Riqueza y estabilidad de los polinizadores de los cirios (Fouquieria columnaris) del desierto sonorense: Un análisis comparativo

The floral visitors of the boojum tree [Fouquieria columnaris (Kellogg) Kellogg ex Curran] in the Sierra Bacha, Sonora were studied and compared with Humphrey's data collected 30 years ago. The boojum, a species protected by CITES, has a distribution restricted to Baja California and the Sierra Bacha, Sonora. In the later locality, the richness of the pollinator guild -including 18 species of bees, several arthropods and one hummingbird species- is higher than any of the sites studied by Humphrey in Baja California. This disjunct population apparently does not exhibit ecological interactions characteristic of a marginal population supporting the hypothesis of a broader continental distribution of boojum in the past. Its pollinator guild is clearly dominated by polylectic bees, generalists that depend on asynchronous flowering of other plant species offering nectar and pollen resources in this hyperarid landscape. It appears that the stability of this pollinator guild is limited by the large climatic variation between years in the Sierra Bacha, and its effect on the production of floral resources year by year. Although the flowers do not conform to the ornithophyllous floral syndrome of other memebers of the genus, "trap-lining" by hummingbirds -repeated visits of widely-spaced flowering trees- was observed in this population.

And then came molecular phylogenetics—Reactions to a monographic study of Hypericum (Hypericaceae)

Completion of a detailed monograph of Hypericum using traditional methods has stimulated the publication of phylogenetic treatments of the genus using molecular methods. The relationships thereby revealed differ from those of the traditional account in several ways that are discussed here. A key point of conflict concerns taxa that share a specific set of morphological characters, i.e. the ‘Elodes’ syndrome (pseudotubular corolla, sterile stamen fascicles, stamen filaments ± united in the fascicle and sometimes petal appendages), which was found to be paraphyletic in each molecular study. The various groups with this syndrome were shown to have arisen from various parts of Hypericum, apparently suddenly, probably as the result of a genetic switch, the action of which can also be reversed. The formerly segregated genera with this floral syndrome should therefore all be re-incorporated in Hypericum. This necessitates the re-establishment of one section, namely Hypericum sect. Elodea, and recognition of two new sections within Hypericum, namely Hypericum sect. Lianthus and Hypericum sect. Thornea, which are proposed here. The remaining species have resolved in various places in recent molecular phylogenetic trees that differ from each other and from the classification adopted in the monograph. In particular, in molecular results the herbaceous species with ‘3’ (i.e. 2+2+1) stamen fascicles all form a single clade; whereas, in the traditional treatment adopted in the monograph, they form three distinct, distantly related groups. In light of recent molecular studies, Hypericum is now interpreted to comprise two distinct groups (respectively mainly Old World and mainly New World) that differ in the presence or absence of dark (hypericin-containing) glands and in the arrangement of the stamen fascicles. These two clades are described as subgenera, with the New World clade named Hypericum subgenus Brathys. By drawing attention to this grouping, the molecular work has improved on the monograph.

Heterostyly accelerates diversification via reduced extinction in primroses

The exceptional species diversity of flowering plants, exceeding that of their sister group more than 250-fold, is especially evident in floral innovations, interactions with pollinators and sexual systems. Multiple theories, emphasizing flower–pollinator interactions, genetic effects of mating systems or high evolvability, predict that floral evolution profoundly affects angiosperm diversification. However, consequences for speciation and extinction dynamics remain poorly understood. Here, we investigate trajectories of species diversification focusing on heterostyly, a remarkable floral syndrome where outcrossing is enforced via cross-compatible floral morphs differing in placement of their respective sexual organs. Heterostyly evolved at least 20 times independently in angiosperms. Using Darwin's model for heterostyly, the primrose family, we show that heterostyly accelerates species diversification via decreasing extinction rates rather than increasing speciation rates, probably owing to avoidance of the negative genetic effects of selfing. However, impact of heterostyly appears to differ over short and long evolutionary time-scales: the accelerating effect of heterostyly on lineage diversification is manifest only over long evolutionary time-scales, whereas recent losses of heterostyly may prompt ephemeral bursts of speciation. Our results suggest that temporal or clade-specific conditions may ultimately determine the net effects of specific traits on patterns of species diversification.

Floral syndrome in Amelanchier nantucketensis (Rosaceae). II. Bee preference and diversity associated with andropetaly

Pollinator preference has been demonstrated to depend on floral morphology in some plant groups. We tested bee preference for Amelanchier nantucketensis, which has pollen-bearing petals or andropetals, over Amelanchier humilis with its normal petals when these flower together at two Maine sites. In an array experiment with equal floral display for Amelanchier nantucketensis and Amelanchier humilis, almost twice as many bees approached the latter first. Bees responded to some aspect of the larger flowers of Amelanchier humilis when number of inflorescences and height above the ground were similar. We captured 539 bees in 43 species individually on flowers, in malaise traps, and in sweeps; most were common, widely distributed solitary and eusocial bees. Bee species diversity differed slightly between plant species, and guilds differed; 11 bee species were unique to Amelanchier nantucketensis, including 39 individuals of Andrena milwaukiensis, and three species were unique to Amelanchier humilis. For 29 bee species shared by both plant species, abundance on Amelanchier nantucketensis was greater than on Amelanchier humilis for 62%, less for 14%, and the same for 24%. Bees might be attracted to Amelanchier nantucketensis less by andropetaly than by proximity of flowers to the ground, floral density, or unidentified features. Key words: Amelanchier, bees, foraging, morphology, Maine, species diversity.

Floral syndrome in Amelanchier nantucketensis (Rosaceae). I. Floral density, bee activity, and characterization of andropetaly

The clonal shrub Amelanchier nantucketensis is andropetalous; a variable number of petals as well as normal anthers both bear germinable pollen. To determine whether floral density associated with andropetaly is related to activity of native bees on flowers, we compared Amelanchier nantucketensis to Amelanchier humilis and Amelanchier stolonifera, which have sterile petals. In samples from four Maine sites, floral density in Amelanchier nantucketensis was 30.3% greater than that for Amelanchier humilis and 39.5% greater than that for Amelanchier stolonifera; in Amelanchier nantucketensis, flowers were more numerous per cubic metre and distance between flowers was shorter. There was a significant correlation across all sites and species between the number of flowers per plant and number of inflorescences visited per bee in 10 min (r = 0.711, p = 0.0001). Statistical t tests separated Amelanchier nantucketensis from both Amelanchier humilis and Amelanchier stolonifera by plant height, nearest stem, nearest flower, and number of inflorescences visited per bee during 10 min. Plant species classification in a canonical discriminant analysis was 83–93% correct with four plant variables, namely distance to nearest flower, distance to nearest inflorescence, plant width, and plant height. Our findings support optimal foraging theory in that bee visits increase with floral density in these Amelanchier species. Key words: Amelanchier, andropetaly, bees, floral density, morphology, Maine.