Gene flow between subspecies
We wanted to examine the magnitude of among-subspecies gene flow in more
detail. The samples collected on the west coast of Australia (population
maBB) were morphologically diagnosed as A. m. marina.However, our genetic data show relatively lowFST values between maBB and A. m.
eucalyptifolia . FST values between maBB and
other A. m. marina populations were comparable with those between
maBB and A. m. australasica populations (Supplementary Table 4).
The NJ tree also clusters maBB with the two A. m. eucalyptifoliapopulations (Supplementary Figure 1). This contrast between
morphological and genetic lines of evidences hints strongly at gene flow
between A. m. marina and A. m. eucalyptifolia in Western
Australia where the two subspecies grow together. The demographic model
assuming that maBB has descended from A. m. marina but exchanges
genes with A. m. eucalyptifolia is the most likely in our ABC
analyses (model v2, posterior probability 0.933, Table 2 and Figure 4a).
We also used TreeMix to capture more potential gene flow events among
populations (Figure 4b). We identified six such events on the population
splitting graph. Among the six events, three were between subspecies,
with one gene flow event between each pair of the three subspecies. Two
gene flow events occurred between pairs of A. m. marinapopulations. The last gene flow event occurred between maBB and the
outgroup species A. alba .