Orchid Pollination: Recent Developments from Brazil
Total Page：16
File Type：pdf, Size：1020Kb
LANKESTERIANA 7: 111-114. 2003. ORCHID POLLINATION: RECENT DEVELOPMENTS FROM BRAZIL RODRIGO B. SINGER Depto Botânica, IB, Unicamp Campinas, SP, Brasil, 13083-970 Because of their remarkable flower morphology, visits. The reasons why Euglossini males collect these orchids are particularly interesting objects of study. compounds are still a matter of speculation (see Most orchid species hold their pollen in discrete Singer & Koehler 2003 for a brief discussion of the packs, so-called pollinia (singular; pollinium). These theories). Yet, it is possible that these compounds are pollinia, together with other pollinium stalks, form somehow used during courtship. In the last six years, more or less complex translatory units, so-called pol- a number of contributions on orchid pollination have linaria (singular: pollinarium). During their visits to been made by Brazilian or Brazilian-based the flowers, orchid pollinators dislodge these polli- researchers. The purpose of this contribution is to naria and deposit their pollen content during succes- give a brief review of these papers and to communi- sive flower visits. Pollinators may be attracted to the cate some – in my opinion - remarkable findings flowers in many ways. Many orchids offer flower which are part of ongoing projects. I have chosen to parts or secretions (nectar, trichomes, wax-like or describe the findings by taxonomic groups. resin-like compounds, aromatic compounds, oils, etc.) that can be gathered/foraged by their pollinators. Subfamily Orchidoideae (including Spiranthoideae, Yet, many orchids “deceive” their pollinators and sensu Dressler 1993). Studied species in this subfami- offer no flower reward. Many orchids are merely ly have been shown to be self-compatible, but polli- “food-frauds”, displaying a set of flower features nator-dependent. Automatic self-pollination – when (colors, fragrances) that apparently elicit the attrac- present - is associated with rostellum narrowing, thus tion of food-seeking animals. A much more sophisti- the stigmatic secretion passively contacts the pollinia. cated kind of deception involves the so-called Bee pollination was recorded for some species of the “pseudocopulation”. In this kind of pollination strate- genera of the so-called “Pelexia alliance” (Spiranthi- gy, flower features (mainly flower fragrance, but also nae: Cyclopogon, Pelexia and Sarcoglottis) (Singer & coloration and – when applicable - indument or pilos- Sazima 1999). Hummingbird pollination was demon- ity) mimic these of some female insects (mostly strated in Stenorrhynchos lanceolatum (Spiranthinae) Hymenoptera). Pollination is achieved when male (fig. 1B) (Singer & Sazima 2000). Moth pollination insects attempt copulation with these “dummy and protandry was recorded in Sauroglossum elatum females”. (Spiranthinae) (Singer 2002b) and Prescottia stachy- Since the times of Darwin, the pollination biology odes (Prescottiinae) (Singer & Sazima 2001b). Bee of the orchids has received the attention of both, lay and moth pollination, in absence of protandry has persons and scientists. The combination of their been recorded in Prescottia densiflora and P. remarkable flower structure plus their often bizarre rodeiensis, respectively (Singer & Cocucci 1999, pollination strategies has played a major role in the Singer & Sazima 2001b). Bee pollination was record- understanding of evolution, morphology and pollina- ed in two Goodyeriinae orchids: the protandrous tion biology as a whole. Erythrodes arietina and the non-protandrous Orchid pollination studies in the Neotropics experi- Aspidogyne longicornu (Singer & Sazima 2001a). enced a boost in the sixties (Van der Pijl & Dodson Mixed moth and crane-fly (Tipulidae) pollination was 1966, and literature therein) with the understanding of documented in Habenaria parviflora (Habenariinae) Euglossini behaviour. The males of these bees gather (fig. 1A) (Singer 2001). Protandry was traditionally fragrances (aromatics, terpenes, sesquiterpenes, etc.) associated with Bumble-bee pollination. Now, it is at specialized parts of the lip of many orchid species clear that this flower feature appears in orchids with from different neotropical subtribes (specially other kinds of flower vectors. Since protandry in Catasetinae, Stanhopeinae and some Zygopetalinae) Orchidoideae has been recorded in species of the and perform the pollination during successive flower closely related subtribes Goodyeriinae, Spiranthinae 112 LANKESTERIANA Nº 7 and Prescottiinae, it has been suggested that this Subtribe Maxillariinae: Meliponini bees of the flower feature arose early in the tribe Cranichideae genus Trigona were recorded as the pollinators of the (where the aforementioned subtribes belong) and was rewardless, honey-scented Maxillaria picta flowers in lost many times, independently (Singer 2002b). southern Brazil (Singer & Cocucci 1999b). Further observations have confirmed that Trigona bees are Subtribe Pleurothallidinae: Pollination by also the pollinators of several other bifoliate Calliphorid flies was recorded in Pleurothallis Maxillarias of the ‘Maxillaria picta’ complex (fig. luteola, from Southern Brazil (Singer & Cocucci 1F). Trigona bees have also been recorded as pollina- 1999c). More recently, Borba & Semir (2001) and tors of Maxillaria brasiliensis. The bees dislodge and Borba et al. (2001) described with great detail the deposit the pollinaria while gathering portions of the pollination biology and breeding system of several wax-like lip callum (actually made-up by many tight- rupicolous Pleurothallis species from southeastern ly packed laminar, unicellular trichomes) (Singer and northeastern Brazil. The pollinators of these 2002). Pollination through “pseudocopulation” medi- orchids are quite specific and these plants apparently ated by Plebeia (Meliponini) drones was recently perform inbreeding depression. demonstrated for Trigonidium obtusum (Singer Subtribe Sobraliinae: Ongoing research has shown 2002a) (fig. 1G). Cultivated plants of the nectar- that at least Elleanthus brasiliensis is protandrous (fig. secreting Maxillaria parviflora have been observed 1C-D). To my knowledge, protandry is herein report- being pollinated by small Meliponini bees and ed for the first time in subtribe Sobraliinae. I have Ponerinae ants as well (R. B. Singer, unpublished) briefly observed the hermit Phaethornis petrei (fig. 1H). (Trochilidae: Phaethorninae) pollinating this orchid in Subtribe Oncidiinae: In the past, it was postulated that southeastern Brazil. Yet, this orchid may be pollinated many “Oncidium” species (here used in its wider sense) by many different hummingbirds, as additional obser- were mimics of Malpighiaceous plants (Van der Pijl & vations will surely reveal. In Colombia, María Argenis Dodson 1966). It was postulated that these species of Bonilla (UNAL) and her students have also observed Malpighiaceae offered nectar and the pollinators of several hummingbird species pollinating some Oncidiinae orchids pollinated these flowers by mistake. Andean Elleanthus spp. (A. Bonilla, pers. comm.). So, plants and pollinators should be involved in mimic- Preliminary evidence indicates that E. brasiliensis is ry complexes (Van der Pijl & Dodson 1966). However, self-compatible, but pollinator-dependent. there is increasing evidence that both, Malpighiaceae Subtribe Bulbophyllinae: Borba & Semir (1999) plants and many Oncidiinae orchids produce oils, and Borba et al. (1999) have described in detail fly- which are gathered by females of several bee genera of pollination in several rupicolous Bulbophyllum family Apidae (these genera were formerly included in species from southeastern Brazil. In these orchid the no longer accepted family Antophoridae) (Singer & species, pollination is wind-assisted. The lip is hinged Cocucci 1999b, Reis et al. 2000 and literature therein). to the base of the lip and vibrates with the slightest Therefore, it seems safer to assume that both, orchids breeze. The fly pollinator adequately positioned in the and Malpighiaceae are part of a guild of plants pollinat- lip surface is pushed against the column and adheres ed by these oil-gathering bees, rather than pieces of a the pollinarium on the scutellum. In order to be mimicry complex. deposited on the stigmatic surface, the pollinia have Pollination by oil-collecting Tetrapedia bees was to dehydrate considerably (Borba & Semir 1999), a documented for Oncidium paranaense (Singer & fact that prevents self-pollination. Cocucci 1999b). A female of Tetrapedia was captured when pollinating flowers of Oncidium pubes (R. B. Subtribe Angraecinae: Campylocentrum aroma- Singer, unpublished). The bee dislodged a pollinarium ticum, from southern Brazil was recorded as mainly when collecting the oil secreted in a superficial, lamel- bee-pollinated (mostly by Halictidae bees) (fig 1E). lar elaiophore, at the lip surface. Vespidae wasps were Yet, a few bug and fly species are able to dislodge pol- recorded as the pollinators of Capanemia thereziae linaria and, perhaps, can act as accessory pollinators (Singer & Cocucci 1999b). The wasps adhere and (Singer & Cocucci 1999a). Meliponini bees were deposit pollinaria while licking nectar secreted in a recorded as the pollinators of the leafless shallow nectary, on the surface of the lip. Campylocentrum burchellii (Singer & Cocucci 1999a). Recently (Singer & Koehler 2003), some aspects of Mayo 2003 SINGER - Orchid pollination 113 Figure 1. A. Habenaria parviflora (Orchidoideae: Habenariinae) being pollinated by a Tipulidae crane-fly.