THE birds and the bees do it – and so, Matie scientists have discovered, does the hairy-footed gerbil.
Stellenbosch University of doctoral student Chris Johnson has uncovered what he calls a remarkable relationship between a species of rare flower and a rodent called the hairy-footed gerbil: the rodent pollinates the flower.
The flower, a Redelinghuys pincushion, is known to occur only in the sandveld fynbos between the Swartland towns of Redelinghuys and Aurora – and only on three farms. It is described as “critically rare” in the SA National Botanical Institute’s Red List of Plants.
Johnson said its rarity was largely because of habitat destruction, as most of the natural veld has been destroyed by agriculture.
Johnson’s study began some time ago when he was doing a project that entailed collecting all species of pincushions.
“I found that the Redelinghuys pincushion was incredibly different from other pincushions.”
One of the differences was that the flower’s nectar was unusually viscous. Also, although the nectar was produced at the base of the nectar tube, this pincushion then transported the nectar up to the tip of the petals where it was held in a cup-like structure. This is known to be a unique adaptation to facilitate pollination by rodents.
It was one thing to wonder whether rodents could be the pollinators for this flower, quite another to establish that this was the case.
First step was to catch some rodents in the area and check their fur and faeces for pollen grains. He found the hairy-footed gerbil had pincushion pollen in both. The next step was to see them in action, and to compare the role of rodents as pollinators versus birds and insects. This entailed constructing “cages” around the flowers, three different constructions to exclude the different pollinators.
“It’s pretty easy to keep out the insects, but it’s more difficult to exclude birds and rodents.”
He constructed the cages of chicken wire, some with holes at the top to allow bird pollinators, others with openings at ground level to allow rodent pollinators. Then he spent days sitting and watching.
Sure enough, the little gerbils went through the holes in the cages and supped on the nectar.
Why would a flower evolve to attract rodents to pollinate them rather than rely on birds and insects?
Johnson says the answer could be because birds and bees are already very busy – “heavily utilised” – pollinating other flower species.
“So if all your sources for pollination are already occupied, or if you are not doing very well in attracting birds and bees, then you switch to a new strategy.”
But unlike birds and bees, the gerbils are not as effective in retaining the pollen on their fur, as they often wash their little faces with their paws and shake their fur.
One reason could be that if the plant specialised in attracting the hairy-footed gerbil it ensured that the rodent would move from it to another flower of the same species, whereas a bird or a bee could move on to a completely different species of flower, and so its chance of pollination would be lost.