Saturday, December 21, 2013

Four-lined Snake Phylogeography

Elaphe quaturolineata, Photo credit: Carlo Catoni
The four-lined snake, Elaphe quatuorlineata, has a fragmented distribution, restricted in continental regions of Europe and islands in the Italian and Balkan peninsulas.

Within E. quatuorlineata, several subspecies have been recognized (E. q. parensis from Paros Island, central Aegean; E. q. scyrensis from Skyros Island, northern Aegean; and E. q. muenteri from several central Aegean islands, this also includes the uniformly patterned Elaphe rechingeri from Amorgos Island. Elaphe  q. quatuorlineata is distributed in the remaining part of the species’ range.

The subspecies are differentiated on the based on differences in body size, mid-body scale rows, and color patterns in juvenile, subadult and adult animals. The insular subspecies (E. q. parensis, E. q. scyrensis and E. q. muenteri) are significantly smaller, while E. q. quatuorlineata (found on mainland but also on several islands) is one of the largest European snakes.

In an early on-line view of a new study in Zoologica Scripta, Panagiotis Kornilios and colleagues used mtDNA sequences to investigate the four-lined snake's evolutionary and biogeographical history. The authors report the phylogeography of Elaphe quatuorlineata is the result of both vicariant and dispersal events, some of them over water and others with the help of  human transport.

Four-lined snakes started to diversify approximately 3.5 Mya and it continued during the Pleistocene glacial periods, when the snake’s distribution was restricted in the Italian and Balkan peninsulas. Populations subsequently expanded from subrefugia, which acted as pockets of biodiversity.  The study supports the recognition of three genetic lineages that roughly correspond to the morphological subspecies, although the authors suggest morphological characters used for their discrimination should be re-evaluated because some subspecies correspond to ecomorphs associated with changes in body size due to the the island-dwarfism phenomenon.

The formation of clade A, occurred about 3.5 Mya and corresponds to a sea barrier between Evvoia and Andros Island. This land connection that was never re-established, despite sea level changes caused by the glacial cycles. The separation of clade B occured about 3 Mya when specimens colonization Skyros Island by over-watder dispersal. Clade C includes all the remaining continetal populations (Italian and Balkan peninsulas) as well as several islands of the Adriatic. Within clade C, four subclades with unresolved relationships were found. This radiation  is probably related to climatic fluctuations, occurred in the Pleistocene.

Two specimens in clade C from Italy are not associated with the Italian subclade, but instead belong to the Balkan clade One of these shares the same mtDNA haplotype with a specimen from southern Greece, differing only by a single substitution. The authors suggest this could have resulted from a very recent, possibly human-induced dispersal from Greece to Italy. They note an old and close relationship between humans and this particular snake species.

The four-lined snake was considered sacred by ancient Greeks and Romans, and it was used in religious rituals from Roman times until the present day in central-southern Italy. Elaphe quatuorlineata and other non-venomous serpents were used in shrines of the Greco-Roman god of medicine (Asklepios or Aesculapius), because they were believed to have the power of healing superficial lesions with their saliva. Italian researchers have suggested the healing power occurs of skin growth factors present in the saliva of the four-lined snake.

Citation
Kornilios P., Thanou E., Lymberakis P., Sindaco R., Liuzzi C. & Giokas S. (2013). Mitochondrial phylogeography, intraspecific diversity and phenotypic convergence in the four-lined snake (Reptilia, Squamata). —Zoologica Scripta

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