FERGUSON, DIANE M.* AND TAO SANG. Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824. - Testing hypotheses of hybrid speciation in peonies (Paeonia; Paeoniaceae) using the low-copy nuclear gene alcohol dehydrogenase (Adh).
DNA sequence data from the low-copy nuclear gene alcohol
dehydrogenase (Adh) were used to test the putative hybrid
origin of several diploid and tetraploid species of peonies belonging
to Paeonia section Paeonia (Paeoniaceae). Two
paralogous loci (Adh1 and Adh2), duplicated prior to the
diversification of Paeonia species, were amplified with
locus-specific primers and cloned for one or more accessions from each
species. All distinct clone copies were included in a single
simultaneous parsimony search for each locus. Adh1 and
Adh2 support that several tetraploid species, including the
"arietina" species group (P. arietina, P. humilis, P.
officinalis, P. parnassica), P. peregrina, and P.
banatica, are of allopolyploid origin. After the initial
hybridization event, tetraploid peonies may have gone on to speciate
and further hybridize, creating new species such as P.
officinalis. For putative hybrid diploids, distinct sequences
were found at the Adh2 locus for P. emodii, and
Adh1 sequence polymorphism was detected for P. japonica
and P. obovata. This may imply that heterozygosity resulting
from hybridization can be maintained at a nuclear locus but
homogenized at the other following genome rearrangement in a diploid
hybrid. Overall, Adh2 corroborates many of the findings based
on Adh1; however, the tempo of gene duplication and deletion at
that locus is much more dynamic than Adh1, with many
pseudogenes found in several species.
Key words: alcohol dehydrogenase (Adh), allopolyploidy, hybridization, molecular systematics, Paeonia, speciation