Does getting defensive get you anywhere?—Seasonal balancing selection, temperature, and parasitoids shape real‐world, protective endosymbiont dynamics in the pea aphid
Does getting defensive get you anywhere?—Seasonal balancing selection, temperature, and parasitoids shape real‐world, protective endosymbiont dynamics in the pea aphid
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DOI：
10.1111/mec.15906
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发表时间：
2021-04
影响因子：
4.9
通讯作者：
Andrew H. Smith;M. O’connor;B. Deal;Coleman Kotzer;Amanda Lee;Barrett Wagner;Jonah Joffe;
中科院分区：
文献类型：
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作者：
Andrew H. Smith;M. O’connor;B. Deal;Coleman Kotzer;Amanda Lee;Barrett Wagner;Jonah Joffe;
在大多数昆虫物种中发现了中等流行率的兼性、可遗传的内共生体，在其宿主抵御环境压力方面发挥着频繁的作用。集中在汉密尔顿防御，一种常见的细菌内共生体的蚜虫，我们测试的假设，这种压力施加季节性平衡选择，形成广泛的感染多态性。在我们研究的豌豆蚜虫（Acyrthosiphon pisum）种群中，在为期6个月的纵向调查中，Hamiltonella频率范围为23.2%至68.1%。快速的峰值和下降往往是一致的跨领域，我们估计，选择系数汉密尔顿感染蚜虫改变了这个领域的季节。先前的实验室研究表明，抗寄生虫防御的主要Hamiltonella的好处，和寄生虫的情况下的成本。虽然先前的实地研究表明，这些力量有时可以在季节性平衡选择的制度中作为平衡物，但我们目前的调查显示，寄生蜂和汉密尔顿氏菌的流行之间没有显着的关系。田间笼实验提供了一些解释：拟寄生虫驱动适度的10%的提升汉密尔顿频率，这将是很难检测到的控制条件下。他们还表明，在寄生蜂排斥下，汉密尔顿氏菌并不总是昂贵的，这与另一个预测相矛盾。相反，我们的纵向调查-和两个越冬研究-表明温度是汉密尔顿患病率的最强预测因子。与之前的一些实验室发现相匹配，这表明与寄生无关的热敏感成本和收益可以塑造汉密尔顿氏菌的动力学。这些结果增加了越来越多的证据表明，在多化性生物的快速，季节性适应，这表明这种适应可以通过遗传细菌内共生体的不同影响介导。
Facultative, heritable endosymbionts are found at intermediate prevalence within most insect species, playing frequent roles in their hosts’ defence against environmental pressures. Focusing on Hamiltonella defensa, a common bacterial endosymbiont of aphids, we tested the hypothesis that such pressures impose seasonal balancing selection, shaping a widespread infection polymorphism. In our studied pea aphid (Acyrthosiphon pisum) population, Hamiltonella frequencies ranged from 23.2% to 68.1% across a six‐month longitudinal survey. Rapid spikes and declines were often consistent across fields, and we estimated that selection coefficients for Hamiltonella‐infected aphids changed sign within this field season. Prior laboratory research suggested antiparasitoid defence as the major Hamiltonella benefit, and costs under parasitoid absence. While a prior field study suggested these forces can sometimes act as counter‐weights in a regime of seasonal balancing selection, our present survey showed no significant relationship between parasitoid wasps and Hamiltonella prevalence. Field cage experiments provided some explanation: parasitoids drove modest ~10% boosts to Hamiltonella frequencies that would be hard to detect under less controlled conditions. They also showed that Hamiltonella was not always costly under parasitoid exclusion, contradicting another prediction. Instead, our longitudinal survey – and two overwintering studies – showed temperature to be the strongest predictor of Hamiltonella prevalence. Matching some prior lab discoveries, this suggested that thermally sensitive costs and benefits, unrelated to parasitism, can shape Hamiltonella dynamics. These results add to a growing body of evidence for rapid, seasonal adaptation in multivoltine organisms, suggesting that such adaptation can be mediated through the diverse impacts of heritable bacterial endosymbionts.