PDF(Pubmed)
Abstract：
Insects frequently associate with intracellular microbial symbionts (endosymbionts) that enhance their ability to cope with challenging environmental conditions. Endosymbioses with cuticle-enhancing microbes have been reported in several beetle families. However, the ecological relevance of these associations has seldom been demonstrated, particularly in the context of dry environments where high cuticle quality can reduce water loss. Thus, we investigated how cuticle-enhancing symbionts of the rice-weevil, Sitophilus oryzae contribute to desiccation resistance. We exposed symbiotic and symbiont-free (aposymbiotic) beetles to long-term stressful (47% RH) or relaxed (60% RH) humidity conditions and measured population growth. We found that symbiont presence benefits host fitness especially under dry conditions, enabling symbiotic beetles to increase their population size by over 33-fold within 3 months, while aposymbiotic beetles fail to increase in numbers beyond the starting population in the same conditions. To understand the mechanisms underlying this drastic effect, we compared beetle size and body water content and found that endosymbionts confer bigger body size and higher body water content. While chemical analyses revealed no significant differences in composition and quantity of cuticular hydrocarbons after long-term exposure to desiccation stress, symbiotic beetles lost water at a proportionally slower rate than did their aposymbiotic counterparts. We posit that the desiccation resistance and higher fitness observed in symbiotic beetles under dry conditions is due to their symbiont-enhanced thicker cuticle, which provides protection against cuticular transpiration. Thus, we demonstrate that the cuticle enhancing symbiosis of Sitophilus oryzae confers a fitness benefit under drought stress, an ecologically relevant condition for grain pest beetles. This benefit likely extends to many other systems where symbiont-mediated cuticle synthesis has been identified, including taxa spanning beetles and ants that occupy different ecological niches.
摘要：
昆虫经常与细胞内微生物共生体（内共生体）联系在一起，从而增强了它们应对挑战性环境条件的能力。已经在几个甲虫家族中报道了与角质层增强微生物的内共生。然而,这些协会的生态相关性很少得到证明，特别是在干燥环境中，高角质层质量可以减少水分流失。因此，我们研究了水稻-象鼻虫的角质层增强共生体，米丝菌有助于抗干燥。我们将共生和无共生（共生生物）甲虫暴露于长期压力（47％RH）或放松（60％RH）的湿度条件下，并测量了种群的增长。我们发现共生体的存在有利于宿主的健康，特别是在干燥条件下，使共生甲虫在3个月内将其种群数量增加33倍以上，而在相同条件下，类动物的数量无法超过起始种群。为了理解这种剧烈效应背后的机制，我们比较了甲虫的大小和体内含水量，发现内共生体赋予更大的体型和更高的体内含水量。虽然化学分析显示，长期暴露于干燥胁迫后，表皮碳氢化合物的组成和数量没有显着差异，共生甲虫的失水速度比共生甲虫慢。我们认为，在干燥条件下的共生甲虫中观察到的抗干燥性和更高的适应性是由于它们的共生体增强的较厚的角质层，提供了防止角质层蒸腾的保护。因此，我们证明，在干旱胁迫下，麦角菌的角质层增强共生具有健身益处，谷物害虫甲虫的生态相关条件。这种好处可能扩展到许多其他系统，在这些系统中，已经确定了共生体介导的表皮合成，包括跨越甲虫和蚂蚁的类群，它们占据不同的生态位。
