For outgroups we used Kageneckia, Lindleya, and Vauquelinia, the closest relatives of the traditionally circumscribed, pome-fruited subfamily.
CpDNA supports (Chamaemespilus, Torminalis) at a 100% bootstrap (BS) level and (Aria, Cormus) at 71% BS in a larger, weakly supported clade that also includes Sorbus s.s.
This lack of resolution is at least partly the result of low sequence divergence (about 0.5-2.0% in cpDNA data), which is remarkable in that several maloid genera are known as fossils from the Middle Eocene.
Moreover, because cpDNA is maternally inherited in most angiosperms, the use of that marker may be particularly informative for clarifying genetic relationships between the taxa of a predominantly agamic polyploid complex such as Brevivalvula, in which pollen has little influence on gene exchange.
It is an easy-to-use method which has the main advantage of providing an estimate of cpDNA variation in the whole molecule and not only in a part of it, as is the case with methods using complementary probes intended for hybridization or specific primers for PCR amplification.
In those species, the average proportion of cpDNA diversity attributable to differentiation between populations reached 85% and was attributed to both low seed dispersal and, more importantly, to the occurrence of substantial interspecific hybridization and cytoplasmic introgression (Dumoulin-Lapègue et al., 1997).
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