Ilse Silberbauer-Gottsberger

Olfactory and visual attraction of Erioscelis emarginata (Cyclocephalini, Dynastinae) to the inflorescences of Philodendron selloum (Araceae)

Observations and experiments show that Erioscelis emarginata (Dynastinae, Scarabaeidae), the sole pollinator of Philodendron selloum (Araceae), is guided at dusk to the inflorescences in their female stage by a combination of olfactory and visual stimuli. At close range, visual stimuli are induced by olfactory stimuli and the beetles orient themselves by the light inner side of the spathe. Light models are more attractive than dark ones. Nonfragrant spathes or spathe models, which are put closest to the odor sources, are most visited. Odoriferous inflorescences in the female stage emit stimuli for Erioscelis that are present to remain, while in male-stage inflorescences such stimuli are absent. Light inhibits beetles from leaving male-stage inflorescences.

A polinização e sua relação com a termogênese em espécies de Arecaceae e Annonaceae da Amazônia Central

The present study is a comparison of the flower biology and pollination of some thermogenic species of palms and Annonaceae. In the palms eleven representatives of the genera Astrocaryum, Attalea, Bactris, and Oenocarpus, and in the Annonaceae nine representatives of the genera Anaxagorea, Duguetia, and Xylopia were studied in the region of Manaus (AM). All the studied palm species are monoecious and the anthesis of their inflorescences occurs at night during a period which varies from two days to five weeks. The investigated species of the Annonaceae are protogynous with the anthesis of a single flower lasting for two days and occurring at night or during the day. Flower visiting insects are attracted by strong odours which are intensified through thermogenesis. The species-specific odours range from fruit-like to unpleasant and pungent. Most of the flower visiting insects are beetles of the families Scarabaeidae, Nitidulidae, Staphylinidae, Curculionidae, and Chrysomelidae, and additionally thrips and drosophilid flies. Further insects which visit the flowers are bees, wasps, ants, and other fly groups. However, palms and Annonaceae with thermogenic flowers most frequently showed beetle pollination. It is notable that flowers of some species of both families were visited bythe same families and even species of beetles, which might be due to similar morphological and physiological adaptations of the flowers, including production of similar odour components.

Über sphingophile Angiospermen Brasiliens

In order to study the functional differentiation in flowers of 15 sphingophilous Brazilian Angiosperms, anthesis, flower morphology, flower odours and the behaviour of visiting animals were investigated. All 15 species were found to have nocturnal anthesis, but only 13 proved to be predominantly visited by hawk-moths. Of the 3Lafoensia populations studied, one was pollinated only by hawk-moths, one was chiropterophilous and one had a mixed bat-moth pollination; there are corresponding differences in flower dimensions.

Flowering, pollination, nectar standing crop, and nectaries ofEuterpe precatoria (Arecaceae), an Amazonian rain forest palm

Flowering and pollination biology of the monoecious palmEuterpe precatoria was studied in the forest of the “Reserva Ducke” near Manaus, Brazil, during two annual flowering periods (middle of October to end of March) between 1991 and 1993. Individuals produced one to four bisexual inflorescences per flowering period. Inflorescences have staminate and pistillate flowers in triads. The anthesis of the whole inflorescence averaged 26 days, with the male phase extending over the first 17 days, followed by six days without any open flowers, and the female phase covering the last three days. The distinct dichogamy of the inflorescence results in obligate outcrossing. The pollen-ovule ratio is high (42000). Both male and female flowers emit an almond oil-like scent and produce nectar in septal nectaries. The concentration and total amount of sugar of the nectar of female flowers (37% and 0.021 mg) were significantly higher than that of male flowers (9% and 0.007 mg). The nectar is hexose-rich and with a moderately high amino acid concentration (68 µg/ml).Euterpe precatoria seems to be a generally entomophilous palm with a predominance of beetles and bees as potential pollinators. The most constant visitors were beetles of the familiesCurculionidae, Chrysomelidae, Staphylinidae, and bees of the familyHalictidae. The actual composition of the insect spectrum depends on climatic and biotic factors. Additionally, wind pollination may occur. Fruit development lasted four months and ripe fruits are swallowed by toucans who thus disperse the seeds.

VARIATION ON THE POPULATION, RACIAL, AND SPECIES LEVEL IN THE PRIMITIVE RELIC ANGIOSPERM GENUS DRIMYS (WINTERACEAE) IN SOUTH-AMERICA

Statistical analyses and scatter diagrams illustrate for the polymorphic E. and SE. BrazilianDrimys brasiliensis a clear correlation between morphological variation and eco-geographical differentiation. This is backed by data on the (ultra)structure of the lower leaf surface. A new infraspecific taxonomy is proposed, andD. roraimensis andD. angustifolia are recognized as distinct species of the Guyana Highlands and S. Brazil, respectively. The affinities between these and other taxa of the paleopolyploid genus, its evolution and its position within the family are discussed.

Evidence for Behavioral Attractiveness of Methoxylated Aromatics in a Dynastid Scarab Beetle-Pollinated Araceae

Many plants attract their pollinators with floral scents, and these olfactory signals are especially important at night, when visual signals become inefficient. Dynastid scarab beetles are a speciose group of night-active pollinators, and several plants pollinated by these insects have methoxylated aromatic compounds in their scents. However, there is a large gap in our knowledge regarding the compounds responsible for beetle attraction. We used chemical analytical analyses to determine temporal patterns of scent emission and the composition of scent released from inflorescences of Philodendron selloum. The attractiveness of the main components in the scent to the dynastid scarab beetle Erioscelis emarginata, the exclusive pollinator of this plant, was assessed in field biotests. The amount of scent increased rapidly in the evening, and large amounts of scent were released during the activity time of the beetle pollinators. Inflorescences emitted a high number of compounds of different biosynthetic origin, among them both uncommon and also widespread flower scents. Methoxylated aromatic compounds dominated the scent, and 4-methoxystyrene, the most abundant compound, attracted E. emarginata beetles. Other compounds, such as (Z)-jasmone and possibly also the methoxylated aromatic compound 3,4-dimethoxystyrene increased the attractiveness of 4-methoxystyrene. Methoxylated aromatics, which are known from other dynastid pollinated plants as well, are important signals in many scarab beetles in a different context (e.g., pheromones), thus suggesting that these plants exploit pre-existing preferences of the beetles for attracting this group of insects as pollinators.

The Key Role of 4-methyl-5-vinylthiazole in the Attraction of Scarab Beetle Pollinators: a Unique Olfactory Floral Signal Shared by Annonaceae and Araceae

Cyclocephaline scarabs are specialised scent-driven pollinators, implicated with the reproductive success of several Neotropical plant taxa. Night-blooming flowers pollinated by these beetles are thermogenic and release intense fragrances synchronized to pollinator activity. However, data on floral scent composition within such mutualistic interactions are scarce, and the identity of behaviorally active compounds involved is largely unknown. We performed GC-MS analyses of floral scents of four species of Annona (magnoliids, Annonaceae) and Caladium bicolor (monocots, Araceae), and demonstrated the chemical basis for the attraction of their effective pollinators. 4-Methyl-5-vinylthiazole, a nitrogen and sulphur-containing heterocyclic compound previously unreported in flowers, was found as a prominent constituent in all studied species. Field biotests confirmed that it is highly attractive to both male and female beetles of three species of the genus Cyclocephala, pollinators of the studied plant taxa. The origin of 4-methyl-5-vinylthiazole in plants might be associated with the metabolism of thiamine (vitamin B1), and we hypothesize that the presence of this compound in unrelated lineages of angiosperms is either linked to selective expression of a plesiomorphic biosynthetic pathway or to parallel evolution.

Respiration and temperature patterns in thermogenic flowers of Magnolia ovata under natural conditions in Brazil

The roles of floral thermogenesis in pollination biology include attraction and reward of insects. Magnolia ovata (A.St.-Hil.) Spreng. produces ~56 g, bisexual, protogynous and scented flowers. Two distinct episodes of thermogenesis occur during anthesis: one beginning at about sunset and lasting ~3 h in the female phase and another that occurs synchronously 24 h later and lasting 4 h in the male phase. Female stage flowers produce up to 0.36 W to reach 27.3°C, which is 3.9°C above ambient air. In the male stage, corresponding values are 0.79 W, 29.7°C and 5.4°C, respectively. Most heat is generated in the petals in both phases (74 and 65%). Maximum, mass-specific rate of respiration is 23 nmol s–1 g–1 in the petals and 100 nmol s–1 g–1 in the anthers. The flowers are apparently not thermoregulatory, because respiration rate decreases, rather than increases, with decreasing ambient temperature. Scarab beetles, Cyclocephala literata, enter the floral chamber created by the petals in the female phase, mate, consume floral parts (mainly petals) and then depart in the male phase. Temperatures maintained in the floral chamber are sufficient to provide beetles with significant energy savings during their activities in both phases. Thermogenesis is, therefore, consistent with volatilisation of floral fragrances and energy rewards to beetle visitors.

Fruit Dispersal and Trypanocarpy in Brazilian Cerrado Grasses

Abstract28 grass species from one hectare of cerrado vegetation in Botucatu, State of São Paulo, were studied with regard to the morphology and dispersal of their fruits. 13 species have dispersal units with smooth surfaces which are predominantly dispersed by big herbivorous mammals or birds which swallow them together with their food, e.g., during grazing (accidental endozoochory). On the other hand, smaller animals, including birds, also feed directly on the grains; some of them may escape trituration and digestion or may be even stored (synzoochory). 11 species are principally epizoochorous: 8 of these are ± exclusively adapted to epizoochory, adhering to the animals by scabrid awns or sharply pointed calli, while the rest behave as epizoochores and anemochores. 4 other species are predominantly anemochorous with their dispersal units bearing soft hairs, sometimes together with very small scabrid awns; in a wet state they also can adhere to animals (occasional epizoochory). Beside this, most grass fruits can behave as passive ballists, as passing animals, wind and rain may cause their dispersal units to fall to the ground (passive autochory). — Among the 28 species, 12 have dispersal units which are awned. In 7 of them the awns are spirally twisted; the base of the dispersal unit runs out into a sharply pointed callus and has harpoone-like hairs. These awns show hygroscopical movements which may lead to a drilling of the basal part of the dispersal unit into the sandy cerrado soil. This trypanocarpy is important for establishment but without function for dispersal.

Anthese und Bestäubung der RubiaceenTocoyena brasiliensis undT. formosa aus dem Cerrado Brasiliens

1. Die langen Stieltellerblüten der beiden brasilianischen RubiaceenTocoyena, brasiliensis undT. formosa zeigen Merkmale, die sie gut in den sphingophilen Blütentyp eingliedern lassen. 2. Die Knospen springen in der Abenddämmerung ruckartig auf und die Kronblattzipfel breiten sich anschließend langsam bis zur Sternform aus. 3. Die Blüten sind stark protandrisch. Bereits in der Knospe geben die Antheren ihren Pollen auf die Außenseiten der Narbe ab. Neu geöffnete Blüten befinden sich einige Tage lang im männlichen Zustand, wobei die Pollenmasse auf der ungeöffneten Narbe klebt. Im weiblichen Zustand mit gespreizter Narbe verbleibt die Blüte wiederum einige Tage. 4. Schwärmer, angelockt durch Duft, Farbe und Form der Blüten, kommen nachts, um den Nektar auszubeuten und übertragen dabei mit ihrem Rüssel den Pollen von Narbe zu Narbe. Die Narbe ist also das eigentliche Pollen-tragende Organ. 5. Die Bestäubung könnte auch dann zu einer Befruchtung führen, wenn sie nur im männlichen Zustand der Blüte erfolgt, da der vom Insekt auf die Außenseite der Narbe abgegebene fremde Pollen auskeimt und die Pollenschläuche auf die empfängnisfähigen Stellen gelangen. 6. Versuche zeigen, daßT. formosa allogam ist. Die langen Stieltellerblüten der beiden brasilianischen RubiaceenTocoyena, brasiliensis undT. formosa zeigen Merkmale, die sie gut in den sphingophilen Blütentyp eingliedern lassen. Die Knospen springen in der Abenddämmerung ruckartig auf und die Kronblattzipfel breiten sich anschließend langsam bis zur Sternform aus. Die Blüten sind stark protandrisch. Bereits in der Knospe geben die Antheren ihren Pollen auf die Außenseiten der Narbe ab. Neu geöffnete Blüten befinden sich einige Tage lang im männlichen Zustand, wobei die Pollenmasse auf der ungeöffneten Narbe klebt. Im weiblichen Zustand mit gespreizter Narbe verbleibt die Blüte wiederum einige Tage. Schwärmer, angelockt durch Duft, Farbe und Form der Blüten, kommen nachts, um den Nektar auszubeuten und übertragen dabei mit ihrem Rüssel den Pollen von Narbe zu Narbe. Die Narbe ist also das eigentliche Pollen-tragende Organ. Die Bestäubung könnte auch dann zu einer Befruchtung führen, wenn sie nur im männlichen Zustand der Blüte erfolgt, da der vom Insekt auf die Außenseite der Narbe abgegebene fremde Pollen auskeimt und die Pollenschläuche auf die empfängnisfähigen Stellen gelangen. Versuche zeigen, daßT. formosa allogam ist. The long-tubed whitish flowers of the Brazilian Rubiaceae speciesTocoyena brasiliensis andT. formosa are visited and pollinated by hawkmoths during night; they possess all features of typical sphingophilous flowers. The insects are guided to the flowers by smell, color and form. Flowers expose in the evening and remain open for several days. Already in bud stage the anthers split and deposit their pollen on the outside of the stigma. After opening of the strongly protandrous flowers the stigma carries the adherent pollen and presents it to visitors. About three days later the stigma lobes spread apart, and the flowers remain in this female receptive stage for some further days. Both species are cross-pollinated andT. formosa is, as experiments showed, self-incompatible. Foreign pollen can start to germinate not only in the female but probably already in the male stage of the flowers with stigmas still unspread: it germinates on the outside of the stigma, the pollen tubes reach the receptive parts of the stigmas meanwhile spread, and fecundation can be brought about.