A detailed study of over 50 long-tongued fly species endemic to Southern Africa has shown that species known to science only account for about half of the diversity of this ecologically important pollinator group.
Southern Africa's long-tongued flies (Nemestrinidae) are unique for their exceptionally long proboscises. The most well-known is Moegistorhynchus longirostris with a proboscis that reaches a remarkable 90 to 100mm in length – with a body length of 15 mm, the proboscis is more than five times the length of its body. These long-tongued flies are the only pollinators of many long-tubed flowers such as the critically endangered Hesperantha oligantha, endangered species such as Disa scullyi and the dwarf nerine (Nerine humillis), as well as various Pelargonium, Plectranthus, Gladiolus, Watsonia and Lapeirousia species.
Yet, despite being so charismatic, the family has received little taxonomic attention. The last revision of known southern African nemistrinid species was published more than 90 years ago, and included 44 named species.
In a recent paper, published in the journal Invertebrate Systematics, Dr Genevieve Theron and colleagues estimates that more than half of the South African species in the Nemestrinidae family are currently undescribed. The work formed part of her doctoral research at the Centre for Functional Biodiversity at the University of KwaZulu-Natal, and included contributions from scientists at UKZN, Stellenbosch University and Rhodes University.
Population ecologists use mark-recapture techniques to estimate the population sizes of animals like rhinos. Here, they have a known number of marked animals in a population and by using the ratio of marked to unmarked animals observed during surveys, it is possible to estimate the total population size. Dr Theron used a similar technique to estimate long-tongued fly diversity.
The research team collected 136 specimens from their known range in South Africa, Eswatini and Lesotho. Dr Theron then used DNA sequencing and morphological analysis to show that there were actually at least 58 distinct species, of which only 29 were currently recognised species. The remaining 29 could not be identified and therefore probably represent species that have not yet been described, suggesting that actual fly diversity is double the described diversity.
“We estimate that the total nemestrinid diversity in southern Africa may eventually add up to more than 80 species," she explains.
According to Prof Timo van der Niet, associate professor at the Centre for Functional Biodiversity at UKZN and senior author on the paper, the paper challenges the common perception among the public that most species are known to science.
“This study shows that even in a country like South Africa, with a strong tradition of natural history, much of the invertebrate diversity is likely undescribed. If this is the case for a charismatic group like long-tongued flies, it is likely even more the case for smaller insects," he warns.
Prof Bruce Anderson, an evolutionary biologist in the Department of Botany and Zoology at Stellenbosch University (SU) and co-author, says studies such as this one contribute significantly towards improved estimates of global insect diversity and are important for a better understanding of local ecology and conservation.
“We used to think that there were about 150 plant species that were completely reliant on about nine long-tongue fly species for pollination. If these flies were to disappear, many rare and endangered South African plants would probably go extinct," he explains.
But this study suggests that the ecologically important long-tongue fly species may represent more than nine distinct taxa. Furthermore, many of the undescribed fly species are likely to be involved in intricate plant interactions of their own, expanding their importance well beyond what is currently thought, he adds.
Dr Theron's task for the next three years, as a postdoctoral fellow at the KwaZulu-Natal Museum, will be to identify and describe those 29 unknown species (and many others held in collections all over the world).
The researchers hope that the findings from the study will provide a valuable basis for future conservation strategies for this important pollinator group.
- The paper titled “We don't know half of it: morphological and molecular evidence reveal dramatic underestimation of diversity in a key pollinator group (Nemestrinidae)" was published 5 January 2023 in the journal Invertebrate Systematics.
On the images above, Long-tongue flies must fully insert its proboscis into the flower to obtain a tiny droplet of nectar at the bottom of the tube. In the process pollen is placed on or removed from its head by the long-tubed iris, Lapeirousia anceps (on the left) and the endangered Nerine humillis (on the right). Images: Bruce Anderson and Ethan Newman
Dr Genevieve Theron
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Prof Timo van der Niet
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Prof Bruce Anderson
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