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BMC Evolutionary Biology 2008, 8:56 http://www.biomedcentral.com/1471-2148/8/56

Background in: [22]]. However, Bonfiglio [14] also hypothesized a
On the phylogeographic patterns of terrestrial Sicilian Lower Pleistocene African origin of fossil elephants
fauna (Elephas falconeri) as a debatable alternative to derivation
Since Busack [1,2], the faunal relationships between from European/Italian E. antiquus [Bonfiglio in: [22]].
North Africa and Iberia have been the focus of numerous Other paleontologists have also discussed whether Sicily
molecular phylogeographic studies, yet little attention has had early Pleistocene connections to Africa, as in an, in
been drawn to the consequences that the last landbridge this respect, unresolved investigation of a Pleistocene
between Africa and Sicily may have had on Mediterranean amphisbaenid lizard from Sicily [23]. All these authors
biogeography. As was the Strait of Gibraltar, the Strait of [22-24], however, refer to the lack of conclusive evidence
Sicily (no universally accepted name in English; other for a Pleistocene landbridge. Recent molecular data have
names include Sicilian Strait, Sicilian Channel, Channel suggested phylogeographic links across the Strait of Sicily,
of Sicily, Pantelleria Channel) is purported to have either based on very little data, or, with some speculation
formed at the end of the Messinian salinity crisis (5.3 on the dating of these divergences [[20,25]; see Discus-
Mya), at the Miocene/Pliocene boundary [e.g. [3-6], F. sion].
Rögl pers. comm.]. The Messinian [4] was a geological
period from 5.59 to 5.33 Mya during which the Mediter- On green toads in the western Mediterranean region and
ranean Sea was isolated from the Atlantic Ocean, resulting North Africa
in a large decrease in the Mediterranean Sea level and the Green toads are widespread in the Palearctic region where
formation of landbridges between Africa, Europe and they have differentiated into several lineages [26]. The
most Mediterranean islands. This included a well-docu- occurrence of three bisexually reproducing ploidy levels
mented landbridge between Africa and a landmass that [27] makes them a uniquely interesting vertebrate group.
later became part of Sicily, which may be the last terres- A recent survey of mtDNA variation characterized a deeply
trial connection between the African mainland and the branched assemblage of at least twelve major haplotype
island. However, while it is known that Sicily and Tunisia groups [28]. Other data on green toad variation from
are at present approximately 140 km apart, low Pleis- North Africa have been relatively scarce [29,30]. Research
tocene sea levels of about -120 m [7-9] would have repeat- has been mainly restricted to faunistics [31-33] or analy-
edly drawn the north African paleo-coast and the Sicilian ses of single populations (Egypt [34]) without taxonomic
landmass closer than ~50 km (Figure 1). In addition, cur- or phylogeographic focus. Green toad biology and ecol-
rent shoals [10,11] may be remnants of Pleistocene "step- ogy are relatively well known from the Balearic Islands
ping stone islands" that may have facilitated terrestrial [35,36], Corsica [[37] incl. refs.], Sardinia and mainland
animals, including humans [12], in overcoming the sea Italy [38]. In addition, morphometric analyses of green
barrier. Therefore, the phylogenetic depths of sister rela- toads in Italy have been restricted to peninsular and Sar-
tionships between Sicily and Africa may vary as they do dinian (plus Corsican) populations [38,39] until mor-
for trans-Gibraltarian relationships [2,13]. Observations phometric data for a population from northwestern Sicily
of this pattern in widespread taxa might be explained by became available [40]. Otherwise, regional research has
multiple invasions across the Strait of Sicily and/or addi- been restricted to classical biogeography and faunistics
tional potential invasions from the region that now forms including ecological and taxonomic remarks [41-43] and
the Italian (Apennine) Peninsula. studies on phenology [40,44].

As expected for an island with a long Pliocene isolation To gain insight into the phylogeography of the region, we
[14], endemic (island specific) forms in several animal test a wide range of possible substitution rates in order to
groups on Sicily have been revealed by molecular analyses better date the African-Sicilian divergence of green toads:
(e.g.: hedgehogs, Erinaceus [15]; shrews, Crocidura [16]; Based on only two haplotypes from Sicily, Stöck et al. [28]
mice, Apodemus [17]; beetles, Pachydemidae [18]; terra- roughly calibrated their tree by "assuming that the last
pins, Emys [19]; skinks, Chalcides [20]). Using these meth- landbridge between North Africa and Sicily broke about
ods, some of these species have been shown to be sister 5.3 Mya." Alternatively, this divergence could be younger.
taxa to populations from the Apennine Peninsula (e.g. Here, we examine genetic data from many individuals and
Apodemus, Erinaceus) or to be of very recent Apennine many more localities in Tunisia, Italy and Sicily, to scruti-
peninsular (or Calabrian) origin (reviewed in [21]). This nize the North Africa-Sicily divergence employing a Baye-
pattern may be explained by "an intermittent filter barrier sian coalescent demographic reconstruction method
in the area of the Strait of Messina [which] probably con- (BEAST 1.4.6). Using two mitochondrial and two nuclear
trolled the processes and timing of the Late Middle Pleis- sequence markers and additional morphological, pheno-
tocene-Late Glacial vertebrate faunal dispersal in Sicily" logical, bioacoustic and biogeographic data, we character-
[Bonfiglio in: [22]]. Many Pleistocene fossil megafaunal ize green toads from Sicily as a separate evolutionary
elements entered Sicily from peninsular Italy [Bonfiglio lineage that is a sister taxon to African green toads, but

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