Balancing selection across mate compatibility loci in
differentiated populations inferred from FST, pi, and
Tajima’s D
We used FST, pi, and Tajima’s D as measures of gene flow
and selection and tested whether the contigs that contain mating-type
loci were differentiated among populations. FST was
comparable among all populations (Fig. 4A and 4D), but decreased when
the South Australian, Tasmanian, and Victorian population was removed
(mean FST of all populations at the HD locus = 0.36;
mean FST of all populations sans South
Australian, Tasmanian, and Victorian population = 0.26). This difference
in FST supports gene flow or shared ancestry among the
eastern populations of P. subaeruginosa in Australia, which are
less differentiated from each other than from the South Australia,
Tasmanian, and Victorian population.
Nucleotide diversity (pi) varied greatly across populations for these
two regions (Fig. 4B and 4E) and was generally low (<0.2)
across the contigs that contained mating-type genes.
Mating-compatibility loci did not have higher or lower nucleotide
diversity than other parts of the contig, which may reflect genetic
drift since populations became isolated.
Tajima’s D was positive across the contigs that contained mating-type
loci (Fig. 4C and 4F), which is expected when multiple alleles are
maintained in populations under balancing selection.