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BMC Evolutionary Biology BioMed Central

Research article Open Access
Post-Messinian evolutionary relationships across the Sicilian
channel: Mitochondrial and nuclear markers link a new green toad

from Sicily to African relatives
1,3
1
1
Matthias Stöck* , Alessandra Sicilia , Natalia M Belfiore , David Buckley ,
2
2
Sabrina Lo Brutto , Mario Lo Valvo and Marco Arculeo 2
2
1
Address: University of California, Berkeley, Museum of Vertebrate Zoology, 3101 Valley Life Sciences Building #3160, Berkeley, CA 94720-3160,
USA, 2 Dipartimento di Biologia Animale, Via Archirafi, 18, 90123 Palermo, Italy and 3 Dept. Ecology and Evolution, University of Lausanne,
Biophore, CH-1015 Lausanne, Switzerland
Email: Matthias Stöck* - matthias.stoeck@unil.ch; Alessandra Sicilia - ale.sicilia@unipa.it; Natalia M Belfiore - nmb@berkeley.edu;
David Buckley - dbuckley@berkeley.edu; Sabrina Lo Brutto - sabrilob@unipa.it; Mario Lo Valvo - mlovalvo@unipa.it;
Marco Arculeo - marculeo@unipa.it
* Corresponding author

Published: 23 February 2008 Received: 14 August 2007
Accepted: 23 February 2008
BMC Evolutionary Biology 2008, 8:56 doi:10.1186/1471-2148-8-56
This article is available from: http://www.biomedcentral.com/1471-2148/8/56
© 2008 Stöck et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract
Background: Little attention has been paid to the consequences of the last landbridge between Africa and Sicily
on Mediterranean biogeography. Previous paleontological and scarce molecular data suggest possible faunal
exchange later than the well-documented landbridge in the Messinian (5.3 My); however, a possible African origin
of recent terrestrial Sicilian fauna has not been thoroughly tested with molecular methods. To gain insight into
the phylogeography of the region, we examine two mitochondrial and two nuclear markers (one is a newly
adapted intron marker) in green toads (Bufo viridis subgroup) across that sea barrier, the Strait of Sicily.
Results: Extensive sampling throughout the western Mediterranean and North Africa revealed a deep sister
relationship between Sicilian (Bufo siculus n.sp.) and African green toads (B. boulengeri) on the mitochondrial and
nuclear level. Divergence times estimated under a Bayesian-coalescence framework (mtDNA control region and
16S rRNA) range from the Middle Pliocene (3.6 My) to Pleistocene (0.16 My) with an average (1.83 to 2.0 My)
around the Pliocene/Pleistocene boundary, suggesting possible land connections younger than the Messinian (5.3
My). We describe green toads from Sicily and some surrounding islands as a new endemic species (Bufo siculus).
Bufo balearicus occurs on some western Mediterranean islands (Corsica, Sardinia, Mallorca, and Menorca) and the
Apennine Peninsula, and is well differentiated on the mitochondrial and nuclear level from B. siculus as well as from
B. viridis (Laurenti), whose haplotype group reaches northeastern Italy, north of the Po River. Detection of
Calabrian B. balearicus haplotypes in northeastern Sicily suggests recent invasion. Our data agree with
paleogeographic and fossil data, which suggest long Plio-Pleistocene isolation of Sicily and episodic Pleistocene
faunal exchange across the Strait of Messina. It remains unknown whether both species (B. balearicus, B. siculus)
occur in sympatry in northern Sicily.
Conclusion: Our findings on green toads give the first combined mitochondrial and nuclear sequence evidence
for a phylogeographic connection across the Strait of Sicily in terrestrial vertebrates. These relationships may have
implications for comparative phylogeographic research on other terrestrial animals co-occurring in North Africa
and Sicily.

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