Floral scent and pollinator visitation in relation to floral colour morph in the mixed‐mating annual herb Collinsia heterophylla

Josefin A Madjidian,Åsa Lankinen,Mattias C Larsson

doi:10.1111/njb.03025

Josefin A Madjidian, Åsa Lankinen + Show 1 more

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https://doi.org/10.1111/njb.03025

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Abstract

Even though floral scent is of major importance for pollinator attraction, it is less investigated than other floral traits. Previous studies suggest the importance of joint exploration of olfactory and visual floral cues to understand plant–pollinator interactions. We investigated flower scents in Collinsia heterophylla, a bee‐pollinated, annual herb a with mixed‐mating system combining self‐ and outcross‐pollination. In Collinsia, floral size and development variation is related to mating system, ranging from large‐flowered mixed‐mating species to small‐flowered self‐pollinated species. However, to our knowledge, flower scent has not been described in any species in the genus. We also studied whether flower‐emitted volatiles were coupled to presence versus absence of a coloured band on the upper lip within a population in C. heterophylla, and if these colour morphs affected pollinator visitation. We performed headspace collections of volatiles in the greenhouse from potted flowering plants, and compared these to controls in the bud stage. Flower‐specific volatiles were highly dominated by terpenoid compounds typical of bee‐pollinated plants, such as β‐myrcene, (Z)‐ and (E)‐ocimene and sesquiterpenes (E)‐α‐bergamotene and β‐sesquiphellandrene. The aliphatic ester methyl hexanoate was also prominent, together with additional esters, whereas methyl cinnamate constituted the only aromatic compound. Floral colour morphs showed no qualitative difference in volatiles, but the coloured morph produced significantly higher quantities for seven of the 26 individual flower compounds. A field experiment performed within a natural population, using behavioural observations and florescent dyes dusted on the flowers, could not detect any differences in pollinator visitation between colour morphs. We conclude that C. heterophylla flowers emit volatile compounds commonly associated with attraction of their most important pollinators. It would be highly interesting to explore the function of floral scent for pollinator attraction and relate floral scent to mating system variation across Collinsia for a better understanding of pollinator influence on floral evolution.

Highlights

Floral trait variability in the angiosperms is known to be extremely large, and is often believed to be linked to selection exerted by pollinating agents (Van Der Niet et al 2014, FarréArmengol et al 2015, Gervasi and Schiestl 2017) or to other factors
Ten compounds were found in similar amounts in both flowering plants and control plants in the bud stage, and assumed to be general plant odours primarily released from green tissues of C. heterophylla
This study demonstrates that Collinsia heterophylla releases a rich bouquet of defined volatile organic compounds from its flowers

Summary

Introduction

Floral trait variability in the angiosperms is known to be extremely large, and is often believed to be linked to selection exerted by pollinating agents (Van Der Niet et al 2014, FarréArmengol et al 2015, Gervasi and Schiestl 2017) or to other factors (floral antagonists and abiotic factors, Strauss and Whittall 2006, Caruso et al 2018, Friberg et al 2019). Floral traits of significance for plant–pollinator interactions include both visual and olfactory cues, such as large and colourful flowers or inflorescences with scents and rewards, e.g. nectar and pollen (Harder and Johnsson 2009, Parachnowitsch and Manson 2015). It is possible that colour appears more unreliable because of the difference in how humans (that performed the study) and pollinating insects perceive colour variation (Paine et al 2019). Olfactory cues can be perceived very differently by humans and insects, potentially leading to floral scents being overlooked in a species. Floral scents are known to be of importance for pollinator attraction in species that appear scentless or weakly scented to the human nose (Ashman et al 2005, Parachnowitsch et al 2012)

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