HOOT, SARA B.*, W. CARL TAYLOR, AND E. WAGNER. Department of Biological Sciences, University of Wisconsin, Milwaukee, WI 53201 and Botany Department, Milwaukee Public Museum, Milwaukee, WI 53233. - Species delimitation and hybrid origins in North American Isoëtes based on LEAFY intron data.
Sequences from the second intron of a homolog of LEAFY, a
meristem identity gene, are highly variable in Isoëtes and
other plants (including flowering plants). The LEAFY data is
approximately four times more variable than ITS sequences in
Isoëtes and is useful at both the species and population level.
For species delimitation, we have identified numerous substitutions
and indels that characterize the North American species of
Isoëtes. For example, I. echinospora has virtually
identical sequences for populations from such distant locations as
Iceland, Maine, Wisconsin, and Montana. In contrast, while two
populations of I. melanopoda from Mississippi and Louisiana are
very similar, a third population from Arkansas differs at numerous
sites, indicating a cryptic species. For determining parental origins
of hybrids and allopolyploids, we cloned the intron region to separate
the sequences originating from the parental species. Using this
method, we were able to enter the two hybrid sequences into an
extensive data set of North American species to identify the putative
parents. For example, intron sequences from both I.X
eatonii (a known diploid hybrid) and I. riparia (an
allotetraploid) have virtually identical sequences with the putative
parental species (I. engelmannii and I. echinospora).
The sequences of the allotetraploid, I. louisianensis, are not
similar to any of the North American species. One sequence is weakly
supported as sister to a clade consisting of I. tegetiformans,
and I. lithophila. The other sequence is sister to a clade
consisting of I. virginica, I. melanopoda, and I.
echinospora.
Key words: hybrid origins, Isoëtes, LEAFY, species delimitation