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Spaht, Nathan J.
Comportamiento de agregacin y la propiedad de nido de Crawfodapis luctuosa (Diphaglossinae: Apidae)
Aggregational behavior and nest ownership of Crawfodapis luctuosa (Diphaglossinae: Apidae)
Crawfordapis luctuosa is a large, black, diurnal bee found in aggregations on exposed clay sites above
1500m in elevation from the highlands of Mexico to Panama. Many past studies have attempted to classify
the exact sociality and nest ownership of this species; this study follows their examples in an attempt to
better define these behaviors. Data was gathered on nest usage, visitation behavior as well as aggressive
and non-aggressive interactions. This study reaches no definite conclusions as to the patterns of nest
ownership in the five days of observation. Individuals consistently visited more than one nest and up to
seven different nests. These multiple visits are likely searches for abandoned nests or new nests if previous
nests have been stolen by Pseudoxycheila tarsalis or other members of the colony. Instances of two bees
inhabiting the same nest simultaneously were observed and concluded to demonstrate a degree of
cooperation, though some interactions ended violently. This study has concluded that C. luctuosa is a
mostly solitary bee and that interactions between individuals are mostly random, and although there is evidence
of both cooperation and competition within the colony, it is limited.
Crawfordapis luctuosa es una abeja grande, negra y diurna encontrada en agregaciones en sitios arcillosos expuestos por encima de los 1500m, en las zonas altas desde Mxico hasta Panam. Muchos estudios anteriores han intentado clasificar la propiedad exacta de la sociabilidad y de la jerarqua de esta especie. Este estudio sigue sus ejemplos en un intento por definir mejor estos comportamientos.
Text in English.
Tropical Ecology 2008
Ecologa Tropical 2008
t Monteverde Institute : Tropical Ecology
Aggregational behavior and nest ownership of Crawfodapis luctuosa (Diphaglossinae: Apidae) Nathan J. Spaht Department of Biology, Kansas State University, Man hattan, Kansas. ABSTRACT Crawfordapis luctuosa is a large, black, diurnal bee found in aggregation s on exposed clay sites above 1500m in elevation from the highlands of Mexico to Panama. Many past studies have attempted to classi fy the exact sociality and nest ownership of this spec ies; this study follows their examples in an attemp t to better define these behaviors. Data was gathered on nest usage, visitation behavior as well as aggress ive and non-aggressive interactions. This study reaches no definite conclusions as to the patterns of nest ownership in the five days of observation. Individ uals consistently visited more than one nest and up to seven different nests. These multiple visits are l ikely searches for abandoned nests or new nests if previous nests have been stolen by Pseudoxycheila tarsalis o r other members of the colony. Instances of two be es inhabiting the same nest simultaneously were observ ed and concluded to demonstrate a degree of cooperation, though some interactions ended violent ly. This study has concluded that C. luctuosa is a mostly solitary bee and that interactions between i ndividuals are mostly random, though there is evide nce of both cooperation and competition within the colo ny, it is limited. RESUMEN Crawfordapis luctuosa es una abeja grande, negra y diurna encontrada en agregaciones en sitios arcillosos expuestos sobre los 1500 m de, en las zonas altas desde Mxico hasta Panam. Muchos estudios anterior es han intentado clasificar la propiedad exacta de la sociabilidad y de la jerarqua de esta especie. Est e estudio sigue sus ejemplos en un intento por definir mejor estos comportamientos. Los datos fueron recopilados en el uso de la nido, comportamiento del visita as co mo interacciones agresivas y no agresivas. Este est udio no alcanza una conclusin definida en cuanto a los patrones de la propiedad de la jerarqua en los cin co das de observacin. Los individuos visitaron constantem ente ms de un nido y hasta siete. Estas visitas mltiples son bsquedas probables de nidos abandona dos o nuevos nidos si loss anteriores han sido roba das por los Pseudosicheila tarsalis u otros miembros de la colonia. Los casos de dos abejas que habitaban el mismo nido fueron observados y concluidos simultne amente para demostrar un grado de cooperacin, aunque algunas interacciones terminaron violentamen te. Este estudio ha concluido que C. luctuosa es un a abeja sobre todo solitaria y que las interacciones entre los individuos son mayoritariamente azarosas, aunque hay evidencia de que tanto la cooperacin y la competencia dentro de la colonia es limitada. INTRODUCTION Sociality can be observed from some of the smallest macroorganisms, such as ants and termites, to the absolute largest animals on the pl anet, blue whales. The order Hymenoptera which contains nearly all social insects and vario us ranges of sociality, is of particular interest in the quest to understand s ociality. This division contains solitary individuals, which meet solely for mating purposes, to highly eusocial colonies that have reproductive division of labor, cooperative care fo r their young and overlapping of two or more generations capable of labor (Wilson, 1971). B etween these two extremes lie many finely stepped levels of behavior, but there are tw o levels of sociality most commonly
recognized: primitively social and semisocial. In primitively social collections, females are found to cooperate outside of simply mating and random contact, but have not evolved to divide labor. Semisocial groups are foun d to have a limited division of labor but only in reference to egg laying and food gather ing (Hanson and Gauld 1995). Primitively social insects of Hymenoptera often bu ild their nests in the immediate vicinity of one another in large aggregations, and several reasons for the evolution of this behavior have been postulated. Such assemblages of nests may help in defense of predators and parasites alike, occur due to a scarc ity of select habitat available or display a tendency for individuals to return to their locat ion of origin (Hanson and Gauld 1995). This behavior displays how higher levels of sociali ty are hypothesized to have evolved. Aggregations such as these are thought to be one of the first steps in the evolution to increasingly complex social behaviors spawning from the close proximity at which the organisms live and interact. The close proximity at which these individuals live may also lead to antisocial behaviors such as cleptoparasiti sm, competition for habitat or food and territoriality that would steer the species away fr om an increased level of sociality otherwise attained (Hanson and Gauld 1995). The large, black bee, C. luctuosa is a diurnal insect characterized by golden pubescence on the thorax and is associated with bur rows within exposed sites on and near clay roads or fresh landslides. They occur most com monly at or above 1500m in elevation in Lower Montane Wet Forests (Nadkarni an d Wheelright 2000). This particular species of the genus Crawfordapis ranges throughout Central America from Mexico to Panama (Otis et al. 1982). Results from a study by Calabrese (1998) have noted in many instances that more than one female h as inhabited the same nest simultaneously. The same study has also noted that individual females often visit many nests through the course of a single day. These fi ndings have indicated a slightly increased level of sociality in the species above t heir primitively social definition. A vast majority of interactions between individuals were o f limited duration and non-violent in nature. It was contemplated that these confrontati ons most commonly occur at or near nest entrances and were simply mistakes in locating a burrow. Any prolonged interactions were between males and females only an d were determined to be mating behavior and non-aggressive in nature. It has also been speculated that females prefer certain nesting sites and that the aggressive inter actions observed resulted from the search for abandoned nest sites or as a result of competit ion for limited available substrate in which to make nests. Cleptoparasitism of pollen was also thought to spark aggressive interactions, though the study lacked sufficient da ta to support this hypothesis (Roubik et.al 1984). Prior experiments with C. luctuosa including Hubbard (1997), Yang et al. (1996) and Calabrese (1998), which studied nest ownership and behavior, have not been able to produce sufficient data to determine the precise le vel of sociality, nest ownership or the extent of interactions of bees in vicinity of one a nother. This study aims to use observations and speculations gathered from previou s studies to further examine the extent of aggregations behavior and nest ownership in C. luctuosa in hopes of furthering the understanding of this primitively social bee. I hypothesize that C. luctuosa is a solitary bees because of results from previous stud ies and predict that interactions between females are random in nature.
METHODS The project was performed in Monteverde, Puntarenas Province, Costa Rica on the Pacific slope of the continental divide. The unpac ked soils of the south shoulder of the clay access road to the Cerro Amigos television tow ers at approximately 1800m in elevation were chosen for this study. The surface area of the road was avoided due to vehicle traffic and low nest density, which has mos t likely resulted from the former. A 7m x 2.5m area was chosen on the basis of high acti vity and high nest density. This plot contained 53 burrow entrances of which 50 were marked and observed for this study. Leaves of Clusia sp. were initially chosen to cryptically mark nest entrances, but the bees did not react well to them. In some cases an individual would simply hover around the nest entrances and repeated ly bump the leaf, but would not enter the nest. These leaves were replaced with smaller and less distracting, numbered flags placed no more than two inches away from the burrow entrance. These flags were not only less distracting to the bees, but allowed for more accuracy in locating individual nests from my position across the road approximatel y three meters away. The aggregation was observed between July 21st and July 31st for a total of five days from 10:00 a.m. each morning until no less tha n 4:00 p.m. Individuals were trapped using Ziploc bags placed over nest entrances and he ld in place with four to six 75mm nails after they were observed entering. Nest numbe r, duration of stay, time of day, and weather conditions were noted immediately after the trap was set and when the bee exited the bag was pinched off around it and the trap was removed. Initially entomologistÂ’s forceps were used to hold the individuals while the y were painted, but it was found that by simply holding the bee through the plastic bag w hile, allowing it plenty of air so as not to suffocate it or cause over inhalation of paint f umes, was much easier for both parties involved. Bees were marked on the dorsal surface o f their thorax with solid colors or stripped patterns of two or three varying colors of oil-based paint. These patterns of colors along with an assigned number were subsequen tly used to identify the individual. Red, orange, yellow, blue, green and silver were us ed for this process. The paint used was determined to have no adverse effects on the fl ight or behavior of the bees as there was no change in behavior following marking. Durin g the painting process, sex of the bee was noted as well wing wear to determine the ap proximate age of the individual. Severe wing wear was a sign of older individuals wh ereas wings that were entire characterized younger individuals. They were held for three minutes to allow the paint surface to dry and were then placed in a holding ja r for another three minutes to ensure complete dryness. After the first day of collection any new individuals collected were inspected with a 10x magnifying glass for traces of paint to ensure that they were in fact novel. Once marked, the bees were able to be observed with more accuracy. Because of their high density, all nests were able to be obser ved simultaneously allowing the functions of the colony as a whole to be seen more simply. Throughout the five day span marked individuals were observed and the nest numbe r, duration, time of day, and weather were noted every time an individual entered a nest. Each visit fell into one of three categories of time which determined the possi ble purpose of the visit. Individuals that entered a nest only momentarily fell into the first category, which characterized entering a wrong nest in an attempt to find a home nest. The second category, in which
individuals entered a nest for less than five minut es characterized an exploratory entrance, whether to raid pollen stores or in an at tempt to claim a new nest. Individuals that inhabited a nest for over five minutes fell in to the third category. These individuals are most likely to be the nests formal owners and a re probably depositing pollen, ovipositing, or are improving their nest site. The se distinctions differ from the ones made in Otis et al. (1982), which separated categories i nto visits of less than one minute and greater than one minute because it is believed furt her grouping is necessary in order to understand the social behaviors of this bee. All s ocial interactions observed were recorded along with the time at which they occurred as well as the sex of the parties involved. Special note was made of interactions tha t appeared to be aggressive in nature, including a complete description of the altercation RESULTS Throughout the course of this study, 30 females wer e marked and observed. Of the 50 nests observed, 28 were inactive and received no vi sitation (Figure 2). Despite this fact an average of 5 new burrows appeared each day througho ut the five day observation period. Though there was a visible pattern of nest ownershi p and the majority of individuals (23/30) observed visited one nest only (Figure 3), there were also 14 observable cases when a single nest was visited by more than one bee with the maximum number of visitations being seven bees (Figure 2). Of the in stances in which individuals were observed inhabiting the same nest nearly all occurr ed for no more than one day. There was only one observable instance that two females s hared the same nest for two days. Duration of nest visitation was unevenly distribute d between the three categories. 10 of 58 nest visitations lasted for less than 30 s econds and were attributed to confusion of nest site (Table 1). Then 20 of 58 nest visitati ons lasted less than five minutes, but greater than 30 seconds and were deemed exploratory in nature (Table 1). Finally, 28 of 58 nest visitations were greater than five minutes in duration and indicated formal nest ownership (Table 1). Individuals with known home ne sts were observed continuously searching for new nest sites, constantly testing th e substrate of new locations and investigating other burrows. There was an increase d density of nest entrances in areas where the substrate was less fractured, softer and more uniform. Most interactions observed were, as noted in previo us studies, non-aggressive in nature though some of these interactions were diffi cult to classify with absolute certainty. Of the 17 interactions observed, all contained sole ly females and only two were deemed aggressive. In both cases a second bee entered an already inhabited burrow for an extended period of time and the first bee grappled head to head with the second, which was physically pushed from the nest. During one pa rticularly aggressive confrontation the turret of the nest was destroyed by these aggre ssive actions. In each case there was a clear victor who returned to the nest to continue i ts work. Most interactions on the ground occurred in areas of high nest density, whic h most likely caused a confusion of nests that trigged the interactions. On more than one occasion tiger beetles of the species Pseudoxychila tarsalis was observed stealing previously occupied nests. In the latter case the beetle would simply occupy the burrow unti l the bee returned and not allow the bee to reenter the nest, severing the leg of one in dividual. These beetles were observed in very high densities within the area of study, densi ties of three beetles per square meter
were common and densities of up to six beetles per square meter were observed. Homeless bees are thought to contribute to the nonrandom sampling seen in this study, in which a select few individuals were observed a f ar greater number of times, and often had stays of short duration (Figure 4). A chi-squa red test was performed for this data (1.754438), results were non-random. DISCUSSION Findings of this study indicate single nests typica lly contain only one bee at a time, but can have more than one inhabitant as well, though r are. Of the instances in which individuals were observed inhabiting the same nest nearly all occurred for no more than one day. In the cases of two females sharing a nest for more than one day it is possible but unlikely that they simply did not meet each oth er. This sharing of nests may point to cooperation within the colony or simply a fluke. T he irregular dispersion of nests seen in this colony is likely be fueled by scarcity of viab le substrate for nest building, cleptoparasitism, or cooperation. Little of the da ta collected supports the idea of cooperation between or among individuals. Though s everal individuals used more than one nest over the observational period the overall trend was that each bee used only one nest (Figure 1). Compared to a Poisson distributio n by chi-square (2.344086), results were non-random. The use of two or more nests coul d be an adaptation to avoid total loss in the event of nest predation or cleptoparasi tism by flies or beetles (Hanson and Gauld 1995). The duration and behavior before entering a nest is used to determine the purpose of the visit and nest ownership. The momentary entr ances that made up the majority of observed visits indicate that the bees are most lik ely searching for new sites. Whether it is their home nest or a new nest to overtake is not kn ow for each case and is unclear on the whole. Due to the beeÂ’s strong navigational abilit y as described by Illes (1993) it is unlikely that the bees are randomly searching for t heir own nest entrance. However, the navigational ability as described in the study was over longer ranges and this ability may differ at shorter ranges. Stays of longer duration, but less than five minutes, were characterized as exploratory in nature and likely i ndicate an attempt to steal a previously occupied burrow for reasons mentioned in the follow ing paragraph. Stays lasting longer than five minutes could be an indication of formal nest ownership. The lack of an explicit nest owner has most likely led to the cleptoparasitism observed in the study, as well the aggressive inter actions seen. Theft of nest sites by P tarsalis has forced individuals to seek new nest sites. T his is likely to have led lead to increased cleptoparasitism between individuals of C. luctuosa given the high density of the beetle in the beeÂ’s habitat. Because these ind ividuals inhabit exposed soil habitats only, the lack of viable substrate available for us e once a colony has grown may also fuel theft of nests and restrict the development of soci ality. Habitat in this case is restricted even further by the presence of the access road whe re substrate is unyielding and disturbance is high due to vehicle traffic. Though there are many reasons for aggressive intera ctions to occur, the absence of these interactions indicated that these bees are not aggressive in nature and are relatively indifferent toward each other. The major ity of interactions, even in prolonged
instances, were not aggressive in the least. The t wo instances of aggressive confrontation seem to be very provoked, both of which, likely inc luded attempted nest or pollen theft. The results of this study conclude that C. luctuosa is a generally solitary bee. Though there is some evidence to support a hypothesis that these bees are cooperating on some level, there is also a quantity of data to support the contrary. Competition between individuals most likely reflects the huge energy ex penditure associated with building nests, which are worth both stealing and protecting even aggressively. Despite the hostile behavior observed, the beeÂ’s ability to tol erate each other in such close proximity may indicate a step toward a greater sociality. Th ere are still many unknowns in reference to the biology and behavior of C. luctuosa. Further studies with longer observational periods are needed to resolve many of the debatable behaviors observed. ACKNOWLEDGEMENTS First and foremost, a great thanks goes out to all of the people that assisted in the design and execu tion of this project. Thank you Sonali Gandhi for your exp ert assistance in data gathering and company during long rainy days on the clay road. My mama Tica, An a Elena Loria, for putting up with my clay caked clothes day after day I would also like to thank Tania Chavarria Pizarro for my project idea. LITERATURE CITED Calabrese, J.M. 1998 Nesting Behavior and Natural History of Crawfordapis luctuosa (Apidae: Diphaglossinae) Spring 1999 Tropical Ecology and Conservation. CIEE. Hanson, P.E. and Gaule I.D. 1995 The Hymenoptera o f Costa Rica Oxford University Press. Oxford, New York, Tokyo Hubbard, K.M. 1997 Nesting Behavior of Crawfordap is luctuosa (Apidae:Diphaglossinae) Fall 1997 Tropical Biology and Conservation. CIEE. Illes, A. 1993. Homing ability of Crawfordapis luctuosa. Fall 1993 UCEAP Tropical Biology Program. Nadkarni, N.M. and Wheelwrighr N.T. 2000 Biotropic a Oxford University Press. Oxford, New York Otis, G.W.,R.J. McGinley, L. Garling, L. and L. Mal aret. 1982 Biology and systematics of the bee genu s Crawfordapis (Colletidae, Diphaglossinae). Psyche 89: 279-296. Roubik, D.W. and C.D. Michener. 1984 Nesting biolo gy of Crawfordapis in Panama (Hymenoptera, Colletidae). J. Kansas Entomological Society 57: 6 67-671. Wilson, E.O. 1971 The Insect Societies. Harvard University Press. Cambridge, MA, USA. Yang Y., C.T Wuellener and C.S. Scott. 1996 Float ing and fidelity in nest visitation by Crawfordapis luctuosa (Hymenoptera:Colletidae) Springer Publish ing, New York, NY
Table 1. Number of nest visits as classified in thr ee categories of time. Time spent in nest <30 seconds Time spent in nest <5 minutes but >30 seconds Time spent in nest >5 minutes 10 20 28 Figure 1. Frequency of nest use 0 2 4 6 8 10 12 14 16 18 20 1234567 # of Separate Nests Visited
Figure 2. Frequency nest use per nest Nest # 0 1 2 3 4 5 6 7 8 1471013161922252831343740434649 0 1 2 3 4 5 6 7 1357911131517192123252729 Individual # Figure 3. Number of nests visited by each individua l
Figure 4. Number of times individuals were observed 0 5 10 15 20 25 123456789 # of Total Nests Visited# of Individuals