Population genetics of the São Tomé caecilian (Gymnophiona: Dermophiidae: Schistometopum thomense) reveals strong geographic structuring

• Published in: PloS one 2014-08, Vol.9 (8), p.e104628-e104628
• Main Authors: Stoelting, Ricka E, Measey, G John, Drewes, Robert C
• Format: Article
• Language: English
• Subjects: Africa; Amphibia; Amphibians - anatomy & histology; Amphibians - classification; Amphibians - genetics; Amphibians - physiology; Animals; Bayes Theorem; Bayesian analysis; Biodiversity; Biological evolution; Biology and Life Sciences; Color; Correlation coefficient; Correlation coefficients; Data processing; Deoxyribonucleic acid; Dispersal; Dispersion; DNA; DNA, Mitochondrial - genetics; Ecology and Environmental Sciences; Evolution, Molecular; Extreme values; Fauna; Gene sequencing; Genetic analysis; Genetic structure; Genetic Variation; Genetics; Genetics, Population; Gymnophiona; Haplotypes; Hypotheses; Islands; Lava; Mitochondrial DNA; Nucleotide sequence; Phylogenetics; Phylogeny; Phylogeography; Pigmentation; Population genetics; Population growth; Population studies; Regression analysis; Reptiles & amphibians; Schistometopum; Schistometopum thomense; Sequence Analysis, DNA; Spatial analysis; Spatial distribution; Variance analysis; Variation; Volcanic activity
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0104628

Islands provide exciting opportunities for exploring ecological and evolutionary mechanisms. The oceanic island of São Tomé in the Gulf of Guinea exhibits high diversity of fauna including the endemic caecilian amphibian, Schistometopum thomense. Variation in pigmentation, morphology and size of this taxon over its c. 45 km island range is extreme, motivating a number of taxonomic, ecological, and evolutionary hypotheses to explain the observed diversity. We conducted a population genetic study of S. thomense using partial sequences of two mitochondrial DNA genes (ND4 and 16S), together with morphological examination, to address competing hypotheses of taxonomic or clinal variation. Using Bayesian phylogenetic analysis and Spatial Analysis of Molecular Variance, we found evidence of four geographic clades, whose range and approximated age (c. 253 Kya-27 Kya) are consistent with the spread and age of recent volcanic flows. These clades explained 90% of variation in ND4 (φCT = 0.892), and diverged by 4.3% minimum pairwise distance at the deepest node. Most notably, using Mismatch Distributions and Mantel Tests, we identified a zone of population admixture that dissected the island. In the northern clade, we found evidence of recent population expansion (Fu's Fs = -13.08 and Tajima's D = -1.80) and limited dispersal (Mantel correlation coefficient = 0.36, p = 0.01). Color assignment to clades was not absolute. Paired with multinomial regression of chromatic data, our analyses suggested that the genetic groups and a latitudinal gradient together describe variation in color of S. thomense. We propose that volcanism and limited dispersal ability are the likely proximal causes of the observed genetic structure. This is the first population genetic study of any caecilian and demonstrates that these animals have deep genetic divisions over very small areas in accordance with previous speculations of low dispersal abilities.