JOBSON, RICHARD W.1,2* and VICTOR A. ALBERT2. 1Department of Botany, The University of Queensland, Brisbane, QLD 4072, Australia; 2Biodiversity and Systematics, Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL 35487-0345. - Molecular rates parallel diversification contrasts between carnivorous plant sister lineages in Lentibulariaceae.
In the carnivorous plant family Lentibulariaceae, the bladderwort lineage
(Utricularia and Genlisea) is substantially more species-rich
and morphologically divergent than its sister lineage, the butterworts
(Pinguicula). Bladderworts have a
relaxed body plan that has permitted the evolution of terrestrial,
epiphytic, and aquatic forms that trap prey in intricately-designed
suction bladders. In contrast, the flypaper-trapping butterworts
maintain vegetative structures typical of angiosperms. We found that
bladderwort genomes evolve significantly faster across seven loci (the
trnL intron, the second trnL exon, the trnL-F
intergenic spacer, the rps16 intron, rbcL, coxI,
and 5.8S rDNA) representing all three genomic compartments. Generation
time differences did not show a significant association. We relate
these findings to the contested speciation rate hypothesis, which
postulates a relationship between increased nucleotide substitution
and increased cladogenesis. Body-plan relaxation would lower selection
pressure as individuals with novel phenotypes establish founder
populations and diverge. In agreement with known prey specificities
and interbreeding barriers among bladderworts, the strong correlation
between bladder variety and phylogeny (estimated from 69
Lentibulariaceae and 10 outgroups based on trnL-F and
rps16 intron sequences) suggests that diversifying (disruptive)
selection on trap form has further driven rate increases.
Additionally, bladderwort features such as rootlessness, asymmetrical
phyllotaxy, and leaf-shoot indistinction resemble phenotypes of known
auxin transport mutants, suggesting that one or few genes of large
effect could underlie bladderwort developmental release (see abstract
by Albert and Jobson, Botany2001). Finally, we argue that molecular
and speciation rate increases may amplify each other as greater
genetic variation feeds into the system, resulting in
"explosive" radiation (i.e., punctuational evolution).
Key words: Lentibulariaceae, molecular evolution, Pinguicula, speciation rate, Utricularia