Abstract
BackgroundAnopheles subpictus sensu lato, a widespread malaria vector in Asia, is reportedly composed of four sibling species A - D. Mosquitoes morphologically identified as belonging to the Subpictus complex were collected from different locations near the east coast of Sri Lanka, and specific ribosomal DNA sequences determined to validate their taxonomic status.MethodsAnopheles subpictus s.l. larvae and blood-fed adults were collected from different locations in the Eastern province and their sibling species status was determined based on published morphological characteristics. DNA sequences of the D3 domain of 28 S ribosomal DNA (rDNA) and the internal transcribed spacer -2 (ITS-2) of mosquitoes morphologically identified as An. subpictus sibling species A, B, C and D were determined.ResultsPhylogenetic analysis based on D3 domain of rDNA resulted in two clades: one clade with mosquitoes identified as An. subpictus species A, C, D and some mosquitoes identified as species B, and another clade with a majority of mosquitoes identified as species B with D3 sequences that were identical to Anopheles sundaicus cytotype D. Analysis of ITS-2 sequences confirmed a close relationship between a majority of mosquitoes identified as An. subpictus B with members of the An. sundaicus complex and others identified as An. subpictus B with An. subpictus s.l.ConclusionsThe study suggests that published morphological characteristics are not specific enough to identify some members of the Subpictus complex, particularly species B. The sequences of the ITS-2 and D3 domain of rDNA suggest that a majority that were identified morphologically as An. subpictus species B in the east coast of Sri Lanka, and some identified elsewhere in SE Asia as An. subpictus s.l., are in fact members of the Sundaicus complex based on genetic similarity to An. sundaicus s.l. In view of the well-known ability of An. sundaicus s.l. to breed in brackish and fresh water and its proven ability to transmit malaria in coastal areas of many Southeast Asian countries, the present findings have significant implications for malaria control in Sri Lanka and neighbouring countries.
Highlights
Anopheles subpictus sensu lato, a widespread malaria vector in Asia, is reportedly composed of four sibling species A - D
Identification of An. subpictus sibling species and morphological variations in sibling species B A total of 246 blood-fed An. subpictus s.l. were collected from the four field sites in this study and based on number of ridges on the laid eggs, 2, 152, 11 and 6 females were tentatively characterized as belonging to species A, B, C and D respectively
Phylogenetic analysis based on D3 ribosomal RNA (rRNA) Construction of a phylogenetic tree based on D3 ribosomal DNA (rDNA) sequences (Additional file 1) resulted in three stable clades
Summary
A widespread malaria vector in Asia, is reportedly composed of four sibling species A - D. Anopheles culicifacies species E is the major vector of malaria in Sri Lanka [1]. The four members of this complex have been described as possessing characteristic paracentric fixed inversions on the X-chromosome viz. Stage-specific morphometric characteristics e.g. the number of ridges in egg floats, larval mesothoracic seta 4, pupal setae and ornamentation of the palpi of adult females, have been reported to be useful for differentiating An. subpictus sibling species in field studies [7]. Initial studies based on a single inversion in the X chromosome suggested the presence of An. subpictus species A and B in Sri Lanka [8]. The bio-ecological differences between members of the An. subpictus complex in Sri Lanka [1] and elsewhere [5] have been recently reviewed
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