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El efecto de la recompensa y el patrn de colores en la alimentacin de la mariposa en Lantana camara (Verbenaceae)
The effect of reward and color pattern on butterfly foraging in Lantana camara (Verbenaceae)
Lantana camara has inflorescences composed of young, nectar-producing yellow flowers surrounded by older orange flowers that no longer produce nectar (Moldenke 1973). We examined the relationship between L. camara and its butterfly pollinators to see if the preference for yellow flowers (Peters 1998) is innate or learned. Further, we altered the position of flower color on the inflorescence to see if the normal yellow-centered bulls eye pattern increased visitation over other patterns. We collected data for butterflies foraging on L. camara with six patterns of yellow and orange flowers by painted these colors on the inflorescences. Next, we watched these same patterns with a 20% sucrose solution injected to all of the flowers on an inflorescence. Butterflies demonstrated an innate preference for yellow flowers as an addition of nectar to orange flowers showed no change in preference. Likewise, butterflies showed a preference for yellow flowers in all cases (df = 1, x2 = 4.734, p = 0.02). Varying the pattern of yellow and orange flowers in an inflorescence showed that butterflies prefer a solid yellow inflorescence. Therefore, it appears that the pattern of flower color and butterfly preference have not coevolved to enhance visitation and hence, pollination. While butterflies benefit from innately visiting yellow flowers most frequently, L. camara may increase pollinator visits by keeping its older flowers yellow in order to create a solid yellow inflorescence.
Las inflorescencias de Lantana camara estn compuestas por las flores jvenes amarillas que producen nctar, y las flores mas viejas de color naranja que no producen nctar. Nosotras examinamos la relacin entre Lantana camara y las mariposas que polinizan esta planta, para observar si la preferencia por las flores amarillas es un comportamiento innato o aprendido. Adems, alteramos la posicin del color de las flores en la inflorescencia para observar si el patrn del objetivo con las flores amarillas en el centro aumenta la visita sobre los otros posibles patrones.
Text in English.
Butterflies--Feeds and feeding
Mariposas--Alimentos y alimentacin
Tropical Ecology 2008
Plant and pollinator coevolution
Ecologa Tropical 2008
Coevolucin de plantas y polinizadores
t Monteverde Institute : Tropical Ecology
The Effect of Reward and Color Pattern on Butterfly Foraging in Lantana camara (Verbenaceae) Jenna Short and Tara Florida Department of Neuroscience, Northeastern University and Department of Biology, Indiana University ABSTRACTLantana camara has inflorescences composed of young, nectar-produc ing yellow flowers surrounded by older orange flowers that no longer produce nectar (Molde nke 1973). We exameine the relationship between L. camara and its butterfly pollinators to see if there prefe rence for yellow flowers (Peters 1998) is innate or learned. Further, we altered the position of flower color on the infl orescence to see if the normal yellow-centered bull s eye pattern increased visitation over other patterns. We collec ted data for butterflies foraging on L. camara with six patterns of yellow and orange flowers by painted these colors o n the inflorescences. Next, we watched these same patterns with a 20% sucrose solution injected to all of the flowe rs on an inflorescence. Butterflies demonstrated a n innate preference for yellow flowers as an addition of nec tar to orange flowers showed no change in preferenc e. Likewise, butterflies showed a preference for yellow flowers in all cases (df = 1, x2 = 4.734, p = 0.02). Varying the pattern of yellow and orange flowers in an inflorescence showe d that butterflies prefer a solid yellow infloresce nce. Therefore, it appears that the pattern of flower color and but terfly preference are not coevolved to enhance visi tation and hence, pollination. While butterflies benefit from innate ly visiting yellow flowers most frequently, L. camara may increase pollinator visits by keeping its older flowers yell ow in order to create a solid yellow inflorescence. RESUMEN Las inflorescencias de Lantana camara estn compuestas por flores jvenes amarillas que producen nctar, y flores ms viejas de color naranja que no producen nctar. Nosotras examinamos la relacin entre Lantana y las mariposas que polinizan esta planta, para observar si la pref erencia por las flores amarillas es un comportamien to innato o aprendido. Adems, alteramos la posicin del color de las flores en la inflorescencia para observar s i el patrn del objetivo con las flores amarillas en el centro aume nta la visita sobre otros posibles patrones. Colec tamos datos de mariposas que forrajean sobre plantas con seis patr ones de colores pintando los colores en la inflores cencia. A continuacin, observamos estos mismos patrones con un 20% de sacarosa inyectada a estas inflorescencia s. Las mariposas demostraron un preferencia innata por las flores amarillas, y la adicin de nctar a las flo reas naranjas no mostr cambio en la preferencia. Asimismo, las mar iposas muestran preferencia por las flores amarilla s en todos los casos (df = 1, x2 = 4.734, p = 0.02). Al variar lo s patrones de coloracin en las inflorescencias se muestra que las mariposas muestran una preferencia slida por las f lores amarillas. Por lo tanto, parece que el patr n de coloracin no han cohevolucionado para mejorar las visitas y p or lo tanto la polinizacin. Mientras el beneficio de las mariposas por visitar las flores amarillas ms frec uentemente, L. camara puede aumentar las visitas de los polinizadores manteniendo las flores amarillas ms viejas en orden de crear una inflorescencia amarill a slida. INTRODUCTION Plants enhance their pollination efficiency by offe ring a reward to pollinators, and by evolving to most affectively attract the best pollinators. In addition, pollinators increase foraging efficiency by specializing on certain plants (Moldenke 1973). Over time, these plant-pollinator relationships become tightly coevolved since certai n colors, patterns and rewards attract specific
pollinators. In butterfly pollination ecology, fav ored flowers are red, orange and yellow, with short corollas that offer a reward (Moldenke 1973). Lantana camara is a butterfly pollinated plant that has infloresc ences that are arranged in a bulls eye pattern, with yellow flowers in the center and orange flowers on the outside (Moldenke 1973). The orange flowers are older and no longer produce nectar, while yellow flowers are young and nectar producing (Moldenke 1973). Accord ing to Peters study in 1998, butterflies more frequently visit the yellow flowers, but it is unknown whether this preference is innate or learned. It has been theorized that orange flowers are retained on an inflorescence to increase the landing platform for butterflies and therefore incr ease the attractiveness of the inflorescence. Butterfly pollinators may learn their visual prefer ences through experience with flower reward (Zurinskas 2003). Pieris rapae cabbage butterflies, were studied regards to thei r flower consistency on 16 different taxa, and proved to sti ck with their normally preferred inflorescences, even when others were filled with n ectar. She attributed this to a limited memory capacity of butterflies (Lewis 1989). Restricted me mory capacity in butterflies may cause them to innately prefer yellow flowers, or they may choo se to frequent yellow L. camara flowers because they learn through experience that yellow f lowers are signals for efficient foraging (Zurinskas 2003). We hypothesize that yellow flowers on a bulls eye pattern will be innately preferred. Considering this, we investigate whether butterfly preference for yellow is innate or preferred by seeing if their preference changes when orange flow ers are rewarding. Further, we study how efficient the bulls eye inflorescence is in attrac ting butterflies by varying color contrasts and inflorescence arrangement to see if they prefer the natural pattern. METHODS This investigation took place at Gold Mine Adventur e in La Sierra, Costa Rica, from November 4th to November 11th. There are several bushes of Lantana camara located there that we observed during sunny hours ranging from 7:00 am to 2:00 pm. L. camara originally from the West Indies, is a common weedy shrub in Costa Rica that thrives in the sun (Zuchowski, 2007). It flowers and fruits throughout the year. The bull s eye formation is made of young, yellow, nectar-producing flowers in the center. Surroundin g the yellow center are older, orange flowers that no longer produce nectar. L. camara flowers change from yellow to orange over a 24-hou r period and will remain on the inflorescence for thr ee days (Moldenke 1973). Nectar variation We observed foraging behavior of the butterflies Anartia fatima Anartia jatrophae and the long-tailed skipper, Urbanus proteus on L. camara to establish color preference. The smallest inflorescence on the shru b had 20 flowers, and we controlled for size by removing flowers from inflorescences with more t han twenty. We removed yellow and/or orange flowers so there was about a 2:1 ratio respe ctively. We used a syringe to fill both yellow and orange flowers with 20% sucrose solution to imi tate nectar. We then observed butterfly foraging behavior on both orange and yellow flowers to see if the addition of nectar to both colors had an effect on butterfly color preference. We filled all twenty flowers on the eighteen inflorescences with the sucrose solution to make su re that they all offered an equivalent quality
and quantity of nectar. Flower color choice was pl aced on a time line noting color of flowers probed per inflorescence for three 20-minute sessio ns to see if orange flower probing increased over time. Each inflorescence received a rank th at indicated order of visitation. The same inflorescences were re-filled with nectar after eve ry 20-minute session to assure that all flowers continued to reward visitors. Pattern variation Tempera paint was used on 18 size controlled inflo rescences to create six different color patterns (three inflorescences of e ach pattern). The first group was an unpainted control. The second inflorescence type was painted but the same bulls eye pattern that naturally occurs. This group acted as a second typ e of control to assure that paint did not affect foraging behavior. The remaining four inflorescence types were all yellow, all orange, inverted bulls eye (with orange inside and yellow outside), and a random mix of yellow and orange flowers on the same inflorescence. Number of visit s to each flower color recorded for three 20minute sessions. In between sessions, we moved to a new location of 18 inflorescences on the shrub, since the paint eventually caused the flower s to shrivel. Combined variation Finally, we combined the first two parts of our ex periment to vary both color and reward aspects. We put the sucrose solut ion in all flowers and used the six color variations that were used in part two of our experi ment. Activity was recorded on a time line for three 20-minute sessions, with 18 new inflorescence s and a refill of sucrose solution after every session. RESULTS On the nectar variation, the percent of yellow flow ers probed decreased over time, but not significantly (Figure 1). A t-test was used to dete rmine the differences between the order of orange and yellow visits (t =.829, df = 244, p = .4 076). The average order of the yellow flowers probed was 5.79 3.06 (N = 332), and the average order of orange fl owers probed was 4.43 3.18 (N = 114). This means that yellow flowers wer e not initially preferred and then lost as more orange flowers were visited. Instead, yellow flower s were preferred throughout and orange flowers were just as likely to be visited earlier a s later.
When patterns were varied, yellow flowers were pref erred in all cases, representing nearly all of the visits flowers, regardless of inflorescence typ e (see Figure 2). Demonstrating this trend most clearly are the control inflorescences, where 239 t otal flowers were visited, 233 of which were yellow flowers (df = 1, x2=1.741, p=0.187). However, some types of infloresc ences were more attractive to butterflies, as indicated here by the number of flowers probed per inflorescence. Yellow only inflorescences were significantly the m ost attractive with 289 visits, followed by the unpainted control with 239 visits (df = 1, x2 = 4.734, p = 0.02), and the painted control with 21 1 visits. Inverted (151 flowers visited) and mixed i nflorescences (144 flowers visited) had about half or slightly more than half of the floral visit s to yellow only inflorescences. Orange only inflorescences were least favored, with 99 flowers visited. In this case, all flowers visited were orange. Figure 1. Trend line showing the percent of yellow flowers probed as order increased. The order of flower visits did not statistically differ over time when comparing means of orange and yellow flowers using a t-test (t =.829, df = 24 4, p = .4076).
Figure 2. This shows number of flowers probed for e ach of the pattern variations. Orange bars indicate the total number of flowers (orange and ye llow) probed for each pattern, and yellow bars show how many of the total flowers probed were yell ow rather than orange. Figure 3. The number of flowers probed on each of p attern variations under the combined variation circumstances. Orange bars indicate the t otal number of flowers (orange and yellow) probed for each pattern, and yellow bars show how m any of the total flowers probed were yellow rather than orange.
Control inflorescence flowers were favored when all flowers were enhanced with artificial nectar (df = 1, x2 = 39.41, p = 3.44*10-10). All other inflorescences were visited about hal f the amount of times as the unpainted control, except for orang e inflorescences, which had no visits. Also, orange flowers were visited more often than before, as there was a difference between the total amount of flowers probed, and just the yellow flowe rs probed on the unpainted control (df = 1, x2 = 9.363, p = .002). The number of total flowers vis ited on the control inflorescence was greater than the total flowers visited on the painted contr ol inflorescence (see Figure 3; df = 1, x2 = 9.363, p = .002). In general, fewer flowers were p robed during combined variation sessions (N=483) than painted variation sessions (N=1,133). In regards to the number of visits from each butter fly species, A. fatima were the most common pollinators. For the pattern variation, 963 flower s foraged on were A. fatima and the two other species were observed to visit 199 flowers. DISCUSSION The results demonstrated that butterflies have a pr eference for yellow flowers that does fundamentally change if orange flowers also offer r eward. This suggests that the yellow preference is either learned early and unlikely to change, or it is innate. If the butterflies were captable of overriding their initial preference for yellow, they would have been expected to take more and more orange flowers once artificial nectar was placed in them. Instead, we noticed that butterflies tried each yellow flower multiple times before even checking the orange flowers to see if they contained nectar. We can therefore conc lude from this that butterflies show a likely innate preference for yellow flowers, and did not n ecessarily learn that yellow flowers are the only nectar producing flowers on an L. camara inflorescence. Nonetheless, butterflies did occasionally visit orange flowers and with greater frequently when they had nectar. For pattern variation, control and painted control comparisons showed us that butterflies did not mind foraging on flowers that were painted. We fou nd that the bulls eye pattern is more effective with yellow in the center, rather than or ange. Foraging pattern on the inverted bulls eye pattern was different than regular bulls eye p attern, in that butterflies still pollinated the yellow flowers, which were located on the outside ring around the orange. We believe that butterflies had a difficult time foraging on outsid e flowers because they were harder to reach, existed less than center flowers, and did not conta in nectar. Therefore, they chose the inverted inflorescences patterns fewer times and were attrac ted to patterns in which yellow flowers were easily accessible. In addition to showing yellow fl ower preference on both bulls eye patterns, the all yellow inflorescence was visited more than the bulls eye, suggesting that butterflies prefer an all yellow inflorescence over the natural pattern. Adding nectar to all flowers produced a surprising result. The number of flowers visited declined for all inflorescence types. This may be due to an increased foraging time on flowers that were filled with nectar and as a result less f lowers visited during the allotted time. Beyond this, butterflies overwhelmingly chose the unpainte d control. All other inflorescence types had steep drops in visitation compared to when artifici al nectar was not added. Since butterfly
foraging behavior was clearly affected by the paint on this variation and not on the variation where no nectar was added, we think that the butter flies could afford to be picky about their inflorescence choice when flowers were full of nect ar. In the pattern variation, butterflies were forced to visit inflorescences other than the unpai nted control in order to find nectar. We believe the reason that the yellow inflorescence was not pr obed the most in this variation is just because they did not want to visit painted inflorescences. Our variations show that L. camara has not evolved in a way that maximizes butterfly visits. We have shown that it may be more beneficial for the i nflorescences to keep their older flowers yellow instead of turning them orange, therefore cr eating a solid yellow inflorescence. Older flowers may turn orange due to an inevitable pigmen t change. If energy is expended by the plant in turning flowers orange, L. camara can save its energy in addition to attracting more pollinators by discontinuing this adaptation. Butt erflies on the other hand, are foraging in the most efficient way. They have evolved to visit yel low flowers overwhelmingly more than orange because of their innate preference, and sinc e the yellow flowers are the only nectar producing flowers, it would not be beneficial for t hem to forage on orange flowers. Since a majority of the butterflies that pollinated the shr ubs we observed were A. fatima the mutualistic relationship may be tightly coevolved between the t wo species. This means it is important for L. camara to keep catering to its most common pollinators by keeping older flowers yellow. Coevolution of plants and pollinator is shown to be a long process that can be affected by behavior in either plant or pollinator. In this cas e, the pollinator may cause the plant to evolve differently into the future. If it L. camara does not evolve differently to attract more pollin ators, and a preference for all yellow inflorescences is m aintained, the tight plant-pollinator relationship may be detrimental to L. camara if A. fatima become more attracted to other inflorescences that are all yellow. Future studies could investigate the effect of a h yper-reward system, in which only the orange flowers are injected with nectar. Also, research c ould be conducted on inflorescences in which all of the orange flowers are pulled off of the inf lorescence. This would create a solid yellow inflorescence that is more attractive to butterflie s, but a smaller platform. Results of this study could tell whether or not retaining old flowers for a bigger platform is beneficial toward L. camara pollination. ACKNOWLEDGEMENTS We would like to thank Silvio and all other friends at Gold Mine Adventure for allowing us observe the ir L. camara shrubs. We thank the display of compressed life zo nes in Costa Rica, for without them, we would not b e able to travel only one and a half hours outside of Monteve rde to find sunny weather and no rain every day. M oncho and Pablo are given thanks for their help with everythi ng from statistics to power points. We are thankfu l for Dr. Alan and Dr. Karen Masters, the two best professors we h ave had, for imparting their vast knowledge in all aspects of biology and ecology and their continuous support du ring a tough semester. Finally, we thank all of th e other students in the Fall 2008 CIEE program for showing us how amazing a group of 24 people can be.
LITERATURE CITED Lewis, Alcinda C. 1989. Flower Visit Consistency in Pieris rapae the Cabbage Butterfly. The Journal of Animal Ecology. Volume 58. No. 1: 1-13. Hawson, Sadie A., D. Goulson, J. C. Stout. 1997. Ca n Flower Constancy in Nectaring Butterflies Be Expl ained by Darwin's Interference Hypothesis? Oecologia, Volume 112, No. 2: 225-231. Kelber, Almut. 2002. Pattern Discrimination in a Ha wkmoth: Innate Preferences, Learning Performance an d Ecology. Proceedings: Biological Sciences, Volume 2 69: 2573-2577. Milius, Susan. 1998. How Bright Is a Butterfly? S cience News, Volume 153: 233-235. Mittelback, Gary, et al. 2007. Evolution and the la titudinal diversity gradient: speciation extinction and biogeography. Ecology Letters, Volume 10: 315-331. Moldenke, H. H. 1973. Verbenaceae. In Flora of Pana ma, ed. R. E. Woodson and A. W. Echery. Ann. Missou ri Bott. Gard. 60:41-148. In Costa Rican Natural Histo ry. Ed. Janzen, D. H. 1983. The University of Chica go. pp. 266-268 Peters, F. 1998. Use of Visual Cues when Locating N ectar by Dionne moneta poeyii, Heliconius charitonius and Heliconius clysonymus montanus. Pages 69-72. In Tro pical Ecology and Conservation Biology, Council on International Education Exchange, Summer. Monteverd e, Costa Rica. Schappert, Phil. 2000. A World for Butterflies: The ir Lives, Behavior and Future. Firefly Books. Schemske, Douglas W. 1976. Pollinator Specificity i n Lantana camara and L. trifolia (Verbenaceae). Biotropica, Volume 8: 260-264. Zurinskas, Marika. 2003. The Importance of the Bull s-Eye Coloration Pattern on the Rate of Inflorescen ce Visitation of Lantana Camara. Pages 126-132. Tropic al Ecology and Conservation Biology, Council on International Education Exchange, Summer. Monteverd e, Costa Rica.