SECRET POLLINATORS OF NERINE LATICOMA
As part of a team of researchers from the University of KwaZulu-Natal, last year I went on a mission to the Kalahari to try and find out what was pollinating Tswalu’s annual display of Nerine laticoma. These geophytes hide below ground during the Kalahari’s cold, dry winter, their strap-shaped leaves only emerging in spring when conditions improve. When these beautiful bulb flowers make an appearance en masse at Tswalu, they decorate the otherwise pale summer landscape. In this unique habitat, where rain is scarce and showy flowers occur in their thousands, our team was curious to know what pollinates these special flowers.
As we travelled through the Kalahari our team spotted patches of pink along the road, but had no idea how glorious the display of Nerines was going to be at Tswalu. Added to the prolific display of flowers were thousands of butterflies. Were they the best pollinators? Our first day in the field was spent measuring and observing everything we saw. We thought we knew what to expect from our knowledge of other Nerine species, but we were still pleasantly surprised by the sheer diversity of pollinators attracted to Nerine laticoma. All sorts of creatures, both big and small, visited our study patch of flowering Nerines, which left us wondering which one of these many visitors was the most effective pollinator?
To find out which visitor was doing the best job at pollinating the flowers, we set up camera traps and observed pollinator activity during the day and in the evening. We also collected pollen from the insect visitors we caught in order to put a number to each of their efforts.
What we found was that many of the insects were contributing equally to the pollination of these flowers. Bees, although better at carrying pollen than other insects, were scarce; butterflies, although abundant, didn’t carry much pollen. These differences in pollinator abundance and pollen carrying capacity suggest that different pollinators could be collectively contributing to successful seed production in these flowers.
We also wanted to assess whether the daytime pollinators were more important than those that visited at night, so an experiment was set up to help answer that question. Daytime visitors were excluded from landing on certain flowers and nighttime visitors were excluded from others. We then compared the two different sets of flowers to those that continued to receive visitors at any time. Unfortunately, this experiment didn’t yield very clear answers, but we think that day and night visitors are more or less of equal importance.
Since Nerine species generally tend to have only one or two pollinators, the glorious proliferation of pollinators of this particular species is fascinating and has led to more questions.
Due to the variable annual rainfall, it may be that pollinators in the Kalahari rarely have access to abundant sources of nectar which makes them less picky about which flowers they visit compared to pollinators in other places. Alternatively, Nerine species other than Nerine laticoma may have more specific traits, like a stronger fragrance or brighter colour, attracting similarly specific pollinators. Nerine laticoma may have very general traits, thereby attracting a wider selection of pollinators. However, without further research this will all remain speculation.
So far our field work has shown that these Nerine plants take full advantage of available pollination services, even if it means being a bit ‘promiscuous’ in rewarding insects with nectar. It may be a clever long-term survival strategy, as insect species become further endangered and the effects of climate change accelerate. As these plants probably rely on annual mass flowering events to attract as many pollinators as possible, the importance of this for the production of healthy, genetically diverse seeds for the next generation cannot be underestimated. Habitat destruction and shrinkage is increasingly threatening the survival of pollinators and the plants, like the beautiful Nerine laticoma species, that rely on them.
The following team is currently working on this research project and will co-author the thesis that will arise from the findings from Tswalu:
Prof Steve Johnson, Principal investigator, Dr Carolina Diller, Postdoctoral researcher, Miguel Castañeda-Zárate, PhD candidate, and Genevieve Theron, PhD candidate, all from the University of KwaZulu-Natal, South Africa.
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