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Dose and developmental responses of Anopheles merus larvae to salinity.

ABSTRACT: Saltwater tolerance is a trait that carries both ecological and epidemiological significance for Anopheles mosquitoes that transmit human malaria, as it plays a key role in determining their habitat use and ecological distribution, and thus their local contribution to malaria transmission. Here, we lay the groundwork for genetic dissection of this trait by quantifying saltwater tolerance in three closely related cryptic species and malaria vectors from the Afrotropical Anopheles gambiae complex that are known to differ starkly in their tolerance to salinity: the obligate freshwater species A. gambiae and A. coluzzii, and the saltwater-tolerant species A. merus. We performed detailed comparisons of survivorship under varying salinities, using multiple strains of A. gambiae, A. coluzzii and A. merus, as well as F1 progeny from reciprocal crosses of A. merus and A. coluzzii. Additionally, using immunohistochemistry, we compared the location of three ion regulatory proteins (Na(+)/K(+)-ATPase, carbonic anhydrase and Na(+)/H(+)-antiporter) in the recta of A. coluzzii and A. merus reared in freshwater or saline water. As expected, we found that A. merus survives exposure to high salinities better than A. gambiae and A. coluzzii. Further, we found that exposure to a salinity level of 15.85 g NaCl l(-1) is a discriminating dose that kills all A. gambiae, A. coluzzii and A. coluzzii-A. merus F1 larvae, but does not negatively impact the survival of A. merus. Importantly, phenotypic expression of saltwater tolerance by A. merus is highly dependent upon the developmental time of exposure, and based on immunohistochemistry, salt tolerance appears to involve a major shift in Na(+)/K+-ATPase localization in the rectum, as observed previously for the distantly related saline-tolerant species A. albimanus.

SUBMITTER: White BJ

PROVIDER: S-EPMC3749906 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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Dose and developmental responses of Anopheles merus larvae to salinity.

White Bradley J BJ Kundert Peter N PN Turissini David A DA Van Ekeris Leslie L Linser Paul J PJ Besansky Nora J NJ

The Journal of experimental biology 20130901 Pt 18

Saltwater tolerance is a trait that carries both ecological and epidemiological significance for Anopheles mosquitoes that transmit human malaria, as it plays a key role in determining their habitat use and ecological distribution, and thus their local contribution to malaria transmission. Here, we lay the groundwork for genetic dissection of this trait by quantifying saltwater tolerance in three closely related cryptic species and malaria vectors from the Afrotropical Anopheles gambiae complex ...[more]

PMID: 23966587

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Project description:BACKGROUND:Anopheles multicolor is known to be present in the arid areas of Africa north of the Sahara Desert, especially in oases. To date, its presence in Mauritania has not been reported. Here, we present the first record of its presence in Nouakchott, the capital of Mauritania. The larvae of An. multicolor, together with those of An. arabiensis, the major malaria vector in the city, were found thriving in highly saline surface water collections. METHODS:Entomological surveys were carried out during 2016-2017 in Nouakchott. Mosquito larval habitats were investigated through larval surveys while indoor resting culicid fauna were collected using hand-held aspirator. Physicochemical parameters of the larval habitats were measured on-site, at the time mosquitoes were collected. Larvae and pupae were reared to adults in the insectaries. Morphological and polymerase chain reaction (PCR)-based methods were used to identify newly emerged adults. Batches of fourth-instar larvae were used to assess salinity tolerance by exposing them to increasing concentrations of NaCl, and mortality was monitored throughout development. RESULTS:Morphological and molecular results confirmed that the specimens were An. multicolor and An. arabiensis. Sequences of 24 An. multicolor adult mosquitoes showed 100% nucleotide identity with the published sequences of An. multicolor from Iran. The physicochemical analysis of the water from the two larval habitats revealed highly saline conditions, with NaCl content ranging between 16.8 and 28.9 g/l (i.e. between c.50-80% seawater). Anopheles multicolor and An. arabiensis fourth-instar larvae survival rates at 17.5 g/l NaCl were 86.5% and 75%, respectively. Anopheles arabiensis larvae showed variable levels of salt tolerance according to the larval habitat. Adult An. multicolor specimens were collected resting indoor at low frequency (0.7%) compared to the other culicid mosquitoes. CONCLUSIONS:To the best of our knowledge, this paper is the first report of An. multicolor in Mauritania, extending the known distributional range of the species to the south, as well as to the west. Highly salt-tolerant populations of An. arabiensis and An. multicolor were observed. Because salt-water collections are widespread in Nouakchott, the relevance of these findings for the dynamics and epidemiology of malaria transmission needs to be assessed.

Project description:BackgroundPredation of aquatic immature stages has been identified as a major evolutionary force driving habitat segregation and niche partitioning in the malaria mosquito Anopheles gambiae sensu stricto in the humid savannahs of Burkina Faso, West Africa. Here, we explored behavioural responses to the presence of a predator in wild populations of the M and S molecular forms of An. gambiae that typically breed in permanent (e.g., rice field paddies) and temporary (e.g., road ruts) water collections.MethodsLarvae used in these experiments were obtained from eggs laid by wild female An. gambiae collected from two localities in south-western Burkina Faso during the 2008 rainy season. Single larvae were observed in an experimental arena, and behavioural traits were recorded and quantified a) in the absence of a predator and b) in the presence of a widespread mosquito predator, the backswimmer Anisops jaczewskii. Differences in the proportion of time allocated to each behaviour were assessed using Principal Component Analysis and Multivariate Analysis of Variance.ResultsThe behaviour of M and S form larvae was found to differ significantly; although both forms mainly foraged at the water surface, spending 60-90% of their time filtering water at the surface or along the wall of the container, M form larvae spent on average significantly more time browsing at the bottom of the container than S form larvae (4.5 vs. 1.3% of their overall time, respectively; P < 0.05). In the presence of a predator, larvae of both forms modified their behaviour, spending significantly more time resting along the container wall (P < 0.001). This change in behaviour was at least twice as great in the M form (from 38.6 to 66.6% of the time at the wall in the absence and presence of the predator, respectively) than in the S form (from 48.3 to 64.1%). Thrashing at the water surface exposed larvae to a significantly greater risk of predation by the notonectid (P < 0.01), whereas predation occurred significantly less often when larvae were at the container wall (P < 0.05) and might reflect predator vigilance.ConclusionsBehavioural differences between larvae of the M and S form of An. gambiae in response to an acute predation risk is likely to be a reflection of different trade-offs between foraging and predator vigilance that might be of adaptive value in contrasting aquatic ecosystems. Future studies should explore the relevance of these findings under the wide range of natural settings where both forms co-exist in Africa.

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Dose and developmental responses of Anopheles merus larvae to salinity.

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Dose and developmental responses of Anopheles merus larvae to salinity.

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