Floral colour change in Randia dumetorum: a cue for visually guided insect visitors?
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1
Indian Institute of Science Education and Research Thiruvananthpuram, Biology, India
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2
Indian Institute of Science Education and Research Pune, Biology, India
Signals are rarely private channels of communication between signaler and receiver. This poses a special challenge for the evolution of signals since they must be attract intended receivers and evade unintended receivers. Flowers signal to pollinators using a suite of visual floral traits such as colour, shape and pattern. In a vast majority of angiosperms, a suite of generalist pollinator species visits flowers. Floral signals are likely to reflect the conflict between using being attractive to pollinators and repelling or evading the attention of unintended receivers. Floral colours serve as indicators of food rewards for many visually guided insects.
We investigated the phenomenon of floral colour change in Randia dumetorum (Family Rubiaceae), a tropical deciduous tree species in the drier parts of the Western Ghats, India. Flowers offer nectar rewards, are visited by a variety of generalist pollinators, and the pollen are sticky and likely specialized for insect pollination. A prominent functional explanation in the literature for the phenomenon of colour change in flowers is the enhanced visual attraction of pollinators. Individual flowers of R. dumetorum are held on the plant for an unusually extended length of time of 6-12 days. The flowers change colour from white when newly open to pale yellow and finally bright yellow over the course of its lifespan. We measured the spectral shift in these three colour stages and estimated their nectar volume and quality. Visitation by insects, mostly bees diurnally and moths nocturnally, was monitored. Nectar rewards and insect visitation were lowest in the bright yellow stage, suggesting that the older bright yellow flowers may be implicated in increasing the overall visual display of the plant to generalist visitors. Experimental manipulations of flower numbers in the different colour stages on a plant appeared to indicate that visitation increased when the floral display size was high, but this may be related to the dominant flower colour. These preliminary results suggest that extended life spans can enhance the long-distance visual attraction of visitors to the plant while pollinators discriminate and visit white and intermediate flowers which were the most rewarding flower colour stages at short-distance.
During the flowering season in March-April 2013, we plan to determine the timing and duration of pollen viability and stigma receptivity of the different colour stages to examine if older bright yellow flowers also contribute to directly to the plant reproductive fitness via fruit/seed set in addition to enhancing visual attractiveness of the plant to insect visitors.
References
Willmer et al. 2009. Current Biology 19, 919–923.
Weiss, M.R., and Lamont, B.B. (1997). Floral color change and insect
pollination: A dynamic relationship. Isr. J. Plant Sci. 45, 185–200.
Briscoe, A.D., and Chittka, L. (2001). The evolution of color vision in
insects. Annu. Rev. Entomol. 46, 471–510.
Giurfa, M., Nun˜ ez, J., Chittka, L., and Menzel, R. (1995). Color preferences
of flower-naı¨ve honeybees. J. Comp. Physiol. A 177, 247–259.
Keywords:
Western Ghats,
Colour vision,
Bee behaviour,
Floral colour,
pollination ecology,
Signalling and communication
Conference:
International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013.
Presentation Type:
Poster presentation preferred
Topic:
Development and evolution
Citation:
Somanathan
H,
Barua
D,
Arulmalar
E and
Parihar
S
(2019). Floral colour change in Randia dumetorum: a cue for visually guided insect visitors?.
Front. Physiol.
Conference Abstract:
International Conference on Invertebrate Vision.
doi: 10.3389/conf.fphys.2013.25.00104
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Received:
28 Feb 2013;
Published Online:
09 Dec 2019.
*
Correspondence:
Dr. Hema Somanathan, Indian Institute of Science Education and Research Thiruvananthpuram, Biology, Trivandrum, Kerala, 695016, India, hsomanathan@iisertvm.ac.in
Dr. Deepak Barua, Indian Institute of Science Education and Research Pune, Biology, Pune, Maharashtra, 411021, India, dbarua@iiserpune.ac.in