The scents of summer

Amy L. Parachnowitsch Plant Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden 75236. email: Summer is always a busy time—especially for those who do their research outside. As the chill of the mornings harkens the coming of fall and the fruits of this year’s research are harvested, I find myself sitting at my desk once again and reflecting on what has passed this season. Both my research and my focus have been drawn more and more to the world of floral scent. Many papers have peaked my interest in the last few months and I think it is an exciting time to be studying floral scent. Hopefully we’ll be able to share a few of our own discoveries soon but here’s a brief overview of some of the recent papers on floral scent.

Rafflesia cantleyi (Rafflesiaceae) a parasitic plant with oviposition site mimicry

Rafflesia cantleyi (Rafflesiaceae) a parasitic plant with oviposition site mimicry. Image by Suk-Ling Wee (University Kebangsaan Malaysia)

Most recently, Jurgens et al have published an analysis of oviposition site mimicking flowers. These flowers include carrion, rotting plant and feces mimics, which often have particular structures that can physically resemble the model as well as scents that can boarder on the repulsive to humans. Jürgens et al show that, in general, these oviposition mimics have converged on producing similar scents (mainly sulfur compounds) and these scents are divergent from other pollination systems. The hypothesis that scent is a key trait in oviposition site mimicry is not new. However, the authors were able to show the generality of these patterns by taking a phylogenic approach that included a wide range of species across many plant families. Their work is certainly a step forward in our understanding of this special pollination system. It will be interesting to see whether the general approach could be used to understand scent in other pollination systems as well. Some system specific papers are also pushing our understanding of floral volatiles forward. Friberg et al have found incredible scent diversity in the Lithophragma-Greya moth system. First used as a stepping point to understanding how geography may influence co-evolution, this system looks like it may also provide some clues to the evolution of floral scents. The diversity of scent found throughout the range and among closely related species is truly remarkable. It will be very interesting to see whether there is a functional role and/or evolutionary significance to the variation. Two other papers explore the issue of local adaptation of floral scents in more detail. Breitkopf et al found scent differentiation and pollinator preferences suggesting local adaptation of orchids to contrasting pollinators. However, there was no genetic differentiation to support divergence at genome level. In a contrasting paper, Chartier et al found no local adaptation in scents of two Arum species, despite pollinator differences. When transplanted, both species trapped the local fauna, likely due to the similarity of their scents. And to remind us that not everything is general in pollination biology, a paper by Maia et al describes the scents involved in a scarab beetle-pollinated plant, Taccarum ulei (Araceae). They find two unusual scents make up the majority of the floral volatiles and are attractive to the beetles.

Image by Amy L. Parachnowitsch

Image by Amy L. Parachnowitsch

For those reflecting back before the summer and looking for a broad perspective on floral volatiles, three recent reviews provide a diversity of viewpoints on the subject. Dudareva et al overviews the biosynthesis, function and engineering of floral scent. This is a good summary of floral volatile biosynthesis and function with a focus on agricultural systems. In particular they outline some of the coming challenges of applying knowledge of the function of floral scent to crops. Taking a more evolutionary approach, Schiestl and Johnson discuss the role of pollinators in shaping floral scent evolution in the broader context of floral signals as a whole. They argue that by understanding pollinators we can better understand how flowers have evolved to exploit them. They also provide compelling examples of how considering floral signals from the pollinators view can provide further understanding of floral convergence. To complete the trio, Farré-Armengol et al address the potential conflict of attracting mutualists but deterring antagonists with floral scent. Furthermore, they take a very broad approach and compare olfactory and visual cues, discuss the functions of patterns of scent emission, as well as how global change may effect floral volatiles. All of the reviews point out what we know and where data are lacking. Thus, taken together these three reviews are a good way to assess where the field is and where it might be going. So indeed, it is an exciting time to be studying floral scents. Now, time to reflect on our own system and the results from the summer.

Breitkopf H, Schlüter PM, Xu S, Schiestl FP, Cozzolino S and Scopece G. 2013. Pollinator shifts between Ophrys sphegodes populations: might adaptation to different pollinators drive population divergence? Journal of Evolutionary Biology:n/a-n/a.

Chartier M, Pélozuelo L, Buatois B, Bessière J-M and Gibernau M. 2013. Geographical variations of odour and pollinators, and test for local adaptation by reciprocal transplant of two European Arum species. Functional Ecology DOI: 10.1111/1365-2435.12122

Dudareva N, Klempien A, Muhlemann JK and I Kaplan. 2013. Biosynthesis, function and metabolic engineering of plant volatile organic compounds. New Phytologist 198:16-32.

Farré-Armengol G, Filella I, Llusia J and Peñuelas J. 2013. Floral volatile organic compounds: Between attraction and deterrence of visitors under global change. Perspectives in Plant Ecology, Evolution and Systematics 15:56-67.

Friberg M, Schwind C, Raguso RA and Thompson JN. 2013. Extreme divergence in floral scent among woodland star species (Lithophragma spp.) pollinated by floral parasites. Annals of Botany 111:539-550.

Jürgens A, Wee SL, Shuttleworth A and Johnson SD. 2013. Chemical mimicry of insect oviposition sites: a global analysis of convergence in angiosperms. Ecology Letters.

Maia ACD, Gibernau M, Dötterl S, Navarro DM dAF, Seifert K, Müller T and Schlindwein C. 2013. The floral scent of Taccarum ulei (Araceae): Attraction of scarab beetle pollinators to an unusual aliphatic acyloin. Phytochemistry 93:71-78.

Schiestl FP and Johnson SD. 2013. Pollinator-mediated evolution of floral signals. Trends in Ecology Evolution 28:307-315.

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