Eck Institute for Global Health, Department of Biology, University of Notre Dame, Notre Dame, IN 46556, USA.
J Exp Biol. 2013 Sep 15;216(Pt 18):3433-41. doi: 10.1242/jeb.087189.
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.
耐盐性是传播人类疟疾的按蚊属的一个生态和流行病学意义重大的特征，因为它在决定其栖息地利用和生态分布方面起着关键作用，从而影响其在疟疾传播中的局部贡献。在这里，我们通过量化三种密切相关的隐种和疟疾媒介按蚊属中的耐盐性，为该性状的遗传剖析奠定了基础，这些按蚊种已知在耐盐性方面存在明显差异：专性淡水种 A. gambiae 和 A. coluzzii 以及耐盐性种 A. merus。我们使用 A. gambiae、A. coluzzii 和 A. merus 的多个品系以及 A. merus 和 A. coluzzii 的正反交 F1 后代，在不同盐度下进行了详细的生存比较。此外，我们使用免疫组织化学比较了在淡水或盐水环境中饲养的 A. coluzzii 和 A. merus 直肠中三种离子调节蛋白（Na(+)/K(+)-ATPase、碳酸酐酶和 Na(+)/H(+)-反向转运体）的位置。正如预期的那样，我们发现 A. merus 比 A. gambiae 和 A. coluzzii 更能耐受高盐度。此外，我们发现暴露于 15.85 g NaCl l(-1) 的盐度水平是一个区分剂量，可杀死所有 A. gambiae、A. coluzzii 和 A. coluzzii-A. merus F1 幼虫，但不会对 A. merus 的存活产生负面影响。重要的是，A. merus 对耐盐性的表型表达高度依赖于暴露的发育时间，并且根据免疫组织化学，耐盐性似乎涉及直肠中 Na(+)/K+-ATPase 定位的重大转变，如先前对远缘耐盐种 A. albimanus 的观察结果所示。
