Reproductive biology and mating system estimates of two Andean melocacti, Melocactus schatzlii and M. andinus (Cactaceae)

BACKGROUND AND AIMS: The genus Melocactus comprises 36 species of globose cacti with the most derived traits in the Cereeae tribe. It is the proper study system to examine what are the most derived reproductive strategies within that tribe. This study aims to characterize the reproductive biology and to estimate the mating system parameters of two Andean melocacti, Melocactus schatzlii and M. andinus. METHODS: The reproductive attributes of the two species were described, including floral morphology, anthesis patterns, floral rewards, floral visitors and visitation patterns. Levels of self-compatibility and autonomous self-pollination were estimated by hand-pollination experiments. Mating system estimates were obtained by conducting progeny array analyses using isozymes. KEY RESULTS: The flowers of the two species present the typical hummingbird-pollination syndrome. Despite their morphological resemblance, the two species differ in flower size, pollen and ovule production and anthesis pattern. Their main pollinator agents are hummingbirds, four species in M. schatzlii and one species in M. andinus. Both cacti are self-compatible and capable of self-pollination without the aid of pollen vectors. Population-level outcrossing rate was higher for M. schatzlii (t(m)=0.9) than for M. andinus (t(m)=0.4). At the family level, outcrossing rates for most mothers of M. schatzlii were higher (t(m)>0.8) than for M. andinus (t(m)<0.5). CONCLUSIONS: Although the two cacti are capable of selfing, M. schatzlii is a predominantly outcrossing species, while M. andinus behaves as a mixed-mating cactus. Hummingbirds are the only pollinators responsible for outcrossing and gene flow events in these species. In their absence, both melocacti set seeds by selfing. Based on its low population size, restricted distribution in Venezuela, low rates of floral visits, and high levels of inbreeding, M. andinus is considered to be an endangered species deserving further study to define its conservation status.     

Reproductive biology of Oreocereus fossulatus (Cactaceae), a long‐lived columnar cactus endemic to the tropical Andes

The geographic dichotomy hypothesis suggests that columnar cacti inhabiting the tropics depend on flower visitors (birds and bats) for their pollination, showing highly specialized animal‐pollinated systems. This pattern has been demonstrated for the northern hemisphere; however, our knowledge of the species of columnar cacti growing in the southern tropics is still scarce. In this study, we studied the reproductive biology of Oreocereus fossulatus (Cactaceae, Tribe Trichocereae), an endemic, columnar cactus of the tropical Andes, to determine if its pollination system tends to be more generalized (mixed systems of autogamy and xenogamy) than specialized (xenogamy) as a consequence of the geographic position of where it lives. Observations of the frequency of visits showed that Patagona gigas (Trochillidae) is its main pollinator. It visits the flowers when they are open, coinciding with the periods of greater floral reward (dusk and dawn of the first day of anthesis). The treatments of autogamy, xenogamy and geitonogamy produced fruits, showing that O. fossulatus exhibits a generalized pollination system, in the same way as its congeneric species O. celsianus, which is distributed farther south in the Prepuna biogeographical region. Our results suggest that species partially specializing in pollination by hummingbirds and, besides, capable of autopollination, could be common in the tropical and subtropical Andes, probably as a response to the unpredictable environments present in their ecosystems.     

Allozyme diversity and morphometrics of Melocactus paucispinus (Cactaceae) and evidence for hybridization with M. concinnus in the Chapada Diamantina, North-eastern Brazil

BACKGROUND AND AIMS: Melocacatus paucispinus (Cactaceae) is endemic to the state of Bahia, Brazil, and due to its rarity and desirability to collectors it has been considered threatened with extinction. This species is usually sympatric and inter-fertile with M. concinnus, and morphological evidence for hybridization between them is present in some populations. Levels of genetic and morphological variation and sub-structuring in populations of these species were assessed and an attempt was made to verify the occurrence of natural hybridization between them. METHODS: Genetic variability was surveyed using allozymes (12 loci) and morphological variability using multivariate morphometric analyses (17 vegetative characters) in ten populations of M. paucispinus and three of M. concinnus occurring in the Chapada Diamantina, Bahia. KEY RESULTS: Genetic variability was low in both species (P = 0.0-33.3, A = 1.0-1.6, H(e) = 0.000-0.123 in M. paucispinus; P = 0.0-25.0, A = 1.0-1.4, H(e) = 0.000-0.104 in M. concinnus). Deficit of heterozygotes within the populations was detected in both species, with high values of F(IS) (0.732 and 0.901 in M. paucispinus and M. concinnus, respectively). Evidence of hybridization was detected by the relative allele frequency in the two diaphorase loci. High levels of genetic (F(ST) = 0.504 in M. paucispinus and 0.349 in M. concinnus) and morphological (A = 0.20 in M. paucispinus and 0.17 in M. concinnus) structuring among populations were found. CONCLUSIONS: The Melocactus spp. displayed levels of genetic variability lower than the values reported for other cactus species. The evidence indicates the occurrence of introgression in both species at two sites. The high F(ST) values cannot be explained by geographical substructuring, but are consistent with hybridization. Conversely, morphological differentiation in M. paucispinus, but not in M. concinnus, is probably due to isolation by distance.     

Reproductive Biology of the Distylous Manettia luteo-rubra (Rubiaceae)

The reproductive biology of Manettia luteo-rubra was studied in the coastal montane Atlantic rain forest of southeastern Brazil. This Rubiaceae is a perennial vine that flowers all the year round, but has a flowering peak during the dry season. It presents reciprocal herkogamy, thus the plants are morphologically distylous. The morphs occur in a 1:1 ratio, and pollen diameter and corolla length vary between short and long-styled flowers. Manettia luteo-rubra displays typical heterostylous self-incompatibility and sets almost no fruits from self- or intramorph pollinations. The flowers are tubular, red with yellow lobes, and odourless. Anthesis is asynchronous, and the flowers last about four days. Concentration of sugars in nectar is similar in both morphs, ca. 24%, this concentration being typical for hummingbird flowers. Three species of hummingbirds are the major pollinators of the flowers of M. luteo-rubra at the study site: the hermits Phaethornis eurynome and P. squalidus, and the trochiline Thalurania glaucopis. Three species of Heliconius butterflies act as minor pollinators. Both morphs of M. luteo-rubra exhibit natural fruit-set of about 80%, this reproductive output being maintained throughout the year by the pollinators' constancy to the flowers.     

Pollination biology and breeding system of Zeyheria montana (Bignoniaceae)

The reproductive biology of Zeyheria montana was studied through field observations of flower visitors and floral events, controlled manual pollinations, and observations of pollen tube growth and ovule penetration by fluorescence microscopy. Analysis of secretory areas of the nectar chamber was made by flower dissections and histology of serial sections. The flower lasted 6–8 days, but pollen exposure and stigma receptivity occurred only up to the end of the first and second days, respectively. Pollination was effected by several species of hummingbirds, especially Colibri serrirostris. The flowers present a rudimentary, non-functional disc, and secretion of nectar is performed by corolla-borne glandular trichomes. Only hand cross-pollinated and natural-pollinated flowers set fruits. Artificially self-pollinated and non-pollinated flowers dried off after anthesis without presenting any swelling of the ovary. Almost all the ovules in selfed and crossed pistils were penetrated 96 h after pollination. However, a delay in ovule penetration in self-pollinated pistils was verified, which indicates the occurrence of late-acting self-incompatibility.We are grateful to Fundo de Apoio ao Ensino e à Pesquisa (UNICAMP) for financial support, and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the fellowship granted to the first author (this work is part of a Ph.D. thesis presented to UNICAMP, Campinas, SP, Brazil).     

Reproductive biology of the Andean-disjunct genusRetanilla (Rhamnaceae)

Various aspects of the reproductive biology of the Andean-disjunct genusRetanilla (DC.) Brongn. were studied in populations ofR. trinervia andR. ephedra located in central Chile and ofR. patagonica in southern Argentina. Flowering extends from -austral- winter (early spring inR. patagonica) to early summer. The small, white, entomophilous flowers are incompletely protandrous and last four to five days. A weak pleasant odor along with nectar and pollen attract thirty-seven diurnal insect species, ten of which are probable pollinators: these include the honey bee, eight species of solitary bees pertaining toAnthophoridae (1 sp.),Colletidae (3 spp.) andHalictidae (4 spp.), and a nemestrinid fly. Although flower morphology and individual flower phenology do not fully prevent self-pollination (and geitonogamy can easily take place), the level of autogamy is low. Therefore, some self-incompatibility mechanism seems operative inRetanilla. Fruit set of open-pollinated flowers is extremely low, with a maximal value of c. 3% inR. patagonica. In this species, ripe fruits contain on average 1.37 viable seeds. Predispersal (maternal) reproductive success (percent ovules becoming viable seeds) is 2.3%. For medium to full-sized individuals this corresponds to c. 4600 potential offspring per year. As presently known,Retanilla is a reproductively uniform group, in which the Andean disjunction seems to have exerted no particular impact, which is consistent with the view that pollination generalization exerts some stabilizing influence on floral morphology and other reproductive traits.Retanilla expresses a basic rhamnacean set of traits (including protandry and self-incompatibility) showing also high pollen production and secondary pollen presentation. The latter two traits seem characteristic of theRetanilla-Trevoa clade, suggesting that a trend to increased male effort and, perhaps, dependence upon polleneating has evolved within the tribe Colletieae.     

Pollination biology of Harrisia portoricensis (Cactaceae), an endangered Caribbean species

Traits associated with self-pollination are common features of island plant communities. In this work, we studied the pollination biology and the breeding system of Harrisia portoricensis, an island columnar cactus, to test for the presence of inbreeding and inbreeding depression. For H. portoricensis, which bears flowers with typical outcrossing morphology, the results from 322 h of direct observations and videotaping showed that visits to flowers by animals were uncommon. Controlled pollinations demonstrated that H. portoricensis has a partially self-compatible breeding system that it is not autogamous and thus requires an external mechanism for the movement of pollen to set fruit. We detected differences in seed size, seed mass, germination success, and multiplicative fitness estimates between self- and cross-pollination treatments. We found that progeny resulting from natural and self-pollination treatments showed signs of inbreeding depression compared with progeny resulting from cross-pollination; however, the magnitude of the inbreeding depression was less than 50%. Our combined results suggest that for this species an endogamous breeding system should be favored by natural selection.     

Reproductive biology of Ferocactus recurvus (Mill.) Borg subsp. recurvus (Cactaceae) in the Tehuacán‐Cuicatlán Valley,Mexico

• Mexico has one of the highest diversities of barrel cacti species worldwide; however, all are threatened and require conservation policies. Information on their reproductive biology is crucial, but few studies are available. Ferocactus recurvus subsp. recurvus is a barrel cactus endemic to the Tehuacán‐Cuicatlán Valley. Our research aimed to characterise its floral and pollination biology. We hypothesised bee pollination, as suggested by its floral morphology and behaviour, and self‐incompatibility, like most barrel cacti studied.
• Three study sites were selected in the semiarid Zapotitlán Valley, Mexico. We examined 190 flowers from 180 plants to determine: morphometry and behaviour of flowers, flower visitors and probable pollinators, and breeding system.
• Flowers showed diurnal anthesis, lasting 2–5 days, the stigma being receptive on day 2 or 3 after the start of anthesis. Flowers produced scarce/no nectar and main visitors were bees (Apidae), followed by flies (Muscidae), ants (Formicidae), thrips (Thripidae) and hummingbirds (Throchilidae); however, only native bees and occasionally wasps contacted the stigma and anthers. Pollination experiments revealed that this species is self‐incompatible and xenogamous. In natural conditions, fruit set was 60% and cross‐pollination fruit set was 100%. Percentage seed germination resulting from cross‐pollination was higher than in the control treatment.
• Our results provide ecological information for conservation programmes to ensure a high probability of breeding and seed production in natural populations of F. recurvus.

     

Reproductive biology ofAsphodelus aestivus (Asphodelaceae)

InAsphodelus aestivus the large number of showy flowers opened per inflorescence, high nectar and pollen production, and absence of automatic self-pollination, so that insect visitation is necessary for pollination, indicate that cross-fertilization is favoured. LargeHymenoptera are the main pollinators. Hand self-pollinations result in some degree of fruit-set, but cross-pollination also yield low fruit- and seed-set. The perennial habit and polyploid status are in agreement with the breeding system of this species, with sexual reproduction being rather inefficient and active vegetative propagation.     

Reproductive biology ofFrangula alnus (Rhamnaceae) in southern Spain

Various aspects of the reproductive biology of the perennial hermaphroditeFrangula alnus Mill. were studied in two populations located in the province of Cádiz, southern Spain. Flowering extends from the second week of May to early July. The small, whitegreenish, entomophilous flowers are incompletely protandrous and last 8–10 days, but pollen transfer takes place only on days 1–3. A very weak, pleasant odour along with nectar and pollen attract over 45 insect species, of which 21 are probable pollinators. These are mainlyDiptera but also includeHymenoptera and the unusual (as flower visitors)Mecoptera. Reproduction is exclusively sexual and strictly xenogamous, with pollen transfer depending solely on insect vectors. Although flower morphology and individual flower phenology do not fully prevent self-pollination, and geitonogamy can easily take place, the level of autogamy was negligible. Therefore, some self-incompatibility mechanism is operative in this species. Only 2.8% of open-pollinated flowers set fruit. At the flower level, fruit initiation was apparently limited by availability of cross-pollen, which in turn seemed influenced by the structure of the population. The seed/ovule ratio in ripe fruits was ca. 50%. Predispersal (maternal) reproductive success (percent ovules becoming filled seeds) was 1.42%. For mature individuals this corresponded to ca. 430 to 1560 potential offspring per year.     

Distyly and sequential pollinators of Psychotria nuda (Rubiaceae) in the Atlantic rain forest, Brazil

Reciprocal herkogamy is known to promote intermorph-pollination in distylous species, which are generally self- and intramorph-incompatible. Legitimate crossing rates are also influenced by pollinator foraging strategy, which determines most of the pollen flow in natural populations. This study reports on the floral morphology, compatibility relations and pollination biology of Psychotria nuda (Cham. and Schltdl.) Wawra in the Atlantic rain forest, southeastern Brazil, based on floral measurements, hand-pollination experiments and focal observation of floral visitors. It was found that P. nuda does not present an exactly reciprocal herkogamy, however, this morphological trait in P. nuda is as good as in most of Rubiaceae. Reproductive experiments showed compatibility relations similar to those frequently observed in distylous species. The hummingbirds Ramphodon naevius and females of Thalurania glaucopis were the main pollinators of P. nuda, presenting the traplining foraging strategy, which seems to maximize intermorph crosses in P. nuda flowers. These hummingbirds pollinated P. nuda flowers sequentially throughout the flowering period.     

Reproductive biology of the genusDamasonium (Alismataceae)

The reproductive biology of the genusDamasonium was studied in cultivation and in nature. A correlation was shown between flowering time and latitude. All species are self-compatible but the N. American member of the genus (D. californicum) is strongly protandrous and probably experiences high levels of outcrossing in nature. In the European taxa the stamens and the stigmas mature simultaneously but the levels of inbreeding appear to be greater in the southern species (D. bourgeai, D. polyspermum) than in the northern (tetraploid) speciesD. alisma. The Australian memberD. minus resembles the southern European species in being strongly autogamous and bud-pollination was shown to occur. Floral morphology, stigma exertion, pollen/ovule (P/O) ratio and seed weight each show a strong correlation with the degree of autogamy. Vegetative reproduction occurs only inD. californicum andD. alisma through the production of corm-buds. This study suggests that autogamy inDamasonium is accompanied by a shift in resource allocation from male (pollen) toward female (seed) function. However, further studies are required to assess the quality of seeds and their survivorship in nature.     

Reproductive biology of twoPrunus species (Rosaceae) in the Northwest Iberian Peninsula

We studied the reproductive biology ofPrunus spinosa andPrunus mahaleb (Prunoideae, Rosaceae) in the northwest Iberian Peninsula. The two species flowered at the same time (peaking on March 9 and 11, respectively in 1990) but differ significantly in their fruit maturation times. Nectar volume peaked in the early morning in both species, and was ten times greater inP. spinosa than inP. mahaleb. Neither species shows apomixis, nor does fruit-set occur if pollinators are excluded. In both species self-pollination resulted in fewer fruits than open pollination. The principal pollinators belong to theApidae family (79% and 63% of visits toP. spinosa andP. mahaleb, respectively). Results are compared with those for other rosaceous plants with fleshy fruits.     

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.     

濒危植物丰都车前的繁育系统与传粉生物学研究

丰都车前为三峡库区特有珍稀濒危植物,目前仅在重庆市江津支坪镇涂家村附近大中坝上有一小种群分布。以野生种群和移栽种群为对象,通过野外观察和人工授粉实验对丰都车前传粉生物学及繁育系统进行研究。结果表明:(1)丰都车前单花花期约4 d,花序花期约8 d,种群花期约3个月;单花开花进程可分为6个时期:花蕾期、雌蕊伸长期、雄蕊初露期、花瓣展开期、花瓣反折期、枯萎凋谢期。(2)花瓣展开前,柱头先伸出花冠,达最高可受性,之后花瓣展开雄蕊才露出,而此时大部分柱头已枯萎失活丧失可受性,只有少部分具可受性。表现出雌雄异熟的特征,一定程度避免了自交的发生。(3)花粉活力始于雄蕊初露期,花瓣展开、花药开裂时花粉活力最高,至枯萎凋谢前均具有活力。花粉活力最高期避开了柱头可受性最佳期,仅有少部分重叠。(4)繁育系统检测显示,花粉/胚珠比为15373.29,杂交指数为3。结合套袋实验表明,丰都车前可能同时具有风媒和虫媒传粉机制,传粉昆虫为中华蜜蜂、食蚜蝇,但数量偏少,不存在无融合生殖,异交为主,部分自交亲和,有时需要传粉者。(5)开花时期避开了其分布地洪水淹没期,能够顺利完成开花授粉及座果。综上所述,丰都车前的花部特征、开花物候和繁育系统为适应分布地夏季洪水水淹胁迫提供了一定的生殖保障,促进了该种群的续存。     

Reproductive biology of the andromonoecious Cucumis melo subsp. agrestis (Cucurbitaceae)

Background and Aims

Cucumis melo subsp. agrestis (Cucurbitaceae) is cultivated in many African regions for its edible kernels used as a soup thickener. The plant, an annual, andromonoecious, trailing-vine species, is of high social, cultural and economic value for local communities. In order to improve the yield of this crop, the first step and our aim were to elucidate its breeding system.

Methods

Eight experimental pollination treatments were performed during three growing seasons to assess spontaneous selfing, self-compatibility and effects of pollen source (hermaphroditic vs. male flowers). Pollination success was determined by pollen tube growth and reproductive success was assessed by fruit, seed and seedling numbers and characteristics. The pollinator guild was surveyed and the pollination distance determined both by direct observations and by indirect fluorescent dye dispersal.

Key Results

The species is probably pollinated by several Hymenoptera, principally by Hypotrigona para. Pollinator flight distances varied from 25 to 69 cm. No evidence for apomixis or spontaneous self-pollination in the absence of insect visitors was found. The self-fertility index (SFI = 0) indicated a total dependence on pollinators for reproductive success. The effects of hand pollination on fruit set, seed number and seedling fitness differed among years. Pollen tube growth and reproductive success did not differ between self- and cross-pollinations. Accordingly, a high self-compatibility index for the fruit set (SCI = 1·00) and the seed number (SCI = 0·98) and a low inbreeding depression at all developmental stages (cumulative δ = 0·126) suggest a high selfing ability. Finally, pollen origin had no effect on fruit and seed sets.

Conclusions

This andromonoecious species has the potential for a mixed mating system with high dependence on insect-mediated pollination. The selfing rate through geitonogamy should be important.     

Triterpenoid saponins from Echinopsis macrogona (Cactaceae)

Triterpene saponins, pachanosides C1, E1, F1 and G1 (1-4), and bridgesides A1, C1, C2, D1, D2, E1 and E2 (5-11) were isolated from Echinopsis macrogona. Compounds 1-4 were saponins with pachanane type triterpene saponins, while the others (5-11) were oleanane type triterpene saponins. While the aglycones of 2-4 and 8-11 were hitherto unknown, the structure of pachanol C was revised in this paper. Their structures were elucidated on the basis of chemical and physicochemical evidence.     

Identification of self-incompatibility groups in<Emphasis Type="Italic"> Hatiora</Emphasis> and<Emphasis Type="Italic"> Schlumbergera</Emphasis> (Cactaceae)

The Cactaceae, a family of about 1,800 species of succulent perennials, contains numerous species that exhibit self-incompatibility (SI). The objective of the current study was to determine the number of incompatibility groups present among diploid (2n=2x=22) cultivars of the genera Schlumbergera Lem. (Christmas cacti) and Hatiora Britton & Rose (Easter cacti). Two partial diallel crosses were performed, one with 19 cultivars of Christmas cacti [= S. truncata (Haworth) Moran and S. × buckleyi (Buckley) Tjaden] and the other with 10 cultivars of Easter cacti [= H. gaertneri (Regel) Barthlott, H. rosea (Lagerheim) Barthlott, and H. × graeseri Barthlott ex D. Hunt]. The compatibility/incompatibility status of crosses was determined by percent fruit set and presence of seed in mature fruit. None of the cultivars set fruit when selfed or crossed with a cultivar in the same incompatibility group, but fruit set ranged from 35% to 100% following compatible crosses. For the Christmas cacti, eight intra-incompatible but reciprocally compatible groups were identified, with 13 of the 19 cultivars assigned to three incompatibility groups (68%). The ten cultivars of Easter cacti yielded nine intra-incompatible but reciprocally compatible groups, with two cultivars in one incompatibility group and the other eight cultivars each assigned to a unique group. One cultivar of Christmas cactus ('Abendroth 6') was incompatible when crossed as a male with cultivars in incompatibility group 2 but was compatible in reciprocal crosses, results that suggest that this cultivar is an S-allele homozygote. The crossing relationships are consistent with a one-locus, gametophytic SI system with multiple alleles. Allozyme locus Lap-1, shown previously to be linked with the S locus (recombination frequency 7%) in Schlumbergera, exhibited insufficient allelic diversity for determining the S genotypes of the 19 cultivars of Christmas cacti. Based on the number of incompatibility groups in each diallel, at least five S-alleles occur in the 19 Christmas cacti and the 10 Easter cacti.Publication 3337 of the Massachusetts Agricultural Experiment Station. This material is based on work supported in part by the Cooperative State Research, Extension, Education Service, United States Department of Agriculture, Massachusetts Agricultural Experiment Station, under Project No. 746