Thursday, September 29, 2016

Key pollinators in the Arctic

Dryas flowers. Credit: Mikko Tiusanen
Global change is causing drastic changes in the pollinator communities of the Arctic. While arctic flowers are visited by a wide range of insects, flies in family Muscidae have been proposed as a pollinator group of particular importance.

Researchers from Finland, Sweden, Denmark and Canada teamed up to record what insects visited flowers of the evergreen dwarf shrubs of the genus Dryas. They chose 15 sites in northeast Greenland, then returned to score the seed set of these flowers to determine if it actually has been pollinated. The results were clear: the more of the house fly -like relatives of the family Muscidae were present, the more flowers set seed. Among these flies, a single spcies best explained seed set, Spilogona sanctipauli.

To record the insects visiting a plant, the researchers invented self-trapping flowers. They cut sticky traps for greenhouses into the shape of natural looking flowers and hid those among the real ones. This saved them from the alternative which would have been to stare at the flowers for a long time to record flies that land on the flower. DNA barcoding was utilized to identify all their victims (some 8000 of them).

While exciting, the current findings also raise concerns. The very same flies which were found to be so important for Dryas species are now declining in this region. Part of this decline may be due to an increasing temporal mismatch between the occurrence of the flies and their flower resources. To test this hypothesis, the researchers recorded if insects visited flowers early versus late in the season, i.e., during peak flowering or later, when there are less flowers in bloom. They found that many insects visited after peak flowering. 

This quite worrying as with the warming of the arctic, flowering time will shift to earlier times, whereas insects seem to be able to adapt to that. Hence, we actually see the timing of avens sliding into the early summer when less flies are there to service the flowers. For the plant, this means less pollinators, and for the flies, this means less food. If this rift expands, then this may threaten arctic pollination.

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