I've been following the interesting discussion about whether or not D. suzukii is a new species or hybrid, probably man made rather than natural, between D. cruentum and tobaense. It seems to me that the DNA analysis by Tomohisa Yukawa that Kathy Barrett pointed out put limits on the discussion.
The sequence analysis reported by Yukawa is not quite enough to resolve the debate, because its focus was to determine which of the closely related species, cruentum or tobaense, was most closely related to suzukii. Yukawa didn't address the question of suzukii being a hybrid. But he clearly states that suzukii has several unique base substitutions in the 917 bp that he compared among the 4 species he reports (D. formosanum was included along with the other 3 as a reference species or outgroup that was not as closely related as the other 3). These unique substitutions do not fit the idea that suzukii is a hybrid of cruentum and tobaense. It would have been useful if Yukawa had explicitly listed these substitutions, but he wasn't considering the hybrid hypothesis. Nonetheless, if suzukii were a hybrid, one would have expected it to inherit half its sequence changes from cruentum and half from suzukii, not to have unique changes. That is apparently not the case, at least for the sequences that were determined.
At the beginning I said these results put limits on the discussion. I think that the only way one could maintain that suzukii is a hybrid would be to say that the sequences Yukawa determined were not representative of at least one of the "species" he looked at. Usually molecular taxonomists determine the sequence of several independently isolated copies of the DNA from a particular plant, but it could be that Yukawa just determined a single sequence from each plant and that the ones he chose to sequence from suzukii (or the others) just happened to be unrepresentative. I think this is very unlikely, but we don't know until we ask him. So I've sent him an email and will report his response.
Until we have that additional information, I think the evidence suggests that D. suzukii is a distinct species, not a cruentum-tobaense hybrid.
Steve Beckendorf Berkeley, California _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
