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Open Access Research article

Genetic diversity in two sibling species of the Anopheles punctulatus group of mosquitoes on Guadalcanal in the Solomon Islands

Arif U Hasan1, Setsuo Suguri1*, Chigusa Fujimoto12, Rodney L Itaki1, Masakazu Harada1, Masato Kawabata3, Hugo Bugoro4 and Bobogare Albino4

Author Affiliations

1 Department of International Medical Zoology, Faculty of Medicine, Kagawa University, 1750-1, Ikenobe, Miki, Kita, Kagawa, 761-0793, Japan

2 Department of Medical Technology, Faculty of Health Sciences, Kagawa Prefectural College of Health Sciences, Hara, Mure, Takamatsu, Kagawa, 761-0123, Japan

3 International Center for Medical Research, School of Medicine, Kobe University, Kusunoki, Chuo, Kobe, 650-0017, Japan

4 Solomon Islands Medical Training and Research Institute, Honiara, the Solomon Islands

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BMC Evolutionary Biology 2008, 8:318  doi:10.1186/1471-2148-8-318

Published: 24 November 2008

Abstract

Background

The 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.

Results

An. 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).

Conclusion

These 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.