Flora 201 (2006) 178–188

Pollination in Turnera subulata (Turneraceae): Unilateral...
C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188

is scarce. Darwin (1877) suggested that visit...

C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188

accessible to pollinators. Each treatmen...
C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188

Small orifices (0.5 mm diameter) between the b...

Table 2.

C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188

Breeding system of Turnera sub...
C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188

Table 3.


Flower visitors of Turnera sub...

C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188


Flower visits









C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188
Pollen of short-styled flowers

Pollen of...
C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188

The questions of whether the beetles use the ...

C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188

em Protomeliturga turnerae (Ducke, 1907)...
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Turnera pollination flora 2006 schlindwein & medeiros

  1. 1. ARTICLE IN PRESS Flora 201 (2006) 178–188 Pollination in Turnera subulata (Turneraceae): Unilateral reproductive dependence of the narrowly oligolectic bee Protomeliturga turnerae (Hymenoptera, Andrenidae) Clemens Schlindweina,Ã, Petrucio C.R. Medeirosb ´ a ˆnica, Universidade Federal de Pernambuco, (UFPE), Av. Prof. Moraes Re ˆgo, s/n, Cidade Universita ´ria, Departamento de Bota 50670-901 Recife, Brazil b ´s-Graduaca em Biologia Vegetal, Universidade Federal de Pernambuco, Recife Programa de Po ¸ ˜o Received 15 March 2005; accepted 1 July 2005 Abstract Turnera subulata Smith (Turneraceae) is a subshrub with distylic flowers, common as a ruderal plant in NE-Brazil. We studied the pollination biology of a population in Joao Pessoa, Paraı´ ba, paying attention to effective pollinators ˜ and characteristics of short- and long-style morphs. The flowers attracted insects of 28 species, predominantely bees. Several bee species were observed to be effective pollinators, including highly eusocial species, polylectic solitary species (Centris and Xylocopa) and 1 oligolectic species, Protomeliturga turnerae (Andrenidae, Panurginae). The latter species shows reproductive dependency on T. subulata. The plant species, on the other hand, does not depend on this specialized bee, as reproductive success was also guaranteed by the other polylectic flower visitors. Floral characteristics of both floral morphs are discussed with respect to pollination biology. r 2005 Elsevier GmbH. All rights reserved. Keywords: Turnera subulata; Heterostyly; Effective pollinators; Oligolectic bees; Northeast Brazil Introduction Turneraceae is 1 of at least 28 angiosperm families showing heterostyly (Barrett, 1992, 2002; Barrett and Richards, 1990; Ganders, 1979). Almost all species of Turnera are distylic while homostylous populations seem to be derived from heterostylic ancestors (Barrett, 1978; Barrett and Shore, 1987). Distyly is expressed in a short-styled form with long stamens and a long-styled one with short stamens and is linked to double incompatibility, permitting fecundity only between longÃCorresponding author. E-mail addresses: (C. Schlindwein), (P.C.R. Medeiros). 0367-2530/$ - see front matter r 2005 Elsevier GmbH. All rights reserved. doi:10.1016/j.flora.2005.07.002 and short-styled plants while intramorphic pollination is incompatible (Darwin, 1877; Ganders, 1979; Richards, 1997; Vuilleumier, 1967). In general, additional features are associated with each morph, like differences in pollen morphology and size, number of pollen grains and stigma morphology, which are controlled by a supergene (Barrett, 2002; Richards, 1997; Shore and Barrett, 1985a, b). These characters may have an adaptive value with respect to the functioning of the mating system (Richards, 1997). Most studies on heterostyly have focused on the genetic mechanism of self-incompatibility (Barrett and Shore, 1985; Charlesworth, 1979; Ganders, 1979; Richards, 1997; Shore and Barrett, 1985a, b, 1987, 1990) while information on interactions with pollinators
  2. 2. ARTICLE IN PRESS C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 is scarce. Darwin (1877) suggested that visitors to distylic flowers receive pollen at different specific parts of the body promoting intermorphic pollination. Ganders (1979) indicated pollination especially by insects in heterostylic plants. Barrett (1978) studied the reproductive biology of Turnera ulmifolia L. (vars. angustifolia (Mill.) DC., elegans (Otto ex Nees) Urb., intermedia Urb., surinamensis Miq.) in northern Brazil and lists insects of 13 species as flower visitors, mainly bees. None of the flower-visiting species is oligolectic. Ducke (1907) described Calliopsis turnerae from ´ the states of Maranhao and Ceara as one of the ˜ most common visitors of Turnera spp. flowers. Later (Ducke 1912) he transferred the species to the new genus Protomeliturga with P. turnerae as the single species. Because of its mouth parts, which are similar to those of long-tongued bees, Ruz (1991) established the tribe Protomeliturgini (Andrenidae, Panurginae) with P. turnerae as the monotypic representative. The bees are oligolectic on flowers of Turnera spp., males establish territories in flower patches of T. subulata Smith and show multiple matings in these flowers (Medeiros and Schlindwein, 2003, Schlindwein, 2003). Recently it was shown that interactions between heterostylic plants and their pollinators can involve highly specialized oligolectic bees like Ancyloscelis gigas (Apidae, Emphorini) that possess extraordinarily long mouth parts with specialized hairs to collect hidden pollen from low-level anthers in flowers of tristylous Eichhornia azurea (Pontederiaceae) (Alves-dos-Santos, 2003; Alves-dos-Santos and Wittmann, 1999, 2000). In this case reproduction of bees and plants are interdependent. In this study we asked the following questions: (1) In which characteristics do long- and short-style flowers of T. subulata diverge? (2) Which are the flower visitors of both floral morphs? (3) Are bees of P. turnerae more effective pollinators than polylectic bees? and (4) Does reproduction of the plant and the oligolectic bee depend on each other? 179 Field studies were carried out from March 1999 to February 2001 in the surroundings of the agricultural experimental research station of EMEPA (Empresa ´ Estadual de Pesquisas Agropecuarias da Paraı´ ba) near Joao Pessoa, Paraı´ ba, NE-Brazil (71110 5800 S; ˜ 0 00 34148 37 W, altitude 30–40 m, about 1 km distant from the coast). The vegetation at the study site consists of fruit crops and ruderal plants surrounded by seminatural vegetation of the Cerrado-like ‘‘Tabuleiro Nordestino’’. The climate is tropical and humid (mean annual precipitation and temperature 1600–1800 mm, 25–26 1C) (Fonseca and Azevedo, 1983; Lima and Heckendorff, 1985). Flower morphology and anthesis Floral structures (diameter, length of petals, stamens, filaments, anthers, styles) of short- and long-styled flowers were measured in 30 flowers of different plants. To test for significant differences in these measurements we used test t (Zar, 1996). Flower buds were numbered and monitored to determine duration, time and sequence of anthesis and number of flowers open per day and plant. The time of stigma receptivity was determined with H2O2 (20%) and a hand lense (Kearns and Inouye, 1993). Pollen viability was verified by staining with acetocarmine jelly (Radford et al., 1974). The number of pollen grains per flower was determined in 15 flowers of different plant individuals per floral morph in non-dehisced anthers, using Neubauer chambers. Fresh pollen grains from 10 different flowers of each morph were measured (30 measurements of equatorial diameter per preparation) and the ornamentation of the exine was analyzed under a microscope. Sugar concentration of nectar was measured with a hand refractometer (Atago, 0–90%) in previously bagged flowers. The nectar amount was determined with micropipettes (5 ml) every 60 min (n ¼ 10 flowers per hour). ´ Vouchers are deposed at the Herbario UPE Geraldo Mariz, Botanical Department of the Federal University of Pernambuco (UFP 24742, 24740, 24748). Materials and methods Breeding system Study site The breeding system was determined by a controlled pollination experiment in both morphs: (1) spontaneous selfing – flower buds were bagged before anthesis and maintained closed until flower senescence; (2) hand selfpollination – flower buds were bagged before anthesis and pollinated with pollen of the same flower; (3) interand intra-morph hand cross-pollination – bagged flowers were opened and pollinated with pollen from other individuals of T. subulata; (4) open, free pollination – for control, marked unbagged flowers were kept T. subulata is a subshrub, common as a ruderal plant in NE-Brazil. The species is part of the T. ulmifolia complex (Solis Neffa and Fernandez, 2000; Urban, 1883). The ephemeral flowers are disc- to funnel-shaped. The petals are cream-colored and show violaceous to blackish nectar guides at the base that help the flower visitors to find the food rewards (Dafni and Giurfa, 1998).
  3. 3. ARTICLE IN PRESS 180 C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 accessible to pollinators. Each treatment was performed in 30 flowers. The flowers were monitored until fruit set. Seeds were counted from all mature fruits. Flower visitors and evaluation of effective pollinators The spectrum of flower visitors was determined in long- and short-styled morphs. Insects were captured with entomological nets and specimens are housed in the Entomological Collection of the Federal University of Pernambuco. The collections were made during 5 consecutive days in January and September 2000. The frequencies of visits by bees to the flowers of T. subulata were determined by counting female and male bees at the flowers during a total of 100 h of observation. During each visit we checked whether the bees came into contact with the stigma. The relative frequencies of stigma contacts were calculated for males and females of each bee species. The relative abundance of Turnera pollen in the scopal loads was taken to quantify the flower constancy of the bees. Ten females of each bee species were captured at flowers of T. subulata. Their pollen loads were stripped off the scopa and some drops of 70% ethanol were added. The pollen grains were mixed, picked up on a small piece of glycerine gelatin, transferred to a microscope slide, mounted with a cover glass and sealed with paraffin wax. Two samples were made of each pollen load, with pure glycerine gelatin and with glycerine gelatin stained with alcohol–fuchsine solution (Westrich and Schmidt, 1986). Pollen loads were analyzed by counting at least 300 pollen grains per sample. The number of pollen grains from short- and long-styled morphs of T. subulata, as well as those of other plant species was counted. We also determined the number and type of pollen grains attached to the stigmas during anthesis. The stigmas of 15 long-styled and 15 short-styled flowers were removed at 7:00, 8:00, 9:00, and 10:00 h. Each stigma was transferred to a microscope slide containing Table 1. glycerin stained with fuchsine. Under the microscope, pollen from short- and long-styled flowers of T. subulata and of other plant species was counted. Fruit set and deposition of pollen grains onto stigmas were determined in a period when the oligolectic bees were present and compared to that of a period when these bees were absent. Results Flower morphology and anthesis T. subulata has erect, disc- to slightly funnel-shaped flowers with cream-colored petals that are dark violaceous at the base (Fig. 1). Flower diameters measure 4.0–6.0 cm (x ¼ 5:1, SD ¼ 0.7, n ¼ 20). The distylic flowers vary in 8 features (Table 1). Stamens and styles show reciprocal hercogamy (Fig. 2). Stamen length of short-styled flowers does not show significant difference from style length of long-styled flowers (t ¼ 1:41, GL ¼ 38, P40:05), as do stamens of long-styled flowers Fig. 1. Longitudinal section of a short-styled (left) and longstyled flower of Turnera subulata. Floral characters in the long- and short-styled morphs of Turnera subulata Floral morph Short-styled (x–SD–n) Style length (mm) Stigma length (mm) Anther length (mm) Filament length (mm) Ovule number Pollen grain number per anther Pollen size (mm) (equatorial axis) Ornamentation patterns of pollen Long-styled (x–SD–n) 4.5–0.5–30 2.6–0.5–30 3.6–0.5–30 9.1–0.9–30 38.5–9.2–30 2720–54.3–15 76.8–2.38–300 Strong reticulum with 1–2 free bacula in lumina 8.6–1.3–30 3.4–0.8–30 2.5–0.5–30 5–0.9–30 53–10.8–30 2900–52–15 64.1–1.92–300 Weak reticulum with 3–6 free bacula in lumina
  4. 4. ARTICLE IN PRESS C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 Small orifices (0.5 mm diameter) between the base of filaments and petals allow access to the nectaries at the base of the ovary. The distance between this aperture and the nectary is less than 1 mm. Nectar, which is already available at the beginning of anthesis, is produced in small quantities (0.8–1.0 ml per flower) and has a mean sugar concentration of 28–32% with little variation during anthesis (Fig. 4a, b). Nectar volume a 1.2 1 Volume [µl] with styles of short-styled flowers (t ¼ 0:77, GL ¼ 38, P40:05). Pollen of both forms is sticky and orange due to abundant pollenkitt. When pollenkitt was removed the grains were light yellow. Pollen grains of short-styled flowers are larger than those of long-styled flowers and also show a more distinct reticulate ornamentation with more free bacula in the lumina. There is no overlap in size variation of pollen grains between both morphs (Fig. 3). Staining with karmin acid indicated high pollen viability in both morphs, 92% (SD ¼ 0.5, n ¼ 15) in short-styled flowers and 94% (SD ¼ 0.6, n ¼ 15) in long-styled flowers. Non-viable pollen grains are empty and smaller and were not considered in the measurements of size. Short-styled flowers produce less pollen grains (13,600) than long-styled flowers (14,500). 181 0.8 0.6 0.4 0.2 16 0 14 06:00 09:00 10:00 7:00 8:00 Hour 9:00 10:00 35 10 30 8 Concentration (%) style length (mm) b 08:00 Hour 6:00 12 07:00 6 4 2 25 20 15 10 5 0 0 2 4 6 8 10 12 14 16 0 stamen length (mm) short-style long-style Fig. 2. Stamen and style length in short- and long-styled morphs of Turnera subulata (n ¼ 30 for each floral morph). Fig. 4. Nectar volume and concentration of sugars in flowers of Turnera subulata. (a) Nectar volume, (b) sugar concentration (n ¼ 10 per hour). long-styled morph Number of grains 60 short-styled morph 50 40 30 20 10 0 60-62 62-64 64-66 66-68 68-70 70-72 72-74 Size classes (µm) 74-76 76-78 78-80 80-82 Fig. 3. Pollen grain size of short- and long-styled morphs of Turnera subulata (n ¼ 300).
  5. 5. ARTICLE IN PRESS 182 Table 2. C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 Breeding system of Turnera subulata Pollination treatment Floral morph n Fruit set (n) Fruit set (%) No. of seeds produced Mean seed set per capsule x (SD) Bagged (not treated) S L S L La  Lb Sa  Sb Sa  Lb La  Sb S 30 30 30 30 30 32 33 32 30 0 0 0 0 0 0 29 31 26 0 0 0 0 0 0 88 97 87 0 0 0 0 0 0 915 713 389 0 0 0 0 0 0 27.7 (14.75) 23 (10.35) 19.5 (9.4) L 30 29 97 397 19.9 (11.2) Hand self-pollinated Hand cross-pollinated Open pollinated flowers (controls) Compatibility and seed set following controlled self-pollination, and intra- and inter-morph cross-pollination (S ¼ short-styled morph, L ¼ longstyled morph, x ¼ average, SD ¼ standard deviation). a Pollen receptor. b Pollen donor. and concentration of sugars in short-styled flowers did not differ from that of long-styled flowers. T. subulata flowered and set fruit during the whole year. Per individual plant, 3–15 flowers opened daily at 6:00 h synchronically closing at about 11:00 h. The fruits took 8–10 days to reach maturity. Breeding system The flowers of T. subulata are self-incompatible (Table 2). Hand self-pollinated as well as intra-morph hand cross-pollinated flowers did not set fruit. Fruit set of open pollinated short- and long-styled flowers was similar. Seed set of these flowers, on the other hand, was reduced when compared with inter-morph hand crosspollinated flowers (Table 2). Short-styled flowers accessible to flower visitors produced on average only 30% and long-styled flowers 36% of the number of seeds as the hand cross-pollinated flowers, and the number of seeds per fruit that resulted from pollination by flower visitors was almost the same in the 2 morphs. Shortstyled flowers visited by bees showed similar seed set (x ¼ 19:5; SD ¼ 16.6; n ¼ 30) as long-styled flowers (x ¼ 19:9; SD ¼ 9.1; n ¼ 30). Pollen–ovule ratio (P/O ratio) was 353.2 in short-styled flowers and 273.6 in long-styled flowers. Considering the mean number of ovules, short-styled flowers produced 43.8% and longstyled flowers 56% of the potential number of seeds in the hand cross-pollinated treatments. Flower visitors, their pollen loads and deposition of pollen grains on stigmas The flowers of T. subulata were visited by insects of 28 species of the orders Hymenoptera, Lepidoptera and Coleoptera (Table 3). Bees were predominant (24 spp.), especially those in the family Apidae. The bees did not differentiate between short- and long-styled flowers. We counted 1408 (48%) flower visits in short-styled flowers and 1534 (52%) in long-styled flowers. In January the most frequent species to visit both flower morphs were highly eusocial species (Apis mellifera 31.5% of the visits, Trigona spinipes 23.9%, Frieseomelitta doederleinii 16.2%) while in September bees of the solitary panurgine Protomeliturga turnerae were the most frequent (27%) followed by social A. mellifera (24%), Trigona spinipes (17%), F. doederleinii (16%), and Plebeia flavocinta (9%) (Fig. 5). In January P. turnerae did not occur. Flower visits were most frequent between 6:30 and 8:00 h, soon after beginning of anthesis of T. subulata (Fig. 6). With the exception of F. doederleinii, bees of all species touched the style frequently (Fig. 7). Large bees, like those of Centris and Xylocopa showed a higher rate of stigma contact than medium- or small-sized species, but showed low frequencies of flower visits. The frequency of stigma contacts during flower visits in long-styled flowers was slightly higher than those in short-styled flowers. Styles of long-styled flowers received more pollen grains than short-styled flowers. In long-styled flowers 55.2% of the pollen grains were legitimate, while shortstyled received only 44.5% of legitimate pollen grains. A higher amount of pollen of short-styled flowers reached the stigmas of both flower morphs. Only 4% of the pollen grains deposited on the stigmas came from other plant species. After only 1 h after the beginning of anthesis 55.1% of the final mean number of pollen grains was deposited on short-styled stigmas and 93% on stigmas of long-styled flowers (Fig. 8).
  6. 6. ARTICLE IN PRESS C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 Table 3. 183 Flower visitors of Turnera subulata in Joao Pessoa, Paraı´ ba ˜ Flower visitors Males Females Hymenoptera Andrenidae Protomeliturga turnerae (Ducke, 1907) Psaenythia variabilis Ducke, 1910 + À + + Apidae Apis mellifera Linnaeus, 1758 Centris (Centris) aenea (Lepeletier, 1841) Centris (Centris) flavifrons (Fabricius, 1775) Centris (Centris) leprieuri (Spinola, 1841) Centris (Hemisiella) tarsata Smith, 1874 Centris (Xanthemisia) lutea Friese, 1899 Ceratina (Crewella) maculifrons Smith, 1844 Ceratinula muelleri Moure, 1941 Epicharis (Xanthepicharis) bicolor (Smith, 1854) Eulaema nigrita Lepeletier, 1841 Frieseomelitta doederleinii (Friese, 1900) Plebeia flavocincta (Cockerell, 1912) Trigona spinipes (Fabricius, 1793) Xylocopa (Megaxylocopa) frontalis (Olivier, 1789) Xylocopa (Neoxylocopa) cearensis Ducke, 1910 Xylocopa (Neoxylocopa) suspecta Moure & Camargo, 1988 Xylocopa (Schonnherria) muscaria (Fabricius, 1775) À + À + + À À À À + À À À À À À À + + + + + + + + + À + + + + + + + Halictidae Augochloropsis sp. Augochlorella sp. Pereirapis semiaurata (Spinola, 1851) Pseudoaugochlora sp. À + + + + + Megachilidae Dicranthidium arenarium (Ducke, 1907) + À Lepidoptera Hesperiidae Nisoniades macarius (Herrich-Schaffer, 1870) ¨ Urbanus dorantes dorantes (Stoll, 1790) Urbanus proteus proteus (Linnaeus, 1758) À À + + + + Coleoptera Curculionidae Pristimerus calcaratus (Boheman, 1843) + + A mean of 5.2 pollen grains of long-styled flowers were deposited on stigmas of short-styled flowers to fertilize 1 ovule and 6 grains of short-styled flowes to fertilize 1 ovule of long-styled flowers. Analysis of the pollen loads of females of the 6 most frequent flower-visiting bee species showed that P. turnerae and Plebeia flavocinta exclusively collected pollen of T. subulata (Fig. 9). The loads of the highly eusocial A. mellifera, Trigona spinipes and F. doederleinii contained only small quantities (1–2%) of pollen grains of other plant species. Females of Augochloropsis sp. always had mixed pollen loads containing predominantely pollen of Borreria verticillata (Rubiaceae) besides those of T. subulata. The pollen loads of all bee species contained more pollen grains of short-styled flowers than of long-styled flowers of T. subulata. Thus, the pollen ratio short- to long-styled to foreign flowers of all visitors was similar to that deposited on the stigmas of both floral morphs, indicating that pollen is not directed to the legitimate stigma. The behavior during flower visits of P. turnerae, A. mellifera, Augochloropsis sp., F. doederleinii, and Trigona spinipes was similar. When visiting flowers of shortstyle-morphs, these bees alighted on the anthers, and collected the pollen grains with the forelegs while maintaining the head directed to the center of the flower. At the same time they generally touched the stigma. Pollen grains adhered mainly to the ventral
  7. 7. ARTICLE IN PRESS 184 C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 300 Flower visits 250 200 150 100 50 Centris lutea Xylocopa frontalis Centris hyptidis Centris aenea Xylocopa muscaria Centris flavifrons Ceratina maculifrons Augochloropsis sp. Plebeia flavocinta Frieseomelitta doederleinii Trigona spinipes Protomeliturga turnerae Apis mellifera 0 Fig. 5. Frequency of flower visitors of Turnera subulata in January and September 2000; January 2000 white bars, September 2000 black bars (50 h of observation in both months). Apis mellifera Trigona spinipes Frieseomelitta doederleinii Plebeia flavocincta Ceratina maculifrons 0 11 0:3 10 0:0 10 30 9: :0 0 10 0: -1 -9 00 9: :3 00 0 :3 0 8: 30 -9 :0 0 8: 00 -8 :3 0 7: 30 -8 :0 0 :3 7: 00 -7 :0 -7 30 6: 6: 00 -6 :3 0 40 35 30 25 20 15 10 5 0 0 Number of flower visits Protomeliturga turnerae Hour (30-min intervalls) Fig. 6. Frequency of flower visits of the most abundant species to Turnera subulata during anthesis (observations during 5 subsequent days in September 2000). region of the meso- and metasoma of the bees. In longstyled flowers, the bees landed on the stigmas, touching them with the ventral region of their meso- and metasoma. Then, they penetrated the flowers with their heads directed downwards to collect nectar. Pollen was collected with the forelegs. Pollen grains adhered mainly to the head and anterior portion of the mesosoma. Females of P. turnerae collected pollen grains of longstyled flowers with rigid hairs of the labrum. Besides the bees, beetles of 3 species were recorded in the flowers of T. subulata: Pristimerus calcaratus (Curculionidae), a meloid and a chrysomelid beetle. The beetles started flower visits at about 8:00 h, collecting nectar, eating stigmas and pollen. Further- more, they used the flowers as mating sites. Ocassionally, we observed that the Pristimerus beetles perforated the petals with their proboscides and closed the flowers with their claws. Discussion Effective pollinators of T. subulata The flowers of T. subulata attract insects of numerous species, especially bees. At the study site, bees of 24 species visited the flowers. When other localities in
  8. 8. ARTICLE IN PRESS 185 100 80 60 40 20 Urbanus dorantes Xylocopa muscaria Centris flavifrons Ceratina maculifrons Augochloropsis sp. Friesiomelitta doederleini Trigona spinipes Apis mellifera 0 Protomeliturga turnerae Frequency of stigma contacts (%) C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 Fig. 7. Relative frequency of stigma contacts by flower visitors to short-styled (black bars) and long-styled flowers (white bars) of Turnera subulata. a Pollen of short-styled flowers Pollen of long-styled flowers Pollen of other spp. Number of pollen grains 350 300 250 200 150 100 50 0 7:00 h 8:00 h 9:00 h 10:00 h Hour b Number of pollen grains 350 300 250 200 150 100 50 0 7:00 h 8:00 h 9:00 h 10:00 h Hour Fig. 8. Number (mean, SD) of pollen grains deposited by flower visitors on the stigmas of short-styled (a) and long-styled flowers (b) of Turnera subulata during anthesis. Legitimate pollen in long-styled flowers comes from the long stamens of short-styled morphs, and in short-styled flowers from the short stamens of long-styled morphs. NE-Brazil are included, this number rises to 46 species (Schlindwein and Medeiros, not published). This shows the importance of the Turnera flowers as pollen and nectar sources for bees, and suggests that they are generalized melittophilous blossoms. As the plants set flowers throughout the year, they are reliable food
  9. 9. ARTICLE IN PRESS 186 C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 Pollen of short-styled flowers Pollen of long-style flowers Pollen of other spp. 70 Pollen amount [%] 60 50 40 30 20 10 0 Apis mellifera Trigona spinipes Protomeliturga Augochloropsis turnerae sp. Plebeia flavocincta Frieseomelita doederleini Fig. 9. Pollen amount (mean, SD) of short-styled flowers, long-styled flowers and of other plant species in the pollen loads of the most frequent flower-visiting bees of Turnera subulata (n ¼ 10 bees per species). sources, especially for perennial bee species. The easy access to pollen and nectar allows flower visits of large and small bees and of bees with short or long tongues. No morphological adaptations seem to be necessary to collect floral resources from T. subulata. By comparing several measurements related to pollinator effectivity like frequency of stigma contacts, relative frequency of flower visits and flower constancy, several species have to be considered effective pollinators: the solitary P. turnerae, the very common, highly eusocial A. mellifera and Trigona spinipes, as well as the less frequent, large, solitary Centris and Xylocopa species. P. turnerae is the only oligolectic species among all flower visitors. Reproduction of this species depends completely on the presence of T. subulata flowers. These flowers are not only the unique pollen source of this species at the study site, but also the sites of male territories and mating (Medeiros and Schlindwein, 2003). Because of this close relation of P. turnerae bees to Turnera flowers, it was to be expected that these bees are more effective pollinators than polylectic species. In fact, in most cases oligolectic bees are the most effective pollinators of their specific food plants (Schlindwein, 2004; Schlindwein and Wittmann, 1995, 1997a, b; Schlindwein and Martins, 2000; Schlindwein et al., 2005). Because of morphological adaptations of the oligolectic bees combined with a highly efficient pollen collection behavior, their specific food plants generally quickly become unattractive for polylectic species in the presence of the specialized bees. In the studied case, P. turnerae indeed is an effective pollinator of T. subulata, but we found no evidence that indicates a competitive advantage of this species over, for instance, the polylectic workers of A. melifera or Trigona spinipes. The dependency of the Protomeliturga bees on the flowers of Turnera is not accompanied by any dependency of the plant species on the oligolectic bee. In the absence of Protomeliturga bees at the study site (January) and at the campus of the Federal University of Pernambuco, Recife, where bees of P. turnerae do not occur, fruit set and pollen deposition on the stigmas of T. subulata is high as well (Schlindwein and Medeiros, not published). For the tristylous flowers of Eichhornia azurea (Swartz) Kunth (Pontederiaceae), Alves-dos-Santos and Wittmann (1999, 2000) showed that the oligolectic bees of Ancyloscelis gigas (Apidae, Emphorini) were the most important pollinators of the short-styled morph, the most hidden level of stigmas and anthers. In our study, the bees of P. turnerae did not show preference to the low-level morph. Stigma contacts to the short-styled morph were not more frequent than those of competitors, and pollen grains from low-level anthers (those of the long-styled morph) were less frequent in their scopae, just as in the other bee species. Thus, bees of P. turnerae are no better or more important pollinators than most of the other bee species found in flowers of T. subulata and dependency of the oligolectic species is unilateral. Surprisingly, the flower-closing curculionid beetle, Pristimerus calcaratus, which competes for floral resources of Pavonia cancellata Cav. (Malvaceae) with the olgolectic bee Ptilothrix plumata (Apidae, Emphorini) (Schlindwein and Martins, 2000), also visited the flowers of sympatric T. subulata. However, their frequency in T. subulata flowers was low and, therefore, an impact on other flower visitors is not to be expected.
  10. 10. ARTICLE IN PRESS C. Schlindwein, P.C.R. Medeiros / Flora 201 (2006) 178–188 The questions of whether the beetles use the T. subulata flowers as well as the flowers of P. cancellata, or if they mistake Turnera for Pavonia flowers, which are similar in shape, color and time of anthesis, need further investigation. Differences between short- and long-styled morphs Long- and short-styled morphs of T. subulata differ in at least 8 characteristics which are similar to the ones detected in other species of the genus (Barrett, 1978; Barrett and Shore, 1985, 1987; Belaoussoff and Shore, 1995; Shore and Barrett, 1984). Short-styled flowers produce less ovules (38.5) and pollen grains (13,600) than long-styled flowers (53, 14,500). P/O ratio is 353.2 for short-styled flowers and 273.6 for long-styled flowers. This P/O ratio, however, is related to illegitimate pollination. The corrected relationship (legitimate pollination), ovules of short-styled flowers compared to pollen of long-styled flowers and vice versa, results in a bigger difference of P/O ratios among both morphs: P/O ratio in short-styled flowers is 376.6 and in long-styled flowers 256.6. Following Cruden (1977), the more difficult legitimate pollen deposition in a given breeding system is, the higher the P/O ratio is, then the shortstyled flowers of T. subulata would receive less pollen grains than the long-styled ones. In fact, in our study the morph which received less pollen, reflecting a hindered pollen deposition, showed the higher P/O ratio (see Fig. 8). In addition, more pollen from short-styled flowers – in other words from long stamens – was deposited on stigmas of both morphs. Despite of the difference of ovule number in both morphs, mean seed set was the same in short- and long-styled flowers of T. subulata. Different as predicted in species with reciprocal hercogamy by Darwin (1877), in the case with T. subulata legitimate pollen transfer is not favored by the flower visitors. The higher P/O ratio in short-styled flowers might be interpreted as a compensation of hampered legitimate pollen flow in this floral morph. It is surprising that heterostyly in T. subulata seems not to have a function in directing pollen in the expected way. Acknowledgements We thank the EMEPA for the permission to work at the Agricultural Experimental Research Station in Joao ˜ Pessoa, Celso Feitosa Martins (UFPB) and Isabel Cristina Machado (UFPE) for suggestions, Evelise Locatelli, Reisla Oliveira Darrault and Celso F. Martins for their help in the field, Scott Vinson Heald (Cornell University) for revising the English and the Brazilian Research Council (CNPq) for financal support. 187 References Alves-dos-Santos, I., 2003. Adaptations of bee proboscides for collecting pollen from Pontederiaceae flowers. 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