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Few people living in or even visiting certain parts of sub-Sahara Africa (Senegal - 140 N to South Africa - 300 S) can fail to notice a unique group of its terrestrial malacofauna: the giant African snails (Achatinidae). The colourful shells and giant size of some species attracted both professional and amateur malacologists and conchologists in the first half of the 20th century. But apart from Bequaert (1950) and Mead (1950), most studies were initiated as simple inventories. Much of the information is therefore scattered as anecdotal comments in the literature.

Taxonomic status

Even their diversity is uncertain. It is not agreed how many species of giant African snails live in what habitats and in which countries. Africa is unexplored malacologically, so the occurrence, exact distribution, abundance and preferred habitat are unknown for most species. Their taxonomy needs to be reviewed since their extensive shell and body colour variation both continuous or discontinuous have often been overlooked or underestimated in early reports. At present, there is insufficient information on their soft anatomy to form satisfactory definitions of the various species. Perhaps even conclusions drawn from the study of their anterior genital anatomy should be regarded as tentative since taxonomic revisions are inevitably recommended as new information is obtained (e.g. Mead, 1979; 1988; 1991; 1995). A number of species remain undescribed and are usually mentioned in passing.

Bruggen (1986) estimated that there were 33 genera of 200 species in the Achatinidae.Of these, 8 genera comprising 55 species qualified as giant African snails (adult shell length > 8 cm). The two main genera are Achatina and Archachatina. These are thought to reach their peak of diversity in the forest zones of West Africa (Parkinson et al., 1987). On the basis of shell features, Bequeart (1950) estimated the possible number of Achatina subgenera alone to be 8 with 65-80 species. Because the shell is generally capable of modification in response to subtle environmental differences there may be a lot of synonymy, with ecotypes of the same species being given different names. This situation is compounded by the observation that some species with different anterior genital anatomy possess the same conchological features or vice-versa (Mead, 1979).

Ecology

Sub-Saharan Africa, the habitat of giant African snails, presents a wide variety of terrestrial habitats which undoubtedly has influenced snail diversity. ìTropical forestî may be dry bush valley, hot sub-tropical bush, warm coastal forest, seasonal forest, thorn bush, montane forest or plantation forest. In countries where snails are eaten, they may be collected in one part but sold and eaten in another. There is a small international snail trade in the West African sub-region. Inadvertent ignorance of any of the above may lead to incorrect records on geographical locations of giant African snails deposited in Natural History Museums. There are no proper geological records of Africa, so re-surveys to monitor stability and change in land snail populations are difficult to interpret (e.g. Tattersfield, 1998). Moreover, the distribution of the species has not been static. Climatic changes and human activities (intensive agriculture, urban growth and pollution) continue to modify distribution patterns. Generally, the total area of suitable habitats is shrinking due to changes in land use and climate.

Some species of giant African snails often turn up outside their hitherto recognised geographical range (e.g. Reid, 1991) and it becomes necessary to revise their distribution pattern. Such has been the case with Achatina fulica. Bequaert (1950) concluded that the ancestral home of A. fulica was East Africa from where it was introduced to Mauritius not long before 1800 From there it was deliberately taken to India and liberated in Calcutta in 1847. From India it has spread to most southeast Asian countries. In West Africa, A. fulica was first reported in Cote d'lvoire (Winter, 1988). Although nobody knows when and how it appeared in Ghana, it is a common sight in the rainy season.

Research potential

The need for correct taxonomy, proper records on general ecology and geographical distribution of giant African snails cannot be over-emphasised and not just for academic interest. The French escargot market, for instance, requires that giant African snails are correctly identified and labelled "achatines". In West Africa, giant Afrian snails suffer selective human predation both between and within species since it is claimed that some species and varieties are tastier than others. Different species therefore attract different prices and customers like to identify the live snails (usually by their shell) before they purchase them. However, recently a farming community in Ghana misidentified Limicolaria sp. as Achatina fulica on the basis of shell characters. By the time the farmers realised they were not the delicacy they had hoped for, the snail population had reached pest proportions and destroyed a lot of maize, cassava and vegetables. Research, therefore, into a suite of morphometric discriminants that may be used in differentiating the various species of giant African snails would prove invaluable.

Giant African snails provide excellent materials for research into the interactions of ecology and genetics because of their extensive shell and body polymorphism. Their polymorphism provides opportunities to investigate evolutionary events in natural populations and gain some understanding of selective pressures influencing the maintenance of variability in a population.

A look into the future


In parts of West Africa where giant African snails are eaten, the source of supply is still collection from the wild, and the ever-decreasing numbers and diminishing size gathered by snail collectors during hunting have given rise for concern. Most snail hunters and collectors are worried about the future of their activity and have expressed a desire to manage snail hunting in a sustainable way. But what is actually needed is commercial farming to supply snails to meet the shortfall between demand and supply collected from the wild in the rainy season. Various laboratories would then be needed to carry out investigations to offer support to the venture as research based industry. Meanwhile basic research would have to answer fundamental questions such as:

a. What species/subspecies can be distinguished?
b. Where do the various taxa occur?
c. What are the general distribution patterns?
d. What are the phylogenetic relationships of the taxa?

In the short-term, detailed information regarding origin and experimental progress on specimens of giant African snails in various laboratories especially Europe, may have to be provided. Planned research on national/continental collections with the backing of university and/or national museums may settle a lot of pertinent issues about the snails.
Current political and economic situations in most African countries may hamper research generally. However, in the long term any researcher(s) determined to brave the mitigating circumstances and challenges could obtain invaluable information for malacology.

References

  1. Bequaert, J. C. 1950. Bulletin, Museum of Comparative Zoology Harvard 105,1-216.
  2. Bruggen, A. C. van (1986) Revue Zoologie Africaine 100, 29-45
  3. Mead, A. R. 1950. Bulletin. Museum of Comparative Zoology Harvard 105, 219-291
  4. Mead, A. R. 1979. Malacologia 18,133-138.
  5. Mead, A. R. 1988. Joumal of Molluscan Studies 54, 363-365.
  6. Mead, A. R. 1991. Proceedings of the 10th Intemational Malacological Congress,Tubingen 1989
    (C. Meier Brook, Ed) 549-553.
  7. Mead, A. R. 1995 Journal of Molluscan Studies 61, 257-273.
  8. Parkinson, B., Hemmen, J. & Groh, K. 1987. Tropical landshells of the world. Wiesbaden Verlag Christa Hemmen, West Germany. 279pp.
  9. Reid, J. C. 1991. Proceedings of the 10th Intemational Malacological Congress, Tubingen 1989
    (C. Meier Brook, Ed) 303-305.
  10. Tattersfield, P. 1998. Journal of Conchology Special Publication No 2, 77-8
  11. Winter A. J. de ( 988). Basteria 52, 2.

Kweku Monney
University of Cape Coast, Ghana



 

 

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