Polemoniaceae

Abstract: Nucleotide sequences of the plastid encoded gene matK were examined for their potential utility in phylogenetic analyses within angiosperm families. Sequences 661 bases in length were obtained from twenty species of Polemoniaceae. Phylogenetic analyses resulted in four equally parsimonious trees with a consistency index of 0.70. Several well supported groups allowed us to test hypotheses of relationship within Polemoniaceae. The segregation of Ipomopsis and Allophyllum from Gilia was supported by the placement of each in distinct groups separate from a group of four species of Gilia. Several strongly supported groups include genera now placed in different tribes. There was no support for the current separation of temperate Polemoniaceae into two tribes. The tropical genera were resolved as basal and paraphyletic within the family. The family as a whole was monophyletic with no support for the segregate family Cobaeaceae. Sequences of matK, a gene that had not been used previously for phylogenetic analyses, provided a sufficient number of reliable characters for phylogenetic analysis within Polemoniaceae. Pairwise comparisons of matK and rbcL sequences of the same taxa were performed. Sequences of matK varied at an overall rate twice that of rbcL sequences. Substitutions at the third codon position predominated in rbcL sequences, while in matK substitutions were more evenly distributed across codon positions.

Abstract: Clines across hybrid zones can be produced by several forms of natural selection. We illustrate an approach to studying pollinator-mediated selection in plant hybrid zones, using two species of Ipomopsis (Polemoniaceae) as a model system. We measured visitation to flowers in natural and experimental populations by two major types of pollinators, hummingbirds and hawkmoths, at up to three different spatial scales. Using measures of pollinator visitation, we calculated phenotypic selection gradients and characterized the form of selection in the hybrid zone. Hummingbirds overvisited Ipomopsis aggregata compared with Ipomopsis tenuituba and morphological hybrids at all spatial scales, especially the largest scale of kilometers. These responses may depend in part on the presence of other hummingbird-visited plants in the community. Hummingbird behavior produced directional selection favoring wide corolla tubes and intense red coloration. Hawkmoths, in contrast, overvisited plants with narrow corolla tubes. Wh...

Abstract: Water loss through inflorescences may place extreme demands on plant water status in arid environments. Here we examine how corolla size, a trait known to influence pollination success, affects the water cost of flowering in the alpine skypilot, Polemonium viscosum. In a potometry experiment, water uptake rates of inflorescences were monitored during bud expansion and anthesis. Corolla volume of fully expanded flowers predicted water uptake during bud expansion (R 2=0.61, P=0.0375) and corolla surface area predicted water uptake during anthesis (R 2=0.59, P=0.044). To probe mechanisms underlying the relationship between corolla size and water uptake, cell dimensions and densities were measured in several regions of fully expanded corollas. Corolla length was positively correlated with cell length in the middle of the corolla tube and cell diameter in the corolla lobe (Pearson's r from 0.26–0.33, n=86, P ≤ 0.05). Cell density was negatively correlated with cell dimensions in the upper corolla tube and lobe (Pearson's r from –0.39 to –0.42, P ≤ 0.0015). These findings suggest that more water may be required to maintain turgor in large corollas in part because their tissues have lower cell wall densities. The carbon cost of water use by flowers was assessed in krummholz and tundra habitats for P. viscosum flowering, respectively, during dry and wet portions of the growing season. For plants in full flower, average leaf water potentials were significantly more negative (P=0.0079) at mid-day in the krummholz (June) than in the tundra (July), but were similar before dawn (P=0.631). Photosynthetic rate at the time of flowering declined significantly with increasing corolla size in the krummholz (P=0.0376), but was unrelated to corolla size on the tundra (P>0.72). Plants losing water through large corollas may close leaf stomata to maintain turgor. If photosynthesis limits growth in this perennial species, then the water cost of producing large flowers should exacerbate the cost of reproduction under dry conditions. Such factors could select for flowers with smaller corollas in the krummholz, countering pollinator-mediated selection and helping maintain genetic variation in corolla size components of P. viscosum.