Saturday, October 30, 2010

The Aesculapian Snake and Human Activity

Humans (including Homo erectus, Neanderthals, and Homo sapiens), have been in Europe for about 2 million years. Therefore humans have interacted with the European landscape and its fauna for a considerable amount of time. One of the snakes humans have impacted is the Aesculapian Snake, Zamenis longissimus (formerly Elaphe longissimus). It is of interest for its role in Greek mythology and in ancient Greek and Roman medicine. The staff of Aesculapius, a long standing symbol of healing and medicine shows this snake coiled around the staff and the image as well as the snake has been long associated with healing. 

While the Aesculapian Snake appears to be widespread in southern Europe, it has a few, small isolated populations in northern Europe. It is also known from fossil remains in northern areas where it currently does not exist, suggesting that longissimus once had a greater natural distribution than it does today. Or, that human transported this snake, possibly for its medical value into more northern latitudes. The first hypothesis is now seen as the more likely scenario to understanding its current relictual distribution and fossil remains. However, this does not mean humans have not introduced this snake at some localities, a population of Aesculapian Snakes is established in the Welsh Mountain Zoo in and nearby gardens; and it is also living in Regent's Park and along the Regent's Canal in the centre of London. This population is thought to have resulted from animals that escaped from the London Zoo.

Capizzi et al. (2008) examined the food habits the Aesculapian Snake in three areas of central Italy. Their study sites formed a gradient ranging from a natural mixed oak forest to an entirely deforested, urban-agricultural habitat. They looked at the total number of prey items eaten by adults in each study area, and the number of individual snakes that had eaten a given prey species. Body sizes were not different and the diets of both sexes were similar. Snakes living in the more undisturbed habitats ate a greater diversity of prey than snakes in disturbed habitats. Their results demonstrated that habitat alteration by humans drives changes in the composition of the diet of the Aesculapian Snake.

The microhabitats used by the Aesculapian Snake have also been altered by human activity. Lelièvre et al. (2010) found that longissimus used all the anthropogenic structures present in their habitats as refuges, these included: roads, barns, and concrete boards. Despite the low availability of these artificial shelters at their study site, 12% of relocations of radio tracked snakes were using man-made refugia. Their study site lacked large rocks that could provide thermally suitable retreats, and they showed that some artificial refuges had better nocturnal thermal conditions than the available natural shelters. Hiding under roads and covered wood stacks allowed Aesculapian Snakes to maintain higher body temperatures at night than they otherwise could in natural shelters. 

How species responded to past climate change may provide information about how they may respond to changes in the current episode of global warming. Musilová, et al. (2010) examined how the Aesculapian Snake responded to the last global warming event at the Pleistocene–Holocene transition, approximately 5000–8000 years ago using phylogenetic and demographic analyses. The present distribution of this snake in the southern half of Europe is a remnant of a much wider range during the Holocene climatic optimum when populations existed as far north as Denmark. The northern populations disappeared as the climate cooled, and the Aesculapian Snake is now extinct over all of central Europe. The exceptions are a few isolated populations in Germany and the Czech Republic. Musilová, et al. identified two major clades that expanded from their respective western and eastern refugia after the last glacial maximum (18,000–23,000 YA). Snakes from the relictual northern populations were most closely related to the Eastern clade. Thus, the snakes that occupied central and northern Europe during the Holocene climatic optimum were probably derived from the Balkans refugia.  They also identified two small, deep-branching clades: one near the Black Sea, and another in Greece. These clades provided evidence for two additional refugia, which did not successfully contribute to the colonization of central and northern Europe. Their results suggest some populations responded to the mid-Holocene global warming by shifting their ranges further north while other populations of the same species may have been unable to do so. Thus, knowing what populations were able to expand in different species may provide information about what populations will be important for a species’ ability to cope with current and future global warming.

All of this is suggests human altered environments caused changes in the diet, thermal behavior, and geographical distribution of the Aesculapian Snake and that future changes to snake habits can be expected as more human activities change the planet.

Capizzi, D., M. Capula, L. Rugiero, L. Luiselli. 2008. Dietary patterns of two sympatric Mediterranean snakes (Hierophis viridiflavus and Zamenis longissimus) along a gradient of habitat alteration. The Herpetological Journal 18(3):141-146,

Lelièvre, H., M. Le Hénanff, G. Blouin-Demers, G. Naulleau and O. Lourdais. 2010. Thermal strategies and energetics in two sympatric colubrid snakes with contrasted exposure. Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology 180(3): 415-425

Musilova, R., V. Zavadil, P. Kotlik. 2007. Isolated populations of Zamenis longissimus (Reptilia: Squamata) above the northern limit of the continuous range in Europe: origin and conservation status. Acta Societatis Zoologicae Bohemicae, 71(3-4):197-208.

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