Table 1.
Location and sample size of populations sampled for allozymes (nallo), nuclear genes (nSAHH, nLyso, nSulfo1, nEF1α) and mitochondrial (nmtCOI) gene.
Figure 1.
Relationship between pairwise genetic distances (θ/(1-θ)) from allozymes and geographic distances (in kilometres).
Figure 2.
Median Joining Networks on the three nuclear genes and the mitochondrial cytochrome oxidase I gene.
For each gene, the sizes of haplotype/allele circles and lengths of connecting lines are proportional to the number of individuals and the number of mutations that separate two linked haplotypes/alleles, respectively (length is not reflected in the 16-substitution link indicated on the mtCOI network). Colours represent divergent clades used for mapping the geographic distribution of alleles in Figure 3. For the nuclear genes, dark blue circles correspond to clades 1 and yellow circles to clades 2 in the manuscript. For mtCOI, light blue circles = clade 1, dark blue circles = clade 2, yellow circles = clade 3. For the Lysozyme gene, position of the 1-bp deletion in the network is represented by red stripes within both the yellow and the blue circles. *, position of individuals from 38°S in the network. Sulfo 1, Sulfotransferase paralogue 1; Lyso, Lysozyme; SAHH, S-Adenosyl Homocysteine Hydrolase; EF1α, Elongation Factor 1α; mtCOI, cytochrome oxidase I.
Figure 3.
Geographic distribution of divergent alleles for three nuclear genes and the mitochondrial cytochrome oxidase I gene.
Colours match divergent clades identified in Figure 2. Stripes indicate the presence of the “deletion” in the Lysozyme gene on either the yellow clade (red stripes on yellow background) or the blue clade (red stripes on blue background). The dashed line depicts the recent barrier to gene flow identified by the Monmonier analysis. The white-block arrow represents the hypothesized northward genetic shift of the tension zone for some genes. Sulfo 1, Sulfotransferase paralogue 1; Lyso, Lysozyme; SAHH, S-Adenosyl Homocysteine Hydrolase; EF1α, Elongation Factor 1α; mtCOI, cytochrome oxidase I; EM, Easter Microplate; GRG, Galapagos Rose Garden; GMB, Galapagos Mussel Bed.
Table 2.
Summary statistics of nucleotide polymorphism according to locality for nuclear genes and mitochondrial gene.
Table 3.
IMa2 estimates and the 95% Highest Posterior Density (HPD) intervals of migration and demographic parameters across the 7°25′S-14°S barrier to gene flow.
Figure 4.
Bifurcated trees showing the correspondence between divergence times between sister clades and times of geological formations.
Clades correspond in those identified in Fig. 2. Grey boxes represent the estimated time of the two barriers: EM, time since the first offsetting of overlapping faults leading to the Easter Microplate (dark grey); TF, time since the formation of Gofar/Discovery transform faults at 7°25′S–14°S latitude (light grey). Striped box represents the estimated time elapsed since the junction between the Pacific Antarctic Ridge and the East Pacific Rise. Grey circles correspond to the geographic position at which the divergence is observed, EM: dark grey and TF: light grey. Dashed lines represent the roots of the trees with the outgroup and calibration point (i.e. Bathymodiolus azoricus, Mid-Atlantic Ridge, about 8–12 Mya). Intervals of estimated divergence, due to the range of the calibration point date, are represented by horizontal thickness of tree nodes. Sulfo1, Sulfotranferase paralogous gene 1; Lyso, Lysozyme; SAHH, S-Adenosyl Homocysteine Hydrolase; mtCOI, mitochondrial cytochrome oxidase 1; EF1α, Elongation Factor 1α. *Lysozyme and EF1α estimates of divergence are indicated but have to be interpreted with caution because these loci did not follow a strict molecular clock.
Figure 5.
Localisation of individuals with both north and south type alleles in SAHH using RFLP analyses.
N/S individuals, individuals that present one allele from the northern clade (blue clade in Figure 2) and one from the southern clade (yellow clade in Figure 2). Left Y-axis is the number of N/S individuals. Right Y-axis is the total number of individuals.