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Variations in salinity tolerance of malaria vectors of the Anopheles subpictus complex in Sri Lanka and the implications for malaria transmission.

Surendran SN, Jude PJ, Ramasamy R - Parasit Vectors (2011)

Bottom Line: Specimens with morphological characteristics of all four Indian An. subpictus sibling species were found in Sri Lanka.Larvae of An. subpictus B/An. sundaicus were found in inland and coastal sites, including a lagoon, with salinity varying from 0 to 30 ppt.The results suggest that An. subpictus species B/An. sundaicus breed in fresh, brackish and nearly saline water while An. subpictus species C and D do so in fresh and less brackish waters in Sri Lanka, as in India.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Zoology, Faculty of Science, University of Jaffna, Jaffna, Sri Lanka. noble@jfn.ac.lk

ABSTRACT

Background: Anopheles subpictus sensu lato, a widespread vector of malaria in Asia, is reportedly composed of four sibling species A-D based on distinct cytogenetic and morphological characteristics. However An. subpictus species B specimens in Sri Lanka are termed An. subpictus B/ An. sundaicus because of recent genetic data. Differences in salinity tolerance and coastal/inland prevalence of An. subpictus sibling species that were not previously established in Sri Lanka are presented here.

Results: Specimens with morphological characteristics of all four Indian An. subpictus sibling species were found in Sri Lanka. Sibling species A, C and D tended to be predominant in inland, and An. subpictus species B/An. sundaicus, in coastal localities. Sibling species C was predominant in both adult and larval inland collections. Larvae of An. subpictus B/An. sundaicus were found in inland and coastal sites, including a lagoon, with salinity varying from 0 to 30 ppt. An. subpictus sibling species A, C and D larvae were present in water of salinity between 0 to 4 ppt. An. subpictus C, D and An. subpictus B/An. sundaicus larvae showed compatible differential salinity tolerance in laboratory tests. The first instar larvae of An. subpictus B/An. sundaicus showed 100% survival up to 15 ppt in comparison to species C and D where the corresponding values were 3 ppt and 6 ppt respectively. However all third instar larvae of An. subpictus B/An. sundaicus survived up to 30 ppt salinity whereas An. subpictus C and D tolerated up to 4 ppt and 8 ppt salinity respectively.

Conclusions: The results suggest that An. subpictus species B/An. sundaicus breed in fresh, brackish and nearly saline water while An. subpictus species C and D do so in fresh and less brackish waters in Sri Lanka, as in India. Because of the established role of An. sundaicus s.l. and An. subpictus s.l. as malaria vectors, the findings indicate a need for greater monitoring of brackish water breeding habitats in Asia. Tolerance to 15 ppt salinity may also constitute a simple method for differentiating An. subpictus B/An. sundaicus larvae from those of An. subpictus species C and D in field studies.

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Photograph of the Kallady lagoon site (30 ppt salinity) where An. subpictus species B/An. sundaicus larvae were collected in association with marine algae >15 m into the lagoon.
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Figure 2: Photograph of the Kallady lagoon site (30 ppt salinity) where An. subpictus species B/An. sundaicus larvae were collected in association with marine algae >15 m into the lagoon.

Mentions: In parallel studies, 1930 larvae could be classified by examination of seta 4M and the results showed that larvae with characteristics of all four An. subpictus sibling species were present in both inland and coastal locations [Table 2]. However there was a tendency for larvae with characteristics of An. subpictus B/An. sundaicus to predominate in coastal localities [Table 2]. Larvae with characteristics of An. subpictus B/An. sundaicus were collected from both inland and coastal locations with salinity levels varying from 0 to 30 ppt (fresh, brackish and saline water are defined as having <0.5, 0.5 to 30 and >30 ppt salt respectively). Furthermore they were the only larvae collected from sites where the salinity was >4 ppt. Larvae with characteristics of An. subpictus A, C and D were only collected from sites where the salinity was ≤ 4ppt. Collection of large numbers of An. subpictus A, C and D larvae in coastal areas was associated with the rainy season (October to January) during which the salinity levels of the water bodies decreased due to dilution by rain water [Table 2]. All the breeding sites, except that in Muthur, were exposed to direct sunlight. All sites, except those in Palaiyutru and Thonikkal, had vegetation such as rooted and un-rooted floating plants (e.g. Hydrilla spp, Nelimbium spp, Salvinea spp and Eichornia spp) and green algae. An. subpictus B/An. sundaicus larvae were also collected ~ 15 m from land in the shallow waters of a lagoon at Kallady where the salinity was 30 ppt. The larvae at this site were found associated with marine algae and plants and exposed to direct sunlight [Figure 2]. The pH and dissolved oxygen concentrations of the breeding sites where the larvae were collected varied from 7.1 to 8.4 and 1.1 to 2.6 mg/L respectively.


Variations in salinity tolerance of malaria vectors of the Anopheles subpictus complex in Sri Lanka and the implications for malaria transmission.

Surendran SN, Jude PJ, Ramasamy R - Parasit Vectors (2011)

Photograph of the Kallady lagoon site (30 ppt salinity) where An. subpictus species B/An. sundaicus larvae were collected in association with marine algae >15 m into the lagoon.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3141743&req=5

Figure 2: Photograph of the Kallady lagoon site (30 ppt salinity) where An. subpictus species B/An. sundaicus larvae were collected in association with marine algae >15 m into the lagoon.
Mentions: In parallel studies, 1930 larvae could be classified by examination of seta 4M and the results showed that larvae with characteristics of all four An. subpictus sibling species were present in both inland and coastal locations [Table 2]. However there was a tendency for larvae with characteristics of An. subpictus B/An. sundaicus to predominate in coastal localities [Table 2]. Larvae with characteristics of An. subpictus B/An. sundaicus were collected from both inland and coastal locations with salinity levels varying from 0 to 30 ppt (fresh, brackish and saline water are defined as having <0.5, 0.5 to 30 and >30 ppt salt respectively). Furthermore they were the only larvae collected from sites where the salinity was >4 ppt. Larvae with characteristics of An. subpictus A, C and D were only collected from sites where the salinity was ≤ 4ppt. Collection of large numbers of An. subpictus A, C and D larvae in coastal areas was associated with the rainy season (October to January) during which the salinity levels of the water bodies decreased due to dilution by rain water [Table 2]. All the breeding sites, except that in Muthur, were exposed to direct sunlight. All sites, except those in Palaiyutru and Thonikkal, had vegetation such as rooted and un-rooted floating plants (e.g. Hydrilla spp, Nelimbium spp, Salvinea spp and Eichornia spp) and green algae. An. subpictus B/An. sundaicus larvae were also collected ~ 15 m from land in the shallow waters of a lagoon at Kallady where the salinity was 30 ppt. The larvae at this site were found associated with marine algae and plants and exposed to direct sunlight [Figure 2]. The pH and dissolved oxygen concentrations of the breeding sites where the larvae were collected varied from 7.1 to 8.4 and 1.1 to 2.6 mg/L respectively.

Bottom Line: Specimens with morphological characteristics of all four Indian An. subpictus sibling species were found in Sri Lanka.Larvae of An. subpictus B/An. sundaicus were found in inland and coastal sites, including a lagoon, with salinity varying from 0 to 30 ppt.The results suggest that An. subpictus species B/An. sundaicus breed in fresh, brackish and nearly saline water while An. subpictus species C and D do so in fresh and less brackish waters in Sri Lanka, as in India.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Zoology, Faculty of Science, University of Jaffna, Jaffna, Sri Lanka. noble@jfn.ac.lk

ABSTRACT

Background: Anopheles subpictus sensu lato, a widespread vector of malaria in Asia, is reportedly composed of four sibling species A-D based on distinct cytogenetic and morphological characteristics. However An. subpictus species B specimens in Sri Lanka are termed An. subpictus B/ An. sundaicus because of recent genetic data. Differences in salinity tolerance and coastal/inland prevalence of An. subpictus sibling species that were not previously established in Sri Lanka are presented here.

Results: Specimens with morphological characteristics of all four Indian An. subpictus sibling species were found in Sri Lanka. Sibling species A, C and D tended to be predominant in inland, and An. subpictus species B/An. sundaicus, in coastal localities. Sibling species C was predominant in both adult and larval inland collections. Larvae of An. subpictus B/An. sundaicus were found in inland and coastal sites, including a lagoon, with salinity varying from 0 to 30 ppt. An. subpictus sibling species A, C and D larvae were present in water of salinity between 0 to 4 ppt. An. subpictus C, D and An. subpictus B/An. sundaicus larvae showed compatible differential salinity tolerance in laboratory tests. The first instar larvae of An. subpictus B/An. sundaicus showed 100% survival up to 15 ppt in comparison to species C and D where the corresponding values were 3 ppt and 6 ppt respectively. However all third instar larvae of An. subpictus B/An. sundaicus survived up to 30 ppt salinity whereas An. subpictus C and D tolerated up to 4 ppt and 8 ppt salinity respectively.

Conclusions: The results suggest that An. subpictus species B/An. sundaicus breed in fresh, brackish and nearly saline water while An. subpictus species C and D do so in fresh and less brackish waters in Sri Lanka, as in India. Because of the established role of An. sundaicus s.l. and An. subpictus s.l. as malaria vectors, the findings indicate a need for greater monitoring of brackish water breeding habitats in Asia. Tolerance to 15 ppt salinity may also constitute a simple method for differentiating An. subpictus B/An. sundaicus larvae from those of An. subpictus species C and D in field studies.

Show MeSH
Related in: MedlinePlus