Hot n’ cold
Top image: The Svalbard poppy (Papaver dahlianum) – here in the white version. Photo: UNIS.
Svalbard plants have precious little time to grow and reproduce during the short and cold summer season. Survival strategies include color, as colorful flowers are believed to be warmer and be more attractive to insects to secure pollination. But how come is 48 % of the Svalbard flora white? A PhD project aims at finding the answer.
18 October 2010
Text: Eva Therese Jenssen
Flower colors are usually explained in connection to color-sensitive bees, i.e. the more colorful a flower, the more likely it will attract bees that will help in the pollination process. This explanation is challenged in Svalbard, where there are no bees, and almost half of the flower species are white.
One theory as to the benefit of color is that they absorb heat from the sun more efficiently, causing the center of the flower to heat up. A warmer center means that the seeds mature faster – which is important in the High Arctic where there is precious little time for the flora to reproduce before the snow comes. However, again the paradox is that such a large portion of the Svalbard flowers are white.
And to throw in one more complexing factor in the equation: some Svalbard species have two colors, such as the Svalbard poppy (Papaver dahlianum) which is found in both yellow (ca. 25 %) and white colors (ca. 75 %).
Lorna Little, PhD student at University of Otago (New Zealand) and UNIS, wants to investigate the reproductive differences between colors – do colored flowers attract more insects, increasing chance of cross pollination and enhanced genetic diversity? Or does color impact on seed maturation, speeding it up in a polar environment?
Her Svalbard research concentrates on the Svalbard poppy. Research completed in Northern Greenland showed that the yellow poppy was about 1,5 degree C warmer in the flower center than the white poppy. Then why are two-thirds of the Svalbard poppies white?
– One explanation is that producing colors is energy consuming for the flowers, and in a polar climate the flowers need to be energy efficient. One should then think that all High Arctic plants would be white in order to conserve energy. But it is not so, says Lorna.
And she wants to find out why the Svalbard poppy have two colors.
– I want to find out what the reproductive benefit of being colored is – the color morph species are an ideal situation in which to investigate this. There is an evolutionary reason, these species originated from the mainland, and there hasn’t been enough time (10 000 years) to lose color if it’s not beneficial. That’s why I am looking at reproductive benefits of being colored, more than evolutionary history, Lorna explains.
Color makes you hotter?
For the past three months she has worked in Svalbard. Her in-field laboratory this summer has been up on the Gruve 7 Mountain. There she has constantly checked on 100 Svalbard poppies. Forty of them (20 yellow and 20 white flowers) have been covered in shower caps, to avoid insects interfering with the pollination process and force the flowers to do the job themselves. Another 40 poppies (20 of each color) have had their anthers removed, as to ensure cross pollination. The last 20 flowers have been the control group, with no interference.
The insects’ attraction for colors has been tested by placing colored cups filled with salt water and counting the amount of insects getting trapped in the cups. She has also measured the heat inside the flowers with thermal image cameras.
Who’s hot – and not
Preliminary results do not show a convincing difference in the color temperature in the center of the yellow and white poppies.
– On the petals, where insects potentially bask, there could be a difference with yellow being slightly warmer. But this is only a preliminary indication, further analysis must be done to conclude, Lorna says.
In total she caught 1300 insects and the insect test showed that flies preferred the yellow cups placed in the sunshine, over all other colors and yellow in the shade.
– What’s interesting with this experiment is that it also showed high numbers of a flying midge species in the red cups, regardless of whether the cups where placed in the sunshine or in the shade, Lorna says.
Are there differences in mature seeds between the poppies doing the job themselves and the ones that were aided by insects?
– Not statistically as yet. The bagged flowers were prevented from being heliotropic, so seed production was affected by me rather than self pollination. But it looks like there might be, potentially, a small difference between colors in some treatments, but this remains to be proven, Lorna explains.
Lorna will now conclude the field work in Svalbard and head south to do similar investigations on Gentiana antarctica, and megaherb species in Campbell Island, south of her native New Zealand.
Hopefully her investigations will give us an answer on who’s hot – and who’s not, and how that relates to survival strategies of polar flowers.