Phylogenetic relationships among 75 species of the carnivorous butterwort and bladderwort family Lentibulariaceae, representing the three recognized genera (Pinguicula, Genlisea and Utricularia), were assessed by cladistic analysis of DNA sequences from the plastid rps16 intron and the rmL-F region. Sequence data from the two loci were analysed both separately and in combination. Consensus frees from all analyses are congruent, and parsimony jackknife results demonstrate strong support for relationships both between and within each of the three demonstrably monophyletic genera.
The cladistic analysis shows that genus Pinguicula is sister to a Genlisea-Utricularia clade, the phylogenetic structure within which closely follows Taylor's recent sectional delimitations based on morphology. Three principal clades are shown within Utricularia, with the basal sections Polypompholyx and Pleiochasia together forming the sister lineage of the remaining Utricularia species.
Of the fundamental morphological specialisations, the stoloniferous growth form apparently arose independently within Genlisea and Utricularia three times, and within Utricularia itself, perhaps more than once. The epiphytic habit has evolved independently at least three times, in Pinguicula, in Utricularia section Phyllaria, and within the two sections Orchidioides and Iperua (in the latter as bromeliad tank-epiphytes). The suspended aquatic habit may have evolved independently within sections Utricularia and Vesiculina.
Biogeographic optimization on the consensus tree demonstrates patterns commonly associated with the boreofropics hypothesis and limits the spatial origin of Lentibulariaceae to temperate Eurasia or fropical America.
The molecular phylogenetic hypothesis for the Lentibulariaceae shows 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 capture prey in intricately-designed suction bladders or corkscrew-shaped lobster-pot traps. In contrast, the flypaper-trapping butterworts maintain vegetative structures typical of angiosperms.
Molecular rate analyses shows that bladderwort genomes appear to 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.
Molecular substitution rate heterogeneity between butterworts and bladderworts is investigated using relative rate tests for eleven coding loci. This work follows the observation of significant rate disparity for non-synonymous rates for the coxI and rbcL coding loci, suggestive of accelerated protein evolution in bladderworts.
In addition, nucleotide substitution rates were examined using relative ratio tests to determine whether absolute rates change proportionally across the Lentibulariaceae lineages at both non-synonymous and synonymous sites. Synonymous rate (Ks) was found to change proportionally across the eleven loci. This is consistent with a 'lineage effect' were genes do not act independently in their rates of change. In contrast, non-synonymous rates (KA) vary significantly for several genes which suggests that negative or positive selective forces may be acting independently among the eleven loci. A similar study using highly divergent taxa correlates with the current study, indicating the above pattern may be generalized across different taxonomic levels.
Evidence of positive selection was found for the coxI and ndhB genes with the ratio of non-synonymous change exceeding that of the synonymous rate.