Engl Tobias, Schmidt Thorsten H P, Kanyile Sthandiwe Nomthandazo, Klebsch Dagmar
Evolutionary Ecology, Institute of Organismic and Molecular Evolution, Johannes Gutenberg-University, 55128 Mainz, Germany.
Research Group Insect Symbiosis, Max-Planck-Institute for Chemical Ecology, 07745 Jena, Germany.
Insects. 2020 Oct 20;11(10):717. doi: 10.3390/insects11100717.
Animals engage in a plethora of mutualistic interactions with microorganisms that can confer various benefits to their host but can also incur context-dependent costs. The sawtoothed grain beetle harbors nutritional, intracellular Bacteroidetes bacteria that supplement precursors for the cuticle synthesis and thereby enhance desiccation resistance of its host. Experimental elimination of the symbiont impairs cuticle formation and reduces fitness under desiccation stress but does not disrupt the host's life cycle. For this study, we first demonstrated that symbiont populations showed the strongest growth at the end of metamorphosis and then declined continuously in males, but not in females. The symbiont loss neither impacted the development time until adulthood nor adult mortality or lifespan. Furthermore, lifetime reproduction was not influenced by the symbiont presence. However, symbiotic females started to reproduce almost two weeks later than aposymbiotic ones. Thus, symbiont presence incurs a metabolic and context-dependent fitness cost to females, probably due to a nutrient allocation trade-off between symbiont growth and sexual maturation. The symbiosis thereby represents an experimentally amenable system to study eco-evolutionary dynamics under variable selection pressures.
动物与微生物之间存在大量互利共生的相互作用，这些微生物能给宿主带来各种益处，但也可能产生取决于环境的成本。锯谷盗体内携带着营养型的胞内拟杆菌，这些细菌为表皮合成补充前体物质，从而增强宿主的抗干燥能力。实验性地去除共生菌会损害表皮形成，并降低在干燥胁迫下的适应性，但不会破坏宿主的生命周期。在本研究中，我们首先证明共生菌种群在变态发育末期生长最为旺盛，之后在雄性体内持续减少，但在雌性体内并非如此。共生菌的缺失既不影响发育至成年的时间，也不影响成虫的死亡率或寿命。此外，终生繁殖不受共生菌存在与否的影响。然而，有共生菌的雌性比无菌共生的雌性开始繁殖的时间晚了近两周。因此，共生菌的存在给雌性带来了代谢和取决于环境的适应性成本，这可能是由于共生菌生长和性成熟之间的营养分配权衡所致。因此，这种共生关系代表了一个便于实验研究可变选择压力下生态进化动态的系统。
