The Iris Project - Betsy

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Iris atropurpurea, a huge, gorgeous, purple iris, is endemic to the Mediterranean coast of Israel. The remaining populations are scattered among a couple of dozen nature reserves, most of them tiny (less than 2 acres), but a couple of them large (probably 200 acres). These reserves were established specially for protection of the irises, but although they protect the iris plants themselves, they may not be big enough because of a peculiarity about the ecological interactions between the irises and their pollinators.

Unlike most plants, the irises offer no nectar to reward their pollinators for visiting. They do have pollen that several insect species, including honeybees, collect, and these pollen collectors may pollinate the iris flowers occasionally. However, the main pollinators are the males of several species of Eucera bees that don’t collect pollen or nectar; their reward is a warm place to sleep.

The iris flower is constructed in an unusual way such that there are three tunnels into which the Eucera bees crawl for the night. Sometimes there are two or even three bees in a tunnel (Kaitlin once found 10 bees in one flower!), but most flowers have no bees because there are lots more flowers than there are bees. Because the bees spend the night in different flowers on different nights, they end up carrying pollen from one flower to the next. During the day, the bees forage for nectar on other plants, and that is the basis of our main question…”Are the reserves big enough to support a sufficient number of nectar-producing plants to maintain the pollinator population which in turn maintains the irises?” We also asked a secondary question…”Does pollen from farther away result in better seed production?” If a population is very small and pollen is generally transferred only within the population, it may be that the population is becoming inbred. Inbreeding generally results in reduced ability of the population to respond to environmental challenges.

We’ve collected data on irises in more than a dozen populations: number of blooming stems, number of bees sleeping in flowers, the other plant species in flower during the iris bloom, and an estimate of the size of the area the irises cover. To see which other flower species might be important to the Eucera bees, we collected some of the sleepers to see what pollen they’re carrying. We’ll do this by matching the pollen to a labeled pollen reference collection we created for the purpose. In addition, we hand-pollinated at least 1500 iris flowers (each with three separate stigmas to pollinate) with pollen from known distances away from the flower. In another month or so, when the fruits are mature, we’ll harvest the fruits to count seeds. After the seeds are counted, they will be returned to the source population.

This is a collaborative project among lots of folks: my host professor, Amots Dafni; his Master’s student, Yuval Shimrat; a post-doc, Yuval Sapir; a research assistant named Bosmat; Kaitlin and me. All this has been great fun and Kaitlin and I have learned a whole bunch of useful pollination ecology techniques to bring back with us.

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