Pollen Partitioning of Three Species of Convolvulaceae Among Oligolectic Bees in the Caatinga of Brazil

Home , Emphorini, Ipomoea pandurata, Melitoma

Plant Syst Evol (2011) 293:147–159 DOI 10.1007/s00606-011-0432-4

ORIGINAL ARTICLE

Pollen partitioning of three species of Convolvulaceae among oligolectic bees in the Caatinga of Brazil

Raquel Andre´a Pick • Clemens Schlindwein

Received: 29 October 2009 / Accepted: 20 February 2011 / Published online: 20 March 2011 Ó Springer-Verlag 2011

Abstract During the rainy season many species of Keywords Ipomoea Emphorini Merremia Convolvulaceae bloom simultaneously in the Caatinga of Oligolectic bees Resource partitioning Pollen flow northeast Brazil. In a Caatinga nature reserve we studied pollination and breeding systems of three sympatric species of Convolvulaceae, Ipomoea bahiensis, I. nil, and Merre- Introduction mia aegyptia, focusing on pollen partitioning among flower visitors and pollen flow. The study showed that only oli- When flowers of different species with similar floral traits golectic bees collected pollen and that these species had occur and set flower at the same place and time, they may different preferences among the three species of Convol- attract the same pollinators and compete for their polli- vulaceae: pollen of Ipomoea bahiensis, the only self- nation service (Armbruster and Herzig 1984; Caruso incompatible species, was collected mainly by Melitoma 1999; Levin and Anderson 1970). In bee-pollinated segmentaria, M. osmioides, and Melitomella murihirta; flowers, the relationships of plant species to bees are often pollen of I. nil by Lithurgus huberi; and that of Merremia based on pollen, the main food resource for bee larvae. In aegyptia by Ancyloscelis apiformis and an undescribed some cases such pollen-driven associations involve species of this genus. Introduced honey bees visited only mainly oligolectic bee species. These are pollen special- flowers of Merremia aegyptia, where they were extraor- ists which permanently restrict their pollen-host plants to dinarily frequent flower visitors. However, they discarded closely related taxa of the same family (Robertson 1925; the pollen grains, which led to almost 50% pollen loss. No Westrich 1989). Pollen specializations range from very polylectic bee species compete for pollen with the oligo- rare associations of a bee species to only one plant spe- lectic species. Partitioning of pollen diminishes competi- cies (monolectic bee species) up to multiple species in tion for floral resources in this specialized plant–pollinator several genera of the same plant family (broadly oligo- association. lectic bee species) (Cane and Sipes 2006; Robertson 1925). An example of an association between several oligolectic bee species with several plant species within one R. A. Pick family is found in the Convolvulaceae, a large family Programa de Po´s-Graduaçaõ em Cieˆncias Biolo´gicas (Zoologia), (about 2,000 species) of vines, herbs, shrubs, and occa- Universidade Federal da Paraı´ba—UFPB, sionally trees, occurring mainly in tropical regions (Souza Joaõ Pessoa, PB 58059-900, Brazil and Lorenzi 2005). The huge genus Ipomoea is estimated e-mail: [email protected] to comprise a total of 600–700 species worldwide and up to C. Schlindwein (&) 500 species in the New World (Austin and Hua´man 1996). Departamento de Botaˆnica, Laborato´rio Plebeia—Ecologia de Other than a few sphingophilous and ornithophilous Abelhas e da Polinizaçaõ, Universidade Federal de Pernambuco, species, the genus shows almost exclusively melittophilous Av. Prof. Moraes Rego, s/n, Cidade Universita´ria, Recife, PE 50670-901, Brazil flowers. Numerous oligolectic species, especially of the e-mail: [email protected] Neotropical tribe Emphorini (Apidae), were shown to be 123 148 R. A. Pick, C. Schlindwein the main flower visitors of Ipomoea species. These are Morphology and flower biology medium-sized ground-nesting solitary bees of the genera Melitoma, Ancyloscelis, and Ptilothrix (Alves-dos-Santos At the nature reserve, 17 species of Convolvulaceae occur, 1999; Austin 1978; Ducke 1908, 1910; Kiill and Ranga belonging to the genera Jacquemontia (2), Cuscuta (1), 2000a, b; Linsley and MacSwain 1957; Linsley et al. 1980; Evolvulus (3), Ipomoea (9), Merremia (1), and Operculina Maimoni-Rodella and Rodella 1992; Maiomani-Rodella (1) (R. Teixeira, unpublished data). In this study, we et al. 1982; Michener et al. 1994; Pinheiro and Schlindw- selected the three most abundant species of Convolvula- ein 1998; Schlindwein 1998). ceae at the study site, all climbers: Ipomoea bahiensis, In the Caatinga, a widespread tropical dry forest in endemic to eastern Brazil, and very common in northeast northeastern Brazil which is characterized by a severe Brazil and Minas Gerais; I. nil, with a pantropical distri- annual drought, Convolvulaceae is, with a total of 103 bution; and Merremia aegyptia, which occurs from south- species, including 21 endemic species, the second most ern Mexico to northern Argentina (Simaõ-Bianchini 2002). species-rich family (Giulietti et al. 2006; Simaõ-Bianchini The species show a cornucopia flowering pattern (Gentry 2002) and a characteristic element of flowering Caatinga. 1974), and produce numerous flowers per day and plant The species, however, set flower only during the short during the rainy season. rainy season. In general, several species of the family For each species, we collected 15 flowers from different flower during the same period and time of day at a given plants to describe floral morphology and measure the place in Caatinga. The seasonal pattern of flowering of length of the nectar chamber (from the base of the nectary the Caatinga plants is accompanied by the seasonal disk to the insertion point of the filaments to the flower activity of most bee species, many occurring only during tube), stamens, styles, flower tube, floral diameter, and the rainy season (Aguiar and Martins 1997; Aguiar and diameter of flower tube. A digital calliper was used for Zanella 2005; Zanella and Martins 2003). This might measuring. Time of flower opening, stigmatic receptivity, increase competition for floral resources of flower-visiting anther dehiscence, and duration of flower longevity were bees and lead to resource partitioning among sympatric determined in 30 previously bagged and marked flowers. species. Stigma receptivity was determined following Kearns and In a Caatinga nature reserve of Rio Grande do Norte, Inouye (1993). northeast Brazil, we studied the pollination of three We made pollen reference slides of the Convolvulaceae co-occurring melittophilous species of Convolvulaceae, species and measured the diameter of 300 grains per spe- Ipomoea bahiensis Willd. ex Roem. & Schult., I. nil (L.) cies (including spine length) under a light microscope Roth, and Merremia aegyptia (L.) Urban and asked: How (4009 magnification). The total number of pollen grains are plant–pollinator associations characterized? Which per flower was determined in 10 flowers of different plant flower visitors are effective pollinators? How is pollen individuals per species. The anthers were opened on a Petri partitioned among the bee species? dish, and the pollen grains were stained with basic fuchsin and counted under a stereo microscope (Wild) with a manual counter. Ovules from 20 flowers were counted, and Materials and methods the pollen-to-ovule ratio was determined. To determine pollen viability, grains from ten flowers of Study area different plant individuals per species were removed from the anthers, fixed with FAA (formaldehyde 38% 5 parts— The study was conducted at the Estaçaõ Ecolo´gica de Se- glacial acetic acid 5 parts—ethanol 70% 90 parts), and rido´ nature reserve (ESEC-Serido´/IBAMA) situated in the transferred to microscope slides containing carmine acetate municipality of Serra Negra do Norte in the State of Rio (1.2%). Three hundred grains were counted per sample, Grande do Norte, Brazil (06°350–06°400S and 37°200– distinguishing between stained (viable) and unstained 37°390W) at altitude of approximately 170 m. Climate is (nonviable) pollen grains (Kearns and Inouye 1993). tropical hot (mean annual temperature 28°C) with a rainy Plant vouchers are housed at the Herbarium UFP Ger- season from January to June (mean annual rainfall aldo Mariz at the Federal University of Pernambuco— 497 mm). In rainy years, annual precipitation exceeds UFPE, Recife. 1,000 mm and in dry years remains below 300 mm (Ibama 1989; Barcellos and Paupitz 1992). The reserve covers Breeding system 1,166.38 ha of arboreal Caatinga vegetation (Duque 1973). Trees and shrubs maintain their leaves only during the To determine the breeding system of Ipomoea bahiensis, rainy season, and the herbaceous layer is dominated by I. nil, and Merremia aegyptia we conducted a controlled therophytes. pollination experiment (spontaneous self-pollination, hand 123 Pollen partitioning of three species of Convolvulaceae 149 self-pollination, hand cross-pollination) in 30 previously Pollen flow bagged flowers of different plant individuals per species and treatment. The hand cross-pollinated flowers were In 10 flowers per species of different individuals, we quan- emasculated before anthesis, and the flowers were polli- tified the pollen grains remaining in the flower at the end of nated with pollen from donors at least 300 m distant from anthesis, differentiating the number of grains adhering to the focal plants, using pollen grains from three anthers of anthers and petals. Moreover, we counted the number of different plant individuals. Another 40 control flowers per conspecific pollen grains deposited on the stigma surface. species were marked and kept open, accessible for flower For the pollen counts, the pollen grains were transferred to visitors. Fruit and seed set were recorded in each treatment microscope slides with glycerine gelatine, stained with basic and compared using Kruskal–Wallis one-way or Mann– fuchsin, and identified under the microscope. Whitney U test. Statistical tests were performed using Ten flowers per species accessible to flower visitors SigmaStat 3.5 (Systat Software, Inc. 2006) for Windows. were emasculated at the beginning of anthesis. At senescence, stigmas were removed, embedded in glycerine, and Flower visitors stained with basic fuchsin. The number of exogenous conspecific pollen grains adhering to the stigma surface In each species, flower visitors were captured with ento- was determined. mological nets from May to July 2006 and 2007. Fre- For the bee species recorded in the flowers of the studied quency of flower visitors was determined in 2007 for the species of Convolvulaceae, whose nests were located in the three studied species. The collected specimens were field, we analyzed the composition of the larval provisions. mounted, identified, and deposited in the Entomological The whole content of the pollen provisions of the brood cells Collections of the Federal University of Pernambuco was transferred to an Eppendorf tube (1.5 ml), and 70% (UFPE) and the Federal University of Paraı´ba (UFPB). ethanol was added. The dissolved pollen grains were mixed Collection data were included in the database of the during 5 min with a vortex stirrer. Representative samples working group. The extended mouthparts of the bees were were removed, and at least 300 pollen grains per sample measured under a stereomicroscope and related to the were counted under the microscope (4009 magnification). length of the nectar chamber of the species of Convolvulaceae. At the study site we intensively searched for nesting Results sites of emphorine bees, especially open areas with exposed soil. Encountered nests were monitored to deter- Morphology and flower biology mine flight period and daily activity period of the bee species. Recently closed brood cells were excavated to gain In the Caatinga at the Serido´ nature reserve, Ipomoea access to the larval pollen provisions. bahiensis, I. nil, and Merremia aegyptia flowered during the same period in the rainy season from April to July. The Effective pollinators three species have funnel-shaped flowers, pink to violet in I. bahiensis, blue with a white flower tube in I. nil, and In each of the three species we counted the flower visits of white in M. aegyptia. The filament bases are fused with the the different bee species to ten flowers per day during four corolla, forming a nectar chamber (Fig. 1) that can be nonconsecutive days until flower senescence, in the 2007 accessed through small orifices between filament and cor- flowering season. Observation time was 28 h in Ipomoea olla. In I. nil the mean length of the nectar chamber was bahiensis (6:00–13:00 h), 24 h in I. nil (5:00–11:00 h), and 9.2 mm, about two times longer than that of M. aegyptia 32 h in Merremia aegyptia (5:00–13:00 h). We deter- (4.3 mm) and about three times longer than that of mined the relative frequency of flower visits of the dif- I. bahiensis (3.0 mm) (Table 1). ferent bee species per plant species and the frequency of The two species of Ipomoea with large to very large, visits per flower in 1 h intervals. During the flower visits spherical, pantoporate pollen grains and M. aegyptia with we recorded the contacts of the flower visitors to stigma large, oblate-spherical to subprolate, tricolpate grains and anthers, the floral resources collected, and the sex of showed no superposition in the size of grains (Table 2). the bee individuals. Similar bee species, which could not The flowers of I. bahiensis produced, on average, 4,703 be discriminated in the field, such as the species of pollen grains, about two times more than M. aegyptia Ancyloscelis, were grouped. In I. nil, which opened (2,556) and about five times more than Ipomoea nil (961) during the night, we made three observations from the (Table 2). Pollen viability of the three species was high beginning of anthesis to record possible nocturnal flower (I. bahiensis 98.95%, I. nil 99.65%, and M. aegyptia visitors. 99.53%). 123 150 R. A. Pick, C. Schlindwein

Fig. 1 Flowers of Ipomoea bahiensis (a–c), I. nil (d–f), and Merremia aegyptia (g–i); frontal view (a, d, g), longitudinal section (b, e, h), and detail of the nectar chamber (c, f, i). nc nectar chamber

The flowers of the three species opened synchronously: Breeding system in I. nil from 3:30 to 4:00 h, and in I. bahiensis and M. aegyptia from 5:00 to 5:30 h. At the beginning of Controlled pollination showed that I. bahiensis was self- anthesis the stigmas were already receptive and the incompatible whereas I. nil and M. aegyptia were self- anthers dehisced in all three species. The flowers of I. nil compatible, producing fruits and seeds in similar numbers wilted between 9:30 and 10:00 h, and those of I. bahi- in all treatments (I. nil fruits: H = 3.782; df = 3; ensis and M. aegyptia between 11:00 and 12:00 h. At P = 0.286, seeds: H = 0.807; df = 3; P = 0.848; senescence, petals recurved at the tip and closed the M. aegyptia fruits: H = 0.543; df = 3; P = 0.909, seeds: flower. H = 0.806; df = 3; P = 0.848) (Table 3). In I. bahiensis,

123 Pollen partitioning of three species of Convolvulaceae 151

Table 1 Measurements of Ipomoea Ipomoea nil Merremia flowers and flower parts of bahiensis aegyptia Ipomoea bahiensis, I. nil, and Mean ± SD Mean ± SD Mean ± SD Merremia aegyptia at Estaçaõ (mm) (mm) (mm) Ecolo´gica do Serido´ (n = 15 flowers per species) Flower length 33.9 ± 2.2 52.5 ± 3.8 18.2 ± 1.8 Floral diameter 62.7 ± 4.1 45.9 ± 4.9 29.0 ± 2.7 Length of flower tube 27.1 ± 1.6 40.0 ± 2.6 16.1 ± 1.2 Diameter of flower tube 10.3 ± 1.2 7.4 ± 0.6 6.4 ± 0.5 Length of nectar chamber 3.0 ± 0.5 9.2 ± 0.6 4.3 ± 0.7 Style length 15.0 ± 0.5 27.9 ± 1.1 10.5 ± 1.0 Filament length 12.6 ± 3.2 26.7 ± 3.8 8.5 ± 1.7 SD standard deviation

Table 2 Number of pollen Species Pollen grains, Pollen diameter, Ovules P/O mean grains and ovules per ﬂower of mean ± SD mean ± SD (lm) Ipomoea bahiensis, I. nil, and Merremia aegyptia (n = 10); Ipomoea bahiensis 4,703 ± 267 92.6 ± 8.0 4 1176 pollen diameter (n = 300) Ipomoea nil 961 ± 237 125.8 ± 5.2 6 160 Merremia aegyptia 2,556 ± 737 61.3 ± 1.8 4 639

Table 3 Breeding system of Ipomoea bahiensis, I. nil, and Merremia aegyptia at Estac¸a˜o Ecolo´gica do Serido´ Ipomoea bahiensis Ipomoea nil Merremia aegyptia FSFS FS

Spontaneous self-pollination 0 0 20 (67%) 82 (46%) 24 (80%) 81 (68%) Hand self-pollination 0 0 24 (80%) 86 (48%) 23 (77%) 75 (63%) Hand cross-pollination 18 (60%) 30 (25%) 17 (57%) 72 (40%) 23 (77%) 83 (69%) Natural pollination 7 (18%) 16 (10%) 26 (65%) 109 (45%) 29 (73%) 98 (61%) Spontaneous self-pollination (n = 30 per species), hand self-pollination (n = 30 per species), hand cross-pollination (n = 30 per species), and natural pollination (flowers accessible to pollinators) (n = 40 per species). F fruits, S seeds, S% part of potentially maximum seed set per treatment (total number of ovules in each pollination experiment = 100%) fruit and seed set in flowers accessible to flower visitors The species recorded showed different frequencies of were much lower than in the other two species (fruits: flower visits to the three studied species of Convolvula- H = 28.261; df = 2; P \ 0.001; Tukey test P \ 0.05; ceae: Lithurgus huberi predominated in the flowers of I. nil seeds: H = 30.556; df = 2; P \ 0.001; Tukey test with 80% of flower visits (Fig. 2b) and Apis mellifera in P \ 0.05). the flowers of M. aegyptia with 90% of visits (Fig. 2c). In the flowers of I. bahiensis, we recorded four species with Flower visitors elevated frequencies: Melitoma segmentaria (34%), Meli- tomella murihirta (27%), Melitoma osmioides (20%), and The flowers of the three species of Convolvulaceae were Lithurgus huberi (18%) (Fig. 2a). The two most frequent visited by insects, mainly bees, of 19 species—14 in flower visitors to I. bahiensis as well as Melitoma osmio- Merremia aegyptia,12inI. bahiensis, and 11 in Ipomoea ides were not recorded in flowers of Merremia aegyptia nil. Most species, including butterflies, were sporadic and were only sporadic visitors to flowers of I. nil.Beesof flower visitors and are not treated here. All bee species Ancyloscelis were recorded in the flowers of all three were solitary with the exception of Apis mellifera. Most studied species but were much more frequent in the flowers species recorded were from Emphorini (Apidae), and in six of Merremia aegyptia (7 visits per flower per day) than in of the seven species of this tribe, female and male bees those of Ipomoea nil and I. bahiensis (less than one visit were recorded (Table 4). per flower per day).

123 152 R. A. Pick, C. Schlindwein

Table 4 Flower visitors of Ipomoea bahiensis, I. nil, and Merremia aegyptia, recorded from May to July 2006 and 2007, at Estac¸a˜o Ecolo´gica do Serido´ Flower visitors Ipomoea bahiensis Ipomoea nil Merremia aegyptia

Andrenidae Calliopsini Acamptopoeum prinii (Holmberg, 1884) $ Apidae Apini Apis mellifera Linnaeus, 1758 $$ Euglossini Eulaema (Apeulaema) nigrita Lepeletier, 1841 #$ Emphorini Ancyloscelis apiformis (Fabricius, 1793) $# $# $# Ancyloscelis sp. $# $# Melitoma segmentaria (Fabricius, 1804) $# $# Melitoma osmioides (Ducke, 1908) $# $# Melitomella murihirta (Cockerell, 1912) $# # Diadasina riparia (Ducke,1907) $#$# Diadasina sp. $ Exomalopsini Exomalopsis analis Spinola, 1853 $# Protepeolini Leiopodus trochantericus Ducke 1907 # Ceratinini $ Ceratina (Crewella) sp. $$$ Megachilidae Lithurgus huberi (Ducke 1907) $# $# $# Halictidae Augochloropsis heterochroa (Cockerell, 1900) $ Augochlora (Augochlora) sp. 1 $$# Augochlora (Augochlora) sp. 2 $$ Hesperiidae/Hesperiinae Perichares philetes adela (Hewitson, 1867) $ Pieridae/Coliadinae Eurema elathera (Cramer, 1777) $$ Total number of species 12 11 14

The flower visitation rate was much higher to M. aegyptia 12:00 h (Fig. 4a). In I. nil, flower visits of L. huberi were (73.5 visits per flower per day) than to I. bahiensis (7.4 visits most frequent between 9:00 and 10:00 h (Fig. 4b). per flower per day) and I. nil (3.5 visits per flower per day) In the flowers of the three species of Convolvulaceae the (Fig. 3) due to the high abundance of honey bee workers females first collected pollen, initiating visits at 5:40 h in (Fig. 4c). The main period of flower visits, 8:00–11:00 h, I. bahiensis, 6:40 h in M. aegyptia, and at 7:50 h in I. nil. was similar in the three species. In this time we recorded 73% Pollen collection ended at about 10:00 h in the flowers of of the flower visits in I. bahiensis, 95% in I. nil, and 73% in all species. After this time the bees visited the flowers M. aegyptia (Fig. 3). The different bee species, however, exclusively to take up nectar. showed slightly different peaks in visitation frequency: bees To collect pollen, females of Melitoma segmentaria, of Melitoma segmentaria and Melitomella murihirta visited M. osmioides, Melitomella murihirta, Lithurgus huberi, flowers of I. bahiensis more frequently between 8:00 and and the two species of Ancyloscelis alighted on styles and 10:00 h, and bees of Lithurgus huberi between 11:00 and stamens, touching stigmas in all visits. The females of

123 Pollen partitioning of three species of Convolvulaceae 153

Fig. 2 Number of flower visits per day of bees of frequent species to Ipomoea bahiensis (a), I. nil (b), and Merremia aegyptia (c), at Estaçaõ Ecolo´gica de Serido´, Brazil (n = 40 flowers per species)

Ancyloscelis collected pollen exclusively in flowers of about 1 month duration, bees of M. osmioides showed M. aegyptia. In the flowers of Ipomoea, they alighted on the shortest flight period of the recorded bee species the margins of the petals, but despite advancing to the (Fig. 6). nectar chamber, they did not contact stigmas or anthers. Larval provisions of Melitoma osmioides and Melitom- Honey bee workers visited flowers of Merremia aegyptia ella murihirta contained mainly pollen grains from exclusively to take up nectar. During the collection trips I. bahiensis, only small amounts of pollen of I. nil, and no they got entirely powdered with white Merremia pollen on pollen of Merremia aegyptia. Brood cells of Melitomella head and mesosoma, but discarded the pollen grains, and murihirta contained on average also 10–21% of pollen of the corbiculae remained empty. In 66% of flower visits, Ipomoea species not studied here. The nest provisions of honey bees touched the stigmas (n = 80). Diadasina riparia exclusively contained pollen of Malva- All frequent flower visitors to I. bahiensis and ceae (Table 5). M. aegyptia showed mouthparts longer than the respective At the end of anthesis, about 12% of the total pollen per nectar chambers. Only two species, however, had mouth- flower remained in the anthers or adhered to petals in parts longer than the nectar chamber of I. nil (Fig. 5). The flowers of I. bahiensis, almost a third (31.9%) in the visits of Ancyloscelis bees to these flowers refer mainly to flowers of I. nil, and almost half of the pollen grains (48%) patrolling males which searched for females and did not in the flowers of M. aegyptia (Fig. 7). In the latter, 35% of take up nectar. pollen grains adhered to petals. All flower-visiting species with the exception of Apis Between 1.6% (I. bahiensis) and 11.4% (I. nil) of pro- mellifera were recorded exclusively during the flowering duced pollen grains were found on stigma lobes. Thus, 44 period of the species of Convolvulaceae. The two species pollen grains per ovule were deposited on stigmas of of Ancyloscelis occurred almost during the whole M. aegyptia and 18 pollen grains per ovule on stigmas of flowering period of the Convolvulaceae species, and I. bahiensis and I. nil. The bees removed, on average, Melitomella murihirta from the beginning of May until 86.4% of the total pollen amount of flowers of I. bahiensis, mid-June. The flight period of the two Melitoma species 57% of the pollen of I. nil, and only 45% of the pollen of initiated about 1 month after that of Ancyloscelis. With Merremia aegyptia.

123 154 R. A. Pick, C. Schlindwein

pollen among the oligolectic species may also influence the local host-plant choice and lead to dynamic changes in the web of interactions between Convolvulaceae and specialized bee pollinators. Our results stress the importance of pollen analyses of food provisions to elucidate trophic niches in oligolectic species, as already pointed out in Cane and Sipes (2006). Moreover, such analyses permit quantification of the relationship of oligolectic bees to pollen hosts, because brood cell provisions contain what larvae really eat (Larsson and Franzeń 2007;Mu¨ller et al. 2006; Schlindwein et al. 2005; 2009). In our study, pollen analysis also revealed that Diadasina riparia, which was recorded in the flowers of the three studied species of Convolvulaceae, construct brood cells exclusively containing pollen of Malvaceae, thereby indicating the species to be a narrow Sida oligolege. Unfortunately, no brood cells of the other oligolectic species found in flowers of Convolvulaceae were available for pollen analysis. Pollen resource partitioning among the oligolectic species in the Caatinga community studied here was strongly influenced by the massive presence of introduced honey Fig. 3 Frequency of flower visits per hour per flower to Ipomoea bahiensis, I. nil, and Merremia aegyptia at Estaçaõ Ecolo´gica do bees in the flowers of M. aegyptia. Worker bees of Apis Serido´, Brazil (n = 40 flowers per species, 4 days of observation) mellifera were 10 times more frequent in the flowers of this species than any of the other bees recorded in the Con- On stigmas of emasculated flowers we found, at the end of volvulaceae species. Honey bees discarded pollen and anthesis, on average, 52.9 conspecific pollen grains in provoked pollen waste leading to loss of almost half of the I. bahiensis, 16.4 in I. nil, and 81.1 in M. aegyptia (Fig. 8). total pollen amount produced by the Merremia flowers, In relation to the average amount of pollen deposited on with loss defined as pollen grains remaining in the flowers stigmas of nonemasculated flowers at the same day, exog- at the end of anthesis not used for pollination or by enous conspecific pollen corresponded to 72% in flowers of effective pollinators. Pollen grains that fell from anthers I. bahiensis, 15% in I. nil, and 47% in M. aegyptia. onto the petals during honey bee flower visits (one-third) became uncollectable by oligolectic bees. However, it is difficult to estimate the extent to which honey bees have Discussion influenced the reproductive success of the two Ancyloscelis species. In this context, it would be interesting to determine The three sympatric Caatinga species of Convolvulaceae the frequency of Ancyloscelis bees in flowers of which flower in the same period during the rainy season M. aegyptia at a site where honey bees do not occur. The partition their pollen almost exclusively among oligolectic massive presence of Apis mellifera, nevertheless, secured bee species. Our study shows that Melitoma segmentaria, pollination of M. aegyptia, because the bees contacted M. osmioides, and Melitomella murihirta show prefer- stigmas in two-thirds of flower visits and flew intensely ences for pollen of Ipomoea bahiensis, Lithurgus huberi among flowers of conspecific plants. for I. nil, and Ancyloscelis apiformis and the undescribed Recent studies with different pollen diets for larvae of Ancyloscelis species for Merremia aegyptia. Pollen anal- oligolectic bees have shown that several oligolectic species yses of the available cell provisions of the oligolectic bees cannot be reared on pollen of melittophilous flowers of showed a narrow relationship of Melitoma osmioides with other plant families, indicating chemical dependence of the flowers of Ipomoea bahiensis. Females of Melitomella oligolege on pollen of specific host plants (Praz et al. murihirta collected also significant portions of pollen 2008). The absence of nonoligolectic pollen-collecting (one-third) of two unidentified, less common species of bees in the flowers of the studied species, on the other Ipomoea, not studied here. This indicates different hand, could suggest that pollen of the involved Convol- degrees of host specialization in the assemblage of oli- vulaceae might be chemically protected from unspecialized golectic Convolvulaceae bees. Nevertheless, changing bees and accessible only for physiologically adapted spe- pollen availability and also interspecific competition for cialists. This could explain the repudiation of pollen of 123 Pollen partitioning of three species of Convolvulaceae 155

Fig. 4 Mean number of visits to single flowers per hour during anthesis in Ipomoea bahiensis (a), I. nil (b), and Merremia aegyptia (c) at Estaçaõ Ecolo´gica de Serido´ (n = 40 flowers per species)

M. aegyptia by the honey bees. Curiously, honey bees also Martins and Borges 1999; Schlindwein 1998), and Cacta- actively discard pollen of other plant taxa dominated by ceae (McFarland et al. 1989; Osborn et al. 1988; Sch- oligolectic bees such as certain Malvaceae and Cactaceae lindwein and Wittmann 1997; Schlindwein 2004). In some (Schlindwein et al. 2009). cases, the oligolectic bee species involved are taxonomi- Communities shaped by several oligolectic bee species cally unrelated, as in Cactaceae in South Brazil, where which interact with taxonomically related plant species are each of the four pollinator species are from different rare and occur in the Neotropics, for instance, in Malvaceae families (Arhysosage cactorum—Andrenidae, Ptilothrix (Gaglianone 2000; Rust 1980; Sipes and Tepedino 2005; fructifera—Apidae, Lithurgus ruﬁventris—Megachilidae, Schlindwein et al. 2009), Onagraceae (Alves-dos-Santos and Cephalocolletes rugata—Colletidae) (Schlindwein and 1999; Gimenes 1997, 2002; Martins and Antonini 1994; Wittmann 1995, 1997).

123 156 R. A. Pick, C. Schlindwein

Fig. 5 Mean length of mouthparts of ﬂower visitors to Ipomoea bahiensis, Merremia aegyptia, and I. nil. Vertical bars indicate mean length of nectar chambers of the three species of Convolvulaceae (bars from left to right: Ipomoea bahiensis, Merremia aegyptia, Ipomoea nil)

Fig. 6 Flowering period of Ipomoea bahiensis, I. nil, and Merremia aegyptia and flight period of bee species recorded on flowers of these species at Estaçaõ Ecolo´gica do Serido´. Records of bees refer to observations and collections of bees in flowers and periods of nesting activity in Melitoma osmioides, Melitomella murihirta, and Diadasina riparia

Different from these previously studied relationships, numerous species of this tribe to ﬂowers of Convolvulaceae the community of Convolvulaceae and bees studied here is is well known and documented for Melitoma, and some dominated by ﬁve emphorine species. The only oligolectic species of Ancyloscelis and Ptilothrix (Alves-dos-Santos species not belonging to Emphorini was the introduced 1999; Ducke 1908, 1910; Linsley et al. 1956, 1980; Lins- Lithurgus huberi (Snelling 1983), an allochthonous ele- ley and MacSwain 1957; Pinheiro and Schlindwein 1998; ment in the Neotropical fauna. Host-plant specialization of Schlindwein 1998), being complemented here by a species

123 Pollen partitioning of three species of Convolvulaceae 157

Table 5 Relative frequency of the different pollen types in brood cell provisions of Melitomella murihirta (n = 7 brood cells), Melitoma osmioides (n = 26 brood cells), and Diadasina riparia (n = 11 brood cells) at Estac¸a˜o Ecolo´gica do Serido´ Melitomella murihirta (%) Melitoma osmioides (%) Diadasina riparia (%)

Ipomoea bahiensis 65.0 98.6 – Ipomoea nil 0.7 1.1 – Ipomoea longeramosa – 0.3 – Ipomoea sp. 1 21.3 – – Ipomoea sp.2 13.0 – – Sida rhombifolia ––68 Sida sp. – – 28.4 Herissantia crispa – – 2.7 Other species of Malvaceae – – 0.9

1980; Schlindwein and Martins 2000; Schlindwein et al. 2009), and Alepidosceles (Schlindwein et al. unpublished), on Pontederiaceae (Ancyloscelis) (Alves-dos-Santos 2000; Alves-dos-Santos and Wittmann 1999, 2000), and on Cactaceae (Ptilothrix, Ancyloscelis) (Schlindwein and Wittmann 1995, 1997). Host-plant changes from or to Convolvulaceae, thus, have appeared at least in Ancyloscelis and Ptilothrix. A study on host-plant evolution and host- plant switches in emphorine taxa, similar to the phylogenetic analyses conducted recently for Diadasia (Sipes and Tepe- Fig. 7 Average number of pollen grains remaining on anthers, dino 2005), Andrena (Andrenidae) (Larkin et al. 2008), and adhering to petals, and deposited on stigmas at the end of anthesis in Chelostoma (Megachilidae) (Sedivy et al. 2008), therefore, flowers of Ipomoea bahiensis, I. nil, and Merremia aegyptia. Percentage values refer to the mean total number of pollen grains would be relevant. per flower of each species (n = 10) The three species studied showed nectar chambers varying strongly in length from 3 mm in Ipomoea bahiensis to 9 mm in I. nil. The presence of the nectar chamber of Melitomella. In a broad study in Mexico that also explains the virtual absence of short-tongued bees (sensu included pollen analysis of brood cells, Linsley et al. Kirby 1802 apud Michener 2007) as flower visitors of the (1980) point to narrow oligolecty of four species of Meli- plant species studied. In contrast to our expectation, how- toma on flowers of Ipomoea. Host-plant preferences of ever, the length of the chamber played no role in selecting Melitoma species for flowers of Ipomoea are even given as bees with an adequate tongue length among the oligolectic a feature on the genus level in taxonomic literature species and, thus, does not explain resource partitioning. (Michener et al. 1994; Michener 2007). Ipomoea bahiensis, the species with the shortest nectar Oligolecty on Convolvulaceae could thus be the ancestral chamber, attracted bees of a total of five oligolectic species state for these genera. Oligolecty on Malvaceae is also very of flower visitors, including M. segmentaria, which was the common in Emphorini, as in Diadasia (Sipes and Tepedino most frequent one and the species with the longest 2005), Diadasina (indicated in this study), Ptilothrix (Rust mouthparts.

Fig. 8 Number of pollen grains deposited on stigmas of emasculated ﬂowers and nonemasculated ﬂowers of Ipomoea bahiensis, I. nil, and Merremia aegyptia at the end of anthesis (mean and standard deviation, n = 10 per treatment)

123 158 R. A. Pick, C. Schlindwein

Acknowledgments We thank Fernando C.V. Zanella (UFCG) for Duque JG (1973) O Nordeste e as Lavouras Xero´filas, 2nd edn. Banco his help in bee identification, Carlos Eduardo Nobre (UFPE) and Olaf do Nordeste, Fortaleza, Ceara´ Hermann Hendrik Mielke (UFPR) for identification of the butterflies, Gaglianone MC (2000) Behavior on flowers, structures involved in Rosaˆngela Simaõ Bianchini for identification of the plants (Instituto pollen transport and nesting biology of Perditomorpha brunerii de Botaˆnica/SP), the staff of the Ecological Research Station ESEC- and Cephalurgus anomalus (Hymenoptera: Colletidae, Andren- Serido´ for logistical support, George Batista for botanical information idae). Rev Biol Trop 48(1):89–99 about plants at the reserve, and IBAMA (Adson Borges Macedo) for Gentry AH (1974) Flowering phenology and diversity in tropical permission to work in the nature reserve. Furthermore, we thank the Bignoniaceae. Biotropica 6:64–68 members of the working group Plebeia-Ecologia de Abelhas e da Gimenes M (1997) Pollination bees and other visitors of Ludwigia Polinizaçaõ for support in fieldwork, laboratory work, and for con- elegans (Onagraceae) flowers at tropical sites in Brazil. Stud structive discussions. The study was financially supported by the Neotrop Fauna Environm 32:81–88 Brazilian Research Council-CNPq (471401/2006-4), Research Pro- Gimenes M (2002) Interactions between bees and Ludwigia elegans gram in Biodiversity-PPBio Semi-a´rido, and grants from Coorde- (Camb.) Hara (Onagraceae) flowers at different altitudes in Saõ naçaõ de Aperfeiçoamento de Pessoal de Nı´vel Superior (CAPES) to Paulo, Brazil. Rev Bras Zool 19(3):681–689 R.A.P. and the Brazilian Research Council to C.S. Giulietti AM, Conceiçaõ AA, Queiroz LP (2006) Diversidade e caracterizaçaõ das fanero´gamas do Semi-a´rido Brasileiro, vol 1. Associaçaõ Plantas do Nordeste, Recife. 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