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Slugs and snails and DNA trails

Date Released: Thu, 13 June 2013 09:30 +0200

The chief curator of Mollusca at the KwaZulu-Natal Museum, Dr Dai Herbert presented an engaging talk on a group of much maligned creatures -slugs and snails- opening up the fascinating world of how he uses DNA analysis to identify and track species.

He was delivering the annual James Duerden lecture recently, held in honour of the Rhodes professor of Zoology and HOD from 1905-1932.

The KwaZulu-Natal Museum has the largest collection of Mollusca in Africa and one of the largest in the Southern hemisphere, but there are also significant collections in the East London and Cape Town museums.

Dr Herbert has published over 70 papers, two books and more than 50 popular articles on molluscs.

“There are 3800 species of Mollusca in southern Africa but this figure is likely an underestimate because new species are still being discovered, especially in the KZN area. Such diversity is similar to that found in fish, amphibians, reptiles, birds and mammals combined,” he said.

He argued that the general public perception of molluscs is threefold: they are considered good to eat, both on a subsistence level (e.g. harvesting mussels and limpets) and as luxury items such as oysters and escargot. They are considered pretty to look at; “collected and made into kitsch tourist curios” and lastly they are seen as “horrible, slimy pests, so the nett result is that we want to kill them.”

“The common European brown garden snail is indeed a pest but generally people are not aware that most pests are in fact introduced species, few of our indigenous molluscs have ever been recorded as doing any harm in the garden,” he said.

Dr Herbert said our alien fauna was not well documented until recently. Together with the Wildlife Society, he initiated an environmental education project for schools called the ‘Snailiens’ Project where data on slugs and snails was gathered to help build up a data base.

In 2010, SANBI published a guide to introduced terrestrial molluscs of South Africa which shows that more than 80% have come from Europe and the Mediterranean, which means that they find the climate in the Cape to be very favourable. There is only one species from Asia, but this likely to change as trade relations with SE Asian countries increases.

“It is one thing to suspect a snail to be an alien, but to identify it to the correct species is much more difficult, especially the smaller species. Bar-coding has helped a great deal in this regard but in order to do this the data base needs to be fully representative.”

In southern Africa, 80% of our indigenous non-marine mollusc species are endemic to the region and 66% endemic to SA itself. Surprisingly, 28% are actually carnivores, “which are definitely allies in the garden as they readily eat the introduced species”.

The largest of these belong to the genus Natalina the cannibal snails that may be over 15 cm long when crawling about mid the 1980s, this family of snails was thought to be restricted to South Africa and Australasia, but in the 1990s it was suggested that they may also occur in Madagascar.

So Dr Herbert travelled to the island to investigate this further. Traversing through wet rainforest in the Andasibe area, they also crossed decimated areas razed of all vegetation, which is burned to make charcoal.

Showing a photo of him and his team wearing raingear and smiling after a long hard day in the field, they had managed to collect the species that they had wanted to find – the putative cannibal snail.  

However, when the specimen was examined in more detail, it was clear that it was in fact a member of another family common on Madagascar. This was also confirmed by analysis of its DNA.  “So now the evidence strongly suggests that cannibal snails do not occur in Madagascar after all,” he added.