'Anti-bee' and 'pro-bird' changes during the evolution of hummingbird pollination in Penstemon flowers

Floral phenotypes may be as much the result of selection for avoidance of some animal visitors as selection for improving the interaction with better pollinators. When specializing on hummingbird-pollination, Penstemon flowers may have evolved to improve the morphological fit between bird and flower, or to exclude less-efficient bees, or both. We hypothesized how such selection might work on four floral characters that affect the mechanics of pollen transfer: anther/stigma exsertion, presence of a lower corolla lip, width of the corolla tube, and angle of flower inclination. We surgically modified bee-pollinated P. strictus flowers changing one trait at a time to make them resemble hummingbird-pollinated P. barbatus flowers, and measured pollen transfer by bumblebees and hummingbirds. Results suggest that, apart from 'pro-bird' adaptations, specific 'anti-bee' adaptations have been important in shaping hummingbird-flowers. Moreover, some trait changes may have been selected for only if changing in concert with other traits.     

Molecular evolution, adaptive radiation, and geographic diversification in the amphiatlantic family Rapateaceae: evidence from ndhF sequences and morphology

Rapateaceae (16 genera, approximately 100 species) is largely restricted to the tepuis and sandplains of the Guayana Shield in northern South America, with Maschalocephalus endemic to West Africa. The family has undergone extensive radiation in flower form, leaf shape, habit, and habitat. To analyze the evolution of these distributions and traits, we derived a molecular phylogeny for representatives of 14 genera, based on sequence variation in the chloroplast-encoded ndhF gene. The lowland subfamily Rapateoideae is paraphyletic and includes the largely montane subfamily Saxofridericioideae as a monophyletic subset. Overall, the morphological/anatomical data differ significantly from ndhF sequences in phylogenetic structure, but show a high degree of concordance with the molecular tree in three of four tribes. Branch lengths are consistent with the operation of a molecular clock. Maschalocephalus diverges only slightly from other Monotremae: it is the product of relatively recent, long-distance dispersal, not continental drift--only its habitat atop rifted, nutrient-poor sandstones is vicariant. The family appears to have originated approximately 65 Mya in inundated lowlands of the Guayana Shield, followed by: (1) wide geographic spread of lowland taxa along riverine corridors; (2) colonization of Amazonian white-sand savannas in the western Shield; (3) invasion of tepui habitats with frequent speciation, evolution of narrow endemism, and origin of hummingbird pollination in the western Shield; and (4) reinvasion of lowland white-sand savannas. The apparent timing of speciation in the Stegolepis alliance about 6-12 Mya occurred long after the tepuis began to be dissected from each other as the Atlantic rifted approximately 90 Mya. Given the narrow distributions of most montane taxa, this suggests that infrequent long-distance dispersal combined with vicariance accounts for speciation atop tepuis in the Stegolepis alliance.     

Evolution and homology of bird pollination syndromes in Erythrina (Leguminosae)

Erythrina L. (Leguminosae: Phaseoleae) is a pantropical genus of over 100 species, all of which are either hummingbird or passerine pollinated. Phylogenetic hypotheses based on morphological and chloroplast DNA restriction site characters suggest that shifts from passerine to hummingbird pollination have occurred a minimum of four times in the genus. In hummingbird-pollinated species the inflorescences are held upright, the flowers are arranged radially along the axis, and the narrow standard petal is conduplicately folded to form a pseudotube. In most of the passerine-pollinated species, the inflorescences are held horizontally, the flowers are secund, and the standard petal is open so that the nectar and androecium are easily visible and accessible. Nectar amino acid concentrations and sucrose to hexose ratios are closely associated with pollination mode. Despite the general resemblance in flower and inflorescence morphology among species with the same pollination type, homology assessment reveals that petal morphology and size, and calyx and pollen morphology differ. Morphological characters, even if comprising modifications associated with adaptive pollination systems, therefore provide useful phylogenetic information.     

Divergence on floral traits and vertebrate pollinators of two endemic Encholirium bromeliads

Shifts in pollen vectors favour diversification of floral traits, and differences in pollination strategies between congeneric sympatric species can contribute to reproductive isolation. Divergence in flowering phenology and selfing could also reduce interspecific crossing between self‐compatible species. We investigated floral traits and visitation rates of pollinators of two sympatric Encholirium species on rocky outcrops to evaluate whether prior knowledge of floral characters could indicate actual pollinators. Data on flowering phenology, visitation rates and breeding system were used to evaluate reproductive isolation. Flowering phenology overlapped between species, but there were differences in floral characters, nectar volume and concentration. Several hummingbird species visited flowers of both Encholirium spp., but the endemic bat Lonchophylla bokermanni and an unidentified sphingid only visited E. vogelii. Pollination treatments demonstrated that E. heloisae and E. vogelii were partially self‐compatible, with weak pollen limitation to seed set. Herbivores feeding on inflorescences decreased reproductive output of both species, but for E. vogelii the damage was higher. Our results indicate that actual pollinators can be known beforehand through floral traits, in agreement with pollination syndromes stating that a set of floral traits can be associated with the attraction of specific groups of pollinators. Divergence on floral traits and pollinator assemblage indicate that shifts in pollination strategies contribute to reproductive isolation between these Encholirium species, not divergence on flowering phenology or selfing. We suggest that hummingbird pollination might be the ancestral condition in Encholirium and that evolution of bat pollination made a substantial contribution to the diversification of this clade.     

Effects of Inbreeding,Outbreeding, and Supplemental Pollen on the Reproduction of a Hummingbird‐pollinated Clonal Amazonian Herb

Understory herbs are an essential part of tropical rain forests, but little is known about factors limiting their reproduction. Many of these herbs are clonal, patchily distributed, and produce large floral displays of nectar‐rich 1‐d flowers to attract hummingbird pollinators that may transport pollen over long distances. The aim of this study was to investigate the effects of clonality, cross‐proximity, and patchy distribution on the reproduction of the hummingbird‐pollinated Amazonian herb Heliconia metallica. We experimentally pollinated flowers within populations with self‐pollen and with pollen of different diversity, crossed flowers between populations, and added supplemental pollen to ramets growing solitarily or in conspecific patches. Only flowers pollinated early in the morning produced seeds. Selfed flowers produced seeds, but seed number and mass were strongly reduced, suggesting partial sterility and inbreeding depression after selfing. Because of pollen competition, flowers produced more seeds after crosses with several than with single donor plants. Crosses between populations mostly resulted in lower seed production than those within populations, suggesting outbreeding depression. Ramets in patches produced fewer seeds than solitary ramets and were more pollen‐limited, possibly due to geitonogamy and biparental inbreeding in patches. We conclude that high rates of geitonogamy due to clonality and pollen limitation due to the short receptivity of flowers and patchy distribution constrain the reproduction of this clonal herb. Even in unfragmented rain forests with highly mobile pollinators, outbreeding depression may be a widespread phenomenon in plant reproduction.     

A female Lucifer Hummingbird (Calothorax lucifer) with iridescent chin feathers

ABSTRACT.   We report an observation of a female Lucifer Hummingbird ( Calothorax lucifer ) with iridescent feathers on the chin, resembling the plumage of the juvenile male. The female and nest were found in a xeric shrubland in Barranca de Metztitlán Biosphere Reserve, Hidalgo State, Mexico. This is the first definitive report of a breeding female with such plumage, supporting a previous observation in which sex was not confirmed by behavior. Although this condition appears be rare in female Lucifer Hummingbirds, females in other species of hummingbirds exhibit much variation in the amount of iridescent plumage on the chin and in some, such as Costa's Hummingbirds ( Calypte costae ), females commonly exhibit colored feathers on the chin.     

Resource value affects territorial defense by Broad-tailed and Rufous hummingbirds

ABSTRACT.   Territorial behavior of Broad-tailed ( Selasphorous platycercus ) and Rufous ( Selasphorous rufus ) hummingbirds in Colorado was measured at sites with feeders containing10%, 20%, and 30% sucrose solutions, respectively. The presence or absence of territory holders, number of intruders, and intensity of defense were measured at the three levels of energy availability. Migrating Rufous Hummingbirds displaced Broad-tailed Hummingbirds from territories they had defended during the breeding season; Broad-tailed Hummingbirds then defended only lower quality sites. Both Broad-tailed and Rufous hummingbirds employed more energetically expensive behaviors when defending high quality sites, with longer chases more often supplemented with chip calls and hovering. Other investigators have suggested that chip calls and hovering are precursors to a chase. However, I found that chasing was the default response to the presence of an intruder. Chip calls and hovering were added to intensify a chase. In the few cases where chip calls were uttered or hovering occurred without a chase, Rufous Hummingbirds were more likely to exhibit this behavior than Broad-tailed Hummingbirds.