Do consecutive flower visits within a crown diminish fruit set in mass‐flowering Hancornia speciosa (Apocynaceae)?

Hancornia speciosa is a self-incompatible, mass-flowering, sphingophilous fruit crop (mangaba) of northeast and central Brazil. The flowers have a precise pollination apparatus, which optimizes pollen transfer between flower and pollinator. While the pollination mechanism avoids self-pollination, mass-flowering promotes geitonogamy. During a flower visit, almost half of the exogenous pollen grains adhering to the proboscis are deposited on the stigma surface. A pollination experiment with a nylon thread simulating six consecutive flower visits within a crown revealed that only the first two flowers visited (positions 1 and 2) are highly likely to set fruit. Super-production of flowers, and consequently obligate low fruit set, seem to be part of the reproductive strategy of the obligate outcrossing plant, Hancornia speciosa.     

The Pollinators of the Malagasy Star Orchids Angraecum sesquipedale,A. sororium and A. compactum and the Evolution of Extremely Long Spurs by Pollinator Shift

The pollination process of the extremely long-spurred orchids Angraecum sesquipedale and A. sororium is described and documented here for the first time. The pollinaria and viscidia load was examined in moths captured in central and south Madagascar. Visits to orchids by hawkmoths were rarely observed in the field and were therefore systematically recorded in large flight tents using a night-vision video technique and flashlight photography. Angraecum sesquipedale in Fort Dauphin is pollinated by Xanthopan morgani praedicta and A. sororium on Mt. Angavokely by Coelonia solani. By combining a deep nectar spur of extraordinary length with a protruding labellum functioning as a landing platform, these orchids overcome the moth's stereotypic swing-hovering flight thus enabling full insertion of the long tongue. Angraecum compactum in Forêt d'Ambohitantely is pollinated by both the shorter and longer-tongued forms of Panogena lingens which never swing-hover but is also exploited by X. morgani and C. solani with wastage of pollinaria. The duration of tongue insertion, nectar exploitation and tongue withdrawal were analyzed: legitimate and illegitimate visitors differ in their time budget and approach to the flower. Nectar volume, nectar level and sugar concentration of A. sesquipedale and A. sororium were compared with the nectar requirements of the pollinating hawkmoths. The evolution of very long spurs in these orchids is likely to have involved a series of pollinator shifts. The orchids adapted to different hawkmoth species with increasingly long tongues which primarily evolved to avoid predator attacks during visits to less specialized flowers. This “pollinator shift” model modifies the classical “coevolutionary race” model. The relevance of the taxon Angraecum bosseri Senghas is questioned.     

The pollination of merremia palmeri (Convolvulaceae): can hawk moths be trusted?

The reproductive biology of Merremia palmeri and the pollination efficiency of its insect visitors were examined for a Sonoran Desert population in northwestern Mexico. Pollen transfer experiments proved that the plant is self-incompatible. Reproduction is, therefore, dependent upon reliable visitation by the primary pollinators, hawk moths. Many aspects of the floral structure are typical of sphingophilous flowers, and the time of flower opening and nectar secretion corresponded to the period of greatest hawk moth activity. A single hawk moth visit to a flower could be sufficient for successful fertilization. Additional visits up to five increased percentage fruit set, but flowers that received six or more visits had lower fruit and seed set. Neither the number of moth visits nor fruit and seed set were correlated with temperature or relative humidity. Over the course of the study >55% of flowers set fruit. We conclude that hawk moths are reliable and efficient pollinators for M. palmeri in a warm desert habitat.     

Monophily and pollination mechanisms in Angraecum arachnites Schltr. (Orchidaceae) in a guild of long-tongued hawk-moths (Sphingidae) in Madagascar

Anthecological relations between a long-spurred angraecoid orchid and pollinating Sphingidae are documented for the first time. In a primary forest on the Central Plateau of Madagascar Angraecum arachnites Schltr. was found to be pollinated by and adapted to a single species of hawk-moth, Panogena lingens (Butler), despite abundance of many concurrent Sphingidae of which several were also long-tongued. Furthermore, P. lingens was dimorphic in the length and breadth of its proboscis and only the morph with the longest and most slender proboscis was recorded to pollinate A. arachnites . Exclusive and precise adaptation to the latter morph of P. lingens existed in floral morphology and probably in other characteristics such as flowering phenology and chemical signalling. Several concurrently flowering orchid species were sharing P. lingens as a pollinator resource. The monophily in A. arachnites is interpreted as a result of a refined long-term specialization developed within an archaic evolutionary relationship in a relatively stable environment. The extraordinary number and diversity of long-spurred Orchidaceae in Madagascar appears to be a direct coevolutionary consequence of an Old-World-unique diversity of long-tongued archaic Sphingidae that has persisted in this isolated land.     

Nocturnal Versus Diurnal Pollination Success in Isertia laevis (Rubiaceae): A Sphingophilous Plant Visited by Hummingbirds

Abstract: Isertia laevis (Rubiaceae) possesses flowers with traits typical for the pollination syndrome of sphingophily. Diurnal flower observation showed that nine different hummingbirds (Trochilidae) and one flower piercer (Coerebidae) were frequent visitors. Their activity on the flowers peaked in the morning hours. Very low nectar volumes were found in the morning (8.00 h) in unbagged flowers. Nectar volumes, however, reached their peaks (27 μl) at night (2.00 h) in bagged, as well as in unbagged flowers. At night few individuals of sphingids were observed. Pollination experiments showed that flowers presented to nocturnal pollinators from 18.00 h to 6.00 h had low fruit set (14 %) but high seed set (59 %). Flowers accessible from 6.00 h to 18.00 h for diurnal flower visitors showed high fruit set of 63 % but low seed set of 14 %. This suggests that pollination of individual flowers is less effective during daytime. Regarding relative reproductive success, i.e., efficiency of pollination defined as fruit set x seed set, both diurnal and nocturnal pollinators, however, are equally successful. We conclude that frequently occurring, but not very effective pollinators contribute substantially to seed production, when the expected pollinators are scarce.     

Scholarine: An indole alkaloid of Alstonia scholaris

A new alkaloid designated scholarine was isolated from the leaves of Alstonia scholaris. It was (±) 12-methoxyechitamidine as determined by chemical and spectroscopic investigations.