Physical defences wear you down: progressive and irreversible impacts of silica on insect herbivores
Physical defences wear you down: progressive and irreversible impacts of silica on insect herbivores
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DOI：
10.1111/j.1365-2656.2008.01472.x
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发表时间：
2009-01-01
影响因子：
4.8
通讯作者：
Hartley, Sue E.
中科院分区：
文献类型：
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作者：
Massey, Fergus P.;Hartley, Sue E.
草叶中的二氧化硅可以作为防御脊椎动物和无脊椎食草动物的屏障。二氧化硅影响食草动物性能的机制尚未很好地表征。在这里，我们将一种食草昆虫Spodoptera（夜蛾）暴露在高硅饮食中，并测试了二氧化硅作为防御的两种机制。首先，二氧化硅降低了树叶的消化率，其次，二氧化硅会导致昆虫下颌骨磨损，这两者都可能影响食草动物的表现。二氧化硅降低了免虫将摄入的食物转化为体重的效率和从食物中吸收的氮量，导致昆虫生长速度降低。草食动物如何有效利用消化食物（ECD）的测量不受二氧化硅的影响。即使短期暴露于富含二氧化硅的食物中，这些影响也会发生，但随着暴露时间的延长，它们也会显著增加，并且对后期幼虫的影响大于早期幼虫。这似乎是由于二氧化硅随着暴露时间的延长而逐渐产生的影响，这表明食草动物不能适应二氧化硅防御，也不能随着年龄的增长而对二氧化硅产生耐受性。暴露在富含二氧化硅的饮食中导致美国人下颌骨磨损增加。这种影响发生得非常快，发生在一个月龄内，进一步降低了取食效率和生长速度。这些对昆虫生长和取食效率的影响是不可逆转的，在食草动物改变饮食后仍然存在。高达三分之一的残余影响可以用以前富含二氧化硅的饮食造成的下颌磨损程度来解释。随着暴露时间的延长，二氧化硅对免虫幼虫的影响是渐进的，即使换一种不同的饮食也无法弥补。因此，食草动物不容易适应诸如二氧化硅之类的物理防御，这表明这种防御将对食草动物的适应性产生重大影响。
Silica in the leaves of grasses can act as a defence against both vertebrate and invertebrate herbivores. The mechanisms by which silica affects herbivore performance are not well characterized. Here we expose an insect herbivore Spodoptera exempta to high-silica diets and test two mechanisms by which silica has been proposed to act as a defence. First, that silica reduces the digestibility of leaves and second, that silica causes wear to insect mandibles, both of which could potentially impact on herbivore performance.Silica reduced the efficiency with which S. exempta converted ingested food to body mass and the amount of nitrogen absorbed from their food, leading to reduced insect growth rates. The measure of how efficiently herbivores utilize digested food (ECD) was unaffected by silica.These effects occurred even with short-term exposure to silica-rich diets, but they also increased markedly with the duration of exposure and affected late instars more than early instar larvae. This appears to be due to the progressive impacts of silica with longer exposure times and suggests that herbivores cannot adapt to silica defences, nor do they develop a tolerance for silica with age.Exposure to silica-rich diets caused increased mandible wear in S. exempta. This effect was extremely rapid, occurring within a single instar, further reducing feeding efficiency and growth rates. These effects on insect growth and feeding efficiency are nonreversible, persisting after the herbivore has switched diets. Up to a third of this residual impact can be explained by the degree of mandible wear caused by previous silica-rich diets.The impacts of silica on S. exempta larvae were progressive with exposure time and could not be compensated for, even by switching to a different diet. Thus, herbivores cannot easily adapt to physical defences such as silica, suggesting this defence will have major implications for herbivore fitness.