Abstract
Floral scent is a key mediator in plant-pollinator interactions. However, little is known to what extent intraspecific scent variation is shaped by phenotypic selection, with no information yet in deceptive plants. In this study, we collected inflorescence scent and fruit set of the deceptive moth fly-pollinated Arum maculatum L. (Araceae) from six populations north vs. five populations south of the Alps, accumulating to 233 samples in total, and tested for differences in scent, fruit set, and phenotypic selection on scent across this geographic barrier. We recorded 289 scent compounds, the highest number so far reported in a single plant species. Most of the compounds occurred both north and south of the Alps; however, plants of the different regions emitted different absolute and relative amounts of scent. Fruit set was higher north than south of the Alps, and some, but not all differences in scent could be explained by differential phenotypic selection in northern vs. southern populations. This study is the first to provide evidence that floral scents of a deceptive plant are under phenotypic selection and that phenotypic selection is involved in shaping geographic patterns of floral scent in such plants. The hyperdiverse scent of A. maculatum might result from the imitation of various brood substrates of its pollinators.
Highlights
88% of angiosperms are cross-pollinated by animals (Ollerton et al, 2011) that are attracted to flowers by multifaceted cues (Chittka and Thomson, 2001)
We investigated the floral scent characteristics and fruit set of A. maculatum in six populations north of the Alps vs. five populations south of the Alps and tested for phenotypic selection on scent in the largest and most extensively sampled population in each of the two regions
This study aimed to answer the following: (1) Do scent and fruit sets differ between north vs. south of the Alps, and among populations within regions? (2) Is there phenotypic selection on floral scent? If so, (3) do compounds, under selection differ between northern and southern populations? This study expects to find pronounced population differences in scent both at the inter-regional level and within the southern region, considering the differences in pollinator abundance and diversity between regions and among southern, but not northern, populations (EspĂndola et al, 2011)
Summary
88% of angiosperms are cross-pollinated by animals (Ollerton et al, 2011) that are attracted to flowers by multifaceted cues (Chittka and Thomson, 2001). With more than 2,000 floral volatile organic compounds (VOCs) described (Knudsen et al, 2006; El-Sayed, 2019), and an average of 20â 60 VOCs per species (Knudsen and Gershenzon, 2020), floral scent blends can tremendously vary among species in terms of composition and quantity. In addition to interspecific variation, floral scent is known to vary intraspecifically, both within and among populations (Delle-Vedove et al, 2017). Natural selection on floral scent emission, both on total scent amount and individual scent components, has been shown by analyses of phenotypic selection, correlating scent phenotypes and fitness measures (e.g., Parachnowitsch et al, 2012; Gross et al, 2016; Chapurlat et al, 2019)
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