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| Cepaea nemoralis by L. Holden |
Species
have been accidentally or purposely disseminated by humans at an alarming rate
over the past century. Most people have
heard about relatively recent invasions and impacts of zebra mussels,
Africanized bees, kudzu and other non-indigenous, exotic, or non-native species
to name a few. What many people may not
realize is that the true globalization and homogenization of the world’s biota
began in 1492 after the “discovery” of the New World by Columbus. After Columbus, ecosystems met and mixed in
an exchange Alfred Crosby referred to as the Columbian Exchange (Mann, 2011). The “exchange took corn (maize) to Africa and
sweet potatoes to East Asia, horses and apples to the Americas, and rhubarb and
eucalyptus to Europe- and also swapped about a host of less-familiar organisms
like insects, grasses, bacteria, and viruses” (Mann, 2011). The Columbian exchange had a profound effect
on the natural ecosystems and landscapes around the world. Exotic species became major staple crops that
most people do not realize are non-native.
They are here. We grow them, we
eat them or pet them or ride them. Even
fewer people are aware that species were introduced accidentally or purposely
thousands of years ago by humans – including terrestrial gastropods!
In June 2013, Adele Grindon and
Angus Davison published a paper in PLOS ONE showing that a peculiar distribution pattern of
Cepaea nemoralis land snails in
Ireland and the Eastern Pyrenees was best explained by transportation by
Mesolithic humans over 8000 years ago.
Apparently, there are a number of species including the Kerry slug, the
Pyrenean glass snail and the strawberry tree that are found exclusively in
Ireland and Iberia. This distribution
pattern has been referred to as ‘Lusitanian’ and has defied any single
explanation. Grindon and Davison chose
to study C. nemoralis because on the West coast of Ireland, C. nemoralis
has a large, white-lipped morph that is common and also found in the Pyrenees
suggesting some connection that warrants investigation. The researchers sampled across Europe
including Ireland, Britain, northern Spain, southern France and the Pyrenees
and sequenced two mitochondrial gene fragments (cytochrome oxidase subunit I
(COI) and 16S rRNA) to estimate phylogenies and examine the resultant
patterns. What Grindon and Davison
observed was that individuals from Ireland had a mitochondrial lineage, C, that is shared
with Central and Eastern Pyrenean populations. This lineage was absent in most other parts of
Europe with minor exceptions. The
authors propose that the best explanation for the disjunct distribution pattern
is a single historic long distance dispersal event between the Pyrenees and
Ireland. The species has apparently been
a food source in the Pyrenees, so may have been transported live to serve as a
source of food. Grindon and Davison’s
paper is not the first documentation of likely human-mediated dispersal of
terrestrial gastropods. Jesse et al. (2011) hypothesized that Neolithic expansion in
the western Mediterranean resulted in the expansion of the range of Tudorella sulcata s. str. and Lee et al. (2007) hypothesized pre-historic inter-island
introductions of an endemic Pacific island tree snail, Partula hyalina. It is
certain that as other unusual distribution patterns are examined other ancient
human-mediated dispersal events will be discovered and shed light on the
history of world’s biota including gastropods.
LITERATURE CITED
Grindon, A. J. and A. Davison.
2011. Irish Cepaea nemoralis land snails have a cryptic Franco-Iberian origin
that is most easily explained by the movements of Mesolithic humans. PLOS ONE 8(6):1-7.
Jesse, R., E. Vela, and M. Pfenninger. 2011.
Phylogeography of a land snail suggests trans-Mediterranean Neolithic
transport. PLOS ONE 6(6):1-7.
Lee, T., J. B. Burch, T. Coote, B. Fontaine, O. Gargominy, P.
Pearce-Kelly, and D. O. Foighill.
2007. Prehistoric
inter-archipelago trading of Polynesian tree snails leaves a conservation
legacy. Proceedings of the Royal Society
B 274:2907-2914.
Mann, C. C. 2011. 1493: Uncovering the New World Columbus
Created. Vintage Books, New York.
