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Small pollen grain volumes and sizes dominatethe diet composition of three South Americansubtropical stingless beesFavio Gerardo Vosslera

a Laboratorio de Actuopalinología, CICyTTP-CONICET/FCyT-UADER, Diamante, ArgentinaPublished online: 23 Jul 2014.

To cite this article: Favio Gerardo Vossler (2015) Small pollen grain volumes and sizes dominate the diet composition ofthree South American subtropical stingless bees, Grana, 54:1, 68-81, DOI: 10.1080/00173134.2014.932838

To link to this article: http://dx.doi.org/10.1080/00173134.2014.932838

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Small pollen grain volumes and sizes dominate the diet composition ofthree South American subtropical stingless bees

FAVIO GERARDO VOSSLER

Laboratorio de Actuopalinología, CICyTTP-CONICET/FCyT-UADER, Diamante, Argentina

AbstractThe pollen preferences of three Meliponini species (Geotrigona argentina, Scaptotrigona jujuyensis and Tetragonisca fiebrigi)were studied in the Chaco forest of South America. Surprisingly, a large number of pollen types with small volumes and sizewere found in pollen masses stored in the 18 nests studied. Small pollen grains are commonly found in small flowers withshort pistils, a flower morphology adapted to the pollination by these small- to medium-sized bees. The prevalence of grainswith small volumes may be due to the preference of Meliponini bees for small flowers with short pistils, supporting apreviously suggested hypothesis of diffuse co-evolution between mass-flowering trees and these tiny bees in Neotropicalhabitats. However, the opportunistic foraging habit of these generalist bees would suggest that the large number of grainswith small size is due to their greater availability in the Chaco forest nearby the nests. This study also provides measurementsand descriptions of pollen cytoplasmic shapes as well as a new classification of pollen volumes based from measurements ofthe five pollen size categories using non-acetolyzed grains.

Keywords: corbiculate bee, cytoplasmic volume, Geotrigona argentina, opportunistic bee, pollen size category,Scaptotrigona jujuyensis, Tetragonisca fiebrigi

The Meliponini bee fauna of the subtropical DryChaco forest of Argentina is composed of at leastseven species (Arenas 2003; Vossler 2012; Roig-Alsina et al. 2013). To maintain their perennial colo-nies with hundreds to thousands of individuals andhigh rates of offspring, these bees have to forage largeamounts of food from a great number of plants fromdiverse families (Roubik 1989; Ramalho et al. 2007).

It is well known that other corbiculate bees such asthe widely studied Apis mellifera L. forage on a broadspectrum of plants. For instance, O’Rourke andBuchmann (1991) found that A. mellifera gatheredsimilar amounts of large, medium and small sizes ofpollen grains in a study carried out in an arid region ofthe Sonoran Desert in Arizona, but Biesmeijer et al.(1992) found that it foraged mainly on small pollengrains in Suriname. Unfortunately, few studies haverecorded the volume and size of the pollen grainsforaged by Meliponini bees to make comparisons.

For instance, it has been reported that the BrazilianTrigona spinipes (Fabricius) forage on a broad spec-trum of pollen sizes from 10 to > 100 µm, whileA. mellifera forage on a smaller range (10 to ≤ 71 µm)in the same area (Cortopassi-Laurino & Ramalho1988). Marques-Souza et al. (2002) reported that pol-len grains of diverse sizes are equally present amongthe pollen gathered by the Brazilian AmazonianFrieseomelitta, Melipona and Scaptotrigona. In the DryChaco forest, Vossler et al. (2010) reported thatGeotrigona argentina Camargo et Moure intensivelyforaged (≥ 5%) on pollen types of very small to med-ium volumes (from 65 to 34 782 µm3).In view of the polylectic specialization category of all

members of this bee tribe, it is expected that the threesubtropical Meliponini species studied forage on awide spectrum of flower sizes having pollen grainsfrom very small (< 10 µm and < 524 µm3) to verylarge (> 100 µm and > 523 583 µm3) both in size and

Correspondence: Favio Gerardo Vossler, Laboratorio de Actuopalinología, CICyTTP-CONICET/FCyT-UADER, Dr Materi y España, E3105BWA,Diamante, Entre Ríos, Argentina. E-mail: favossler@yahoo.com.ar

(Received 16 June 2013; accepted 1 June 2014)

Grana, 2015Vol. 54, No. 1, 68–81, http://dx.doi.org/10.1080/00173134.2014.932838

© 2014 Collegium Palynologicum Scandinavicum

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volume. For this reason, the goals of this study wereto establish the cytoplasmic volume and size categoriesof the pollen grains foraged by three species ofMeliponini bees in the South American Chaco forest,particularly those intensively foraged, to detect a pos-sible relationship between pollen size/volume andflower size, and to give possible explanations aboutwhy certain pollen grains are highly abundant in thesecolonies.

Material and methods

Dry Chaco forest vegetation

The vegetation units of the study area are ‘Quebrachal’of three ‘quebrachos’ belonging to the central ChacoForests, and ‘Quebrachal’ of two ‘quebrachos’ and‘Palosantales’ of Bulnesia sarmientoi Lorentz ex Griseb.both belonging to the western Chaco Forests, sensuPrado (1993). The two former units are characterisedby the dominance of Schinopsis lorentzii Engl. (Anacar-diaceae), Schinopsis balansae Engl. and Aspidospermaquebracho-blanco Schldtl. (Apocynaceae), and thelatter by Bulnesia sarmientoi Lorentz ex Griseb.(Zygophyllaceae). Other floristic elements are Ziziphusmistol Griseb. (Rhamnaceae), Sideroxylon obtusifolium(Roem. et Schult.) T.D. Penn. (Sapotaceae), severalspecies of Prosopis (Fabaceae, Mimosoideae), Caesal-

pinia paraguariensis (D. Parodi) Burkart (Fabaceae,Caesalpinioideae), Pterogyne nitens Tul. (Fabaceae,Caesalpinioideae), Tabebuia nodosa (Griseb.) Griseb.(Bignoniaceae), Aspidosperma triternatum Rojas Acosta(Apocynaceae), Trithrinax schizophylla Drude (Are-caceae), Castela coccinea Griseb. (Simaroubaceae),Achatocarpus praecox Griseb. (Achatocarpaceae), Celtisspp. (Celtidaceae), Schinus fasciculatus (Griseb.) I.M.Johnst. var. arenicola (Hauman) F.A. Barkley (Anacar-diaceae), Capparis atamisquea Kuntze (Capparidaceae),Maytenus vitis-idaea Griseb. (Celastraceae), Moya spi-nosa Griseb. (Celastraceae), Mimosa detinens Benth.(Fabaceae, Mimosoideae), Stetsonia coryne (Salm-Dyck) Britton et Rose (Cactaceae) and several speciesof Capparis (Capparidaceae) and Acacia (Fabaceae,Mimosoideae) (Prado 1993; Vossler 2013).

Pollen sampling and processing

Pollen masses (the pollen content of each cerumenpot) were extracted from one pot if it was completeor closed or a few if they were broken and/or opened.As each nest is an independent sample, pollenmasses taken from the same nest were consideredsubsamples.A total of 86 subsamples of pollen masses from

ten nests were analysed for Tetragonisca fiebrigi

Figure 1. Map depicting the distribution of the subtropical Chaco forest of South America indicating the sites where nest pollen sampleswere obtained. 1, Juan José Castelli (25° 56′ S; 60° 37′ W); 2, Villa Río Bermejito (25° 37′ S; 60° 15′ W); 3, Miraflores (25° 29′ S; 61° 01′W); 4, El Espinillo (25° 24′ S; 60° 27′ W); 5, El Sauzalito (24° 24′ S; 61° 40′ W).

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Table I. Pollen types intensively (xx) (in bold) and slightly (x) foraged by Tetragonisca fiebrigi (Tf), Scaptotrigona jujuyensis (Sj) and Geotrigonaargentina (Ga).

Bee species

Plant family Pollen type Tf Sj Ga

Acanthaceae Justicia x xAchatocarpaceae Achatocarpus praecox xx x xAlismataceae Sagittaria montevidensis x xAlismataceae/Limnocharitaceae Sagittaria montevidensis/Hydrocleys xxAmaranthaceae Alternanthera xAnacardiaceae Schinopsis xx xx xAnacardiaceae Schinus fasciculatus-Schinopsis? xx xxApiaceae Apiaceae x xApocynaceae Apocynaceae xApocynaceae Aspidosperma x xArecaceae Trithrinax schizophylla xx xxAsteraceae Parthenium hysterophorus xx xx xAsteraceae Xanthium spinosum x xAsteraceae Astereae xAsteraceae Baccharis x xxAsteraceae Tessaria dodoneifolia x xAsteraceae Tessaria xAsteraceae Heliantheae xxAsteraceae Holocheilus hieracioides xAsteraceae Vernonia x xBasellaceae Anredera cordifolia xBignoniaceae Fridericia dichotoma x xBignoniaceae Tabebuia xxBoraginaceae Boraginaceae xBoraginaceae Heliotropium xBromeliaceae Bromeliaceae xCactaceae Cactaceae xCapparidaceae Capparis salicifolia/C. tweediana xx xCapparidaceae Capparis speciosa/C. tweediana xx xCapparidaceae Capparis atamisquea xx xCapparidaceae Capparis retusa xx xCapparidaceae Capparis xxCelastraceae Maytenus vitis-idaea/Moya spinosa xx x xxCeltidaceae Celtis xx x xChenopodiaceae Chenopodiaceae xCyperaceae Eleocharis xxEuphorbiaceae Croton xxEuphorbiaceae Sapium haematospermum xx xFabaceae, Caesalpinioideae Pterogyne nitens xx xxFabaceae, Caesalpinioideae Caesalpinia paraguariensis xx xFabaceae, Caesalpinioideae Cercidium praecox xx xFabaceae, Caesalpinioideae Parkinsonia aculeata xx xFabaceae, Mimosoideae Acacia (polyad of 16 pollen grains) x x xFabaceae, Mimosoideae Ingeae 1 (monads from polyad) x xFabaceae, Mimosoideae Ingeae 2 (monads from polyad) x xFabaceae, Mimosoideae Mimosa detinens x xxFabaceae, Mimosoideae Prosopis xx x xxFabaceae? Gleditsia/Fabaceae? xx xLoranthaceae Struthanthus angustifolius x x xxLoranthaceae Tripodanthus acutifolius xLythraceae Heimia salicifolia x xMalpighiaceae Malpighiaceae xMalpighiaceae Mascagnia brevifolia xx xMalvaceae Malvaceae x x xMenyanthaceae Nymphoides indica xNyctaginaceae Boerhavia diffusa xNyctaginaceae Pisonia zapallo xOlacaceae Ximenia americana x xOnagraceae Ludwigia x

(Continued )

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(Schwarz), 18 subsamples from four nests forScaptotrigona jujuyensis (Schrottky), and 63 fromfour nests for Geotrigona argentina (Vossler et al.2010; Vossler 2013). Pollen types were classified intwo categories according to their abundance: ≤ 10%and > 10% (Table I) following Ramalho et al.(1985), Cortopassi-Laurino and Ramalho (1988),and Ramalho (1990). A total of 32 pollen typeswere intensively foraged (> 10%) by the threeMeliponini species studied. Tetragonisca fiebrigiintensively foraged on 24 out of the 52 foraged pol-len types, S. jujuyensis on seven out of 45 and G.argentina on nine out of 41 (Table I). From the 78pollen types identified in all subsamples, 37 of themwere taken at random for both diameter and volumemeasurement.

Pollen type nomenclature follows the recommen-dations of Birks (1973), Birks and Birks (1980),Joosten and De Klerk (2002), and De Klerk andJoosten (2007). In most cases, pollen volumes andsize were measured from reference pollen and there-fore authority was not deleted.

The reference pollen collection was made fromflower buds of plant species collected in variouslocalities from the Chaco province of Argentina(Juan José Castelli [25° 56′ S; 60° 37′ W], Villa RíoBermejito [25° 37′ S; 60° 15′W], El Espinillo [25°24′ S; 60° 27′ W], Miraflores [25° 29′ S; 61° 01′ W]and El Sauzalito [24° 24′ S; 61° 40′W]; Figure 1).

The plant specimens were pressed, dried, identifiedby the author and deposited in the herbaria of theMuseo de La Plata (LP), La Plata, and the MuseoArgentino de Ciencias Naturales ‘BernardinoRivadavia’ (BA), Buenos Aires, Argentina. Plantnomenclature follows Zuloaga et al. (2008). Freshpollen grains from flowers were dyed using fuchsine(but not acetolysed), mounted on slides using a gly-cerine-gelatine mixture and measured under a NikonEclipse E200 light microscope at 1000× magnifica-tion. When pollen from flowers was not available,pollen grains from the colonies were measured. Beeswere identified by Arturo Roig-Alsina and depositedin the Entomology Collection of the MuseoArgentino de Ciencias Naturales ‘BernardinoRivadavia’.

Categories of volume and size of pollen grains

Ten to 15 measurements of both polar and equator-ial axes of pollen grain cytoplasms per each referenceplant were taken. The measurements were fromequatorial view for spherical and ellipsoidal shapes,and from two different views for prism shapes.The pollen size categories were taken from

Wodehouse (1935) and Hesse et al. (2009), beingvery small (< 10 µm), small (10–25 µm), medium(26–50 µm), large (51–100 µm) and very large(> 100 µm). To allocate a particular pollen type to

Table I. (Continued ).

Bee species

Plant family Pollen type Tf Sj Ga

Polygonaceae Polygonum x xPolygonaceae Ruprechtia triflora x xPortulacaceae Portulaca xRhamnaceae Ziziphus mistol xx x xxSantalaceae Acanthosyris falcata x xSapindaceae Urvillaea chacöensis x xSapotaceae Sideroxylon obtusifolium xx x xScrophulariaceae Scoparia xSimaroubaceae Castela coccinea x x xxTyphaceae Typha xUlmaceae Phyllostylon rhamnoides xxVerbenaceae Phyla reptans x x xVerbenaceae Verbena xZygophyllaceae Bulnesia sarmientoi x? Tetrad x x? Unidentified 1 x x? Unidentified 2 x x? Unidentified 3 x? Unidentified 4 x

Number of pollen types ≤ 10% (x) 28 38 32Number of pollen types > 10% (xx) 24 7 9Total number of pollen types per bee species 52 45 41

Note: The number of foraged pollen types varied among these species. These three bee species foraged intensively on a total of 32 pollen types.

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each size category, the longest value of any of the twocytoplasmic diameters was used to establish the cate-gories of whole pollen grains (cytoplasm plus walls),as suggested by Hesse et al. (2009).

To estimate the cytoplasmic volume, pollen grainswere compared to similar geometric shapes: sphere,ellipsoid and triangular base prism. Based on the sizeclasses, five pollen volume categories are used in thepresent study: very small volume (< 524 µm3), smallvolume (524–8181 µm3), medium volume (8182–65 448 µm3), large volume (65 449–523 583 µm3) andvery large volume (> 523 583 µm3). The calculationsof volume categories are based on spherical pollengrains.

Pollen shapes

All shapes found in the samples were identified andmeasured in equatorial view as follows (seeFigure 2A).

Prolate ellipsoid (and prolate ellipsoid polyads) (Figure2A, B). — Main axis p (polar axis) and two minoraxis e of the same length (equatorial axes; e.g.Pterogyne nitens and Mimosa detinens polyad). Theformula is 1/6 π p e2. In the same way, the axis p ofthe prolate ellipsoid polyad was considered the axisof greater length, while e the minor axes.

Flat oblate ellipsoid (and flat polyads) (Figure2A, B). — Minor axis p (polar axis) and two axes e(equatorial axes), they can be of the same length (e2;e.g. Acacia praecox Griseb. and Acacia sp. polyads), orof different lengths (e1 and e2; e.g. polyad ofEnterolobium contortisiliquum (Vell.) Morong). The for-mulae are 1/6 π p e2 or 1/6 π p e1 e2, respectively. In flat

polyads, their thickness (corresponding to the minoraxis) was considered as p axis, while both other majoraxis (height and width of the polyad) were consideredas e axes (or e1 and e2 if they are different in length).

Oblate ellipsoid (Figure 2A). — Similar to prolateellipsoid shape with a rotation of 180°. The mainaxis e (long equatorial axis) and two axes p of thesame length (polar axis and short equatorial axis; e.g.Salvia). The formula is 1/6 π e p2.

Sphere (Figure 2A). — A polar axis p and an equa-torial axis e of approximately the same length (e.g.Polygonum). The ratio between the mean values ofthese two axes must be within the 0.99 to 1.01 range.The formula is 1/6 π p3. In cases where spherical andprolate or flat oblate ellipsoidal pollen grains werefound in the same pollen type, the prolate ellipsoidformula was applied (Figure 2A).

Triangular base prism (Figure 2A). — Being s any ofthe base sides and h the height of the prism(O’Rourke & Buchmann 1991; e.g. Acanthosyris fal-cata Griseb). As both values could not be measuredin the same grain, s and h were measured in differentgrains. The formula is ¼ s2 h √3.

Other shapes such as cubic shapes or those foundin heteropolar pollen grains were not present amongthe pollen grains foraged by Meliponini bees fromthe Dry Chaco forest. Although the oblate ellipsoidshape was not found in the samples, it was describedto avoid mistakes in volume calculations as it is verysimilar to the prolate ellipsoid shape. However, incases where the oblate ellipsoid shape is present, itsvolume should be calculated according to Figure 2A

Figure 2. A. Pollen shapes (a–e) found in the pollen samples studied. Location of axis e and p (of ellipsoidal and spherical shapes) and h ands (of prismatic shape) is provided. B. Scanning photo-micrograph of grains found in pollen masses of Meliponini bees, showing differentshapes and sizes. Scale bar – 50 µm.

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(c). In the same way, Enterolobium contortisiliquum(Vell.) Morong was not found among pollen samplesas a whole polyad, but only as isolated monads.However, due to the fact that this acalymmate polyadcould be broken during foraging or palynologicalprocessing, the formula to describe flat polyads isgiven.

Flower size

Flower measurements were made on those plantspecies whose pollen grains were measured for sizeand volume. Maximum size of flowers was estab-lished mainly from fresh flowers and photographstaken during fieldwork as well as from literature onthe local flora. According to their maximum size,flowers were classified as either small (≤ 1 cm), med-ium (1–2 cm) or large (≥ 2 cm).

Statistical analysis

Correlation (Pearson coefficient) and linear regres-sion analyses were used to examine the dataset.Shapiro–Wilk and Kolmogorov–Smirnov tests fornormality were applied to the data set. Mean pollenvolume, maximum pollen size and maximum flowersize were log-transformed prior to analysis to meetthe assumptions of parametric tests. To investigatewhether the distribution of the pollen types byvolume/size category differed in nest stores and for-est, the null hypothesis was that there is no differencebetween the two distributions. This was tested using

a χ2 goodness-of-fit test, at 5% significance level.The categories very small and very large had anexpected frequency count of less than five. For thisreason, they had to be added to small and large,respectively, as required by this test. For both statis-tical analyses, the program package Statgraphics®Centurion XVI (StatPoint Technologies 2010) wasused.

Results

Volume range of the pollen foraged by Meliponini bees inthe Dry Chaco forest

Pollen volumes varied from 565 µm3 for Xime-nia americana L. (Olacaceae) to 17 450 µm3 forJusticia (Acanthaceae) (Figure 3). The greatest volumevalues calculated (> 10 000 µm3) were from thefollowing families: Acanthaceae, Euphorbiaceae,Polygonaceae, Fabaceae (Caesalpinioideae), Cappa-ridaceae, Malpighiaceae and Bignoniaceae, whilethe smallest (< 2000 µm3) from the following families:Olacaceae, Asteraceae, Fabaceae (Mimosoideae),Fabaceae (Caesalpinioideae), Celastraceae, Cappa-ridaceae, Anacardiaceae, Verbenaceae and Rhamna-ceae (Figure 3).Only two of the five volume categories were iden-

tified in the diet: small and medium (Figure 3).From the total of pollen grains measured in thenests sampled (37 pollen types), 72.97% (27 pollentypes) were small (565–6418 µm3) and 27.03% (10types) medium (8298–17 450 µm3).

Figure 3. Volume (in µm3) of 37 pollentypes of melittophilous plant species ofthe subtropical Dry Chaco forest, indecreasing order. Volume values rangedfrom 565 µm3 for Ximenia americana(Olacaceae) to 17 450 µm3 for Justicia(Acanthaceae).

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Pollen volume of the intensively foraged pollen types

The volume values of 25 out of the 32 intensivelyforaged pollen types ranged from 618 µm3 forParthenium hysterophorus L. (Asteraceae) (smallvolume) to 16 007 µm3 for Sapium haematospermumMüll. Arg. (Euphorbiaceae) (medium volume).When only those pollen types that were intensivelyforaged (> 10% frequency) are considered, smallpollen volumes are also highly represented (76%)(19 pollen types).

Pollen size of the foraged pollen grains

Only three of the five pollen sizes described byWodehouse (1935) were identified in the diet ofthe Chaquenian Meliponini bees: small, mediumand large (Figure 4). Based on the total number ofpollen types measured (37), 62.16% (23 pollentypes) were small (11.4–23.75 µm), 35.13% (13types) medium (25.65–39.9 µm) and only 2.7%(one type) large (63.65 µm). When only those pollentypes that were intensively foraged (> 10% fre-quency) are considered, small pollen sizes are alsohighly represented (66.7%) (16 pollen types).

Flower sizes

Most of the plants (23 out of 35 species) had small-size flowers (≤ 1 cm). They were the following (indecreasing order of their pollen volume): Sapium hae-matospermum (Euphorbiaceae), Polygonum sp.(Polygonaceae), Caesalpinia paraguariensis (Fabaceae,Caesalpinioideae), Prosopis elata (Burkart) Burkart(Fabaceae, Mimosoideae), Acacia praecox (Fabaceae,Mimosoideae), Acacia sp., Schinopsis balansae(Anacardiaceae), Achatocarpus praecox (Achatocarpa-ceae), Apiaceae, Celtis sp. (Celtidaceae), Castela cocci-nea (Simaroubaceae), Schinus fasciculatus var. arenicola(Anacardiaceae), Acanthosyris falcata (Santalaceae),Trithrinax schizophylla (Arecaceae), Sideroxylon obtusi-folium (Sapotaceae), Ziziphus mistol (Rhamnaceae),Phyla reptans (Kunth) Greene (Verbenaceae), Moyaspinosa (Celastraceae), Maytenus vitis-idaea (Celastra-ceae), Baccharis sp. (Asteraceae), Pterogyne nitens(Fabaceae, Caesalpinioideae), Mimosa detinens(Fabaceae, Mimosoideae) and Parthenium hystero-phorus (Asteraceae).

Only six species had medium-size flowers (1–2 cm):Mascagnia brevifolia Griseb. (Malpighiaceae),Cercidium praecox (Ruiz et Pav. ex Hook.) Harms(Fabaceae, Caesalpinioideae), Enterolobium contortisili-quum (Fabaceae, Mimosoideae), Heimia salicifolia

Figure 4. Maximum, minimum and mean values of the largerpollen cytoplasm diameter of 37 pollen types, in increasing orderaccording to their maximum values. Three cytoplasmic sizes arerepresented: small, medium and large. Most pollen types (23)were small size and ranged from 11.4 to 23.75 µm. Values ofpollen type diameters foraged intensively by at least oneMeliponini species are shown within a box.

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(Kunth) Link (Lythraceae), Capparis atamisquea(Capparidaceae) and Ximenia americana (Olacaceae).

Six had large-size flowers (≥ 2 cm): Justicia sp.(Acanthaceae), Capparis salicifolia Griseb. (Cappari-daceae), Fridericia dichotoma (Jacq.) L.G. Lohmann(Bignoniaceae), Capparis tweediana Eichler, Capparisspeciosa Griseb. and Capparis retusa Griseb.

The relationship between flower sizes and volume andsize of pollen grains

A significant positive linear correlation was foundbetween mean pollen volume and maximum flowersize (r = 0.45, P = 0.0055, Figure 5A) as well asbetween maximum pollen size and maximum flowersize (r= 0.42, P = 0.0099, Figure 5B). The maxi-mum flower size explained moderate proportions ofthe variation of both the pollen grain volume (logpollen volume (µm3) = 3.00846 + 0.55853*log max-imum flower size (mm); F [1,34] = 8.79, P = 0.0055)and the maximum pollen size (log maximum pollensize (µm) = 1.18686 + 0.198944*log maximum flowersize (mm); F [1,34] = 7.47, P= 0.0099). In both cor-relation analyses, most points (33) were found within

two standard deviations (mainly between one and twostandard deviations) and only two points in more thantwo standard deviations (Figure 5).Most of the flowers of small size had small pollen

volume ranging from 618 µm3 in Parthenium hyster-ophorus to 6418 µm3 in Acacia (18 species). Only fivepollen types corresponding to species of small-sizeflowers had medium volume (Sapium haematosper-mum, Polygonum, Caesalpinia paraguariensis, Prosopiselata and Acacia praecox) (Figure 3). However, mostof small-size flowers (14 species) had small pollensizes and nine flowers had medium pollen size(Figure 4) but two out of these nine species (Acaciasp. and A. praecox) presented their pollen grainsclustered in polyads. For this reason, if polyad spe-cies were not taken into account, only seven speciespresented small-size flowers producing pollen sizesother than small.Medium and large size flowers (12 species) had

small and medium pollen volumes from 565 to 17450 µm3. These flowers had small, medium or largepollen sizes (seven, four and one pollen types,respectively).

Availability of pollen grains of different volumes and sizesin the xerophilous Chaco forest

Measurements of pollen grain volume (mean) (n=100)and pollen grain size (larger diameter) (n=76) from atotal of 100 floral resources taken at random from theDry Chaco forest were provided (Table II). The fivevolume and size categories were present in the availableflora. For both volume and size, most pollen speciesbelonged to small (51 and 41) and medium (32 and22), followed by large (ten and eight), very small (fiveand four) and very large categories (two and one),respectively.The χ2 goodness-of-fit test showed significant dif-

ference between the distribution of frequencies ofvolume categories from nest stores versus the forest,when all pollen types (χ2 = 10.07; P = 0.018) as wellas only the most important resources for bees(> 10%) (χ2 = 7.81; P = 0.050) were taken intoaccount. Bees used 27 (52.94%) out of 51 smallvolume species and ten (31.25%) out of 32 mediumvolume species available in the forest; the other threecategories were not foraged. However, this test didnot show a significant difference between the distri-bution of frequencies of size categories from neststores and the forest for all pollen types (χ2 = 3.15;P = 0.206) and those represented by more than 10%(χ2 = 3.22; P = 0.19).

Figure 5. A. Correlation analysis showing the relationship betweenpollen volume and flower size. B. Correlation analysis showing therelationship between pollen size and flower size. Both analysesshowed a significant moderate positive correlation (see text).

Pollen grains in Chaquenian Meliponini diet 75

Dow

nloa

ded

by [

Dr

Favi

o V

ossl

er]

at 1

3:05

25

Mar

ch 2

015

Tab

leII.Measuremen

tsof

polle

ngrainvo

lume(m

ean)

(inµm

3)an

dpo

llengrainsize

(largerdiam

eter)(inµm

)of

100floral

resourcesavailablein

theDry

Cha

coforest.

Plant

family

Pollentype

Pollengrain

volume

Pollengrain

size

Pollenvo

lume

catego

ryPollensize

catego

ryReferen

cean

dsampleorigin

c

Acantha

ceae

Justicia

1745

063

.65

ML

thisarticle,

NEST

Tf(n

=10

)Ach

atoc

arpac

eae

Ach

atoc

har

puspra

ecox

4486

23.75

SS

thisarticle,

NEST

Tf(n

=15

)Alism

atac

eae/

Lim

noc

har

itac

eae

Sag

ittariam

onteviden

sis/

Hyd

rocley

s58

2623

.75

SS

Vossler

(201

3),NEST

Ga(n

=10

)

Amaran

thaceae

Alternan

thera

110

6.65

VS

VS

Vossler

(201

3),NEST

Ga(n

=4)

Anac

ardiace

aeSch

inop

sisbalan

sae

4589

25.65

SS

thisarticle,

HERB

(n=15

)Ana

cardiaceae

Schinus

fasciculatus

2469

19.95

SS

thisarticle,

HERB

(n=15

)Anac

ardiace

aeSch

inusfasciculatus(T

f)14

3519

.00

SS

thisarticle,

NEST

Tf(n

=15

)Apiaceae

Apiaceae

3265

36.00

SM

thisarticle,

NEST

Sj(n

=15

)Areca

ceae

Trithrinax

schizop

hylla

2047

25.65

SS

thisarticle,

NEST

Tf(n

=15

)Asterac

eae,

Asterea

eBac

char

is10

0914

.25

SS

thisarticle,

NEST

Sj(n

=15

)Asterac

eae,

Asterea

eBac

char

is/Solidag

och

ilen

sis

1053

15.20

SS

Dalmazzo

andVossler

unpu

blishe

d,NEST

Aa(n

=15

)Asteraceae,

Astereae

Solidagochilensis

4123

19.87a

SS

Torres(200

0),HERB

(n=10

)Asteraceae,

Eup

atorieae

Eup

atorium

arnottian

umb

3976

19.62a

SS

Torres(200

0),HERB

(n=10

)Asteraceae,

Eup

atorieae

Mikan

iaurticifolia

7480

24.12a

SS

Torres(200

0),HERB

(n=10

)Asteraceae,

Helen

ieae

Porophyllum

ruderale

1344

029

.37a

MM

Torres(200

0),HERB

(n=10

)Asteraceae,

Helen

ieae

Tagetes

minuta

1153

327

.87a

MM

Torres(200

0),HERB

(n=10

)Asteraceae,

Helianthe

aeBidenspilosa

8114

24.87a

SS

Torres(200

0),HERB

(n=10

)Asterac

eae,

Helianthea

eHelianthea

e15

4215

.20

SS

Vossler

(201

3),NEST

Tf(n

=15

)Asterac

eae,

Helianthea

ePar

then

ium

hys

tero

phor

us

618

11.40

SS

thisarticle,

NEST

Tf(n

=15

)Asteraceae,

Helianthe

aeVerbesina

encelioides

6115

22.62a

SS

Torres(200

0),HERB

(n=10

)Asteraceae,

Inuleae

Pterocaulon

2577

18.05

SS

Vossler

(201

3),HERB

(n=15

)Asteraceae,

Mutisieae

Holocheilu

shieracioides

230

7.60

VS

VS

Vossler

(201

3),NEST

Ga(n

=15

)Asteraceae,

Mutisieae

Hyalis

argentea

b47

407

44.81a

MM

Torres(200

0),HERB

(n=10

)Asteraceae,

Verno

nieae

Vernoniamollissimab

6370

049

.50a

MM

Torres(200

0),HERB

(n=10

)Asteraceae,

Verno

nieae

Vernonianu

diflorab

3073

938

.75a

MM

Torres(200

0),HERB

(n=10

)Bigno

niaceae

Dolicha

ndra

cyna

nchoides

4435

2M

Ferná

ndez

etal.(200

9),HERB

(n=10

)Bigno

niaceae

Fridericiadichotom

a10

954

39.90

MM

thisarticle,

HERB

(n=15

)Bigno

niaceae

Pith

ecoctenium

cyna

nchoides

5248

1M

Ferná

ndez

etal.(200

9),HERB

(n=10

)Bignon

iace

aeTab

ebuia

nod

osa

5827

25.65

SS

Vossler

(201

3),HERB

(n=15

)Bom

bacaceae

Chorisiaspeciosa

2930

0M

Rou

lstonet

al.(200

0),HERB

(n=5-10

)Boraginaceae

Heliotropium

curassav

icum

2038

21.85

SS

Vossler

(201

3),HERB

(n=15

)Bromeliaceae

Dyckia

3592

26.60

SM

Vossler

(201

3),HERB

(n=15

)Cactaceae

Opu

ntia

acan

thocarpa

b42

780

0L

Rou

lstonet

al.(200

0),HERB

(n=5-10

)Cactaceae

Opu

ntia

arbusculab

41420

0L

Rou

lstonet

al.(200

0),HERB

(n=5-10

)Cactaceae

Opu

ntia

phaecantha

b70

610

0VL

Rou

lstonet

al.(200

0),HERB

(n=5-10

)Cap

par

idac

eae

Cap

par

isatam

isqu

ea13

7916

.15

SS

thisarticle,

NEST

Tf(n

=9)

Cap

par

idac

eae

Cap

par

isretusa

3133

21.85

SS

thisarticle,

HERB

(n=15

)Cap

par

idac

eae

Cap

par

issa

licifolia

1464

038

.00

MM

thisarticle,

HERB

(n=15

)Cap

par

idac

eae

Cap

par

issp

eciosa

4077

23.75

SS

thisarticle,

HERB

(n=15

)Cap

par

idac

eae

Cap

par

istw

eediana

8344

30.40

MM

thisarticle,

HERB

(n=15

)Celastrac

eae

May

tenusvitis-idae

a10

9115

.20

SS

thisarticle,

HERB

(n=15

)

76 F.G. Vossler

Dow

nloa

ded

by [

Dr

Favi

o V

ossl

er]

at 1

3:05

25

Mar

ch 2

015

Celastrac

eae

Moy

asp

inos

a11

8514

.25

SS

thisarticle,

HERB

(n=13

)Celtidac

eae

Celtis

2805

20.90

SS

thisarticle,

NEST

Tf(n

=15

)Con

volvulaceae

Evolvulus

sericeus

2967

9M

Ferná

ndez

etal.(200

9),HERB

(n=10

)Con

volvulaceae

Ipom

oeaalba

109

514

414

4.40

VL

VL

Dalmazzo

andVossler

unpu

blishe

d,NEST

Aa(n

=15

)Con

volvulaceae

Ipom

oeacairica

6247

651

.30

ML

Dalmazzo

andVossler

unpu

blishe

d,NEST

Aa(n

=15

)Con

volvulaceae

Ipom

oeahieronym

ib23

170

6L

Ferná

ndez

etal.(200

9),HERB

(n=10

)Cyp

erac

eae

Eleoc

har

is47

013

.30

VS

SVossler

(201

3),NEST

Ga(n

=10

)Euphor

biace

aeCro

ton

3231

845

.60

MM

Vossler

(201

3),NEST

Ga(n

=15

)Eup

horbiaceae

Croton

7015

351

.17a

LL

Silv

eira

1991

),NEST

Am

(n=25

)Eup

horbiaceae

Croton/Man

ihot

grah

amiib

23759

390

.25

LL

Dalmazzo

andVossler

unpu

blishe

d,NEST

Aa(n

=12

)Euphor

biace

aeSap

ium

hae

matos

permum

1600

739

.90

MM

thisarticle,

NEST

Tf(n

=15

)Fab

acea

e,Cae

salpinioidea

eCae

salpinia

par

aguar

iensis

1513

335

.15

MM

thisarticle,

HERB

(n=15

)

Fab

acea

e,Cae

salpinioidea

eCercidium

pra

ecox

4168

21.85

SS

thisarticle,

NEST

Tf(n

=9)

Fab

acea

e,Cae

salpinioidea

eGleditsiaam

orphoides

5213

26.60

SM

Vossler

(201

3),HERB

(n=15

)

Fab

acea

e,Cae

salpinioidea

ePtero

gyneniten

s78

514

.25

SS

thisarticle,

HERB

(n=15

)

Fab

aceae,

Caesalpinioideae

Senna

occidentalis

2190

0M

Rou

lstonet

al.(200

0),HERB

(n=5-10

)Fab

aceae,

Mim

osoide

aeAcaciapraecox

8298

33.25

MM

thisarticle,

HERB

(n=15

)Fab

aceae,

Mim

osoide

aeAcacia

6418

28.00

SM

thisarticle,

NEST

Sj(n

=15

)Fab

aceae,

Mim

osoide

aeAlbizia

inun

data

4625

766

.50

ML

Vossler

unpu

blishe

d,NEST

Mo(n

=7)

Fab

aceae,

Mim

osoide

aeEnterolobium

(isolatedmon

ad)

3216

23.75

SS

thisarticle,

HERB

(n=15

)Fab

aceae,

Mim

osoide

aeEnterolobium

(who

lepo

lyad

)11

143

286

.45

LL

thisarticle,

HERB

(n=8)

Fab

acea

e,Mim

osoidea

eMim

osadetinen

s74

914

.25

SS

thisarticle,

NEST

Sj(n

=15

)Fab

acea

e,Mim

osoidea

ePro

sopis

elata

8659

28.50

MM

thisarticle,

HERB

(n=15

)Fab

aceae,

Pap

ilion

oide

aeVicia

gran

diflorab

9100

MRou

lstonet

al.(200

0),HERB

(n=5-10

)Lam

iaceae

Salvia

6200

SRou

lstonet

al.(200

0),HERB

(n=5-10

)Lor

anth

acea

eStruthan

thusura

guen

sis

8266

34.20

MM

Vossler

(201

3),NEST

Ga(n

=10

)Lythraceae

Heimia

salicifolia

2111

19.00

SS

thisarticle,

HERB

(n=15

)M

alpighiace

aeMas

cagn

iabrevifolia

1159

533

.25

MM

thisarticle,

NEST

Tf(n

=15

)M

alvaceae

Gossypium

thurberib

19530

0L

Rou

lstonet

al.(200

0),HERB

(n=5-10

)M

alvaceae

Pav

onia

21315

180

.75

LL

Dalmazzo

andVossler

unpu

blishe

d,NEST

Aa(n

=8)

Malvaceae

Sph

aeralcea

ambiguab

4160

0M

Rou

lstonet

al.(200

0),HERB

(n=5-10

)M

alvaceae

Sph

aeralcea

cordobensisb

2380

7M

Ferná

ndez

etal.(200

9),HERB

(n=10

)Nyctagina

ceae

Pisonia

zapa

llo55

6628

.50

SM

Vossler

unpu

blishe

d,NEST

Mo(n

=15

)Olacaceae

Xim

enia

american

a56

513

.30

SS

thisarticle,

NEST

Tf(n

=7)

Passifloraceae

Passifloracaerulea

b70

997

LFerná

ndez

etal.(200

9),HERB

(n=10

)Plantaginaceae

Scopa

ria

465.70

VS

VS

Vossler

(201

3),NEST

Ga(n

=6)

Polygon

aceae

Polygonum

1574

536

.10

MM

thisarticle,

NEST

Sj(n

=15

)

(Contin

ued)

Pollen grains in Chaquenian Meliponini diet 77

Dow

nloa

ded

by [

Dr

Favi

o V

ossl

er]

at 1

3:05

25

Mar

ch 2

015

Tab

leII.(C

ontin

ued).

Plant

family

Pollentype

Pollengrain

volume

Pollengrain

size

Pollenvo

lume

catego

ryPollensize

catego

ryReferen

cean

dsampleorigin

c

Polygon

aceae

Rup

rechtia

triflora

1810

438

.00

MM

Vossler

(201

3),NEST

Ga(n

=13

)Portulacaceae

Portulaca

24881

696

.90

LL

Vossler

(201

3),NEST

Ga(n

=14

)Ran

uncu

laceae

Clematismontevidensis

2156

19.00

SS

Vossler

unpu

blishe

d,HERB

(n=15

)Rham

nac

eae

Ziziphusm

istol

1963

18.05

SS

thisarticle,

NEST

Tf(n

=15

)Rub

iaceae

Borreriadensiflora

2825

SFerná

ndez

etal.(200

9),HERB

(n=10

)San

talaceae

Acanthosyrisfalcata

2070

21.85

SS

thisarticle,

NEST

Tf(n

=9)

Sap

otac

eae

Siderox

ylon

obtusifolium

2041

21.85

SS

thisarticle,

HERB

(n=15

)Sim

arou

bac

eae

Cas

tela

coccinea

2519

19.00

SS

thisarticle,

NEST

Ga(n

=15

)Solan

aceae

Nicotiana

longiflora

9412

MFerná

ndez

etal.(200

9),HERB

(n=10

)Solan

aceae

Solan

um10

6114

.25

SS

Vossler

unpu

blishe

d,NEST

Mo(n

=15

)Solan

aceae

Solan

umeleagnifoliu

m10

300

MRou

lstonet

al.(200

0),HERB

(n=5-10

)Solan

aceae

Solan

umku

rtzian

umb

1360

SFerná

ndez

etal.(200

9),HERB

(n=10

)Solan

aceae

Solan

umlanceifoliu

mb

3900

SRou

lstonet

al.(200

0),HERB

(n=5-10

)Typ

haceae

Typha

latifolia

6900

SRou

lstonet

al.(200

0),HERB

(n=5-10

)Ulm

acea

ePhyllostylon

rham

noides

3248

20.90

SS

Vossler

(201

3),NEST

Tf(n

=15

)Verbe

naceae

Gland

ularia

laciniata

1860

5M

Ferná

ndez

etal.(200

9),HERB

(n=10

)Verbe

naceae

Lan

tana

grisebachiib

1128

5M

Ferná

ndez

etal.(200

9),HERB

(n=10

)Verbe

naceae

Phyla

reptan

s18

6122

.00

SS

thisarticle,

NEST

Sj(n

=15

)Verbe

naceae

Verbena

270

9.50

VS

VS

Vossler

(201

3),NEST

Ga(n

=9)

Viscaceae

Phoradend

roncalifornicum

b68

00S

Rou

lstonet

al.(200

0),HERB

(n=5-10

)Zygop

hylla

ceae

Bulnesiasarm

ientoi

919

14.25

SS

Vossler

unpu

blishe

d,NEST

Ga(n

=15

)Unide

ntified

Unidentified

765

20.90

SS

thisarticle,

NEST

Sj(n

=15

)

Note:

The

polle

ntype

sintensivelyforagedby

bees

areshow

nin

bold.Categoriesof

both

volumean

dsize

includ

eVS(verysm

all),S(small),M

(med

ium),L(large)an

dVL(verylarge).

a Ind

icates

meanvalues

forpo

llengrainsize.

bCon

gene

ricspeciesno

treco

rded

inthestud

yarea.

c Num

berof

polle

ngrains

measured(n)from

referenc

especim

ensde

positedin

herbaria

(HERB)or

from

neststores

(NEST)of

Geotrigonaargentina(G

a),S

captotrigona

jujuyensis(Sj),T

etragonisca

fiebrigi

(Tf),Meliponaorbignyi

(Mo),Augochloraam

phitrite

(Aa),Apismellifera(A

m).

78 F.G. Vossler

Dow

nloa

ded

by [

Dr

Favi

o V

ossl

er]

at 1

3:05

25

Mar

ch 2

015

Discussion

A wide spectrum of pollen types in colonies of threesubtropical Meliponini bees

Meliponini bees carry pollen grains in their corbi-cula, the most specialized structure for transportingpollen among bees (Michener et al. 1978).Corbiculate bees (tribes Apini, Meliponini,Bombini and Euglossini) as well as those with scopaewith sparse hairs moisten pollen grains with nectar.This enables them to increase the size of the pollenload beyond the scopal hair length and favours thecollection of a wide spectrum of pollen sizes (Thorp2000). Leioproctus (Colletidae) for example collectslarge pollen grains (80–90 µm) from Conospermum(Proteaceae) (Houston 1989). The fact thatMeliponini bees moisten their pollen loads with nec-tar could account for the great variety of pollen grainvolumes and sizes foraged by the three species stu-died in the Chaco forest. Thus, pollen from a broadspectrum of plant species of several families can besuccessfully foraged allowing these eusocial bees tosurvive in different seasons and environments.

Small bees, small flowers and small volume and size ofpollen grains

Although the three Meliponini species foraged on alarge number of plants, those of small volume andsize pollen grains were the most intensively foraged,followed by medium grains. Large pollen grains werescarcely gathered. Although large grains supplies lar-ger nutrient biomass (in volume) than small ones(O’Rourke & Buchmann 1991; Vossler et al. 2010),these bees concentrated their foraging on the latter.

It is known that pollen grain volume is positivelycorrelated to the pistil length of the flowers, due tothe important role of the cytoplasm nutrients in thegrowth of the pollen tube, essential to fertilise theovules (Schnack & Covas 1945; Torres 2000). Plantswith small pollen grains produce greater number ofgrains per anther than those with large grains (SubbaReddi & Reddi 1986; Tormo Molina et al. 1996),having a higher number of male gametes available tolocate a flower stigma. Meliponini bees have beenconsidered by some authors as poor pollinatorsbecause they moisten with nectar the transportedpollen load, reducing the chances of losing indivi-dual pollen grains during floral visitation and ofeventually making contact with a stigma (Thorp2000). However, the high number of small grainstransported per corbicula compared to large grainsizes should increase the chance of pollen beingtransferred to floral stigma surface during floral vis-its. Moreover, Meliponini bees appear to be ade-quate pollinators of small flowers clustered in dense

inflorescences, due to the fact that they forage slowlyon a high number of flowers in the same trip.The floral syndromes associated to the small- to

medium-sized Meliponini bees include those flowerssmall in size, with radial symmetry and with easyaccess to pollen and nectar, clustered in dense inflor-escences (Ramalho 1990, 2004). Although thesehighly generalist bees visit a broad spectrum offlower sizes (collecting a broad spectrum of pollenvolumes and sizes), they prefer small flower sizessimilar to their body size, being good candidates aspollinators for this kind of flowers (Ramalho 2004).From this scenario, it appears that the high abun-dance of small pollen grains stored in colonies of thethree studied Chaquenian species of Meliponini isdue to their preference for small flowers of shortpistils. Wilms et al. (1997) and Ramalho (2004)suggested that the tight relationship betweenMeliponini and small flowers clustered in rich inflor-escences is part of a diffuse co-evolutionary processand it seems to be the cause for the high abundanceof mass-flowering trees in Neotropical areas. In thepresent study, a significant positive linear correlationbetween maximum flower size and both mean pollenvolume and maximum pollen size was also found(Figure 5). This tight relationship betweenMeliponini bees and mass flowerings has beenobserved in tropical areas and now can also beextended to South American subtropical xerophilousDry Chaco forest.

Availability of pollen grains of different volumes and sizesin the xerophilous Chaco forest

As it has been observed for other Neotropical envir-onments, the eusocial Meliponini bees forage mainlyon the most locally abundant plants (Ramalho et al.1990) to supply their large colonies throughout theyear. This opportunistic foraging habit would suggestthat the large number of small pollen grains found inthe nest samples of the present study is due to theirhigh availability in this subtropical forest. Moreover, astudy on floral visitation of six Meliponini species inthis region showed that they mainly foraged on themost diverse plant families Fabaceae (subfamiliesMimosoideae and Caesalpinioideae) and Asteraceae(Vossler 2012).These Meliponini bees foraged mainly on the trees

and perennial woody shrubs from the forest, nearby totheir nests. Moreover, this woody vegetation provides ahigher number of flowers per individual compared toherbaceous plants from open areas and the lower stra-tumof the forest (grasslands, forest edges, swarms, etc.),where their preferred nesting substrates (large treetrunk) are scarce or absent. For instance, melitophilousmembers of Asteraceae, Malvaceae, Cactaceae,

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Acanthaceae, Fabaceae (Papilionoideae), Bromeliaceaeand Convolvulaceae, among others, have large to verylarge pollen grains and were highly available in openareas and the lower stratum of the forest but poorlyrepresented or absent in nest pollen stores.

The comparison of volume categories between neststores and Chaco vegetation demonstrates that foragedpollen types do not follow the abundance patternfound in the available flora. This result indicates thatbees preferred certain volume categories (small andmedium volumes) that are present in small flowers ofshort pistils. This finding is in agreement with thehypothesis of Wilms et al. (1997) and Ramalho(2004) for Neotropical habitats. However, when thefive pollen size categories were compared between neststores and the Chaco flora, preference was not found.Therefore, the abundance of small pollen types in nestsamples could be interpreted as opportunism, i.e.Meliponini bees forage floral resources in proportionto their availability in the surrounding environment.This opportunism hypothesis would indicate that ahigh number of plant species having pollen grains ofsmall to medium volume and size is present in thevegetation of the subtropical Dry Chaco forest. Asthese two results are contradictory, both hypothesesremain open.

Conclusion

In the subtropical Dry Chaco forest, the stinglessbees Tetragonisca fiebrigi, Scaptotrigona jujuyensis andGeotrigona argentina foraged on a large number ofplants, mainly those having pollen grains of smallvolumes and sizes, followed by medium ones. Mostof the plant species (23 out of 35 species) had small-size flowers (≤ 1 cm). Most of the flowers of smallsize had both small pollen volume ranging from 618µm3 in Parthenium hysterophorus to 6418 µm3 inAcacia and small pollen sizes. A significant positivelinear correlation was found between mean pollenvolume and maximum flower size as well as betweenmaximum pollen size and maximum flower size.

Two hypotheses are suitable to explain why thesebees mainly foraged on small pollen grains. The firsthypothesis (preference) is in agreement with thefindings of Wilms et al. (1997) and Ramalho(2004) for Meliponini bees in Neotropical habitats.However, the second hypothesis (opportunisticbehaviour) seems to support the absence of prefer-ence for particular pollen size, indicating that thesebees forage on floral resources according to theiravailability in the forest. The opportunism hypoth-esis would indicate that a high number of plantspecies having pollen grains of small to mediumvolume and size is present in the vegetation of thesubtropical Dry Chaco forest.

Acknowledgements

The author thanks Nora Brea, María CelesteScattolini and Anabela Plos for providing sugges-tions and comments on the manuscript. This studywas supported by CONICET (Consejo Nacional deInvestigaciones Científicas y Técnicas).

References

Arenas P. 2003. Etnografía y alimentación entre los toba-ñachilamoleek y wichí lhuku’tas del Chaco Central (Argentina).Buenos Aires, Argentina.

Biesmeijer JC, Van Marwiik B, Deursen K, Punt W, SommeijerMJ. 1992. Pollen sources for Apis mellifera L (Hym, Apidae) inSurinam, based on pollen grain volume estimates. Apidologie23: 245–256. doi:10.1051/apido:19920308.

Birks HJB. 1973. Past and present vegetation of the Isle of Skye – Apalaeoecological study. London: Cambridge University Press.

Birks HJB, Birks HH. 1980. Quaternary palaeoecology. London:Edward Arnold.

Cortopassi-Laurino M, Ramalho M. 1988. Pollen harvest byAfricanized Apis mellifera and Trigona spinipes in São Paulo –

Botanical and ecological views. Apidologie 19: 1–24.doi:10.1051/apido:19880101.

De Klerk P, Joosten H. 2007. The difference between pollen typesand plant taxa: A plea for clarity and scientific freedom.Eiszeitalter und Gegenwart/Quaternary Science Journal 56:162–171.

Fernández VA, Galetto L, Astegiano J. 2009. Influence of flowerfunctionality and pollination system on the pollen size-pistillength relationship. Organisms, Diversity & Evolution 9: 75–82. doi:10.1016/j.ode.2009.02.001.

Hesse M, Zetter R, Halbritter H, Weber M, Buchner R, Frosch-Radivo A, Ulrich S. 2009. Pollen terminology. An illustratedhandbook. Vienna: Springer.

Houston TF. 1989. Leioproctus bees associated with WesternAustralian smoke bushes (Conospermum spp.) and their adapta-tions for foraging and concealment (Hymenoptera: Colletidae:Paracolletini). Records of the Western Australian Museum 14:275–292.

Joosten H, De Klerk P. 2002. What’s in a name? Some thoughtson pollen classification, identification, and nomenclature inQuaternary palynology. Review of Palaeobotany andPalynology 122: 29–45. doi:10.1016/S0034-6667(02)00090-8.

Marques-Souza AC, Miranda IPA, Moura CO, Rabelo A, BarbosaEM. 2002. Características morfológicas e bioquímicas do pólencoletado por cinco espécies de meliponíneos da AmazôniaCentral. Acta amazônica 32: 217–229.

Michener CD, Winston ML, Jander R. 1978. Pollen manipulationand related activities and structures in bees of the familyApidae. University of Kansas Science Bulletin 51: 575–601.

O’Rourke MK, Buchmann SL. 1991. Standardized analyticaltechniques for bee-collected pollen. EnvironmentalEntomology 20: 507–513.

Prado DE. 1993. What is the Gran Chaco vegetation in SouthAmerica? I. A review. Contribution to the study of flora andvegetation of the Chaco. V. Candollea 48: 145–172.

Ramalho M. 1990. Foraging by stingless bees of the genusScaptotrigona (Apidae, Meliponinae). Journal of ApiculturalResearch 29: 61–67.

Ramalho M. 2004. Stingless bees and mass flowering trees in thecanopy of Atlantic Forest: A tight relationship. Acta BotanicaBrasilica 18: 37–47. doi:10.1590/S0102-33062004000100005.

80 F.G. Vossler

Dow

nloa

ded

by [

Dr

Favi

o V

ossl

er]

at 1

3:05

25

Mar

ch 2

015

Ramalho M, Imperatriz-Fonseca VL, Kleinekt-Giovannini A,Cortopassl-Laurino M. 1985. Exploitation of floral resourcesby Plebeia remotaHolmberg (Apidae, Meliponinae). Apidologie16: 307–330. doi:10.1051/apido:19850306.

Ramalho M, Kleinert-Giovannini A, Imperatriz-Fonseca VL.1990. Important bee plants for stingless bees (Melipona andTrigonini) and Africanized honeybees (Apis mellifera) in neotro-pical habitats: A review. Apidologie 21: 469–488. doi:10.1051/apido:19900508.

Ramalho M, Silva MD, Carvalho CAL. 2007. Dinâmica de uso defontes de pólen por Melipona scutellaris Latreille (Hymenoptera:Apidae): Uma análise comparativa com Apis mellifera L.(Hymenoptera: Apidae), no Domínio Tropical Atlântico.Neotropical Entomology 36: 38–45. doi:10.1590/S1519-566X2007000100005.

Roig-Alsina A, Vossler FG, Gennari GP. 2013. Stingless bees inArgentina. In: Vit P, Pedro SRM, Roubik DW, eds. Pot honey:A legacy of stingless bees, 125–134. New York: Springer.

Roubik DW. 1989. Ecology and natural history of tropical bees.New York: Cambridge University Press.

Roulston TH, Cane JH, Buchmann SL. 2000. What governs pro-tein content of pollen: Pollinator preferences, pollen-pistil inter-actions, or phylogeny? Ecological Monographs 70: 617–643.

Schnack B, Covas G. 1945. Hibridación interespecífica enGlandularia (Verbenáceas). Darwiniana 7: 71–79.

Silveira da FA. 1991. Influence of pollen grain volume on theestimation of the relative importance of its source to bees.Apidologie 22: 495–502. doi:10.1051/apido:19910502.

StatPoint Technologies. 2010. Statgraphics® Centurion XVI.StatPoint Technologies, Inc., Warrenton, VA. http://www.stat-graphics.com.

Subba Reddi C, Reddi NS. 1986. Pollen production in someanemophilous angiosperms. Grana 25: 55–61. doi:10.1080/00173138609429933.

Thorp RW. 2000. The collection of pollen by bees. PlantSystematics and Evolution 222: 211–223. doi:10.1007/BF00984103.

Tormo Molina R, Muñoz Rodríguez A, Silva Palaciso I, GallardoLópez F. 1996. Pollen production in anemophilous trees.Grana 35: 38–46. doi:10.1080/00173139609430499.

Torres C. 2000. Pollen size evolution: Correlation between pollenvolume and pistil length in Asteraceae. Sexual PlantReproduction 12: 365–370. doi:10.1007/s004970000030.

Vossler FG. 2012. Flower visits, nesting and nest defence behaviourof stingless bees (Apidae: Meliponini): Suitability of the beespecies for meliponiculture in the Argentinean Chaco region.Apidologie 43: 139–161. doi:10.1007/s13592-011-0097-6.

Vossler FG. 2013. Estudio palinológico de las reservas alimentar-ias (miel y masas de polen) de “abejas nativas sin aguijón”(Hymenoptera, Apidae, Meliponini): Un aporte al conoci-miento de la interacción abeja-planta en el Chaco Seco deArgentina. La Plata: Universidad Nacional de La Plata,Argentina, PhD Diss.

Vossler FG, Tellería MC, Cunningham M. 2010. Floral resourcesforaged by Geotrigona argentina (Apidae, Meliponini) in theArgentine Dry Chaco forest. Grana 49: 142–153.doi:10.1080/00173131003694274.

Wilms W, Ramalho M, Wendel L. 1997. Stingless bees andAfricanized honey bees in the Mata Atlântica rainforest ofBrazil. 30th International Apicultural Congress of Apimondia,Antwerp, Belgium, 1–6 September 1997, 167–170.

Wodehouse RP. 1935. Pollen grains. New York and London:McGraw-Hill.

Zuloaga FO, Morrone O, Belgrano MJ. 2008. Catálogo de lasplantas vasculares del Cono Sur (Argentina, Sur de Brasil,Chile, Paraguay y Uruguay). Volumes 1–3. Monographs inSystematic Botany from the Missouri Botanical Garden 107:1–983, 985–2286, 2287–3348.

Pollen grains in Chaquenian Meliponini diet 81

Dow

nloa

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Dr

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