Geographic variation in cone volatiles and pollinators in the thermogenic African cycad Encephalartos ghellinckii Lem.
Heat and odour production can have profound effects on pollination in cycads. It is therefore expected that these traits would co-vary geographically with pollinator assemblages. Such intraspecific variation, may lead to the evolution of pollination ecotypes, which can be an early stage of pollinator-mediated speciation. We measured cone temperatures using miniature temperature data loggers and examined the composition of cone volatile odours using headspace sampling and analysis with gas chromatography-mass spectrometry in four populations spanning the range of the African cycad Encephalartos ghellinckii. Pollinator assemblages were also investigated in three populations. Male and female cones were thermogenic at pollen shed and receptive stages, respectively, but patterns of thermogenesis did not vary among populations. Scent emissions from cones in populations in the Drakensberg Mountains were characterised by cis-β-ocimene, β-myrcene and (3E)-1,3-octadiene, while camphene and α-pinene were characteristic of scent emissions from cones in populations closer to the coast. These differences in volatile blends corresponded with differences in insect assemblages. These results confirm intraspecific variation in volatile emissions of E. ghellinckii and support the predictions that intraspecific variation in volatile emissions will be associated with shifts in pollinator assemblages. While further work needs to be done to test for local adaptation in this system, this preliminary evidence is consistent with the formation of pollination ecotypes in the E. ghellinckii species complex.
['Suinyuy|T N|TN|http://orcid.org/0000-0001-5136-6852', 'Johnson|S D|SD|']
D000818:Animals D044822:Biodiversity D035264:Flowers D008401:Gas Chromatography-Mass Spectrometry D007313:Insecta D009812:Odorants D054817:Pollination D013019:South Africa D022722:Thermogenesis D055549:Volatile Organic Compounds D032481:Zamiaceae
Encephalartos ghellinckii intraspecific variation pollination ecotypes speciation