Herbivores and plant defences affect selection on plant reproductive traits more strongly than pollinators

Abstract

Pollinators and herbivores can both affect the evolutionary diversification of plant reproductive traits. However, plant defences frequently alter antagonistic and mutualistic interactions, and therefore, variation in plant defences may alter patterns of herbivore‐ and pollinator‐mediated selection on plant traits. We tested this hypothesis by conducting a common garden field experiment using 50 clonal genotypes of white clover (Trifolium repens) that varied in a Mendelian‐inherited chemical antiherbivore defence—the production of hydrogen cyanide (HCN). To evaluate whether plant defences alter herbivore‐ and/or pollinator‐mediated selection, we factorially crossed chemical defence (25 cyanogenic and 25 acyanogenic genotypes), herbivore damage (herbivore suppression) and pollination (hand pollination). We found that herbivores weakened selection for increased inflorescence production, suggesting that large displays are costly in the presence of herbivores. In addition, herbivores weakened selection on flower size but only among acyanogenic plants, suggesting that plant defences reduce the strength of herbivore‐mediated selection. Pollinators did not independently affect selection on any trait, although pollinators weakened selection for later flowering among cyanogenic plants. Overall, cyanogenic plant defences consistently increased the strength of positive directional selection on reproductive traits. Herbivores and pollinators both strengthened and weakened the strength of selection on reproductive traits, although herbivores imposed ~2.7× stronger selection than pollinators across all traits. Contrary to the view that pollinators are the most important agents of selection on reproductive traits, our data show that selection on reproductive traits is driven primarily by variation in herbivory and plant defences in this system.

Predicting the strength of urban-rural clines in a Mendelian polymorphism along a latitudinal gradient

“…Given that cyanogenesis functions as an antiherbivore defense (Santangelo et al. 2018b; Thompson and Johnson 2016; Dirzo and Harper 1982a), some clines could be explained by differential herbivory among urban and rural populations if urbanization reduces herbivore populations (Raupp et al. 2010; Miles et al.…”

“…HCN is known to deter feeding by herbivores (Santangelo et al. 2018b; Angseesing and Angseesing 1973; Saucy et al. 1999; Thompson and Johnson 2016; Dirzo and Harper 1982b), and gradients in the presence or intensity of herbivore pressure have been hypothesized to drive latitudinal and elevational clines in cyanogenesis in white clover's native and introduced ranges (Kooyers and Olsen 2013), due to the cost of producing HCN in the absence of herbivores (Kakes 1989).…”

Analisis Molekular dan Karakteristik Hidrogen Sianida (HCN)

“…Hidrogen sianida (7; 10; 26; 27; 32; [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] atau biasa disebut formic anammonide, asam hidrosianat, atau asam sianida yang merupakan suatu monobasa dari asam Lewisboron lemah yang dapat digunakan sebagai penyepuhan emas,dan pembuatan pewarna prussian blue (blau), (108) . Asam sianida akan larut dalam air (109; 110) , senyawa ini didalam air akanmembentuk ion CNdan ion H + .Senyawa dengan rumus kimia HCN cairan tak bewarna dan sangat beracun.…”

Unclear Intentions: Eavesdropping in Microbial and Plant Systems

“…Similarly, the dominant compound in the scent of flowers of the Neotropical orchid Dichaea pendula attracted bee pollinators and florivorous weevils (Nunes et al, 2016). These eavesdropping herbivores are a major source of selection on floral signals (Hanley et al, 2009;Kessler et al, 2013;Johnson et al, 2015;Santangelo et al, 2018). In a common garden, Santangelo et al (2018) demonstrated that herbivores imposed stronger selection on inflorescence production and size than pollinators.…”

“…These eavesdropping herbivores are a major source of selection on floral signals (Hanley et al, 2009;Kessler et al, 2013;Johnson et al, 2015;Santangelo et al, 2018). In a common garden, Santangelo et al (2018) demonstrated that herbivores imposed stronger selection on inflorescence production and size than pollinators. A recent meta-analysis of phenotypic selection analyses came to a similar conclusion, finding that herbivore-mediated selection on floral traits was stronger than pollinator-mediated selection in twothirds of cases (Johnson et al, 2015).…”