Bees might be the most well-known pollinators, but researchers have found that common white-footed ants are the best pollinators of a rare evergreen tree in the southern Western Ghats.
Syzygium occidentale is a small, wild jamun tree that grows mostly along the banks of the River Periyar in Kerala. It is categorised as ‘vulnerable’ by the International Union for the Conservation of Nature. The survival of such a species is crucial, depending on the fruits it produces, which is only possible if pollinators fertilize its flowers first.
To find out which animals — birds, bats, wasps or bees — are its most important pollinators, researchers from institutes including Kerala’s Central University studied the flowering patterns and timings of around 50 trees that grow along the River Periyar. Visiting the trees daily for three separate flowering seasons between 2010 and 2015, the team quantified the timing of flowering, the volume of nectar available in flowers, the animals that visit the flowers and the frequency of their visits.
They found that 10 species — including sunbirds and cockroaches — visited the large, pleasant-smelling white flowers that bloomed between December and April. Among these, seven species (including bees and two ant species) frequented the flowers the most.
The team then conducted experiments to determine which species was the most effective pollinator. They permitted only one type of pollinator (white-footed ants, weaver ants, night-flying insects, birds or day-flying insects such as bees) to visit freshly bloomed flowers for around two days by using combinations of net bags and glue to keep out other animals during this time. They also tested for the efficacy of wind pollination by using mosquito nets to eliminate all pollinators from visiting the flowers.
After each experiment, the researchers dissected the fruit to confirm the presence of healthy, embryo-carrying seeds: proof that a particular animal group had successfully pollinated the flower. Their results, published in Arthropod-Plant Interactions, shows that ants — especially white-footed ants, the most frequent visitors to the flowers day and night — were the most efficient pollinators of the tree.
This is an interesting finding because ants are usually depicted as poor pollinators. Unlike the white-footed ants, many flower-visiting ant species (such as the weaver ants in this study) attack other pollinators and thus prevent them from pollinating the plant, said co-authors P. A. Sinu from the Central University of Kerala and K.R. Shivanna (Ashoka Trust for Research in Ecology and the Environment).
“This is an interesting and unusual finding,” agreed Dr. Smitha Krishnan, a pollination ecologist and Post Doctoral Fellow at ATREE, by email.
This means that ants could also be possible pollinators of other plant species including crops — which we might have overlooked in the past, she added.
Ants have gained “sufficient notoriety” as “pollen/nectar robbers” or opportunists waiting to prey on the flower-visiting insects, wrote entomologist Dr. Priyadarshan Dharma Rajan (Senior Fellow, ATREE) by email. Further, antibacterial secretions produced by ants can reduce pollen viability, necessitating special adaptations by plants, he said.
“However, this study opens the window to explore more ant-pollinated plant systems in the tropics,” he wrote.