Morphological variation and the process of domestication of Stenocereus stellatus (Cactaceae) in Central Mexico

Morphological variation was analyzed in wild, managed in situ, and cultivated populations of the columnar cactus Stenocereus stellatus in central Mexico. The purpose was to evaluate whether morphological divergence between manipulated and wild populations has resulted from domestication processes. Variation of 23 morphological characters was analyzed among 324 individuals from 19 populations of the Tehuacán Valley and La Mixteca Baja. Multivariate statistical analyses were used to group individuals and populations according to their morphological similarity. Individuals grouped according to the way of management and fruit characteristics were the most relevant for grouping. Within each region, sweet fruits with pulp colors other than red were more frequent in cultivated populations, where fruits were also larger, contained more and bigger seeds, and had thinner peel and fewer spines than fruits from wild individuals. Phenotypes common in managed in situ and cultivated populations generally occur in the wild but in lower frequencies. Artificial selection has thus operated by enhancing and maintaining desirable rare phenotypes in managed in situ and cultivated populations, causing divergent patterns of morphological variation from wild populations. Cultivation has caused the strongest level of divergence, but divergence has also been significant with management of wild populations in situ.     

Bat and hummingbird pollination of an AUTOTETRAPLOID COLUMNAR CACTUS,Weberbauerocereus weberbaueri (Cactaceae)

I present data on flower morphology, pollination, breeding system, and genetic diversity of the columnar cactus Weber-bauerocereus weberbaueri at 2500 m elevation in southwestern Peru. Weberbauerocereus weberbaueri is a self-compatible columnar cactus that is visited and pollinated by one species of rare endemic bat, Platalina genovensium, and two species of hummingbirds, Patagona gigas and Rhodopis vesper. W. weberbaueri exhibits pronounced interplant variation in floral color and size, and flowers exhibit traits corresponding to both bat and hummingbird pollination syndromes. Starch-gel electrophoresis of flower bud tissue indicated that W. weberbaueri is an autotetraploid and that genetic diversity (Hep = 0.257) of the study population was high relative to diploid plants but similar to other tetraploid species. Initial fruit set from pollinator exclusion experiments conducted in 1991 and 1993, at the onset of and after a drought associated with the El Niño event of 1991–1992, revealed that bats were the most important pollinators in 1991, but that hummingbirds and diurnal insects were most important in 1993. In both years, however, autogamy and lepidopteran larval infestation of fruits reduced differences in mature fruit production among pollinator exclusion treatments so that differences in mature fruit set were not statistically significant. Reduced bat pollination in 1993 is attributed to the reduced abundance of bats at the study site during a drought caused by El Niño. I hypothesize that interaction among several factors, including tetraploidy, autogamy, larval infestation of developing fruits, and variation in pollinator abundance, may not result in strong selection for a bat vs. hummingbird floral morph, thus allowing the persistence of floral variation in this cactus.     

Nectar sugar composition and concentration in relation to pollination syndromes in Bromeliaceae

A first comprehensive dataset of nectar sugar composition and concentration in Bromeliaceae is presented, covering 111 species belonging to all three subfamilies. Based on this dataset, we examined the relationship between nectar traits and pollination syndromes in the family. Sugars in samples were assayed by high pressure liquid chromatography. All sampled species were grouped into three broad categories (trochilophilous, chiropterophilous, or lepidopterophilous) according to their main pollination mode. Significant differences between the different pollination syndromes were found in nectar sugar composition as well as concentration. For a total of four genera (Guzmania, Pitcairnia, Tillandsia and Vriesea), a comparison of nectar composition showed significant differences between trochilophilous and chiropterophilous species. Data presented here indicate that the characteristics of nectar in Bromeliaceae are predominantly determined by putative adaptations of nectar sugars to preferences of the pollinators rather than by phylogenetic relations.     

Reproductive biology and the process of domestication of the columnar cactus Stenocereus Stellatus in Central Mexico

Pollination biology, breeding system, and floral phenology of the columnar cactus Stenocereus stellatus were studied in wild, wild managed in situ and cultivated populations of central Mexico, in order to examine whether these aspects have been modified under domestication and whether they determine reproductive barriers between wild and manipulated individuals. Individuals of both wild and manipulated populations are self-incompatible, indicating that artificial selection has not modified the breeding system. Their pollination biology is also similar. Anthesis is mainly nocturnal, with a peak of nectar production between 0200 and 0400 when the stigma presents maximum turgidity. Nocturnal visitors are the effective pollinators. Nearly 75% of flowers exposed for nocturnal pollination set fruit, while none of the flowers exposed for diurnal pollination produced fruits. The bats Leptonycteris curasoae, L. nivalis, and Choeronycteris mexicana (Glossophaginae) are the most likely pollinators, and their time of foraging is synchronized with the time of nectar production and stigma receptivity in S. stellatus. Bats potentially move pollen over a considerable distance, so there is apparently no spatial isolation to prevent pollen exchange between wild and cultivated populations. Phenological studies showed that there are also no apparent temporal barriers. However, manual cross pollination failed between some domesticated and wild phenotypes, suggesting that gene flow between wild and cultivated populations might be limited by pollen incompatibility.     

Diurnal and nocturnal pollination of Silene alba (Caryophyllaceae)

Flowers that are open for >12 h may be visited by both diurnal and nocturnal pollinators. I compared the effectiveness (measured as seed production and pollen movement distance) of diurnal and nocturnal pollinators of Silene alba, a species whose flowers open in evening but close by midmorning the following day. By bagging flowers either during evening hours or during daylight hours or both day and night, I compared seed production caused by diurnal and nocturnal pollinators. Flowers exposed only to nocturnal visitors (mostly sphingid and noctuid moths) produced significantly more seeds than flowers exposed only to diurnal visitors (bees, flies, and wasps). Fluorescent dye applied to anthers moved significantly further and to more stigmas at night than during the day. In both measures of pollination effectiveness, nocturnal-visiting moths are better pollinators of S. alba than are the diurnal-visiting bees, flies, and wasps. These data support the hypothesis that floral phenology is an adaptation to expose flowers to the most effective pollinators.     

Pollination biology of two columnar cacti (Neobuxbaumia mezcalaensis and Neobuxbaumia macrocephala) in the Tehuacan Valley,central Mexico

We document the pollination biology and mating systems of Neobuxbaumia mezcalaensis and Neobuxbaumia macrocephala, two Mexican giant columnar cacti. These two species form mixed forests in the western Tehuacan Valley, Mexico. The flowers of both N. mezcalaensis and N. macrocephala exhibit nocturnal anthesis, are self-incompatible, and are pollinated primarily by three species of nectar-feeding bats (Choeronycteris mexicana, Leptonycteris curasoae, and Leptonycteris nivalis). Neobuxbaumia mezcalaensis is androdioecious, a breeding system that appears to be uncommon among Cactaceae. Neobuxbaumia macrocephala is hermaphroditic. We hypothesize that columnar cacti show a geographical dichotomy in floral biology specialization that probably can be related to predictability in pollinator abundance.     

Maintenance of Phenotypic and Genotypic Diversity in Managed Populations of Stenocereus Stellatus (Cactaceae) by Indigenous Peoples in Central Mexico

The columnar cactus Stenocereus stellatus is used in Central Mexico for its edible fruits which are harvested in wild, managed in situ and cultivated populations. Management in situ of wild populations is conducted by selectively sparing and enhancing the abundance of plants with desirable phenotypes when fields are cleared for agricultural use. Cultivation of desirable phenotypes is carried out by vegetative propagation in homegardens. Effects of human management on morphological and genetic variation of S. stellatus were analyzed by comparing morphological diversity indices (MD, based on Simpson’s index) and expected (H_e) heterozygosity indices from allozyme analysis, in wild, managed in situ, and cultivated populations from La Mixteca and the Tehuacán Valley regions. Morphological diversity was similar among regions, but populations from the wetter La Mixteca region averaged higher genetic variation (H_e = 0.279) than populations from Tehuacán (H_e = 0.265). On average, populations manipulated by people had higher levels of variation (MD = 0.479 ± 0.012, H_e = 0.289 in cultivated populations; MD = 0.461 ± 0.014, H_e = 0.270 in managed in situ populations) than wild populations (MD = 0.408 ± 0.017, H_e = 0.253), which is apparently due to a continual introduction and replacement of plant materials in the manipulated populations. The results illustrate that human management may not only maintain but also increase both morphological and genetic diversity of manipulated plant populations in relation to that existing in the wild. Managed in situ and cultivated populations of S. stellatus are important reservoirs of variation, and are crucial for the general maintenance of diversity in wild populations. These populations may play a principal role in designing strategies for the conservation of variation of this cactus.     

The pollination ofStenorrhynchos lanceolatus (Aublet) L. C. Rich. (Orchidaceae: Spiranthinae) by hummingbirds in southeastern Brazil

Hummingbird pollination is documented for a natural population ofStenorrhynchos lanceolatus Aublet. L. C. Rich. occurring in Rio de Janeiro State, southeastern Brazil. At the study site the plants are pollinated byPhaethornis eurynome (Phaethorninae),Thalurania glaucopis (females only) andLeucochloris albicollis (Trochilinae). The plants offer nectar as a reward and the pollinaria become stuck to the surface of the hummingbird's bill while it is probing the flowers. The orchid population received a few (0–4) hummingbird visits per day, with about 83% of the flowers being pollinated. In spite of the low frequency of visits, the granular structure of the pollinarium plus the behaviour of the most frequent pollinators, which tend to visit all the fresh-looking flowers of each inflorescence, a very high fruiting success was promoted. Experimental evidence suggests that the pollinaria may remain up to 6.30 hours on the hummingbird's bill, enhancing the chances of cross-pollination and long-distance pollen flow.     

Beyond the pollination syndrome: nectar ecology and the role of diurnal and nocturnal pollinators in the reproductive success of Inga sessilis (Fabaceae)

Inga species present brush‐type flower morphology allowing them to be visited by distinct groups of pollinators. Nectar features in relation to the main pollinators have seldom been studied in this genus. To test the hypothesis of floral adaptation to both diurnal and nocturnal pollinators, we studied the pollination ecology of Inga sessilis, with emphasis on the nectar secretion patterns, effects of sequential removals on nectar production, sugar composition and the role of diurnal and nocturnal pollinators in its reproductive success. Inga sessilis is self‐incompatible and pollinated by hummingbirds, hawkmoths and bats. Fruit set under natural conditions is very low despite the fact that most stigmas receive polyads with sufficient pollen to fertilise all ovules in a flower. Nectar secretion starts in the bud stage and flowers continually secreting nectar for a period of 8 h. Flowers actively reabsorbed the nectar a few hours before senescence. Sugar production increased after nectar removal, especially when flowers were drained during the night. Nectar sugar composition changed over flower life span, from sucrose‐dominant (just after flower opening, when hummingbirds were the main visitors) to hexose‐rich (throughout the night, when bats and hawkmoths were the main visitors). Diurnal pollinators contributed less than nocturnal ones to fruit production, but the former were more constant and reliable visitors through time. Our results indicate I. sessilis has floral adaptations, beyond the morphology, that encompass both diurnal and nocturnal pollinator requirements, suggesting a complementary and mixed pollination system.     

Possible pollination by hummingbirds inAnthurium sanguineum Engl. (Araceae)

Species ofAnthurium presumably are pollinated by insects. In the montane rainforests of western Colombia we recorded eight species of hummingbirds paying regular visits to the nectar-producing inflorescences ofAnthurium sanguineum. At peak-floweringA. sanguineum plays an important role in the birds' nutrition. Pollen is deposited on the tip of the birds' bills, indicating that pollination by hummingbirds occurs frequently. As no other flower visitors were recorded, we consider hummingbirds the main pollinators toA. sanguineum.     

Floral biology of Echinopsis chiloensis ssp. chiloensis (Cactaceae): Evidence for a mixed pollination syndrome

In this study the flower biology of Echinopsis chiloensis ssp. chiloensis, a columnar cactus occurring in Central Chile, is investigated, in particular its pollination syndrome, its visitors, their frequencies and behaviors and their pollination efficiencies. As statements on floral anthesis of this species are contradictory, this study also intended to elucidate both its beginning and duration. A pollinator exclusion study of a total of 162 flowers from 12 plants was conducted at one of the two study sites. Fruit and seed production as well as seed viability were documented to evaluate pollinator efficiencies.     

Reproductive conflicts ofPalicourea padifolia (Rubiaceae) a distylous shrub of a tropical cloud forest in Mexico

We studied a population of the distylousPalicourea padifolia (Rubiaceae) in a cloud forest remnant near Xalapa City, Veracruz, México to explore possible asymmetries between floral morphs in the attractiveness to pollinators, seed dispersers, nectar robbers, floral parasites, and herbivores. We first assessed heterostyly and reciprocal herkogamy by measuring floral attributes such as corolla length (buds and open flowers), style and anther heights, stigma and stamen lengths and the distance between the anther tip to the stigma lobe. We then estimated floral and fruit attributes such as flower size, anther height, number and size of pollen grains, fruit size, seed size, nectar production, and flower and fruit standing crops to assess differences between floral morphs in attracting and effectively using mutualistic pollinators and seed dispersers. Also, floral parasitism and nectar robbing were assessed in this study as a measure of flower attractiveness to antagonists. The system seems to conform well to classical heterostyly (e.g. reciprocal stamen/style lengths, pollen and anther dimorphism, intramorph incompatibility) yet, there were several tantalizing differences observed between pin and thrum morphs. Thrum flowers have longer corollas and larger but fewer pollen grains than pin flowers. Both morphs produced the same total number of inflorescences, developed the same number of buds, and opened the same number of flowers per inflorescence during the flowering season. Nectar production and sugar concentration were similar between floral morphs but the reward was not offered symmetrically to floral visitors throughout the day. Nectar concentration was higher in pin flowers in the afternoon. The numbers of developing, fully developed, and ripe fruits were the same between floral morphs, however, fruits and seeds were larger than those of thrums. The incidence of fly larvae was higher among thrum flowers and damage by nectar robbing was the same between floral morphs. Fruit abortion patterns of flowers manually pollinated suggest intra-morph sterility (self and intramorph incompatibility). There were no differences between morphs in fruit and seed set per flower following legitimate pollination although thrums were more leaky than the pins (intramorph compatibility).     

Pedilanthus diazlunanus (Euphorbiaceae): pollination by hymenopterans in a bird-pollinated genus

Pollination in the genus Pedilanthus is commonly effected by hummingbirds. Pollination by vespid wasps in Pedilanthus is documented for the first time based on observations of Pachodynerus nasidens and Eumenes americanus pollinating Pedilanthus diazlunanus. An hypothesis concerning the mechanism by which hummingbird pollination was replaced by insect pollination in Pedilanthus is advanced based on observations of insects on P. bracteatus.     

Modified CTAB Procedure for DNA Isolation from Epiphytic Cacti of the Genera Hylocereus and Selenicereus (Cactaceae)

We present a simple protocol for DNA isolation from climbing cacti, genera Hylocereus and Selenicereus. The abundant polysaccharides present in Hylocereus and Selenicereus species interfere with DNA isolation, and DNA extracts, rich in polysaccharides, are poor templates for amplification using polymerase chain reaction (PCR). We used roots as the source tissue due to the lower viscosity of the extracts relative to that of other tissues. The extraction and isolation procedure we devised consists of the following steps: (1) three washes of ground tissue with the extraction buffer to remove the polysaccharides; (2) extraction with high-salt (4 M NaCl) cetyltrimethylammonium bromide (CTAB) buffer to remove the remaining polysaccharides; (3) removal of RNA by RNase; (4) phenol:chloroform extraction to remove proteins; (5) chloroform extraction to remove remaining phenols. The yields ranged from 10 to 20 g DNA/g fresh roots. DNA samples prepared by our method were consistently amplifiable in the RAPD reaction and gave reproducible profiles.     

Hydrophilous pollination and reproductive morphology in the seagrassPhyllospadix scouleri (Zosteraceae)

In the seagrassPhyllospadix scouleri (Zosteraceae) floral aggregates (spadices) occur on short lateral axes produced by subordinate vegetative shoots. The filamentous pollen is both dispersed on the surface of the sea as well as below the surface. In surface pollination, snowflake-like search vehicles (pollen rafts) float and collide with any rigid female inflorescences that emerge from the water surface. In submarine pollination, collinear bundles of pollen grains are dispersed. Analysis of seed set indicates ovule position within the inflorescence to affect likelihood of fertilization in submarine, but not surface-pollinated inflorescences. Agamospermy appears to be unlikely, but the strongly female-biased shoot sex ratio remains to be explained.     

Old World phytophagous bats (Megachiroptera) and their food plants: a survey

The Megachiroptera, with a single family, 43 genera and 174 species, are confined to the Old World tropics and subtropics where they are exclusively phytophagous, feeding upon floral resources (largely nectar and pollen but also petals and bracts), fruit, leaves and water. A literature survey revealed information on the food sources for only 21 genera of bats, these feeding upon 75 genera of flowers, 145 genera of fruit and 10 genera of leaves in a total of 34 orders, 66 families and 198 genera. The bats are likely to pollinate flowers of at least 31 genera and presumably may disperse the seeds of the majority of fruits consumed. Despite our ignorance about the relationship between Megachiroptera and plants, it appears that most bats are catholic in their choice of food, and most plants are visited by a diversity of bats.     

Size-dependent pollination efficiency in Anchusa officinalis (Boraginaceae): causes and consequences

Summary Bumblebees foraging on the self-incompatible Anchusa officinalis fly between near neighbour plants and between near neighbour inflorescences within plants. Although many-flowered plants attracted most bumblebees these plants received fewer visits on a per flower basis than smaller plants, and each bumblebee visited a smaller proportion of the flowers. The calculated effective visitation rate per flower was highest on plants of an intermediate size. If pollen-carryover was assumed to be limited the most efficient plant was predicted to be smaller since the proportion of fertilized flowers per bumblebee visit is expected to decrease further on the largest plants in relation to the total flower number. These predictions were tested by measuring fruit-set in the field. The percentage fruit-set decreased with plant size at all sizes that were investigated. That the most efficient plant was small indicates that pollen-carryover was indeed limited. However, the low percentage fruit-set associated with large size did not present a serious problem since the total estimated seed production per plant still increased with size. Selection favoring smaller plants may be low or absent in Anchusa.     

Pollination ecology and pollination system of Impatiens reptans (Balsaminaceae) endemic to China

BACKGROUND AND AIMS: China is one of the centres of geographical distribution of Impatiens L. Studies of the pollination ecology of this genus in China have, until now, been unreported. Impatiens reptans, a species endemic to China, was studied. The aims were to examine the pollination ecology and pollination system of this species, to compare its pollination ecology with other Impatiens species growing in Sumatra and Japan, and to discuss possible reasons for its limited distribution. METHODS: The pollination ecology of I. reptans was studied by carrying out continuous observations within three naturally growing populations. Its pollination system was studied using different pollination methods, marking and counting pollen grains, assessing pollen viability and observing pollinator behaviour. KEY RESULTS: The flowering phase of the protandrous I. reptans lasted for 89 d. The life span of an individual flower was 3.6 d. Primary pollinators were honey-bees and bumble-bees. Secondary pollinators were diurnal hawk moths and butterflies. Bombus briviceps and Bombus sp. were nectar gatherers. The mean nectar sugar concentration was 29.5 %, and the mean value of sucrose/glucose + fructose was 0.82. The proportion of seed set ranged from 0.857 to 0.873. Distances that seeds were ejected ranged from 0.58 to 1.17 m. Percentage seed germination under controlled conditions was 23.1. Pollen viability was highest on the day of anthesis and thereafter decreased. Ratios of pollen : ovules ranged from 958.8 to 970.6. CONCLUSIONS: Impatiens reptans reproduces by means of cross-pollination. Its dependence on a specialized habitat, a narrow environmental niche, a low percentage of seed germination, and habitat loss could be reasons for its limited distribution and endemism.     

A new pollination system: brood-site pollination by flower bugs in Macaranga (Euphorbiaceae)

Background and Aims Macaranga: (Euphorbiaceae) is a large genus of dioecious trees with approx.260 species. To date, only one pollination study of the genushas reported brood-site pollination by thrips in M. hullettii.In this study, the pollination system of Macaranga tanariusis reported. Methods: The study was conducted on Okinawa and Amami Islands, Japan.Flower visitors on M. tanarius were collected and their pollenload and behaviour on the flowers examined, as well as inflorescencestructure and reward for the pollinators. Key Results: The most abundant flower visitors found on the male and femaleinflorescences were Orius atratus (Anthocoridae, Hemiptera),followed by Decomioides schneirlai (Miridae, Hemiptera). Pollenload on O. atratus from flowering pistillate inflorescenceswas detected as well as from staminate flowers. Orius atratusand D. schneirlai are likely to use the enclosed chambers formedby floral bracts as breeding sites before and during floweranthesis, and feed on nectar on the adaxial surface of flowerbracts. The extrafloral nectary has a ball-shaped structureand the contained nectar is not exposed; the hemipterans piercethe ball to suck out the nectar. Conclusions: The results indicate that the plant is pollinated by flowerbugs breeding on the inflorescences. This study may be the firstreport of pollination systems in which flower bugs are the mainpollinators. Similarity of pollination systems between M. hullettiiand M. tanarius indicates that the two brood-site pollinationsystems have the same origin. The pollinator species belongsto a predacious group, whose major prey includes thrips. Thepollination system might represent a unique example of evolutionfrom predatory flower visitors feeding on the pollinators (thrips)to the main pollinators.