Nectar guides are markings or patterns seen inflowers of someangiosperm species, that guidepollinators to theirrewards. These markings may appear as lines, spots, or "blotches".[1] Such patterns are also known as "pollen guides" and "honey guides", though some authorities argue for the abandonment of such terms in favour offloral guides (see, for example, Dinkel & Lunau[2]).
Nectar guides serve as aninterspecific signal that the flower contains a reward. Rewards commonly take the form ofnectar,pollen, or both; however, plants may also produce oil,[3] resins,[4]scents,[5] or waxes. Pollinator visitation can select for various floral traits, including nectar guides, through a process calledpollinator-mediated selection. For example, nectar guides are thought to increase pollinator foraging efficiency by reducing handling time.[6] These guides may also decreasenectar robbing, which leads more pollen to be transferred and ultimately increasesplant fitness.[7]
Images ofMeadow buttercup (Ranunculus acris) under visible light (left), ultraviolet light (center) and infrared (right)
Nectar guides are sometimes visible to humans; for instance, theDalmation toadflax (Linaria genistifolia) has yellow flowers with orange nectar guides.[8] However, in some plants, such as themeadow buttercup (pictured to the right), they are visible only when viewed inultravioletlight. Under ultraviolet, the flowers have a darker center, where the nectaries are located, and often specific patterns upon the petals as well. This is believed to make the flowers more attractive topollinators such ashoney bees and otherinsects that can see ultraviolet light.This page on butterflies shows an animated comparison ofblack-eyed Susan (Rudbeckia hirta) flowers in visible and UV light.[9]
The ultraviolet color, invisible to humans, has been referred to asbee violet, and mixtures of greenish (yellow) wavelengths (roughly 540 nm[10]) with ultraviolet are calledbee purple by analogy withpurple in human vision.[11]
^Free, JB.: "Effect of Flower Shapes and Nectar Guides on the Behaviour of Foraging Honeybees".Behaviour Volume 37, Issue 3–4, January 1970, Pages 269–285
^Dinkel T., Lunau K.: "How drone flies (Eristalis tenax L., Syrphidae, Diptera) use floral guides to locate food sources".Journal of Insect Physiology Volume 47, Issue 10, September 2001, Pages 1111–1118
^Buchmann, SL.: "The ecology of oil flowers and their bees".Annual Review of Ecology and Systematics Volume 18, Issue 1, 2000, Pages 343–370
^Reis Mariza G.; de Faria, AD.; Bittrich, V; do Carmo, M.; Amaral E.; Marsaioli, AJ. "The Chemistry of Flower Rewards".Journal of the Brazilian Chemical Society, Volume 11, Issue 6, 2000, Pages 600–608,
^Teichert, Holger; "Pollination biology of cantharophilous and melittophilous Annonaceae and Cyclanthaceae in French Guiana"; Doctoral dissertation at University of Ulm, 2008
^ Hansen, DM.; Van der Niet, T.; Johnson, SD: "Floral signposts: testing the Significance of visual ‘nectar guides’ for pollinator behaviour and plant fitness".Proceedings of the Royal Society B: Biological Sciences, Volume 279, Issue 1729, 2011, Pages 634–639
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