Pollination biology ofOpuntia polyacantha andOpuntia phaeacantha (Cactaceae) in southern Colorado

The phenology, compatibility system, and pollinator fauna ofOpuntia polyacantha Haw. andO. phaeacantha Engelm. in southern Colorado were studied and compared. The total blooming periods overlap, but the peak of blooming differs between the species withO. polyacantha blooming first and for longer. Neither species is apomictic,O. polyacantha is largely self-incompatible andO. phaeacantha is self-compatible but may not automatically fully self-pollinate. Examination of flowering structures showed that the former has larger flowers with more perianth parts and heavier (but fewer) anthers. Further the flowers of the allogamous species are visited by greater diversity (but similar abundance) of pollinators. Medium to large bees of the generaDiadasia, Lithurge, Melissodes, Bombus, Agapostemon andMegachile were found to be effective pollinators of the Opuntias studied. The two species were compared as to their floral attributes, breeding systems, and pollinators, and the possible role of competition for pollinators is discussed with respect to its role in their evolutionary paths.     

Pollination ofOpuntia lindheimeri and related species

The large, yellow, bowl-shaped flowers ofOpuntia lindheimeri, O. discata, O. phaeacantha major, andO. compressa in Texas are visited by various species of beetles and bees. The beetles and small bees (Perdita, Dialictus) are pollen thieves. The pollinators are the medium-sized and larger bees (Melissodes, Diadasia, Lithurge, Megachile, Agapostemon, etc.). Different species of theOpuntia lindheimeri group have the same pollination system and there is no evidence of any floral isolation between them. The pollination system of these species ofOpuntia in Texas is essentially the same as that ofEchinocereus fasciculatus andFerocactus wislizeni in Arizona.Pollination of North American Cacti, II.—SeeGrant & Grant (1979).     

Pollination of Campanula rapunculus L. (Campanulaceae): How much pollen flows into pollination and into reproduction of oligolectic pollinators?

We studied an isolated population of Campanula rapunculus and two oligolectic bee species of Chelostoma (Megachilidae), their main pollinators. The population of C. rapunculus consisted of 2808 plants. Measurements of pollen flow showed that 3.7% of the pollen produced by a flower contribute to pollination, 95.5% was collected by bees for their offspring and 0.8% remained on the styles. Pollen analyses of brood cells of Chelostoma rapunculi revealed that females collected on average 4.9 million Campanula pollen to rear one bee. We calculated that approximately 1588 bees of this species could have been reared at the study site during the studied season. The amount of potentially viable pollen deposited on stigmas was 3.6 to 10.7 times higher than the number of ovules. We discuss morphological features of the flowers which may lower the pollen removal rate per bee visit and consequently cause a high visitation and pollination rate.The study was supported by a joint project CAPES / DAAD (Probral 112/00). We thank NaBu (Naturschutzbund) Bonn and the Untere Landschaftsbehörde Siegburg for the permission to work at the Natural Reserve Dünstekoven.     

Variable self-compatability inNeolloydia intertexta (Cactaceae)

Self and outcross pollination treatments were applied toNeolloydia intertexta. Two distinct patterns of seed production were found, and are correlated with self-pollinated outcrossed treatments. The outcrossed result resembles the field exposed crop. The untouched controls produce a similar pattern to the actively selfed group. The self treatments produce substantially less seed than the outcrosses; thus, self-compatability is incomplete.     

Pre-release assessment ofNanaia sp. [Lepidoptera: Phycitidae] fromOpuntia pascoensis for biological control ofOpuntia aurantiaca [Cactaceae]

Nanaia sp. was collected onOpuntia pascoensis Britton & Rose in Peru and introduced into South Africa for biological control ofOpuntia aurantiaca Lindley. Since this is a new insect-plant association the chances of successful biological control could theoretically be enhanced. However, pre-release insectary studies showed that apart from the adverse affects of insectary rearing, larval development was slower, less larvae survived, smaller adults emerged and reproduction was suppressed onO. aurantiaca compareded toO. pascoensis. The new association ofNanaia sp. onO. aurantiaca will probably not succeed and, although field trials should be conducted to confirm this, an extensive mass-rearing and release programme would be a waste of time, finances and effort.      

Foraging behavior of three bee species in a natural mimicry system: female flowers which mimic male flowers in Ecballium elaterium (Cucurbitaceae)

Summary The behavior of Apis mellifera and two species of solitary bees which forage in the flowers of monoecious Ecballium elaterium (L.) A. Rich (Cucurbitaceae) were compared. The female flowers of E. elaterium resemble male flowers visually but are nectarless, and their number is relatively smaller. Apis mellifera was found to discriminate between the two genders and to pay relatively fewer visits to female flowers (mean of 30% relative to male flowers) from the beginning of their activity in the morning. The time spent by honeybees in female flowers is very short compared to that spent in male flowers. It is surmised that the bees remember the differences between the flowers where they foraged on the previous days. In contrast, the two species of solitary bees Lasioglossum politum (Morawitz) (Halictidae) and Ceratina mandibularis Fiese (Anthophoridae) visit the female flowers with nearly equal frequencies at the beginning of each foraging day and stay longer in these flowers. Over the day there is a decline in the relative frequency of visits to female flowers and also in the mean time spent in them. The study shows that bees can collect rewards at high efficiency from the flowers of Ecballium elaterium because of their partial discrimination ability and the scarcity of the mimic flowers. It is suggested that the memory pattern of some solitary bees may be different from that of Apis mellifera. It seems that the limited memory and discrimination ability of bees can lead to a high frequency of visits to the mimic flowers during a long flowering season.     

Population variability in the genusTrichocereus (Cactaceae) in central Chile

Trichocereus has 4 species in central Chile. Population analyses indicate that introgressive hybridization has occurred betweenT. chilensis andT. litoralis in the Valparaíso and Santiago coast ranges. A taxonomic key is presented.     

Eine neue Untergattung vonGymnocalycium (Cactaceae): SubgenusPirisemineum

A new subgenus ofGymnoalycium is described; its distribution and position within the genus are briefly discussed.

     

Morphology and ultrastructure of Mammillaria gracillis (Cactaceae) in in vitro culture

Morphogenetic status of cactus Mammillaria gracillis Pfeiff. tissue culture was studied by light and electron microscopy. In vitro propagated shoots spontaneously developed callus. This callus regenerated normal and hyperhydric shoots without exogenous hormones. Tumour tissue induced by wild or rooty strains of Agrobacterium tumefaciens never expressed any morphogenetic potential. Light microscopy showed cellular characteristics of morphologically different tissues. Ultrastructural studies revealed changes in plastids: secondary dedifferentiation of mature chloroplasts, thylakoid swelling and disruption, phytoferritin accumulation, plastid elongation and increase in size. Changes in chlorophyll and carotenoid content were in accordance with degradation of the thylakoid system. Plastids were confirmed as very sensitive organelles to an artificial hyperhydric environment as well as to Agrobacteria-mediated cell transformation.     

Competition between the oligolectic beePtilothrix plumata (Anthophoridae) and the flower closing beetlePristimerus calcaratus (Curculionidae) for floral resources ofPavonia cancellata (Malvaceae)

The flowers ofPavonia cancellata, a creeping ruderal half-shrub of northeastern Brazil, open synchronously at 6:00 h with all anthers already dehisced. The oligolectic beePtilothrix plumata was the most effective pollinator. During 90—180 min, female bees make up to 40 brief pollen collection trips to provision their brood cells. The pollen of about 40 flowers ofP. cancellata is needed to feed one bee larva. The most frequent flower visitors, however, are the specialized curculionid beetlesPristimerus calcaratus, which do not crosspollinate the flowers. They perforate the epidermis with their mouthparts, provoking dehydration, and then actively close the loose petals with their legs. Two hours after opening, half of the flowers had already been closed by the beetles. We interpret the fast, uninterrupted pollen foraging ofPtilothrix plumata bees as a strategy adapted to synchronous pollen presentation ofPavonia and to competition withPristimerus calcaratus: the female bees have to provision their brood cells before the beetles succeed in closing the flowers.     

The reproductive biology and effective pollinators of the endangered beardtonguePenstemon penlandii (Scrophulariaceae)

Penland's beardtongue, a rare endemic plant of the Colorado Plateau, displays a mixed breeding system. Plants are partially self-compatible but set more fruits when cross-pollinated than when self-pollinated. Fruit production is significantly increased by pollinators. However, in two years of study there was no indication that fruit set was being limited by inadequate pollinator visitation. Pollinator effectiveness was judged by correlating bee behavior at the flowers with analysis of the pollen carried on bee bodies. The most important pollinators were native megachilid bees, particularly in the genusOsmia. The bees that pollinate Penland's beardtongue are essential to its reproduction and must be preserved along with this rare plant.     

The perfume flowers ofCyphomandra (Solanaceae): Pollination by euglossine bees,bellows mechanism,osmophores, and volatiles

The perfume syndrome and pollination by fragrance-collecting euglossine bees in the neotropic solanaceous genusCyphomandra was confirmed by field observations. In SE Brazil,C. sciadostylis was visited byEufriesea violaceae, andC. diploconos byEuglossa mandibularis; C. hartwegii was pollinated byEulaema meriana in Costa Rica. The primary attractant, fragrant droplets that ooze from the dorsally bulged connectives, is mopped up by the males with the forebasitarsi. Thereby, the poricidal thecae are inadvertently pushed causing the dry pollen to dust the bee's sternum. The number and direction of the pollen jets are related to pollinator size and stigma structure. The flowers are homogamous, selfsterile, and last three days. The androecium is optically non-contrasting or has cryptic colour. Flowers ofC. sciadostylis andC. diploconos undergo a colour change and an almost three-fold increase in corolla size when scent production and visits cease. The dorsal papillar epidermis of the connective is underlain by a glandular parenchyma typical of osmophores. GC techniques revealed germacrene D as the main component in the mentholic scent ofC. sciadostylis, ipsdienol, heneicosane, and tricosane as dominant in the nutmeg-like scent ofC. diploconos, and benzyl acetate and benzyl alcohol in the sweet fragrance ofC. hartwegii. In all cases, these were accompanied by numerous minor components of heterogeneous chemical nature.—Pollen release by means of a peculiar pneumatic bellows mechanism appears as a necessary and probably ubiquitous feature ofCyphomandra. Even a slight pressure exerted upon the thin, elastic thecal walls blows pollen jets through the pores. Unusual anatomic changes accompany anther maturation. Initially voluminous parenchymatic locular intumescences (placentoids) contract completely during meiosis, then expand once more when the pollen is ripe, pushing the grains against the locular wall, and contract a second time, allowing air to enter the thecae.—Cyphomandra pinetorum was found to be exceptional in exhibiting a pollen flower syndrome, and not cryptical but optically contrasting yellow anthers, as known forSolanum.     

Second generation experimental hybridizations in theEchinocereus ×lloydii complex (Cactaceae), and further documentation of dioecy inE. coccineus

Artificial second generation and backcross hybrids involvingEchinocereus dasyacanthus (Texas rainbow cactus),E. coccineus (a species of claret-cup cactus), andE. ×lloydii (Lloyd's hedgehog cactus) were examined for morphological and reproductive characteristics. The hybrids grew from seed to flower in about four years, and they exhibited high fertility as measured by pollen stainability, crossability, and fruit-set. A rare breeding system inCactaceae, dioecy, was further examined inE. coccineus, using field and controlled pollination tests. Functional dioecy was documented forE. coccineus in Trans-Pecos Texas. All results suggested thatE. ×lloydii in eastern Pecos County, Texas, is a complex and dynamic population probably comprising first and later generation hybrids, including backcross hybrids. The experimental hybridizations also tended to support the occurrence of introgression into both putative parental species.     

Pollination in Turnera subulata (Turneraceae): Unilateral reproductive dependence of the narrowly oligolectic bee Protomeliturga turnerae (Hymenoptera, Andrenidae)

Turnera subulata Smith (Turneraceae) is a subshrub with distylic flowers, common as a ruderal plant in NE-Brazil. We studied the pollination biology of a population in João Pessoa, Paraíba, paying attention to effective pollinators and characteristics of short- and long-style morphs. The flowers attracted insects of 28 species, predominantely bees. Several bee species were observed to be effective pollinators, including highly eusocial species, polylectic solitary species (Centris and Xylocopa) and 1 oligolectic species, Protomeliturga turnerae (Andrenidae, Panurginae). The latter species shows reproductive dependency on T. subulata. The plant species, on the other hand, does not depend on this specialized bee, as reproductive success was also guaranteed by the other polylectic flower visitors. Floral characteristics of both floral morphs are discussed with respect to pollination biology.     

Antigenic patterns of seed proteins in Opuntioideae (Cactaceae)

The antigenic patterns recognised by Western blotting in seed proteins of species of Opuntioideae (Cactaceae) were analysed in an attempt to evaluate their usefulness in systematics. Total protein profiles were also analysed by SDS–PAGE. The resulting similarity and distance matrices were further used to carry out Cluster Analysis (UPGMA) and Principal Coordinates Analysis. Populations of Opuntia cardiosperma were found to exhibit a prominent morphological uniformity, a unique electrophoretic pattern and a uniform antigenic pattern. The latter was obtained using anti-O. cardiosperma as antiserum. Results from the qualitative and quantitative interspecific analyses of antigenic profiles helped to characterise all the species studied. Tephrocactus articulatus and Cylindropuntia imbricata evidenced lower affinity with O. cardiosperma than the species of Opuntia s.s. Our results demonstrate that in Cactaceae, Western blotting analysis broadens the usefulness range of immunological techniques at the specific level and complements the information collected from electrophoretic profiles.     

Reproductive biology of the melon cactus, Melocactus curvispinus (Cactaceae)

We examined the reproductive biology of Melocactus curvispinus Pfeiffer (Cereeae, Cactoideae) in xeric areas of northern Venezuela. Floral traits correspond to a classic hummingbird-pollination syndrome; however, pollination is shared between hummingbirds, Leucippus fallax (Bourcier 1843), and anthophorid bees, Ceratina sp. Reproduction occurs during most of the year. Anthesis and nectar secretion occur between noon and sunset. Average daily nectar production per flower was 163.1 l, nectar sugar concentration between 29.1 and 30.2% (w/w). Hummingbirds promoted inter-plant pollen movement and were relatively more reliable floral visitors than anthophorid bees, but these insects had a higher frequency of floral visits (28.75/day) than hummingbirds (4.96/day). M. curvispinus is self-compatible and autogamous. By combining extended reproductive activity, frequent animal-mediated pollination, and selfing capabilities, this cactus possesses a mating strategy that guarantees reproduction under variable environmental conditions. We argue that based on its reproductive biology, M. curvispinus should be considered an example of evolutionary transition towards selfing within tribe Cereeae.     

Differences in pollinator effectiveness of birds and insects visiting Banksia menziesii (Proteaceae)

Summary The effectiveness of nectarivorous birds, introduced honey bees and staphylined beetles as pollinators of Banksia menziesii was assessed. Staphylinids removed substantial amounts of pollen but did not deposit any onto stigmata. Abundance of beetles on inflorescences was related to the mean number of florets opening per day. Honey bees collecting pollen were more likely to effect pollination than those collecting nectar which only contacted stigmata when arriving or leaving an inflorescence. Nectar-foraging birds probed between florets 10.2±0.8 (±SE) times, contacting 8–16 stigmata during each probe. Bees visited inflorescences ten times more frequently than birds although they deposited only 25% of the pollen that birds did on stigmata. Fruit set was ten times greater on inflorescences visited by birds than on inflorescences visited by bees. Bees were capable of removing as much pollen as birds but, because of direct pollen transfer to birds when florets opened during foraging, actual removal was probably much less. Selection for floret opening during nectar foraging by birds may have resulted from pollen removal by non-pollinating animals, such as staphylinids.     

Selenicereus wittii (Cactaceae): An epiphyte adapted to Amazonian Igapó inundation forests

The biology, ecology, and distribution ofSelenicereus (Strophocactus)wittii, one of the least known taxa ofCactaceae, are described. This epiphyte climbs appressed to tree trunks with leaf-like, flattened stems and is found exclusively along the high waterline of black water rivers (Rio Negro, Vaupés, Apaporis) in the Igapó inundation forests of Amazonia. Ecophysiologically,S. wittii is a crassulacean acid metabolism (CAM) plant. It bears white, nocturnal flowers 25 cm in length which emit a fragrance consisting mainly of benzylalcohol, benzyl benzoate, and benzyl salicylate. They exhibit an extreme sphingophilous syndrome as an adaptation to pollination by probably only two species of hawkmoth from the generaAmphimoena andCocytius. The seeds, aberrant for the family, contain air-filled chambers and are water-dispersed. Thus,S. wittii represents the paradoxical life form of an hydrochorous epiphytic cactus which withstands periodical inundation.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday     

The effects of floral display on pollinator visitation vary among populations ofPhacelia linearis (Hydrophyllaceae)

Summary Individual plants in gynodioecious populations ofPhacelia linearis (Hydrophyllaceae) vary in flower gender, flower size, and flower number. This paper reports the effects of variation in floral display on the visitation behaviour of this species' pollinators (mainly pollen-collecting solitary bees) in several natural and three experimental plant populations, and discusses the results in terms of the consequences for plant fitness. The working hypotheses were: (1) that because female plants do not produce pollen, pollen-collecting insects would visit hermaphrodite plants at a higher rate than female plants and would visit more flowers per hermaphrodite than per female; and (2) that pollinator arrival rate would increase with flower size and flower number, the two main components of visual display. These hypotheses were generally supported, but the effects of floral display on pollinator visitation varied substantially among plant populations. Hermaphrodites received significantly higher rates of pollinator arrivals and significantly higher rates of visits to flowers than did females in all experimental populations. Flower size affected arrival rate and flower visit rate positively in natural populations and in two of the three experimental populations. The flower size effect was significant only among female plants in one experimental population, and only among hermaphrodites in another. The effect of flower number on arrival rate was positive and highly significant in natural populations and in all experimental populations. In two out of three experimental populations, insects visited significantly more flowers per hermaphrodite than per female and visited more flowers on many-flowered plants than on few-flowered plants, but neither effect was detected in the third experimental population. Because seed production is not pollen-limited in this species, variation in pollinator visitation behaviour should mainly affect the male reproductive success of hermaphrodite plants. These findings suggest that pollinator-mediated natural selection for floral display inP. linearis varies in space and time.     

Phylogenetic relationships in Peniocereus (Cactaceae) inferred from plastid DNA sequence data

The phylogenetic relationships of Peniocereus (Cactaceae) species were studied using parsimony analyses of DNA sequence data. The plastid rpl16 and trnL-F regions were sequenced for 98 taxa including 17 species of Peniocereus, representatives from all genera of tribe Pachycereeae, four genera of tribe Hylocereeae, as well as from three additional outgroup genera of tribes Calymmantheae, Notocacteae, and Trichocereeae. Phylogenetic analyses support neither the monophyly of Peniocereus as currently circumscribed, nor the monophyly of tribe Pachycereeae since species of Peniocereus subgenus Pseudoacanthocereus are embedded within tribe Hylocereeae. Furthermore, these results show that the eight species of Peniocereus subgenus Peniocereus (Peniocereus sensu stricto) form a well-supported clade within subtribe Pachycereinae; P. serpentinus is also a member of this subtribe, but is sister to Bergerocactus. Moreover, Nyctocereus should be resurrected as a monotypic genus. Species of Peniocereus subgenus Pseudoacanthocereus are positioned among species of Acanthocereus within tribe Hylocereeae, indicating that they may be better classified within that genus. A number of morphological and anatomical characters, especially related to the presence or absence of dimorphic branches, are discussed to support these relationships.