Reproductive ecology of distylous Palicourea Padifolia (Rubiaceae) in a tropical montane cloud forest. I. Hummingbirds' effectiveness as pollen vectors

Abstract

The adaptiveness of distyly has been typically investigated in terms of its female function, specifically pollen receipt. However, pollen loads on stigmas can only provide moderate support for Darwin's hypothesis of the promotion of legitimate crosses. To determine the effectiveness of hummingbirds as pollen vectors between floral morphs and the consequences in terms of male (pollen transfer) and female function (pollen receipt) in Palicourea padifolia (Rubiaceae), floral visitors, their foraging modes, and temporal patterns of floral visitation were observed and documented. Differences in pollen and stigma morphology, pollen flow, rates of pollen deposition, and/or stigmatic pollen loads were then evaluated for their contribution toward differences in reproductive output between floral morphs. A pollination experiment with stuffed hummingbirds that varied in bill size was done to evaluate the contribution of bill variation toward differences between floral morphs in pollen receipt and pollen transfer and female reproductive output. Anthers of long-styled flowers contained significantly more and smaller pollen grains than those of short-styled flowers, independently of corolla and anther lengths. The shape and orientation of the stigma lobes differed between morphs and were significantly longer among short-styled flowers. Hummingbird visitation rates did not differ significantly between floral morphs, and foraging movements from focal plants towards neighboring plants were independent of floral morph. Stigmatic pollen loads under field conditions and those after controlled hummingbird visitation, along with rates of pollen accumulation through the day indicated that stigmas of short-styled flowers receive proportionately more legitimate (intermorph) pollen grains than did those of long-styled flowers. However, the species of hummingbird was marginally significant in explaining variation in pollen deposition on stigmas. Lastly, intermorph pollinations of P. padifolia resulted in significant differences in fruit production between floral morphs, independent of pollination treatment and pollinator species; short-styled flowers proportionately developed almost twice the number of fruits developed by long-styled flowers.

Long‐tongued insects promote disassortative pollen transfer in style‐dimorphic Narcissus papyraceus (Amaryllidaceae)

“…Using artificial flowers, this study concluded that these morphs are able to promote disassortative pollination themselves without any need for reciprocal stigma-anther positioning. Less attention has been paid to the pollinators responsible for such patterns, notwithstanding the fact that the pollination efficiency of floral visitors may vary in terms of the floral morph (Ornduff 1975c;Ornelas et al 2004;Adler & Irwin 2006;Schlindwein & Medeiros 2006;Taki et al 2009). …”

Floral attributes, ornithophily and reproductive success of Palicourea longepedunculata (Rubiaceae), a distylous shrub in southeastern Brazil

“…C.M. Taylor & Lorence resulted in signifi cant difference in fruit production between fl oral morphs, independent of the pollination treatment and pollinator species (hummingbirds); S-morph fl owers developed proportionally almost twice as many fruits as L-morph fl owers (Ornelas et al 2004a). On the other hand, González et al (2005) observed a similar fruit production in P. padifolia morphs, in fi ve years of evaluation at the same study site as Ornelas et al (2004a).…”

“…the number of infl orescences and open fl owers) of each morph, which contribute to attract fl oral visitors (Ornelas et al 2004b). The fl oral dimorphism, i.e., differences in the length of the corolla, style, stigma and stamen and in the pollen sizes between the morphs, common in distylous species, is another factor that may infl uence the reproductive success of the morphs (Lloyd 1979, Ornelas et al 2004a, González et al 2005.…”

“…The fl owers have tubular corolla and are odorless, brightly colored and hummingbird-pollinated (e.g. Feinsinger & Busby 1987, Feinsinger et al 1988, Ree 1997, Contreras & Ornelas 1999, Coelho & Barbosa 2003, Lau & Bosque 2003, Ornelas et al 2004a, b, Mendonça & Anjos 2006, Santos et al 2008. Palicourea longepedunculata Gardner is a distylous shrub found in the forest understory in southern Brazil (Taylor 1997, Pereira et al 2006.…”

Fruit set of distylous Psychotria carthagenensis Jacq. (Rubiaceae) mediated by Apis mellifera (Apidae) and species of Augochloropsis (Halictidae)

“…Among heterostylous species that lack a heteromorphic incompatibility system, morphological differences between morphs particularly exert a strong influence over breeding patterns between individuals (Barrett et al 2004). In heterostylous species, reciprocal herkogamy is expected to promote intermorph pollination through deposition of pollen from different morphs in separate parts of the pollinators' body (Lloyd & Webb 1992;Ornelas et al 2004;Massinga et al 2005).…”