Ugolini Alberto, Ungherese Giuseppe, Mercatelli Luca, Saer Doumett, Lepri Luciano
Dipartimento di Biologia Evoluzionistica, Via Romana 17, Università di Firenze, Firenze, 50125, Italy.
J Exp Biol. 2009 Mar;212(Pt 6):797-801. doi: 10.1242/jeb.025452.
The role of salinity in the ecophysiology of many intertidal invertebrates has been extensively investigated. Calcium (Ca(2+)), magnesium (Mg(2+)), potassium (K(+)) and sodium (Na(+)) are the major constituents of seawater and it has been demonstrated that sandhoppers tested under the sun in diluted seawater (3.5 per thousand) head seaward, instead of going landward as expected. Therefore, the variation in seawater salinity (from 35 per thousand to 3.5 per thousand) influences their directional choice. This paper investigates the contribution of different cations to the sea-land directional choice of Talitrus saltator (Crustacea, Amphipoda) by the sun compass orientation mechanism. Results of releases carried out in basic seawater selectively deprived of Ca(2+), Mg(2+) or K(+) and containing the same concentration of Na(+) indicate that only the reduction in Ca(2+) concentration affects the capacity of solar orientation. The pH does not influence the directional choice of sandhoppers and nor do small variations in salinity in the range 32-39 per thousand. Moreover, the clear photopositive tendency registered in experiments of phototaxis in Ca(2+)-deprived seawater indicates that the absence of Ca(2+) does not affect the normal functioning of the visual cells. Therefore, our results show that Ca(2+) seawater concentration is important for the correct functioning of one of the principal mechanisms of orientation in supralittoral amphipods and it could affect their survival in the field.
盐度在许多潮间带无脊椎动物生态生理学中的作用已得到广泛研究。钙（Ca(2+)）、镁（Mg(2+)）、钾（K(+)）和钠（Na(+)）是海水的主要成分，并且已经证明，在阳光下于稀释海水（千分之3.5）中测试的跳虫会头朝海，而不是如预期那样朝陆地移动。因此，海水盐度的变化（从千分之35到千分之3.5）会影响它们的方向选择。本文通过太阳罗盘定向机制研究了不同阳离子对盐沼跳虾（甲壳纲，端足目）海陆方向选择的贡献。在选择性去除了Ca(2+)、Mg(2+)或K(+)且含有相同浓度Na(+)的基础海水中进行释放实验的结果表明，只有Ca(2+)浓度的降低会影响太阳定向能力。pH值不会影响跳虫的方向选择，千分之32 - 39范围内的盐度小变化也不会。此外，在去除Ca(2+)的海水中进行趋光性实验时记录到的明显的正趋光倾向表明，Ca(2+)的缺失不会影响视觉细胞的正常功能。因此，我们的结果表明，Ca(2+)海水浓度对于潮上带端足类动物主要定向机制之一的正常运作很重要，并且可能会影响它们在野外的生存。
