xml version 1.0 encoding UTF-8 standalone no
record xmlns http:www.loc.govMARC21slim xmlns:xlink http:www.w3.org1999xlink xmlns:xsi http:www.w3.org2001XMLSchema-instance
leader 00000nas 2200000Ka 4500
controlfield tag 008 000000c19749999pautr p s 0 0eng d
datafield ind1 8 ind2 024
subfield code a M39-00044
Eficiencia de los polinizadores en Blakea gracilis (Melastomataceae)
Pollinator efficiency in Blakea gracilis (Melastomataceae)
Blakea gracilis (Melastomataceae) is one of 20,000 species of flowering plants whose flowers have poricidal anthers. This morphology is adapted for buzz-pollination, where bee-induced vibrations result in the expulsion of pollen through the anther pores. The frequency of vibrations significantly affects pollen release, with peak anther discharge occurring at 500 Hz. Bees, however, are only able to buzz at about 300 Hz, and rarely reach frequencies higher than 400 Hz. This gap leaves the potential for a most efficient pollinator, a particular bee able to buzz at the highest frequency, thereby procuring the most pollen per visit and moving more pollen from flower to flower. In this study, I aimed to determine whether a most efficient pollinator exists for Blakea gracilis. I focused on large-bodied bees and small-bodied bees, predicting that larger bees would be capable of reaching higher frequencies and therefore would be better pollinators than their smaller counterparts. I found that large- and small-bodied bees open the same number of anthers per visit (t = 0.553, df = 36.277, p = 0.584), even though small bees spend significantly more time buzzing each flower (t = 3.753, df = 22.5, p = 0.001). Large-bodied bees achieved the same success as their smaller counterparts in less time by opening more anthers per second (t = -3.266, df = 36.3, p = 0.002). Despite their length of visitation, the amount of time each size-class spent buzzing a flower did not affect how many anthers they opened (large-bodied: R2 = 0.061, p = 0.080, t = 1.786; small-bodied: R2 = 0.169, p = 0.057, t = 2.019). I found one exception in Bombus sp., which was able to open more anthers the longer it vibrated the flower (Spearmans Rho = 0.576, p = 0.041, N = 10). I found that there is no most efficient pollinator of Blakea gracilis, instead the results are consistent with those of past studies which concluded that buzz-pollination is generalized to all bee visitors.
En este estudio, yo tena como objetivo determinar si existe un polinizador ms eficiente para Blakea gracilis. Me enfoqu en abejas grandes y pequeas, prediciendo que las abejas grandes seran capaces de alcanzar frecuencias ms altas y por lo tanto seran mejores polinizadores que sus contrapartes ms pequeas.
Text in English.
Pollination by bees--Costa Rica--Puntarenas--Monteverde Zone
Polinizacin por abejas--Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology 2008
Ecologa Tropical 2008
t Monteverde Institute : Tropical Ecology
Pollinator efficiency in Blakea gracilis Melastomataceae Sullivan Peraino Department of Agronomy, Purdue University ABSTRACT Blakea gracilis Melastomataceae is one of 20,000 species of flowering plants whose flowers have poricidal anthers. This morphology is adapted for Â€buzz pollination,Â where bee induced vibrations result in the expulsion of pollen through the anther pores. The frequency of vibrations significantly affects pollen release, with peak anther discharge occurring at 500 Hz. Bees , however, are only able to buzz at about 300 Hz, and rarely reach frequencies higher than 400 Hz. This gap leaves the potential for a Â€most efficientÂ pollinator, a particular bee able to buzz at the highest frequency, thereby procuring the most pollen p er visit and moving more pollen from flower to flower. In this study, I aimed to determine whether a Â€most efficientÂ pollinator exists for Blakea gracilis . I focused on large bodied bees and small bodied bees, predicting that larger bees would be capabl e of reaching higher frequencies and therefore would be better pollinators than their smaller counterparts. I found that large and small bodied bees open the same number of anthers per visit t = 0.553, df = 36.277, p = 0.584, even though small bees spe nd significantly more time buzzing each flower t = 3.753, df = 22.5, p = 0.001. Large bodied bees achieved the same success as their smaller counterparts in less time by opening more anthers per second t = 3.266, df = 36.3, p = 0.002. Despite their length of visitation, the amount of time each size class spent buzzing a flower did not affect how many anthers they opened large bodied: R 2 = 0.061, p = 0.080, t = 1.786; small bodied: R 2 = 0.169, p = 0.057, t = 2.019. I found one exception in Bombus sp. , which was able to open more anthers the longer it vibrated the flower SpearmanÂ‚s Rho = 0.576, p = 0.041, N = 10. I found that there is no Â€most efficientÂ pollinator of Blakea gracilis , instead the results are consistent with those of past studies which concluded that buzz pollination is generalized to all bee visitors. RESUMEN Blakea gracilis Melastomataceae es una de las 20,000 especies de plantas con flores que poseen anteras porosas. Esta morfologÂƒa es especializada para la Â€polinizaciÂ„n p or zumbido,Â donde vibraciones inducidas por abejas resultan en la expulsiÃ³n del polen a travÃ©s de los poros de las anteras. La frecuencia de las vibraciones afecta significativamente la liberaciÃ³n de polen, con un pico de descarga que ocurre a los 500 Hz . Las abejas, sin embargo, son capaces de zumbar solamente a 300 Hz, y raramente estas frecuencias superan los 400 Hz. Este vacÃo crea un espacio para polinizadores Â€mÂ…s eficientes,Â una abeja en particular capaz de vibrar a mayores frecuencias, asÂƒ proc urando el mayor polen por visita y moviendo mÃ¡s polen de flor a flor. En este estudio, yo busco determinar si existe un polinizador mÃ¡s eficiente para B. gracilis . EnfocÃ¡ndome en abejas grandes y pequeÃ±as, prediciendo que abejas mÃ¡s grandes serÃ¡n capaces de alcanzar frecuencias mayores, y asÃ ser mejores polinizadores que sus contraparte mÃ¡s pequeÃ±as. EncontrÃ© que abejas grandes y pequeÃ±as abren el mismo nÃºmero de anteras por visita t=0.553, df=36.277, p=0.548, aun cuando las abejas pequeÃ±as pasan mÃ¡s tiempo zumbando en cada flor t=3.753, df=22.5, p=0.001. Abejas grandes alcanzan el mismo Ã©xito que las pequeÃ±as en un menor tiempo, abriendo mÃ¡s anteras por segundo t= 3.226, df=36.3, p=0.002. MÃ¡s allÃ¡ del largo de la visita, la cantidad de tiempo de cada clase de tamaÃ±o usado zumbando en una flor, no afecta cuantas anteras ellas abren grandes: R 2 =0.061, p=0.08, t=1.786; pequeÃ±as: R 2 = 0.169, p= 0.057, t= 2.019. EncontrÃ© una excepciÃ³n en Bombus sp. , el cual es capaz de abrir mÃ¡s anteras durante un mayor tiempo de zumbido en la flor SpearmanÂ´s Rho = 0.576, p= 0.041, N= 10. EncontrÂ† que no existe un polinizador Â€mÂ…s eficienteÂ para B. gracilis , en cambio los resultados son consistentes con estudios anteriores que concluyen que la polinizaciÃ³n po r zumbido es generalizada para todas las abejas visitantes.
INTRODUCTION The angiosperm family Melastomataceae is one of 72 families world wide whose flowers have poricidal anthers. In this flower morphology, each anther is separated into thecae, or an ther halves, which contain two pollen sacs. The thecae open by dehiscing along a longitudinal slit, the stomium, which runs the entire length of the thecae Fig. 1. The 20,000 species with such poricidal anthers are presumed to be Â€buzz pollinated,Â whe re bee induced vibrations result in the expulsion of pollen through the anther pores Buchmann, 1983; Knudsen & Olsen, 1993. The anthers come together in a cone shape, which forces the bee to assume a position where the pollen is placed in locations on the beeÂ‚s body where it cannot be removed during in flight grooming. These flowers are called Â€solenoid,Â where morphology localizes pollinator flower contact to enhance pollen transport Renner, 1989. Old World members and New World members of all 72 families share this morphology and nearly every family within Apoidea use this pollen collecting behavior. The independent evolution of these solenoid flowers in unrelated families represents millions of years of coevolution between these plants and their buzz pollinating bees, resulting in an Â€adaptive peakÂ for buzz pollinated plants Renner, 1989; Harder & Barclay, 1994. This evolutionary achievement is supported by Macior 1971, who observed that buzz pollination is so successful that it is rarely s ucceeded by any other mechanism, even in species rich groups. Bees and one species of Syrphid fly are the only natural pollinators able to effectively buzz open poricidal anthers. The frequency of vibration is the trigger for anther dehiscence, and poll en collection is possible artificially by touching a tuning fork to the anthers Buchmann, 1983. It has also been found that the vibration frequency significantly affects pollen removal, with peak anther sensitivity at 500 Hz. Large bodied b ees are able to buzz at a frequency of ~300 Hz, rarely buzzing any higher than 400 Hz. Due to the difference between peak sensitivity and bee ability, Harder & Barclay 1994 concluded that the anthers of buzz pollinated plants are Â€tuned outÂ of the freq uencies used by their pollinators. This allows the plant to promote pollen transport on many different pollinators, thereby enhancing reproductive fitness Harder & Barclay, 1994. Figure 1. The intact poricidal anther. Each pore opens at the apex of the individual theca anther halves containing the male sporangia. The thecae are pressed tightly together prior to buzz pollination, after which they splay open. Buzzing opens the pores, and pollen is released explosively. Figure from Buchmann, 1983.
Owing to the wide range of frequencies recognized by poricidal anthers 300 500 Hz, it is reasonable to question if a specific bee is able to reach a higher, more anther responsive frequency, thereby procuring more pollen per visit. If a bee is able to extract more pollen per visit, they would effectively move more pollen f rom flower to flower, thereby acting as a more efficient pollinator than those bees restricted to lower frequencies. In this study, I aimed to determine whether there exists a Â€most efficientÂ pollinator of the buzz pollinated, poricidal Blakea gracilis Melastomataceae. I focused on two broad categories of pollinators: large bodied bees two species in the family Anthophoridae, S.F. Anthophorinae, and one species of the genus Bombus , Apidae and small bodied bees Apis mellifera , Apidae, one species of Euglossinae, and a small member of Anthophoridae. I predicted that the large bodied bees would be able to vibrate at a higher frequency than the small bodied bees, thereby eliciting more pollen per visit. MATERIALS AND METHODS I observed two individual s of B. gracilis in Monteverde, Costa Rica for a period of three weeks. One individual was a large bush and the other was an epiphytic vine. I observed each individual in the early morning, beginning at sunrise 0600 hrs when pollinator visitation was at its highest. To rank pollinator success, I used the separation of the anthersÂ‚ thecae as a proxy for apical dehiscence. In newly opened flowers that have not been visited, the anthers are stuck together in a semi circular cone, and each antherÂ‚s theca e are tightly Â€gluedÂ together. Once visited by a bee, the thecae are separated, and it is clearly visible which anthers have dehisced and which are still unopened. Upon arriving at each study site, I surveyed all open and reachable flowers. I marked those which had been buzzed by clipping the tip of one sepal. After observing a bee visit a flower, I recorded the type of bee, the amount of time the bee spent buzzing the flower, total number of anthers, and the number of anthers opened after the visit. The pollinatorÂ‚s success was measured as the proportion of anthers opened during the visit all but two observed flowers had 12 anthers. RESULTS I recorded 73 visits by a total of six different pollinators. I observed visits by three species in the family Anthophoridae S.F. Anthophorinae, one species of the genus Bombus Apidae, Apis mellifera Apidae, and one species of Euglossinae. I recorded 51 visits from large bodied bees two species in the family Anthophoridae, S.F. Anthophorinae, and one species of the genus Bombus , Apidae and 22 visits from small bodied bees Apis mellifera Apidae, one species of Euglossinae, and a small member of Anthophoridae. I found that large and small bodied bees opened the same proportion of anthers per v isit t = 0.553, df = 36.277, p = 0.584 Fig. 2, even though small bodied bees spent significantly more time buzzing each flower t = 3.753, df = 22.5, p = 0.001. Large bodied bees achieved the same success as their smaller counterparts in less time by opening more anthers per second t = 3.266, df = 36.3, p = 0.002. Despite their length of visitation, the amount of time each size class spent buzzing a flower did not predict how many anthers they opened large bodied: R 2 = 0.061, p = 0.080, t = 1.786 ; small bodied: R 2 = 0.169, p = 0.057, t = 2.019.
0.00 0.20 0.40 0.60 0.80 1.00 1.20 0 5 10 15 20 25 30 Time Spent Buzzing Flower sec Proportion of Anthers Opened 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0 10 20 30 40 50 60 70 Time Spent Buzzing Flower sec Proportion of Anthers Opened Figure 2. The proportion of anthers opened as a function of the time spent buzzing the flower. The amount of time large bodied bees A and small bodied bees B spent buzzing a flower did not affect the proportion of anthers that were opened R 2 A = 0.06, p A = 0.08, n A = 51; R 2 B = 0.17, p B = 0.06, n B = 22 A. B.
I also focused on a specific set of pollinators to see if the size class patterns were consistent at a smaller scale. I analyzed data from three pollinators, a large bodied species of Anthop horinae Anthophoridae, Bombus sp. Apidae, and Apis mellifera Apidae. I found most patterns at the size class level carried through to these three species. Anthophorinae, Bombus sp., and A. mellifera opened the same number of anthers per visit Krus kall Wallis Test, X 2 = 2.366, df = 2, p = 0.306, N = 59 Fig. 3. 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 Mean Proportion of Anthers Opened Apis mellifera , the smallest of the three bees, spent significantly more time than both Anthophorinae and Bombus sp. buzzing each flower Kruskal Wallis Test, X 2 = 18.661, d f = 2, p = 0.000, N = 59 Fig. 4A.. Anthophorinae and Bombus sp. were able to open more anthers per second than A. mellifera Kruskal Wallis Test, X 2 = 12.452, df = 2, p = 0.002, multiple comparison showed that Anthophorinae and Bombus sp . were not sign ificantly different, Q = 2.98, Q 0.005, 3 = 3.314 Fig. 4B.. An interesting trend did surface, however, when correlating the amount of time spent buzzing and the number of anthers opened. In the size class comparison, the time spent buzzing did not affe ct the total number of anthers opened. However in the tri pollinator analysis, I found that Bombus sp . was able to open more anthers the longer it buzzed the flower SpearmanÂ‚s Rho = 0.576, p = 0.041, N = 10. Anthophorinae and A. mellifera opened the sa me number of anthers regardless of how long they buzzed the flower Anthophorinae: SpearmanÂ‚s Rho = 0.171, p = 0.166, N = 34; A. mellifera : SpearmanÂ‚s Rho = 0.003, p = 0.496, N = 15. Figure 3. The mean and standard error of anthers opened by each pollinator. All three pollinators are equally successful at opening a nthers Kruskal Wallis Test, X 2 = 2.366, df = 2, p = 0.306, N = 59 Apis mellifera Bombus sp. Anthophorinae
0 5 10 15 20 25 30 35 40 Average Time Spent Buzzing seconds -0.05 0 0.05 0.1 0.15 0.2 0.25 Mean Proportion of Anthers Opened per Second Figure 4 A,B. A The mean and standard error of the amount of time each pollinator spent buzzing individual flowers. Bombus sp. and Anthophorinae spent the same amount of time buzzing, while A. mellifera spent a significantly longer period at each flower. A. mellifera spent an average of 22.3 seconds buzzing each flower. B The proportion of anthers opened per second by each pollinator. Anthophorinae and Bombus sp . opened more anther s per second than A. mellifera Kruskal Wallis Test, X 2 = 12.452, df = 2, p = 0.002, multiple comparison showed that Anthophorinae and Bombus sp . were not significantly different , Q = 2.98, Q 0.005, 3 = 3.314. A. B . Apis mellifera Anthophorinae A pis mellifera Bombus sp. Anthophorinae Bombus sp.
DISCUSSION I have determined that there is no Â€most efficientÂ pollinator of B. gracilis. My findings are consistent with those of past studies suggesting that buzz pollinated flowers are generalized to all pollen gathering bees in a given region, and that the only requirement for pollen extraction is the ability to Â€buzzÂ Larson et al. , 1999. Blakea gracilis falls into the same category as other buzz pollinated species, all of which are presumed to have generalized bee pollinators Knudsen & Olsen, 1993. The ability of the large bodied bees to open more anthers per second does give them the potential to visit more flowers and plants in a given day, which may enhance their performance as pollination vectors. In future studies, it would be valuable to keep a t horough record of how many flowers and plants individual bee species visit, in order to determine whether expedited pollen removal allows for more efficient pollen transfer. In the tri pollinator analysis, the results were consistent with the size clas s trends. The two larger bees, Anthophorinae and Bombus sp., spent less time buzzing and were able to open more anthers per second than A. mellifera. All three pollinators achieved the same success during their visits, supporting the idea that B. gracili s is generalized to all bee fauna. The ability of Bombus sp. to open more anthers the longer it buzzed an individual flower was inconsistent with the broader comparison, however. Buchmann 1983 observed that Bombus sp. had an added advantage, since they utilize energy gained from consuming honey while in the nest prior to foraging in the early morning. Bumblebees are also able to thermoregulate, which is in fact enhanced during the buzzing of flowers when the bee vibrates about twice as fast as it does during flight Harder & Barclay, 1994; Thorp, 1979. Possibly the honey derived energy and superior thermoregulation ability allow Bombus sp . to exert more energy over a longer period of buzzing, thus achieving a higher frequency later in the visit, and m aking a longer visit more rewarding. Anthophorinae, due to its lack of non pollen sustenance, and A. mellifera , due to its small size, are perhaps unable to maintain a favorable frequency over a long visitation period, and therefore open the same number of anthers regardless of how long they spend vibrating. Buzz pollination of B. gracilis is generalized, but perhaps to the flowerÂ‚s favor. The generalization of the flower to a wide range of frequencies promotes more efficient pollination than if it were specialized to a narrow range. If one bee were able to gather all of the pollen, the probability of the pollen being deposited on another plantÂ‚s stigma would decrease. By regulating pollen expulsion and promoting transport on multiple vectors, B. graci lis is increasing the probability of successful pollination, and furthermore its reproductive fitness. The range of anther receptivity also increases the speciesÂ‚ resilience in face of stochastic events that may alter the composition of the pollinator com munity. If one species of buzzing bee is removed from the community, B. gracilis will still have a plethora of capable pollinators. AKNOWLEDGEMENTS I sincerely appreciate all of the help and advice I received from Karen Masters. My mornings would not have been half as enjoyable if I had not been able to spend them in her garden! Also, I would like to thank Patricia Maynard for giving me access to her property. Last but not least, Pablo Allen for his patience and skills in statistics and bee identifi cation, and Mancho CalderÃ³n, for endless support and advice.
LITERATURE CITED Buchmann, S.L. 1983. Buzz pollination in angiosperms. In C. E. Jones & J. R. Little Eds.. Handbook of Experimental Pollination Biology, pp. 73 113. Van Nostrand Reinh old, New York. Harder, L.D. and R.M.R. Barclay. 1994. The Functional Significance of Poricidal Anthers and Buzz Pollination: Controlled Pollen Removal from Dodecatheon. Functional Ecology. 8:24. 509 517. Knudsen, J. T. and J. M. Olesen. 1993. Buzz P ollination and Patterns in Sexual Traits in North European Pyrolaceae. American Journal of Botany. 80:8. 900 913. Larson, B. M. and S. C. Barrett. 1999. The Pollination Ecology of Buzz Pollinated Rhexia virginica Melastomataceae. American Journal o f Botany 86:4. 502 511 Macior, L. W. 1971. Co evolution of plants and animals Â‡ systematic insights from plant insect interactions. Taxon. 20: 17 28. Renner, S. S. 1989. A survey of reproductive biology in Neotropical Melastomataceae and Memecylac eae. Annals of the Missouri Botanical Garden. 76: 496 518. Thorp, R. W. 1979. Structural, Behavioral, and Physiological Adaptations of Bees Apoidea for Collecting Pollen. Annals of the Missouri Botanical Garden. 66:4. 788 812.