Repeated landmass reformation limits diversification in the widespread littoral zone mosquitoAnopheles sundaicussensu lato in theIndo‐OrientalRegion

Abstract

Southeast Asia harbours abundant biodiversity, hypothesized to have been generated by Pliocene and Pleistocene climatic and environmental change. Vicariance between the island of Borneo, the remaining Indonesian archipelago and mainland Southeast Asia caused by elevated sea levels during interglacial periods has been proposed to lead to diversification in the littoral zone mosquito Anopheles (Cellia) sundaicus (Rodenwaldt) sensu lato. To test this biogeographical hypothesis, we inferred the population history and assessed gene flow of A. sundaicus s.l. sampled from 18 populations across its pan-Asian species range, using sequences from mitochondrial cytochrome c oxidase subunit 1 (CO1), the internal transcribed spacer 2 (ITS2) and the mannose phosphate isomerase (Mpi) gene. A hypothesis of ecological speciation for A. sundaicus involving divergent adaptation to brackish and freshwater larval habitats was also previously proposed, based on a deficiency of heterozygotes for Mpi allozyme alleles in sympatry. This hypothesis was not supported by Mpi sequence data, which exhibited no fixed differences between brackish and freshwater larval habitats. Mpi and CO1 supported the presence of up to eight genetically distinct population groupings. Counter to the hypothesis of three allopatric species, divergence was often no greater between Borneo, Sumatra/Java and the Southeast Asian mainland than it was between genetic groupings within these landmasses. An isolation-with-migration (IM) model indicates recurrent gene flow between the current major landmasses. Such gene flow would have been possible during glacial periods when the current landmasses merged, presenting opportunities for dispersal along expanding and contracting coastlines. Consequently, Pleistocene climatic variation has proved a homogenizing, rather than diversifying, force for A. sundaicus diversity.

Anopheles sundaicus complex and the presence of Anopheles epiroticus in Indonesia

“…sundaicus and An. epiroticus, or due to periodic recurrent gene flow between landmasses [23]. This study provides the first definitive evidence for the presence and geographical extent of An.…”

“…The theory that periodic sea-level changes caused by repeated glaciation events may have created secondary isolation barriers (i.e., vicariance) and genetic bottleneck events during the Pleistocene epoch (2.6 million-11,700 mya) has been advanced as a biogeographical hypothesis of population history and gene flow in this region [25]. This hypothesis of ecological and allopatric speciation has been challenged based on analyses that indicates species divergence often appears no greater between than within landmasses, thus providing sufficient and recurrent gene flow during recent geologic periods of Earth [23].…”

“…However, this is contradictory with more current findings based on DNA evidence indicating that An . epiroticus appears confined to mainland Southeast Asia and not present in Indonesia or eastern Malaysia (Borneo) [ 20 , 22 , 23 ]. Form B has been found in sympatry with Form A at inland freshwater sites near Purworejo (south-central Java), and South Tapanuli (northern Sumatra).…”

Molecular forms of Anopheles subpictus and Anopheles sundaicus in the Indian subcontinent

“…3). This molecular form was identical to haplotype 'TK' designated by Zarowiecki et al [57] and referred hereafter as An. sundaicus (TK).…”

Anopheles species diversity and distribution of the malaria vectors of Thailand

“…epiroticus was a common species in coastal areas of eastern and southern Thailand ( Figure 4A, Table S17 in the supplementary material online). Recent work on the Sundaicus Complex showed eight genetic and geographical groupings in the Indo-Oriental region, with evidence for recent gene flow among them [84]. It is apparent that more work is needed on this important species complex involved in malaria transmission along coastal zones.…”