Optimal energy allocation and behavior modification in provisioning Crawfordapis luctuosa David Gardner Department of Neuroscience, Northeastern University Abstract Behaviors and actions of species can be described according to optimality. Crawfordap is luctuosa , an understudied endemic species to Central America, has little information pertaining to its behavior. Energy allocation can provide insight on what actions are most important to C. luctuosa. Measured times spent inside and outside provision ed nests indicate that manipulations involving the covering of nests influence these times. Optimal energy allocation for behaviors observed during a manipulation are noted and studied. Different behaviors could account for the amount of provisioning the bee needs to maintain. Further research on cost benefit analyses and C. luctuosa could better describe the natural history and behavior of the species and other insects of the Order Hymenoptera. Resumen Comportamientos y acciones de especies pueden ser descritas de acuerdo a la optimalidad. Crawfordapis luctuosa , una especie poco estudiada y endÃ©mica para CentroamÃ©rica posee poca informaciÃ³n con respecto a su comportamiento. La utilizaciÃ³n de la energÃa puede proveer informaciÃ³n de cuales acciones son mÃ¡s importantes para C. luctuosa . Mediciones del tiempo usado tanto dentro como fuera del nido indica que la manipulaciÃ³n cubriendo el nido influencia estos tiempos. La utilizaciÃ³n Ã³ptima de la energÃa de comportamientos fueron notados en este estudio. Diferentes comportamientos pueden influir en la cantidad de provisiones que la abeja debe mantener. Futuras investigaciones en el anÃ¡lisis de costo beneficio y C. luctuosa puede describir mejor la historia natural y el comportamiento de la especie y otro s insectos del orden Hymenoptera. Keywords: Crawfordapis luctuosa , Optimal Energy Allocation, Hymenoptera Introduction Organisms optimize their behaviors to sequester resources in the most efficient way possible. Optimality is harmonious with adapting to the environment to further enforce natural selection on all individuals, and favor ones who optimize most successfully. Optimal energy models suggest that organisms put certain amounts of energy into certain actions, such as reproduction and parenting depending on which life stages they are at (Perrin 1993). Resources are allocated when there is a high selection pressure, and organisms perform best when these levels are in synch (Perrin 1993). Energy allocation designated toward the care of young in o rder to produce fit individuals is critical. Nest building and burrowing animals especially put an incredible amount of energy into their homes. According to Hansell (1993), building nests causes the brood to be more stable and constant, favoring fitness and a population close to the carrying capacity that can be achieved. An optimal amount of energy allocated to building nests forces the act to be exhausting, which leads animals to be less likely to leave the nest. Reluctance to leave a costly nest als o causes the formation of
elaborate colonies and nests. The stress of emigrating and building another nest with high energetic costs therefore forces these organisms to remain with their nests for long periods of time (Hansell 1993). This study focuses on Crawfordapis luctuosa, a solitary bee found in Costa Rica whose underground nests are arranged in aggregates. Crawfordapis luctuosa nests in disturbed, high elevation areas in Central America. They are only known from few locations in the world and hav e fairly specific habitat requirements (Hanson and Gauld 1995). Prior to human disturbance, nesting sites were found on recent landslide areas, therefore nesting sites were patchy and bees had to move fairly regularly. Currently, C. luctosa is able to nest on the banks and surrounding muddy, soft soils of roads. Their ground nests are located in the slope nearly 12cm from the entrance, a sphere like chamber between the goose neck and entrance, and ending cells consisting of larvae and/or eggs (Wuellner and Jang 1996). The patchiness of nesting sites as well as the length and form of the nest assumes creating nests is energy expensive in C. luctuosa. The nest aggregatio ns include both provisioning and non provisioning females. Provisioning females quickly enter and exit their nests as they collect pollen or nectar. When leaving the nest, provisioning females hover above the hole while flying back and forth, eventually circling the hole in progressively larger circles and flying away. Non from nest to nest in search for an abandoned nest (Wuellner and Jang 1996). This study in volves observations of the nesting and nest making behavior of C. luctuosa following an experimental simulation of provisioning nests being buried under a layer of soil. This simulation represents a typical disturbance in C. luctuosa sts were covered while C. luctuosa was away provisioning and finally returned, then there would be a change in behavior, which will be based on the costs and benefits of making and finding nests. Optimality suggests that the provisioning bees would be inc lined to remove the covering, since the nests are so elaborate that it must take a significant amount of energy to produce and maintain them. If the nests are not worth the energy it takes to remove the covering, then it is assumed that the nests are not expensive to build and the bee will abandon the disturbed nest and either fly away or build a new one. It may also be a more efficient use of energy to try stealing a nest from another bee. If C. luctuosa is provisioning for larvae, then depending on how far along developmentally the larvae are, there could be different observed behaviors in accordance with optimal energy allocation, for example very developed larvae may mean that C. luctuosa will be inclined to dig the nest out. Based on energy expendit ure, what would be the optimal solution for provisioning C. luctuosa ? Information pertaining to C. luctuosa is limited, therefore this study also provides additional knowledge to the natural history and behaviors of this taxa. Methods Study Site C. l uctuosa inhabit a clay road near the top of Cerro Amigos in Monteverde, Puntarenas Province, Costa Rica, at 1800m in elevation. This study focused on a large aggregate of approximately 140 nests. Nests were found in the clay road and in short
vegetation of the road edges. Provisioning and non provisioning nests are scattered throughout the aggregations. Study Organism Crawfordapis luctuosa is a solitary bee in Order Hymenoptera (Colletidae) . Females collect pollen and nectar from buzz pollinated plants from the families of Melastomataceae, Sapotaceae and Begoniaceae to provision their young (Wuellner and Jang, 1996). Males never enter the nests yet hover and fly quickly above the aggregations, and although are not considered territorial, chase any nearb y flying objects (Otis, 1982). Very little is known about C. luctuosa , especially their behavior, and this is most likely due to their rarity. All data was collected between 20 April and 28 April 2010. Baseline: Time spent inside and outside the nest Nes ts of C. luctosa were marked with a flag as provisioning or non provisioning (abandoned) according to the behavior of the bee. Bees were considered provisioning by their flight behavior when entering and exiting a nest. Foraging trips (time outside the n est) and provisioning inside the nest were both timed for four days between the hours of 0900 and 1400 to use as baseline information. 20 holes were observed. Nest manipulation : Time spent inside and outside the nest Bees were observed leaving their nest s for a foraging trip, and upon flying away, the nests were covered with 100 colones coins to simulate a landslide covering their nest. Coins were left for 30 minutes then removed. The time the bees spent inside the nest and outside the nest following mani pulation was recorded. 27 holes were observed. Nest manipulation : Observed behaviors while nest was covered Bees returning from foraging displayed certain behaviors when they found their nests were inaccessible. All behaviors were observed and recorded f or 30 minutes when they were not able to enter the nest. The behaviors recorded included: 1) walking along the coin edge and around the nest; 2) hovering above the nest; 3) flying away for more than five minutes; 4) flying in close proximity of the nest; 5 ) digging near the nest; 6) inspecting and/or visiting another hole; or 7) pushing the coin away and entering the hole. When a behavior was displayed for roughly one minute, the behavior was noted with a tally mark. For the pushing behavior, one tally wa s given if the coin was pushed out of the way successfully and entrance into the nest occurred, otherwise the behavior was marked as a zero. 27 total holes were observed. Additional Observations Several other behaviors displayed by C. luctuosa were note d throughout the experiment. When provisioning bees returned to their holes, their flight patterns were consistent; flying uphill in the same patterns and homing into the hole at the same position.
When holes were covered, bees would commonly fly away fo r a few seconds, then return to the hole in the same flight pattern and approach the hole in the same location. Males were observed flying quickly, grabbing females and attempting copulation on the ground with other males hovering over the two. On occasi on, buzzing noises were audible from a few holes, however the significance of these noises is unknown. Statistical Analysis To determine if there was a difference between means of time in and out before and after manipulation, a one way ANOVA followed by a Tukey Kramer HSD were used. To determine if there was a difference in the mean counts of behaviors during the manipulation phase, a one way ANOVA followed by a Tukey Kramer HSD were used. Results Mean time measured in minutes for times in and out be fore manipulation and after manipulation were compared and differences were found to be statistically significant using a one way ANOVA (F 3, 90 = 8.78; P <0.0001; Fig. 1). There was only a significant difference between means of In Before and Out Before ( Tukey Kramer HSD: q = 7.975, p < 0.05), and there was a trend toward significance between In After and In Before (Tukey Kramer HSD: q = 1.753, p < 0.05). However, after the nest manipulation, bees spent more time inside and outside the nest than they did prior to nest manipulation. Behaviors varied when nests were covered (One way ANOVA: F 6, 175 = 13.25; P <0.0001; Fig.2). There were statistically significant differences between means of Fly Around and Dig (Tukey Kramer HSD: q = 1.012, p < 0.05), Fly Aro und and Fly Away (Tukey Kramer HSD: q = 2.704, p < 0.05), Fly Away and Walk (Tukey Kramer HSD: q = 1.858, p < 0.05), and Fly Away and Other Hole (Tukey Kramer HSD: q = 1.089, p < 0.05). According to the means for the behavior Push, only 23% of the bees ma naged to push the coin out of the way and enter their nest. Discussion This study examined the differences between time spent inside a nest and time spent outside foraging, behaviors manipulated from covering nests, and the effects of the manipulation s on time spent inside and outside the nest. A difference in the means of In Before and Out Before indicates that C. luctuosa spend different amounts of time in and out of their nests. Optimally, there is a benefit in spending more time outside the nest than inside, possibly to forage more for itself, eggs and larvae. There was a trend in time spent inside the nest before and after the manipulations with more time spent in the hole after the manipulation. Spending more time in the nest after a manipulati on suggests an effect from the manipulation, possibly stress. This could be a more efficient use of time, by being inside the hole, in case there is another disturbance. This also suggests that the hole is costly to maintain; if there were no trend towar d a difference, then C. luctuosa would not need to expend much energy maintaining the hole and would not be bothered if it was covered or not. The overall counts of behaviors from each hole suggest a multitude of findings. The mean counts for each beha vior imply a sort of optimal energy budget for C. luctuosa . It is worth the energy to walk around the coin in search of a way to enter the nest, and it is worth
flying around the area to observe their surroundings or to make sure they arrived at the corre ct location. It was also worth the energy to hover above the coin and to go into other holes, however entering other holes could result physical altercations or the option of finding an abandoned hole to provision. The act of provisioning a hole costs a large amount of energy, along with reproducing and maintaining pupae and larvae. The different behaviors observed could also indicate how much energy the female has used to provision, and how much energy she has allocated toward taking care of young. Thi s would suggest that females who have larvae that are closer to the adult stage would be more inclined to use more energy to get into their hole compared to a female who has put little energy into rearing new larvae. Some nests may also have more larvae a nd pupae than other nests, which would be shown in behaviors that are more exhaustive. Optimally, it was not sufficient to fly away for an extended period of time from the hole, suggesting that the hole is still costly to the female. Digging and pushing the coin away from the entrance occurred infrequently, implying that it costs a large amount of energy to do so, though resulting in success. This could be explained by some females having more young that were less developed than others. Optimal energy allocation also suggests which behaviors are displayed and could explain the processes involved in the decision making of these actions. After future studies, more information can further describe such species as C. luctuosa and generalize findings to oth er Hymenoptera. Acknowledgments I would like to thank workers at Cerro Amigos for helpful information and full support. Thank you to Dr. Anjali Kumar for constant and positive support during my project. Thank you to Pablo Allen for the creative insp iration for my proposal. Thanks to Colleen Nell for helping with data collecting. A special thanks goes to Candi for the utmost support during difficult data collecting days. Thank you to Gracy Huntley and Keisha Bates for helping with material collecti ng. Literature Cited HANSELL, M. H. 1993. The ecological impact of animal nests and burrows. Functional Ecology 7, 5 12 HANSON, P.E., and I. D. Gauld. 1995. The Hymenoptera of Costa Rica. Oxford University Press. Oxford, UK. OTIS, G. W., R. J. McGin ley, L. Garling, L. Malaret. 1982. Biology and Systematics of the Bee Genus Crawfordapis (Colletidae, Diphaglossine). Psyche 89 : 279 296 PARKER, G. A. & J. M. Smith. 1990. Optimality Theory in Evolutionary Biology. Nature. Vol. 348. pp 27 33. PERRIN, N. R., M. Sibly. 1993. Dynamic Models of Energy Allocation and Investment. Annu. Rev. Ecol. Syst. 24:379 410 SCHMID HEMPEL, P., A. Kacelnik, & Houston, A. I. 1985. Behav. Ecol. Sociobiol. 17 , 61 66 WUELLNER, C. T. and Y. Jang. 1996. Natural History of a G round Nesting Solitary Bee Crawfordapis luctuosa (Hymenoptera: Colletidae) Journal of the Kansas Entomological society. 69(3), pp. 211 221
FIGURE 1 . Time measured (in minutes) in and out of hole, before and after m anipulation for C. luctuosa . Times are means for In and Out After (N = 27) and In and Out Before (N = 20, control). Standard error represented in error bars. Means (mean se) for In After, In Before, Out After and Out Before were 25.18 4.12 , 14.35 2.45 , 25.00 5.59 , and 30.66 2.01 respectively. A and B represents Tukey Kramer HSD differences. A B
FIGURE 2 . Frequency of observed behaviors during manipulation phase for provisioning C. luctuosa . Counts are averaged across all manipulated nests (N = 27). Standard error represented in error bars. Mean (mean se) counts for Dig, Fly Around, Fly Away, Hover, Other Hole, Push, and Walk were 2.31 0.58 , 5.77 0.58 , 0.62 0.58 , 3.58 0.58 , 4.15 0.58 , 0.23 0.58 , and 4.92 0.58 respectively. A, B, C, and D represent Tukey Kramer HSD statistical differences. A B C D
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La asignacin energtica ptima y la modificacin de conducta en el aprovisionamiento de Crawfordapis luctuosa
Optimal energy allocation and behavior modification in provisioning Crawfordapis luctuosa
Behaviors and actions of species can be described according to optimality. Crawfordapis luctuosa, an understudied endemic species to Central America, has little information pertaining to its behavior. Energy allocation can provide insight on what actions are most important to C. luctuosa. Measured times spent inside
and outside provisioned nests indicate that manipulations involving the covering of nests influence these times. Optimal energy allocation for behaviors observed during a manipulation are noted and studied. Different
behaviors could account for the amount of provisioning the bee needs to maintain. Further research on cost/benefit analyses and C. luctuosa could better describe the natural history and behavior of the species and other
insects of the Order Hymenoptera.
Los comportamientos y las acciones de especies pueden ser descritos de acuerdo a la optimalidad. Crawfordapis luctuosa, es una especie poco estudiada y endmica para Centroamrica y posee poca informacin con respecto a su comportamiento. La utilizacin de la energa puede proveer informacin de cuales acciones son ms importantes para C. luctuosa. Las mediciones del tiempo usado tanto dentro como fuera del nido indican que la manipulacin cubriendo el nido tiene una influencia en estos tiempos. La utilizacin ptima de la energa de comportamientos fueron notados en este estudio. Diferentes comportamientos pueden influir en la cantidad de provisiones que la abeja debe mantener. Futuras investigaciones en el anlisis de costo-beneficio y C. luctuosa puede describir mejor la historia natural y el comportamiento de la especie y otros insectos del orden Hymenoptera.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone
Alimentos de animales
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Spring 2010
Optimal energy allocation
Ecologa Tropical Primavera 2010
Asignacin energtica optima
t Monteverde Institute : Tropical Ecology