KELCHNER, SCOT A.*, RANDALL J. BAYER, ROBERT J. CHINNOCK, MICHAEL D. CRISP, AND JUDY G. WEST. Centre for Plant Biodiversity Research, CSIRO Plant Industry, G.P.O. Box 1600, Canberra, ACT 2601, AUSTRALIA. - A data partition analysis of noncoding sequence evolution in Bontia and Myoporaceae.
The monotypic genus Bontia, endemic to the Caribbean, is the extreme
outlier of a primarily southern-hemisphere Old World family, the
Myoporaceae. Ninety-five percent of the 250 species of Myoporaceae
sensu R. J. Chinnock (in press) are endemic to Australia. Only six
species in the family occur north of the equator; of these, all but
Bontia daphnoides are locally distributed in the western Pacific. Is
the evolutionary history of Bontia truly shared with Myoporaceae, or
has it descended instead from the family's probable sister lineage,
the Leucophylleae (Scrophulariaceae) of Mexico and Central America? We
examined the possibility that Bontia is indeed an outlying member of
the Myoporaceae by sequencing the rpl16 intron of the chloroplast
genome for 60 taxa representing all major morphological lineages
within the family, and representatives of probable outgroups that
include the Leucophylleae. The sequence data were partitioned based on
the probable secondary structure of the Group II intron; partition
categories were defined as stem, loop, and interceding sequence.
Relative rate of base change per partition was estimated using the
method of Vawter and Brown (1993). The method does not assume rate
constancy and allows for base composition bias between taxa and
secondary structure components; therefore, relative rates of
substitution can be compared between sequence partitions to study the
amount of mutation occurring in stem, loop, and interceding sequence.
We present the results of this partition study and the phylogeny
estimate based on this data set. In this topology, Myoporaceae is
monophyletic, Leucophylleae is sister to Myoporaceae, and Bontia is
derived from within Myoporaceae. The results suggest that the
distribution of Bontia is due to dispersal from an Australian
ancestral lineage.
Key words: biogeography, data partitioning, methodology, Myoporaceae, noncoding sequences, secondary structure