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Herbivore‐mediated negative frequency‐dependent selection underlies a trichome dimorphism in nature
Evolution Letters ( IF 5 ) Pub Date : 2020-01-09 , DOI: 10.1002/evl3.157
Jay K. Goldberg 1 , Curtis M. Lively 1 , Sonya R. Sternlieb 2 , Genevieve Pintel 3 , J. Daniel Hare 4 , Michael B. Morrissey 5 , Lynda F. Delph 1
Affiliation  

Negative frequency‐dependent selection (NFDS) has been shown to maintain polymorphism in a diverse array of traits. The action of NFDS has been confirmed through modeling, experimental approaches, and genetic analyses. In this study, we investigated NFDS in the wild using morph‐frequency changes spanning a 20‐year period from over 30 dimorphic populations of Datura wrightii. In these populations, plants either possess glandular (sticky) or non‐glandular (velvety) trichomes, and the ratio of these morphs varies substantially among populations. Our method provided evidence that NFDS, rather than drift or migration, is the primary force maintaining this dimorphism. Most populations that were initially dimorphic remained dimorphic, and the overall mean and variance in morph frequency did not change over time. Furthermore, morph‐frequency differences were not related to geographic distances. Together, these results indicate that neither directional selection, drift, or migration played a substantial role in determining morph frequencies. However, as predicted by negative frequency‐dependent selection, we found that the rare morph tended to increase in frequency, leading to a negative relationship between the change in the frequency of the sticky morph and its initial frequency. In addition, we found that morph‐frequency change over time was significantly correlated with the damage inflicted by two herbivores: Lema daturaphila and Tupiochoris notatus. The latter is a specialist on the sticky morph and damage by this herbivore was greatest when the sticky morph was common. The reverse was true for L. daturaphila, such that damage increased with the frequency of the velvety morph. These findings suggest that these herbivores contribute to balancing selection on the observed trichome dimorphism.

中文翻译:

草食动物介导的负频率依赖性选择是自然毛状体二态性的基础

负频率依赖性选择(NFDS)已被证明可以维持多种性状的多态性。NFDS的作用已通过建模,实验方法和遗传分析得到证实。在这项研究中,我们调查了野生曼陀罗(Datura wrightii) 30多个双态种群在20年间的形态频率变化,研究了野生型NFDS。。在这些种群中,植物要么具有腺毛(粘性),要么具有非腺毛(绒毛),并且这些形态的比率在种群之间存在很大差异。我们的方法提供了证据,表明NFDS而不是漂移或迁移是维持这种二态性的主要力量。大多数最初是双态的种群仍然是双态的,并且总体的平均和形态频率的方差不会随时间变化。此外,词素频率差异与地理距离无关。总之,这些结果表明,方向选择,漂移或迁移都没有在确定变体频率中发挥重要作用。但是,正如通过负频率依赖的选择所预测的那样,我们发现稀有的变体倾向于增加频率,导致粘性变体的频率变化与其初始频率之间存在负相关关系。此外,我们发现,随时间变化的词素频率变化与两种食草动物造成的损害显着相关:勒马daturaphilaTupiochoris notatus。后者是粘性变体的专家,当粘性变体很常见时,这种草食动物的伤害最大。对于曼陀罗氏杆菌,情况恰恰相反,因此损害随着天鹅绒状变体的频率而增加。这些发现表明,这些草食动物有助于在观察到的毛状体二态性上平衡选择。
更新日期:2020-01-09
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