas An. irenicus was only collected from fresh water bodies on Guadalcanal Island. An. irenicus is distributed evenly with An. farauti s.s. (ΦSC = 0.033, 0.38%) and its range overlaps in three of the seven sampling sites. However, there is a significant population genetic structure between the species (ΦCT = 0.863, P < 0.01; ΦST = 0.865, P < 0.01 and FST = 0.878, P < 0.01). Phylogenetic analyses suggest that An. irenicus is a monophyletic species, not a hybrid, and is closely related to the An. farauti s.s. on Guadalcanal. The time estimator suggests that An. irenicus diverged from the ancestral An. farauti s.s. on Guadalcanal within 29,000 years before present (BP). An. farauti s.s. expanded much earlier on Malaita (texp = 24,600 BP) than the populations on Guadalcanal (texp = 16,800 BP for An. farauti s.s. and 14,000 BP for An. irenicus).ConclusionThese findings suggest that An. irenicus and An. farauti s.s. are monophyletic sister species living in sympatry, and their populations on Guadalcanal have recently expanded. Consequently, the findings further suggest that An. irenicus diverged from the ancestral An. farauti s.s. on Guadalcanal.
Highlights
The mosquito Anopheles irenicus, a member of the Anopheles punctulatus group, is geographically restricted to Guadalcanal in the Solomon Islands
An. irenicus is only found on Guadalcanal [1,2,4], but An. farauti s.s. is distributed from the east through New Guinea, the Bismarck Archipelago and the Solomon Islands to Vanuatu and southward into northern Australia [5,6]
CFioglulercetio1n sites and frequencies of Anopheles farauti s.s. and Anopheles irenicus mosquitoes used in this study Collection sites and frequencies of Anopheles farauti s.s. and Anopheles irenicus mosquitoes used in this study
Summary
The mosquito Anopheles irenicus, a member of the Anopheles punctulatus group, is geographically restricted to Guadalcanal in the Solomon Islands. Extensive sampling and genetic studies have suggested that an endemic mosquito named Anopheles irenicus resides exclusively in the northern part of Guadalcanal Island (one of the Solomon Islands), along with An. farauti sensu stricto (An. farauti s.s.), An. hinesorum, An. punctulatus and An. koliensis [1,2]. All these mosquitoes are members of the An. punctulatus group, which was originally considered to comprise four closely related species, An. farauti Laveran, An. punctulatus Donitz, An. koliensis Owen and An. clowi Rozeboom & Knight ([3] and references therein). An. farauti s.s. almost always breeds in brackish water, whereas even though An. irenicus shows potential tolerance of brackish water, it is always found in breeding sites containing fresh water [7]
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