Phylogeographic Analysis of Tick-borne Pathogen - Recent Advances and Issues in Environmental Science - page 86

genotypes included in the analysis were exclusive to a particular ecoregion cluster:
genotype A to ecoregion cluster 2, genoytpe B to ecoregion cluster 1 and genotype F to
ecoregion cluster 3. A signifi cant genetic differentiation was found between ecoregion
clusters for MSP1a microsatellite genotype frequencies, with overall F ST = 0.16 (P <
0.0001). The ecoregion clusters 1 and 2 were clearly distinct from the other ecoregion
clusters, and the largest F ST value (0.28) was found between ecoregion clusters 1 and 4
while signifi cant genetic differences were not found between ecoregion clusters 3 and
4 (Table 4). To control for potential confounding effects of geography, we investigated
genetic differentiation between broad geographic regions. This showed that genetic
differentiation is mostly dependent on ecoregion-based clustering of the strains, with
the highest F ST value being 0.07 for South America and the Mediterranean (see Table
4). The AMOVA showed that 84% of the variance accounted for within-ecoregion
cluster differences, while a geographic-based AMOVA showed that within-population
variation explained less (73%) of the variance (Table 5).

Table 4. Ecoregion and geographic cluster pairwise FST significance tests (bottom half of each
section) and P-values (top half of each section) of A. marginale MSP1a microsatellites.

Ecological Ecological 1 Ecoregion 2 Ecoregion 3 Ecoregion 4

Ecological 1 - 0.019 ± 0.001 0.000 ± 0.000 0.001± 0.000

Ecological 2 0.09 - 0.027 ± 0.001 0.032 ± 0.001

Ecological 3 0.22 0.07 - 0.312 ± 0.003

Ecological 4 0.28 0.15 0.016 (NS) -

Geographical North America South America Mediterranean South America

North America

- 0.324 ± 0.003 0.016 ± 0.001 0.232 ± 0.003

South America 0.004 (NS) - 0.036 ± 0.001 0.452 ± 0.003

Mediterranean 0.06 0.07 - 0.101 ± 0.002

South Africa 0.01 (NS) -0.01 (NS) 0.07 (NS) -

Abbreviation: NS, not sign ifi cant.

Table 5. Hierarchical analysis of molecular variance (AMOVA) for MSP1a microsatellites.

Source of variation d. f. Sum of squares Variance components Percent variation

Ecological
Among ecoregions 3 3.99 0.04 16.31

Within ecoregions 109 24.49 0.22 83.69

Total 112 28.48 0.27 ...

Geographic
Among continents 2 1.16 -0.08 -35.70
Among populations within continents 6 8.76 0.15 63.18
Within populations 104 18.57 0.18 72.52
Total 112 28.48 0.25 ...
Table shows Wright's fi xation index, FsT· Statistical signifi cance was calculated from 20,000 random permutations.
Fixation indices and P-values:
(Ecological) FsT = 0.16 (P = 0.00 ± 0.00), (Geographic) FsT = 0.29 (P = 0.00 ± 0.00).