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