Move Over Bees — Ants Please!
(Note: the flower in the image above is not a Smokebush flower)
Humans aren’t the only species feeling vulnerable these days about having all their eggs in one basket.
Here is a stunning example of how intelligent flowers can be in their quest to survive. Edith Cowan University (ECU) in Australia has announced that a group of shrubs located at the biodiversity hotspot Swan Coastal Plain, also known as Kwongan in Western Australia, has successfully evolved to use ants as well as native bees for pollination by overcoming their own antimicrobial defenses. This is a world first.
The trait was discovered by ECU PhD student Nicola Delnevo. While observing these plants, he noted native ants including sugar ants (Camponotus consobrinus), meat ants (Iridomyrmex purpureus) and bull ants (Myrmecia infima) frequently visited, along with a native bee species (Leioproctus conospermi). Delnevo said that ant pollination of plants is incredibly rare because ants secrete an antimicrobial fluid that wards off bacterial and mold-related infections and kills pollen grains.
Ants love nectar, which plants secrete to attract pollinators so they can spread their pollen to reproduce. So, ants have traditionally been considered menaces—pure nectar thieves—whose aggression keeps away other pollinating insects.
Perhaps the tenacity of the ants is attractive to the plants, because this particular group of plants in Western Australia known as the Smokebush family (Conospermum), has adapted and evolved to survive, making pollination changes so they can use ants to their advantage as pollinators, and replace bees.
This 50-second-long video shows some Conospermum species:
After ant contact, the smokebush germination rates were about 80%, or no different to when pollinated by native bees, but in other plant species rates dropped to 10%. This indicates that pollination was not occurring due to fewer ant secretions, as has been found in the other rare cases of ant pollination in dry regions, but that the smokebush species evolved tolerance.
Nearly 88% of wild flower plants reply on insects to disperse their pollen. But environmental issues like land clearing disrupt this process, leaving the flowers more isolated. Without pollination the species will die off.
Delnevo, who is working to conserve the endangered native smokebush (Conospermum undulatum), took fresh pollen from the flowers of several smokebush species and other plants, and different species of native bees and ants back to the lab to run germination assays to investigate their role in pollination. They tested the effect of the antimicrobial secretion from 3 ant species found locally on the flowers of 6 Western Australian plant species. The results were nothing short of startling.
The Conospermum plants adapted the biochemistry of their pollen grains to cope with the antimicrobial properties of the ants. This is the first plant species known to have adapted traits to enable a mutually beneficial relationship with ants. The ants carry a high load of plant-relevant pollen grains, so they are important contributors to smokebush seed dispersal.
Although about 46 examples of ant pollination have been documented around the world, these were due to ants producing less-toxic secretions that allow them to pollinate.
According to Delnevo, these Conospermum plants can’t rely on honeybees for pollination, so ant pollination is very good news for them. The honeybee is imported and is of no use to smokebush plants since these tubular flowers evolved to optimize pollination by native bees. They have no scent and are too narrow for honeybees to wriggle inside to pollinate.
They rely on native insects that carry a suitable pollen load from flower to flower for their own pollination and have co-evolved with a native bee (Leioproctus conospermi) that is a specialist feeder on these flowers. Although this is a mutually beneficial relationship, from an evolutionary point of view it is risky for the plant to rely on just the native bee for pollination.
More research will be conducted on how common ant pollination is in the flora of south-western Australia and how this trait of overcoming ant defenses has evolved in the plants. This revelation just highlights the complexity of ant-flower relationships and indicates that our understanding of these systems is still in its infancy.
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