YOUNG, NELSON D.*, CAROLINE YOON, AND MITRA AZODI. Department of Biology, Trinity University, San Antonio, TX 78212. - Speciation by allopolyploidy in Castilleja: the case of C. dissitifora.
Castilleja dissitiflora N. Holmgren is a montane species,
endemic to central Nevada, and a tetraploid (2n=48). It is thought to
be a genomic allopolyploid descendant of a cross or crosses between
C. linariifolia Benth. (2n=24) and C. applegatei Fernald
ssp. pinetorum (Fernald) Chuang & Heckard (2n=24). This
hypothesized relationship is based on the fact thatC.
dissitiflora is intermediate between the two putative parents in
floral morphology and overall aspect. Although currently, C.
dissitiflora is only sympatric with one putative parent, C.
linariifolia, the other putative parent, C. applegatei
ssp. pinetorum approaches it to within 200 km on the west and
north of its range. It is commonly held that allopolyploids are most
successful when the parents are not close relatives, for if they are,
tetrasomic inheritance may generate unbalanced gametes. Although the
two putative parents are both in subgenus Castilleja, C.
linariiflora is is in section Castilleja, whereas C.
applegatei is in section Viscidulae. The phylogenetic
relationship among sections of Castilleja can reveal just how
close or distant these two sections are. Sequences of the plastid
trnK intron and nuclear ITS are used along with morphology and new
chromosome counts to assess the validity of the hypothesized
allopolyploidy. A skeletal phylogeny of the genus Castilleja is
used to determine the degree of relationship between the sections with
the two putative parent species. Castilleja is a member of the
newly redefined Orobanchaceae.
Key words: allopolyploid speciation, Castilleja dissitiflora, chromosome counts, ITS, Orobanchaceae, trnK intron