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RECONSTRUCTION OF THE EVOLUTION OF REPRODUCTIVE CHARACTERS IN PONTEDERIACEAE USING PHYLOGENETIC EVIDENCE FROM CHLOROPLAST DNA RESTRICTION‐SITE VARIATION
Author(s) -
Kohn Joshua R.,
Graham Sean W.,
Morton Brian,
Doyle Jeff J.,
Barrett Spencer C. H.
Publication year - 1996
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1996.tb03919.x
Subject(s) - biology , evolutionary biology , phylogenetic tree , chloroplast dna , variation (astronomy) , mitochondrial dna , phylogenetics , genetics , gene , physics , astrophysics
We reconstructed the phylogenetic history of Pontederiaceae using chloroplast DNA restriction‐site variation from approximately two‐thirds of the species in this family of aquatic monocotyledons. The molecular phylogeny was used to evaluate hypotheses concerning the evolution of reproductive characters associated with the breeding system. The family has four main genera, two of which ( Eichhornia and Pontederia ) have tristylous, predominantly outcrossing species, while two ( Monochoria and Heteranthera ) have enantiostylous taxa. Self‐incompatibility is restricted to some but not all tristylous species. In Eichhornia and Pontederia , predominantly selfing species with small monomorphic flowers (homostyly) have been hypothesized to result from the multiple breakdown of tristyly. Restriction‐site variation provided a well supported phylogeny of ingroup taxa, enabling the mapping of reproductive characters onto trees. Two contrasting optimization schemes were assessed, differing in the relative weights assigned to shifts in character states. The reconstructed sequence of floral character‐state change was used to assess competing hypotheses concerning the origin and breakdown of tristyly, and the relationships between tristylous and enantiostylous syndromes. Our results indicate that the class of optimization scheme used was the most critical factor in reconstructing character evolution. Despite some topological uncertainties and difficulty in reconstructing the primitive floral form in the family, several broad conclusions were possible when an unordered, unequally‐weighted optimization scheme was used: (1) tristyly originated either once or twice, while the occurrence of enantiostyly in Monochoria and Heteranthera was always found to have independent origins; (2) tristyly has repeatedly broken down leading to selfing, homostylous taxa; and (3) self‐incompatibility probably arose after the origin of floral trimorphism, a sequence of events that conflicts with some evolutionary models.