TOMMERUP, MEGAN M.* AND J.MARK PORTER. Rancho Santa Ana Botanic Garden, 1500 North College Avenue, Claremont, CA, 91711. - Evolution of the heterostylous syndrome in Aliciella (Polemoniaceae).
Aliciella heterostyla represents the only documented case of
the unusual breeding system heterostyly in Polemoniaceae. Two
competing hypotheses, explaining the origin of heterostyly, have been
proposed. These hypotheses differ with respect to the predicted order
in which characteristics associated with the heterostyly syndrome
arise (e.g., Darwin 1877; Lloyd and Webb 1992 versus Charlesworth and
Charlesworth 1979). This syndrome includes reciprocal herkogamy,
self-incompatibility and a host of ancillary morphological
characteristics, such as variation in pollen size and shape. Sequence
data from the internal transcribed spacer (ITS) region of nuclear
ribosomal DNA are used to estimate the phylogenetic relationships
among A. heterostyla and its relatives. The resulting
molecular phylogeny is used as an evolutionary setting to estimate the
order of development of physiological and morphological characters
associated with heterostyly. Although reciprocal herkogamy is
uniquely derived in A. heterostyla , compatibility is more
complicated. Both self-compatibility (SC) and self-incompatibility
(SI) are present in Aliciella . Within A. heterostyla ,
however, a mixed mating system (cryptic self-incompatibility and
intra-morph compatibility) is exhibited. The ancestral condition of
this trait is greatly influenced by assumptions about the relative
ease of deriving SC from SI versus deriving SI from SC. As a
consequence, both the Lloyd and Webb and the Charlesworth and
Charlesworth models may be consistent with the Aliciella data,
depending upon assumptions made about the evolution of compatibility.
Key words: Aliciella, heterostyly, Polemoniaceae, self-incompatibility