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Ghose, Sonia Lorraine
Los efectos de Xanthosoma spp. (Araceae) en la temperatura, el olor, y las flores de frecuencia de apareamiento de Cyclocephala sexpunctata (Scarabaeidae)
The effects of Xanthosoma spp. (Araceae) temperature, scent, and flowers on the mating frequency of Cyclocephala sexpunctata (Scarabaeidae)
Many pollinators have evolved very specified obligate mutualisms with the plants that they pollinate. One example of this kind of mutualism, in which the reproduction of both organisms relies on their relationship, is Xanthosoma spp. and Cyclocephala sexpunctata in Monteverde, Costa Rica. Xanthosoma spp. thermoregulate, attracting beetles because of a combination of heat, scent, and visual components of the inflorescence. The beetles crawl inside of the spathe and spadix inflorescence, where they both eat and mate. The specific stimuli that prompt the beetles to mate once inside the flower had not yet been widely examined. Through my experiments, I found that heat was the only
factor that had a significant positive affect on mating frequency, as well as on the level of activity exhibited by beetles. The presence of flowers and the presence of scent did not have significant affects on mating frequency or activity. In addition, I was able to estimate that in a patch of 214 mature Xanthosoma spp., the population of males was about 200.6 individuals. About half as many females were captured, but an accurate estimate of female population could not be calculated because they were either not always present in inflorescences or they traveled farther to different patches more often than did males. These results add to a relatively small body of knowledge concerning this fascinating relationship between Araceae plants and their Scarabaeidae pollinators, and are
important to understanding complex reproductive mutualisms.
Varios polinizadores han evolucionado mutualismos obligados de forma muy especfica con las plantas que ellos polinizan. Un ejemplo de esta clase de mutualismo, en el cual la reproduccin de ambos organismos depende de esta relacin es entre Xanthosoma spp. y Cyclocephala sexpunctata en Monteverde, Costa Rica. Xanthosoma spp. termo regula, atrayendo a los escarabajos debido a una combinacin de calor, olor, y los componentes visuales de la inflorescencia.
Text in English.
Scarabaeidae--Costa Rica--Puntarenas--Monteverde Zone
Scarabaeidae--Costa Rica --Puntarenas--Zona de Monteverde
Tropical Ecology 2009
Ecologa Tropical 2009
t Monteverde Institute : Tropical Ecology
The Effects of Xanthosoma spp. (Araceae) temperature, scent, and flowers on the mating frequency of Cyclocephala sexpunctata (Scarabaeidae) Sonia Lorraine Ghose Department of Biochemistry, Occidental College ABSTRACT Many pollinators have evolved very specified obligate mutualisms with the plants that they pollinate. One example of this kind of mutualism, in which the reproduction of both organisms relies on their relationship, is Xanthosoma spp. and Cyclocephala sexpunctata in Monteverde, Costa Rica. Xanthosoma spp. thermoregulate, attracting beetles because of a combination of heat, scent, and visual components of the inflorescence. The beetles crawl inside of the spathe and spadix inflorescence, where they both eat and mate. The specific stimuli that prompt the beetles to mate once inside the flower had not yet been widely examined. Through my experiments, I found that heat was the only factor that had a significant positive affect on mating frequency, as well as on the level of activity exhibited by beetles. The presence of flowers and the presence of scent did not have significant affects on mating frequency or activity. In addition, I was able to estimate that in a patch of 214 mature Xanthosoma spp., the population of males was about 200.6 individu als. About half as many females were captured, but an accurate estimate of female population could not be calculated because they were either not always present in inflorescences or they traveled farther to different patches more often than did males. Thes e results add to a relatively small body of knowledge concerning this fascinating relationship between Araceae plants and their Scarabaeidae pollinators, and are important to understanding complex reproductive mutualisms. RESUMEN Varios polinizadores han evolucionado muy espec ficos mutialismos obligados con las plantas que ellos polinizan. Un ejemplo de esta clase de mutualismo, en el cual la reproduccin de ambos organismos depende en esta relacin es entre Xanthosoma spp. y Cyclocephala sexpunctata en Monteverde, Costa Rica. Xanthosoma spp. termorregula, atrayendo escarabajos debido a la combinacin de componentes de calor, esencia y visual de la inflorescencia. Los escarabajos se mueven dentro del espdice y la espata, donde ambos se reproducen. El estmulo especfico que produce que estos se reproduzcan dentro de la flor no ha sido bien examinado an. Con mi experimento, encontr que el calor es el nico que presenta una relacin positiva en la frecuencia de cpulas, as como en el nivel de activi dad exhibido por los escarabajos. La presencia de flores y de esencia no tiene un efecto significativo en la frecuencia de cpulas o actividad. Adems fui capaz de determinar que en un parche de 214 plantas adultas la poblacin de adultos es de alrededor de 200.6 individuos. Alrededor de la mitad de hembras fueron capturadas, pero una estimacin precisa de la poblacin de hembras no puede ser calculada debido a que no siempre se encontraban en la inflorescencia o a que ellas viajan lejos a otros parches ms frecuentemente que los machos. Estos resultados se unen al conocimiento previamente adquirido a esta fascinante relacin entre las plantas de la familia Araceae y sus polinizadores, y es importante entender la complejidad de este mutualismo.
INTROD UCTION Thermoregulatory plants radiated during the Mesozoic era at the same time in history as the endothermic beetles that coevolved to pollinate them (Seymour 2001). It has been hypothesized that the heat produced by plants developed to offer a refuge f or beetles that was as significant an energetic reward as pollen or nectar in cold times (Seymour 2001). Xanthosoma spp( Araceae), one example of a thermoregulatory plant, utilize an interesting method to pollinate their flowers, employing a mutualism with scarab beetles of the family Scarabaeidae. Xanthosoma spp. inflorescences consist of a spathe and spadix, with unisexual and sterile flowers vertically stratified on the spathe, surrounded by a fleshy spadix (Sica 1999). The plants have temporally separate d sexual functions, meaning the female and male flowers are sexually active at different times (Young 1986). Their inflorescences heat up on the first night when the female flowers at the bottom of the spadix are mature and receptive, and again to a lesser extent the next night when the male flowers on the top part of the spadix produce pollen (Gottsberger and Silberbauer Gottsberger 1991, Golwasser 2000). The first night the inflorescence heats to peak temperatures of 40 42 ¡ C (Goldwasser 2000) between 6:0 0 7:00pm ( Goldwasser 2000, Garca Robledo et al. 2004), and this heat helps to release and disperse a pleasant odor, which attracts scarab beetles pollinators, Cyclocephala (Coleoptera: Scarabaeidae), who enter the spathe (Silbert 2001, Endress 1994). They remain there for the next 24 hours until the inflorescence heats again to about 34 ¡ C, at which time they climb out of the inflorescence, taking pollen with them to the next plant who has both heated up and released its scent (Silbert 2001, Endress 1994, G oldwasser 2000). When the beetles enter the inflorescence of a Xanthosoma spp they both eat the ring of sterile flowers located in the middle of the spadix, and mate (Sica 1999, Goldwasser 2000). Xanthosoma spp. uses much of its energy to produce the heat ing of the spadix, and it has been shown that its respiratory rate will increase when ambient temperature is lower in order to maintain the same inflorescence peak temperatures (Seymour 2001). The heating of the spadix will not decrease, even when ambient temperature reaches the freezing point (Gottsberger and Silberbauer Gottsberger 1991). It has been hypothesized that heat is produced to increase volatility of odorous compounds released from inflorescences to attract beetles (Garca Robledo et al. 2004, L eBrun 2001). However, because the plant puts so much energy into producing heat, it seems that heat itself is incredibly important to this system, and may act as reward for the pollinator in and of itself (Seymour 2001). There are many factors that have been hypothesized to contribute to attracting beetles to inflorescences such as those discussed above, however the factors that prompt beetles' mating activity once inside the inflorescences has not been widely studied. It seems that many of the same facto rs discussed to attract beetles would also be those that stimulate their mating behavior. Studies have shown that Cyclocephala are not attracted to each other by pheromones, and that possibly the scent of the inflorescence acts as a pheromone for them (Gib ernau et al. 1999), or even perhaps that visual signs from the presence of inflorescence itself attracts them (Gottsberger and Silberbauer Gottsberger 1991). However, experiments concerning the effects of these factors on copulation frequency have not yet been performed. One experiment performed by Lauren Silbert in Monteverde, Costa Rica questioned whether there was a relationship between the temperature of the inflorescence and the number of copulation events, especially because the plants put such an inc redible amount of energy into heating. Although the beetles mated under laboratory conditions, no correlation was found between temperature and mating (Silbert 2001).
This study aimed to answer the following questions: Why do Cyclocephala beetles mate ins ide of the inflorescences of Xanthosoma spp ? Which factor, or combination of factors, most positively affects the frequency of copulation? My experiments are modeled after those of Silbert 2001, though in addition to retesting the affects of temperature, I explored the presence of the scent produced by flowers and presence of flowers themselves as possible factors affecting mating behavior. Elucidating this information will add to the body of knowledge concerning behavior of Cyclocephala beetles, as well as behavior of other Scarabeidae beetle pollinators (of both Xanthosoma and other Araceae plants) that utilize this same mutualistic system of reproduction. MATERIALS AND METHODS I. Natural History of Cyclocephala sexpunctata There are two species of Cyclo cephala that pollinate Xanthosoma plants in Monteverde, Costa Rica, C. sexpunctata and C. nigerrima (Goldwasser 2000). However, as C. sexpunctata is far more common, this species was the one studied. These beetles are light brown with black spots, and rang e in size from 1.0 to 2.5cm (Goldwasser et al 1993, Goldwasser 2000). They are sexually dimorphic; males have enlarged tarsi on their forelegs, and females have grooves on the edges of the elytra which the males'tarsi hook into during copulation (Goldwass er et al 1993). Beetles have been found within the inflorescences in a proportion of 1:1 (Gottsberger and Siber Gottsberger 1991). However, a more recent study found that in the Monteverde area, there was a ratio of 1:1.6 (females to males) (Venkatesan 2 001). Little is known about the lifecycle of the beetles apart from their feeding and mating activity inside the Xanthosoma spp. Inflorescence, except that oviposition does not occur in the inflorescence, and that larvae develop underground (Garca Robledo et al 2004). II. Collection of Beetles and Inflorescences I collected Cyclocephala sexpunctata from different patches of Xanthosoma spp. in the Monteverde area of Costa Rica. Xanthosoma are freestanding terrestrial plants that can be as tall as an adu lt man, and can have leaves of 1m in length and width (Goldwasser 2000). One of the patches studied was located on Fred Morrison's property, down the road from the Monteverde Cloud Forest Reserve. All other plants were located on farms near the roadside ar ound the Santa Elena Reserve and Selvatura. Beetles were collected both in the evening and during the day, and all were collected the same day or night that they were used in experiments. They were located in flowers in their first night of heating and rel easing scent. The average number of beetles found in Xanthosoma spp. in the Monteverde area has previously been estimated at 7 individuals per inflorescence (Goldwasser 2000), so many plants were searched on each excursion. I found anywhere between 1 and 1 5 beetles per inflorescence. The beetles were first collected in large Zip Lock plastic bags, and then placed into separate containers in the laboratory. I also collected two first night inflorescences each time I collected beetles. III. Laboratory Set U p In the laboratory, I used a two treatment system to test how the beetles' mating behavior is affected by different factors. One treatment was heat, and the other was an inflorescence treatment. The inflorescence treatment was either the presence of flowe rs that the beetles could
congregate on and eat, the presence of the scent of the inflorescence without access to the flowers, or neither of these. Two buckets (40 cm diameter) were each painted black to recreate the darkness within an inflorescence at n ight. In one of them I cut three holes, and affixed one 40 W light bulb (spray painted black with fire resistant spray paint) in each hole to create the heat treatment maintained at the average temperature of a first night inflorescence (40 42 ¡ C) (Goldwass er 2000, Silbert 2001). A thermometer was kept inside this system, and the light bulbs were turned on and off to maintain the temperature in this range. The other bucket was kept at ambient temperature, which was my no heat treatment. Both buckets had a wi re mesh floor inserted about halfway up the bucket fixed in place with clay, and this was to prevent beetles from coming into contact with the light bulbs in the heat treatment. For both the heated and the non heated systems (the heat treatment), I added one inflorescence treatment. I would either place a first night spathe inside the bucket (to provide access to flowers), place a first night inflorescence above the bucket on the mosquito netting (to provide scent but no access to flowers), or put nothing in or on the bucket (to test only the presence of heat). This meant that each night I recoded data for six different systems, to test the inflorescence treatment (flower, scent or neither) crossed with the heat treatment (heat or no heat). IV. Data Colle ction All experiments were conducted at night after 6:00 pm, as this was when beetles were most active, and when the first night inflorescences would usually be heating and opening to release their odor. 10 beetles were used in each treatment. Equal number s of females and males (5 males and 5 females) were placed in a combination of the two treatments. All combinations of treatments were performed each night, and I observed each constantly for 15 minute periods. The number of copulations during each 15 minu te interval was recorded (as soon as the male had hooked his tarsi into the female's elytra, it was considered one mating). I also took note of their level of activity, and decided whether there was no activity, low activity, or high activity. After all te sts were complete, beetles were labeled using paint pens, and released the next day at the location they were collected from. They were labeled so that it would be ensured that no males were reused in any experiment. Females were reused because after obser vation it was concluded that they had no choice in mating, so only male mating behavior was significant. 8 replications (using 10 beetles in each) were produced for all six combinations of the two treatments. V. Analysis of Mating/Activity Data To test t he effects of the two treatments on mating frequency, I performed a two way analysis of variance using the data from experiments involving 10 beetles. The number of sample replications was 8. To analyze the relationship between the level of activity observ ed under different treatments, chi squared tests were performed (one to compare level of activity to the presence of heat, and one to compare level of activity to the presence of an inflorescence treatment (smell, presence of flower, or presence of nothing ). VI. Estimation of Scarab Beetle Population on Fred Morrison's Property Most beetles were collected from Fred Morrison's property located down the road from the Monteverde Cloud Forest Reserve. Many beetles that I had labeled after experimentation were recaptured each time, and I made note of all recaptures for eight incidences. From this data I
attempted to estimate the total population size of the beetles in this patch of 214 mature fruiting/flowering plants, and 52 saplings. This was done using the Sc hnabel Method for each sex. RESULTS The average number of matings of Cyclocephala sexpunctata for each of the treatments (heat or components of inflorescence) is presented in FIG. 1. The inflorescence treatment had no effect on the copulation frequency (F ratio=1.2016; p=0.3108; df=2). The interaction of heat and inflorescence treatment was also not significant (F ratio=0.7439; p=0.4814; df=2). However, heat itself was found to have a significant affect on mating frequency (F ratio=4.2916; p=0.0445; df=1 ). FIG. 1. Mean ( + SE) number of Cyclocephala sexpunctata matings for two treatments (presence of heat, and presence of a component of the inflorescence). Beetles were highly active with the presence of heat, (X 2 =26.0819; p< 0.0001; df=2; FIG. 2a.). F IG. 2b shows the effects of smell, flowers on the amount of activity. No significant relationship was found (X 2 =5.164; p=0.2708; df=4), though a trend of more high activity with scent or flowers did seem to be present.
(a.) (b.) FIG. 2. The number of cases of different levels of activity observed during treatments. a. shows the relationship between heat and activity. b. shows the relationship between different components of the inflorescence (scent, prese nce of flower, or neither) and activity. I estimated the Cyclocephala sexpunctata population size from a large patch of Xanthosoma sp. (214 flowering/fruiting plants and 52 saplings) located on Fred Morrison's property near the Monteverde Cloud Forest R eserve. Table 1 shows all data recorded for the capture, marking, and recapture of male beetles, and Table 2 shows all data for females. The male beetle population was estimated to be about 200.6 individuals; the confidence intervals of population size wer e estimated with 95% confidence to be between 158.5 and 273.4. FIG. 3 is a plot that tests if the underlying assumptions of the Schnabel method are met. If the relationship between the proportion marked in catch and the number previously marked is linear, then the assumptions have been met, and if it is curvilinear, then they have not. Because the relationship for males (blue) is linear (R 2 = 0.7175) then the assumptions are met. The female population of C. sexpunctata was estimated to be 95.7 individuals, however, as shown in FIG. 3, the relationship of the proportion marked in catch to the number of previously marked individuals for females was curvilinear (R 2 = 0.2935). Therefore, some of the assumptions of the Schnabel Method were not met, and a confidenc e interval was not calculated. Day Number Caught (Ct) Number Recaptured (Rt) Number Newly Marked (less deaths) Marked Beetles at Large (Mt) 1 13 0 13 13 2 30 0 30 43 3 36 6 30 73 4 24 12 9 73 5 6 4 2 75 6 37 16 21 96 7 26 19 7 103 8 30 22 8 1 11 Totals 202 79 120 Table 1. Data for Males Cyclocephala sexpunctata Caught, Marked, and Recaptured from Xanthosoma sp. patch on Fred Morrison's Property near the Monteverde Cloud Forest Reserve.
Day Number Caught (Ct) Number Recaptured (Rt) Number Newly Marked (less deaths) Marked Beetles at Large (Mt) 1 4 0 4 4 2 10 4 6 10 3 16 3 13 23 4 13 4 9 32 5 3 2 1 33 6 15 4 11 44 7 19 14 5 49 8 17 6 11 56 Totals 97 37 60 FIG. 3. Schnabel method of population estimation for female (red) and male (blue) Cyclocephala sexpunctata A plot of the accumulated number of marked animals (Mt) against the proportion of marked animals in each sample (Rt/Ct). DISCUSSION AND CONCLUSIONS The main goal of my experiments was to find which factors present in a first night Xanthosoma spp. inflorescence influence the copulation frequency of Cyclocephala sexpunctata As secondary results, I also found the effects of these same factors on the level of activity of the beetles in all treatments. Finally, I attempted to estimate the population size of beetles present in one patch of Xanthosoma spp. The inflorescence treatment (presence of flowers, the presence of scent, or neither) and the interaction of the inflorescence treatment with the heat treatment did not have an effect on copulation frequency. This demonstrates that although scent and visual aspects of the flower may attract beetles to the inflorescence (Gottsberger and Sil berbauer Gottsberger 1991), these factors did not influence their behavior any further than this. In addition, the presence of the spadix did Table 2. Data for Female Cyclocephala sexpunctata Caught, Marked, and Recaptured from Xanthosoma sp. patch on Fred Morrison's Property near the Monteverde Cloud Forest Reserve.
not prompt them to mate, though they could both climb and feast on the spadix while also experiencing the affects of its floral scent. This indicates that the presence of edible sterile flowers, as well as the familiar location of congregation, both do not act as aphrodisiacs though they are important to beetles for different reasons. Although beetles benefit from asp ects of the inflorescence in many ways, it seems that the benefits they receive from the inflorescence (food, shelter, and a mating place) are separate, without any interactions between them. The one treatment that did affect mating was heat, which prompte d beetles to mate more frequently. This challenges the results of the previous study concerning the affects of temperature on copulation frequency conducted by Silbert (2001), where no correlation was found. The level of activity of beetles was unaffecte d by the inflorescence treatment, but was found to be significantly higher in all systems with heat than in those without heat. This, along with the results on heats' affects on copulation frequency, supports an idea presented in a previous study, stating that heat helps to maintain an elevated body temperature of beetles on cool evenings to keep them active (Gibernau et al 1999). The fact that heat both positively affects activity and copulation frequency makes sense because more active beetles will have more of a chance of moving around in the inflorescence to find females and mate. The relationship between heat and activity/matings also offers some reasoning for why Xanthosoma spp puts so much energy into maintaining such high temperatures at times when the beetles enter the inflorescences. If beetles mated more when they traveled to warmer inflorescences, these plants would have been selected for over time. Because beetles are so positively affected by heat, it is curious that after the first burst of heat produced by Xanthosoma spp. inflorescences eventually cool down to ambient temperature throughout the night (once the beetles are inside) (Goldwasser 2000). It would be interesting to find if beetles mate more frequently in the first few hours they a re in the inflorescence. My results would indicate that this would be true, and that the level of their activity would significantly decrease late in the night when the inflorescence was at ambient temperature. I was also able to make an estimate of the male population size of beetles in a patch of Xanthosoma spp. of 214 mature plants (plants that were flowering/fruiting) and 52 saplings. There were about 200.6 males (between 158.5 and 273.4), and this was proven to be true with 95% confidence. The female population on the other hand, could not be accurately estimated because the assumptions of the estimation method were not met. The inaccurate estimate of female beetle population was 95.7, about one half of the male population, so I believe that there wer e more females in other locations where I did not have an equal chance of catching them. One of the assumptions of the Schnabel Method is that all individuals have the same chance of getting caught, and therefore it is likely that this assumption was not m et. This could be true because females need to leave the inflorescences to lay eggs, which develop into larvae under ground (Garca Robledo et al 2004). If they leave the inflorescences for some amount of time, thereby not traveling to inflorescences ever y night as do males, then there could be far more of them on the ground that I could not always find. Another reason the estimated population of females could have been incorrect is if their population was not closed, as this is another assumption of the S chnabel Method. This would have meant that females didn't stay in the same patch but instead traveled farther distances while males remained in the same area. I only captured beetles from plants in the area surrounding this patch of plants on one occasion, and did not recapture any of the beetles from this patch. This would indicate that they were not leaving the patch, however further research would need to mark and recapture multiple times both in this patch and in the surrounding area to find if the fema les were leaving the patch or not. If they are
flying farther away than males, I have not found any studies on this idea, but it would be interesting to see if females do preferentially travel farther than males, perhaps to achieve more genetic variability I found that the heat produced by the plant in a first night inflorescence (between 40 42 ¡ C) positively affected the beetles' copulation frequency as well as their level of activity. I secondarily was able to estimate the population size of males for a specific patch of plants, while also finding the result that females' presence in inflorescences, or possibly their persistence in specific patches of Xanthosoma spp., is not as constant as that of males. These findings about the effects of heat as well as the population dynamics of C. sexpunctata elucidate a bit more about this relationship that has not been sufficiently studied. They will hopefully lead to future studies on the behavior of these scarab beetles, and their association with Xanthosoma spp. which could apply to many other species and genera of Scarabaeidae and Araceae plants. ACKNOWLEDGEMENTS I would like to thank my advisor, Pablo Allen, for all of his assistance throughout this process, especially with the statistical analyses that I cou ld not have done without him. Great thanks to Rafael Santamaria, for always taking me to catch beetles, as well for his knowledge of plants in the Monteverde area, without which I never would have located so many Xanthosoma spp. I also am incredibly gratef ul to the following people for assisting me in catching beetles on so many evenings: Amber Fandel, Brittany Kolehmainen, Danny Goldish, Anjali Kumar, and Yi men Araya. Thanks to Jos Carlos Caldern for translating my Resumen. Finally, thanks to Fred Morri son for allowing me to study his plants, and to Alan Masters and the rest of the CIEE staff for this amazing semester in paradise. Literature Sited Endress, Peter K. 1994. Diversity and evolutionary biology of tropical flowers. Cambridge University Pr ess, Cambridge, Great Britain. Garca Robledo, C., Gustavo Kattan, Carolina Murcia, and Paulina Quintero Martn. 2004. Beetle pollination and fruit predation of Xanthosoma daguense (Araceae) in an Andean cloud forest in Columbia. Journal of Tropical Eco logy. 20:459 469. Gibernau, M., Denis Barab, Philippe Cerdan, and Alain Dejean. 1999. Int. J. Plant Sci. 160(6): 1135 1143. Goldwasser, Lloyd. 2000. Scarab beetles, elephant ear ( Xanthosoma robustum) and their associates. Pp. 268 271 in Nadkarni, N. M & Wheelwright, N.T. (eds). Monteverde: Ecology and conservation of a tropical cloud forest Oxford University Press, Oxford. Goldwasser, Lloyd, George E. Schatz, and Helen J. Young. 1993. A New Method For Marking Scarabaeidae And Other Coleoptera. The Coleopterists Bulletin 47(1): 21 26. Gottsberger, G. and I. Silberbauer Gottsberger. 1991. Olfactory and visual attraction of Erioscelis emarginata (Cyclocephalini, Dynastinae) to the inflorescences of Philodendron selloum (Araceae). Biotropica. 23(1): 23 28.
LeBrun, J.R. 2001. Effects of climate on inflorescences of the aroid (Araceae) Xanthosoma sp. and visitation rates of their scarab beetle pollinators, Cyclocephala sp. Council on International Education and Exchange. Seymour, R. S. 2001. Biophy sics and physiology of temperature regulation in thermogenic flowers. Bioscience Reports. 21(2). Sica, A. 1999. The effectiveness and abundance of scarabid pollinators of Xanthosoma sp. (Araceae). Council on International Education and Exchange. Silber t, Lauren. 2001. The aroid scarab mutualism: importance of floral temperature for scarab attraction and copulation. Council on International Education and Exchange. Venkatesan, M. 2001. The movement, composition and behavior of scarab beetles and othe r insects visiting inflorescences of Xanthosoma robustum (Araceae). The University of California Education Abroad Program Spring 2001. Young, H. J. 1986. Beetle pollination of Dieffenbachia longispatha (Araceae). American Journal of Botony. 73(6): 931 944.