From a cytogeography paper produced by Barlow (1971?) the Eremaeon ancestral stock of eremophila species was diploid. The emergence of tetraploid biotypes helped the species to colonise the remainder of the continent because of an increased availability of adaptive effects in the genome. Barlow proposed that the ancestral diploid biotypes occur in Western Australia and the remainder of the country has been colonised as a result of the emergence of the tetraploid biotype. However, in my recent work and in other papers a number of diploid populations of Eremophila species have been identified in NSW. So does this mean Barlow was wrong, or can this be worked into his hypothesis?
Dear Sadgrove,
Barlow (1971) has stated that polyploidy biotypes MAY lead to geographical expansion. Further Barlow again stated that polyploidy MAY be effective in fixing the adaptive recombinants. To my mind the word MAY is important here. In my opinion things may change in a period of more than 4 decades. Because, Barlow did work in 1971 and you have done the work recently. During this much time, cytogeography may have changed due to one or the other reason. So Barlow was not wrong. The word MAY has been used thrice in summary of the paper, one may think about hypothesis.
To be consistent with Barlow's hypothesis, you could hypothesis that the NSW diploid populations are recent transplants from Western Australia. Alternatively, you could hypothesise that they are spontaneous reversion to diploid status from a local tetraploid. Spontaneous reversions seems less likely, if they retain the same karyotype as the WA diploid populations though.
I guess to get towards an answer, you might propose to sequence a number of individuals from each population, and see the story the genetic relationships tell you?
Barlow's hypothesis is an interesting and valuable one, which like all hypotheses requires testing. You may be in a good position to do this. An obvious test would be to plot ploidy level on a robust phylogeny for the genus. Predictions of Barlow's hypothesis would be that the basal Eremophila nodes would resolve to diploid, that (perhaps) one or a few transitions from diploid to polyploid could be identified, and that diploids are restricted to, or over-represented in, WA. Of course, as in all evolutionary and biogeographic hypotheses, a very neat, clean result is unlikely, but some trends may well emerge.
Thankyou all very much for your helpful input. I am resolving to do some molecular work to see what the story tells me. Cheers
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