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




            time estimates were also derived using the 16S data (see  from 0.164 to 3.603 My (mean 2.051) for the 16S rRNA,
            Material & Methods for details). Results were similar to  probably excludes human  introduction  and reveals an
            those obtained using the mtDNA control region (diver-  infrequently-studied phylogeographic relationship in ter-
            gence between African and Sicilian haplotypes: 95% HPD  restrial vertebrates. This evolutionary connection may be
            from 0.164 to 3.603 My (mean: 2.051); split of balearicus/  significant for the phylogeography of the Mediterranean
            viridis  clades: 95% HPD from 0.18 and  3.795  (mean:  and have implications for research on other terrestrial ani-
            2.123). All the dates estimated in our analysis seem to rep-  mals. While some biogeographic studies have suggested
            resent post-Messinian divergence events.            common ranges for terrestrial vertebrates (for example the
                                                                "Siculo-Maltese-Maghrebin" range type of Turrisi and Vac-
            Multivariate morphometric comparisons               carro [42]), and paleontologists discuss a possible early
            A discriminant  analysis  using all  20 characters demon-  Pleistocene faunal exchange with North Africa (see intro-
            strated the  distinctness of toads from Sicily by  correct  duction), so far, very few molecular studies have suggested
            reclassification of  100% of individuals into the four  any genetic relationships  within terrestrial  vertebrates
            groups from: (i) Sicily, (ii) N-Africa, (iii) Corsica and Sar-  across the Strait of Sicily. Two examples come from spe-
            dinia,  and  (iv) the Apennine Peninsula.  Although  cies (e.g. Discoglossus [25]; Chalcides [47,20]), for which
            encoded as belonging to different geographic groups, the  human introduction elsewhere at circum-Mediterranean
            genetically more  closely-related groups (iii) and (iv) of  sites has been demonstrated and for which African-Sicil-
            the B. balearicus clade showed fewer differences (Figure 4),  ian relationships have never been demonstrated using any
            making us confident of the power of the analyses' and this  nuclear sequence data. Despite some recent speculation
            morphometric dataset. However, in order to test for  (e.g.  Crocidura sicula, potential Messinian origin from
            potential over-parameterization of the analysis, we also  North Africa [16]), a possible African origin of terrestrial
            reduced the number of morphometric characters to five,  Sicilian  fauna has rarely been thoroughly tested with
            which again reclassified 100% of the individuals into their  molecular methods,  and  never using any  nuclear
            four respective groups.                             sequence, and thus supported by both mitochondrial and
                                                                nuclear sequence data. To our knowledge, a genetic Afri-
            Discussion                                          can-Sicilian link has only been inferred in two other ter-
            A phylogeographic relationship between Africa and Sicily  restrial  species, but even these  have  ambiguous
            We have demonstrated a sister relationship on the mito-  information on  timing and  direction: (i)  Phylogenetic
            chondrial and nuclear levels between  green toads from  inference based on allozymes regarding relationships
            Sicily (B. siculus,  see  below) and those from  the entire  among Chalcides lizards from Sicily, Africa, the Apennine
            North African range (B. boulengeri). The phylogenetic  Peninsula and Sardinia [47] showed Sicilian skinks most
            depth of this divergence, which may range between 0.63  closely related to Italian mainland skinks (Calabria in the
            My and 3.5 My (mean 1.83 My) for the control region and  south to Liguria in the north), while lizards from Tunisia

            Table 3: Within-clade (numbers in italics) and between-clade (numbers in regular font) divergence time estimates obtained using a
            coalescent-Bayesian framework as implemented in BEAST v1.4.6 applied to the mitochondrial control region and 16S sequences (not
            available for B. variabilis). The African-Sicilian divergence time estimates (boulengeri to siculus) are printed in bold. Estimates are
            shown in My. Values in parentheses show the 95% highest posterior density intervals (95% HPD); they represent the shortest intervals
            that contain 95% of the posterior sampled values.
                  MtDNA clade(s)    Divergence time estimate          MtDNA clade(s) and/or Geographic region

                                        Control region
                                           16S
                   boulengeri          1.2 (0.394–2.351)  boulengeri                  N-Africa
                                       1.57 (0.099–2.80)
                     siculus          0.677 (0.115–1.53)   siculus                     Sicily
                                       1.56 (0.101–2.69)
                    balearicus        0.914 (0.227–1.875)  balearicus  Apennine Peninsula, Corsica, Sardinia, Balearic Islands
                                       1.84 (0.15–3.365)
                    variabilis        0.85 (0.172–1.838)  variabilis                Balkan, Anatolia
                     viridis          0.527 (0.096–1.152)  viridis                 Central, E-Europe
                                      1.44 (0.196–2.785)
               balearicus-variabilis-viridis  1.956 (0.66–3.795)            balearicus-variabilis-viridis
                   boulengeri        1.833 (0.635–3.509)                          siculus
                                      2.05 (0.16–43.60)
                 boulengeri-siculus   2.749 (1.188–4.906)                   balearicus-viridis-variabilis



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