Mitochondrial genome sequences reveal deep divergences among Anopheles punctulatus sibling species in Papua New Guinea

Abstract

Background: Members of the Anopheles punctulatus group (AP group) are the primary vectors of human malaria in Papua New Guinea. The AP group includes 13 sibling species, most of them morphologically indistinguishable. Understanding why only certain species are able to transmit malaria requires a better comprehension of their evolutionary history. In particular, understanding relationships and divergence times among Anopheles species may enable assessing how malaria-related traits (e.g. blood feeding behaviours, vector competence) have evolved.

Methods: DNA sequences of 14 mitochondrial (mt) genomes from five AP sibling species and two species of the Anopheles dirus complex of Southeast Asia were sequenced. DNA sequences from all concatenated protein coding genes (10,770 bp) were then analysed using a Bayesian approach to reconstruct phylogenetic relationships and date the divergence of the AP sibling species.

Results: Phylogenetic reconstruction using the concatenated DNA sequence of all mitochondrial protein coding genes indicates that the ancestors of the AP group arrived in Papua New Guinea 25 to 54 million years ago and rapidly diverged to form the current sibling species.

Conclusion: Through evaluation of newly described mt genome sequences, this study has revealed a divergence among members of the AP group in Papua New Guinea that would significantly predate the arrival of humans in this region, 50 thousand years ago. The divergence observed among the mtDNA sequences studied here may have resulted from reproductive isolation during historical changes in sea-level through glacial minima and maxima. This leads to a hypothesis that the AP sibling species have evolved independently for potentially thousands of generations. This suggests that the evolution of many phenotypes, such as insecticide resistance will arise independently in each of the AP sibling species studied here.

Figure 1

Support of the Anopheles phylogeny using the concatenated DNA sequences of all mitochondrial protein coding genes. The values on the tree correspond to the posterior probabilities of each node.

Figure 2

Phylogenetic tree of Anopheles using the concatenated DNA sequences of all mitochondrial protein coding genes. The bars illustrate the 95% credibility intervals for the divergence times and the numbers in brackets above each node display the actual values in millions of years. The panel on the right indicates the geographic distribution of the samples: the green bar indicates mosquitoes from South America (SA), red from North America (NA), grey from Africa (AF), blue from Southeast Asian (SEA) and orange from Papua New Guinea (PNG).

Figure 3

Distribution of all sampled divergence times for the MRCA of the An. albitarsis (green) and An. punctulatus (red) groups obtained using BEAST (after burn-in)