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Maternal defensive behavior of Umbonia ataliba Treehoppers

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Title:
Maternal defensive behavior of Umbonia ataliba Treehoppers
Translated Title:
Comportamiento defensivo maternal de los salta hojas Ataliba Umbonia ( )
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English
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Anvik, Sarah
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Membracidae   ( lcsh )
Insects--Behavior   ( lcsh )
Membracidae
Insectos--Comportamiento
Tropical Ecology 2006
Maternal defensive behavior
Ecologia Tropical 2006
Comportamiento defensivo maternal
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Reports   ( lcsh )
Reports

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Abstract:
A population of Umbonia ataliba (Homoptera: Membracidae) located between 1300 and 1500 m in Monteverde, Costa Rica was studied from October to November 2006. The maternal defensive behavior exhibited by these subsocial insects toward nymphs of different developmental stages was experimentally investigated. The purpose of my study was to determine how the defensive behavior changed from eggs to adults and in response to two different predator types. I attached dead wasps to long wooden sticks and then simulated predator approaches toward family groups of eggs, second instar and fourth instars nymphs. I found that the defensive behavior by females guarding nymphs of different ages differed from random in type and frequency. I determined that female parents with second instars were the most aggressive, and that the most common behavior type among all groups proved to be kicking. In regards to the behavior changes exhibited against predator types, females were generally more aggressive when approached with the black wasp, but there was no significant change in the frequency of behaviors.
Abstract:
Estudie de octubre a noviembre del 2006 una población de Umbonia ataliba (Homoptera: Membracidae), ubicado entre los 1300 y 1500m en Monteverde, Costa Rica. Estudie la conducta defensiva maternal en las diferentes etapas de desarrollo de las ninfas. El propósito de mi estudio fue determinar como la conducta defensiva cambia de los huevos a adultos y en respuesta a dos tipos diferentes de depredadores.
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Maternal Defensive Behavior of Umbonia ataliba Treehoppers Sarah Anvik Department of Environmental Studies College of Arts and Sciences University of Colorado, Boulder ABSTRACT A population of Umbonia ataliba (Homoptera: Membracidae) located between 1300 and 1500 m in Monteverde, Costa Rica was studied from October to November 2006. The maternal defensive behavior exhibited by th ese subsocial insects toward nymphs of different developmental stages was experime ntally investigated. The purpose of my study was to determine how the defensive behavi or changed from eggs to adults and in response to two different predator types. I attached dead wasps to long wooden sticks and then simulated predator approaches towa rd family groups of eggs, second instar and fourth instars nymphs. I found that the defensive behavior by females guarding nymphs of different ages differed from random in type and frequency. I determined that female parents with second instars were the most aggressive, and that the most common behavior type among all groups proved to be kicking. In regards to the behavi or changes exhibited against predator types, females were genera lly more aggressive when approached with the black wasp, but there was no significant change in the freque ncy of behaviors. RESUMEN Estudie un poblacin de Umbonia ataliba (Hom optera:Membracidae) localizada entre de 1300 y 1500 m en Monteverde, Costa Rica de Octubre a Noviembre 2006. Estudie la conducta defensiva maternal en las diferentes etapas de desarrollo de las nintas. El propsito de mi estudio fue a determinar co mo la conducta defensiva cambia de huevos a adultos y en respuesta a dos diferentes depr edadores. Concret av ispas muertas a palos de madera y simul el aceramiento del depredador en grupos familiares de la madre con huevos y nintas a diferentes ed ades. Encontre que la conduc ta defensiva de las hembras al proteger las ninfas, difiere de aleatoria en tipo y frequencia. Determin que madres con ninfas en segundo estado de desarrollo son las ms agresivas, y el tipo de conducta ms comn entre todos grupos fu e patear. Consider que la conducta exhibida contra los despredadores difiri porque las hembras estaban mas agresiva se acerc una avispa negra, pero con el cambio en la conducta no fue significativo. INTRODUCTION 1

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Females of the genus Umbonia are semelparous, with the ability to produce only one brood of young in their lifetime. Different types of maternal behavior make them subsocial insects. Accord ing to Tallamy and Wood (1986) subsocial behavior is the most primitive level of soci al interaction involving pare nts and offspring. Subsocial behavior of treehoppers, including Umbonia is restricted to maternal care of eggs and nymphs (Chung-Ping et al. 2004). Egg guarding is the most common form and is defined as the female remaining on top of the egg mass for a period of time after oviposition. In this case the body of the female is used as a shield to protect her young from predation and parasitism (Chung-Ping et al. 2004). A ccording to Zink (2003) guarding behaviors are important for the protection and survival of eggs. In U. ataliba sibling s are reared together under the care of the mother who embeds 50-100 eggs into the branch tip of the host plant (Mimosaceae) and then tends the offspring throughout development (Masters 2000). The development stages include eggs, nymphs and adults. Egg development is lengt hy and usually lasts about 40 days (Masters 1994). Nymph development, in which the young ma ture from first to fourth instars, lasts approximately 44 days (Masters 1994). The mother will remain with her young until they reach adulthood. Since the female is semelparous, her investment in the brood is extremely high and thus she exhibits several types of parent al care. Tallamy (1983) describes parental care as any parent-offspring interactions that promote the survival, growth, and development of immature insects. Two type s of parental care exhibited by females of this species include behaviors that physica lly protect the young from danger and those that facilitate offspring feeding. Following egg guarding the mother drills a series of slits in a spiral around the branch tip using her ovipositor (Wood 1973). When the nymphs hatch they cluster around the slits, which facilitate access to the plants vascular tissue. The nymphs remain in this aggregation ar ound the plants host stem with the mother positioned below (Cocroft 1999). The placement of the mother and the nymphs are essential in allowing the mother to provide another type of pa rental care, physical. Maternal defensive behavior in Umbonia is crucial for the survival of the brood as they are vulnerable to a number of invertebrates and are high ly preyed upon. Their most common predators are wasps, and in Mont everde, assassin bugs (Reduuvidae) are common as well. In the case of Umbonia crassicornis wasps approach family groups from the air and land on or near the aggregation, attempting to remove nymphs through biting and then pulling them from the branch (Cocoroft 2002). In order to protect the brood, the females defenses have become ex tremely specialized and include behaviors such as kicking, wing fanning and running toward s the predators. These actions are often effective in deterring predator s and therefore increase the su rvival of the brood. Visual and chemical stimuli are both important in allowing the mother to sense predators and actively defend her young (Wood 1975). A study by Wood (1973) on U. crassicornis showed that when a brood was left without the mother, 100% of them died within ten days. Maternal defense is therefore impor tant for both eggs and developing nymphs. The purpose of my project was to obse rve and compare the mothers protective behavior from eggs to adults in U. ataliba. As the nymphs age, they occupy more space on the branch, making it increasi ngly difficult for the mother to defend them. At the same time, the nymphs become better suited to defend themselves. My hypothesis is that 2

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the mother will defend her brood through all developmental stages but that the effectiveness of the behaviors will vary. My prediction is that the frequency of defensive behavior types will differ as the nymphs age. METHODS AND MATERIALS Study site My study was conducted on a fallow pasture at approximately 1500 m in Monteverde, Costa Rica from October to November 2006. Ten years ago, trees of family Mimosaceae (known host) were planted on this land and occupy much of the property. Many of the tree species, such as Inga punctata are clumped, with up to f our individuals in close proximity of eachother, while ot hers are solitary, such as Zygia palmanum Tree species suitable for examination included Zygia palmanum, Inga punctata, Inga sierrae and Cojoba costaricensis Group location Umbonia ataliba groups were located on branch tip s of Mimosaceae trees and covered with mesh bags. This ensured that the gr oups would be safe from predation. Groups were monitored for nymph maturation. Defensive behavior experiment Mothers with eggs, second instars and fourth instars were tested for defensive behaviors against simulated black and yellow wasps, both known predators. In order to test the maternal defensive behaviors, it was nece ssary to imitate incoming predators. To accomplish this, I first collected a dozen dead wa sps, half of them black and half of them yellow. I then carefully atta ched each of the wasps to the pointed end of a long wooden sticks using super glue. I al ways glued the stick to the unde rside of the abdomen, leaving the wasps unaltered on the top to create a more realistic appearance. In order to test the females behavior certain abiotic factors were necessary including warm temperatures without direct precipitation; these conditions increased the likelihood of the female displaying active re sponses. A good indicator of a favorable testing day was the presence of active butterflies. As I a pproached the group with the wasp, I would gently wiggle the stick in or der to simulate the appearance of a flying wasp. The group was approached from both the front and the rear, and the wasp was moved up and down the branch. The wasp was brought close enough to the female and the group for direct contact to take place. I tested each group for two minutes; making tallies next to the demonstrated behaviors. In order to give the female a chance to respond, I allowed her to show a behavior at le ast five times before stopping to record the data. After two minutes had passed, I made final tallies and re-covered the group. In order to minimize infection, I removed any dead leaves or debris from the mesh bag before placing it over the bran ch, being careful not to dist urb the mother or the young. With each group I ran tests in a similar fashion, noting environmental conditions and predator type before I be gan. The five types of behavi or I tested for were kicking, fanning, running, covering and tilting by nymphs (T able 1). Each family group was tested for these behaviors on two separate occasi ons, once with the black and once with the 3

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yellow wasp. The order of te sting varied; some groups were approached with the black wasp first and others with the yellow. Statistical Analysis A 3x6 contingency table was constructed and ex amined with a Goodness of fit test; used to analyze maternal defensive behavior agai nst two predator type s. Running behavior was not included in the analysis because it never occurred more than once for any developmental age and for some groups it never occurred at all. The tilting behavior is mainly a defense of the nymphs and not of the mother, and hence it was analyzed separately. A Goodness of fit test was th en used to analyze the frequency of demonstrated maternal behaviors. A Chi-s quared test of independence was also run to determine if females are more aggressive overall towards a particular wasp color morph. RESULTS Among the four species of the family Mimosaceae examined for this project, individual females were found on Z. palmanum and I. sierrae but family groups were only present on I. punctata I studied 33 different females and their families. The difference in observed versus expected values was signi ficant as it differed from random (Goodness of fit test, 2 = 131.696, p < 0. 0001, df=10) (Fig.1). This indicates that the frequency of the mothers behavior deviates from random. Defense of eggs, second instars and fourth instars For females with eggs, the most common type of behavior was kicking with 97 (yellow) and 106 (black) occurrences, followed by fanning (4 and 3 respectively). Mothers with eggs more often than expected by random, whereas the frequency of fanning is lower than expected by random (Figure 2) Next, mothers with second instar nymphs also favored kicking, exhibiting this behavior 134 (yellow) and 154 (black) times. However, the expected value for kicking was less than actually observed. By contra st, mothers with second instars fanned and covered more than expected, showing more occurrences of covering (43 and 56) than fanning (26 and 36) (Fig.2). Finally, mothers with fourth instar nymphs also demonstrated kicking more than any other defensive behavior, demonstrati ng it 98 times with the yellow and 121 times with the black wasp. Covering was rare for mo thers with this age, who showed this type of behavior only once for both predator types. Similarly, the mothers did not choose to fan very often, although the numbers are signif icantly higher for fanning than expected by chance (Fig. 1). Also interesting to note is the high number of tilting behavior examined by the nymphs of this age (Table 2). Although tilting is a behavior of the nymphs rather than adults, I compared its frequencies and found that it too differed in frequency from one developmental stage to the next. Defensive behavior The defensive behavior most common among all group ages was kicking (Fig. 3). Kicking behavior occurred at the highest fr equency with second instar groups, followed by mothers with fourth instars and lastly in dividuals with eggs. Covering was the next 4

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most common behavior and was only used with seconds, followed by fanning, also used mainly for seconds (Fig. 3). These examinations allowed for the conclusion that mothers with second instar nymphs are the most aggr essive of all mother s tested. The total number of defensive behaviors exhibited by the mothers for eggs, second instars and fourth instars were 212, 449, and 256 respectively. Responses to Black versus Yellow Wasp Females respond to black and yellow wasp s with the same frequency of defense behaviors. However, the Chi-squared test of independence revealed that mothers are overall more aggressive toward black wasps than they are toward yellow wasps showing significance at the .05 level ( 2=8.27, df=1) (Figure 4). DISCUSSION My hypothesis for this study was that the mother would defend her brood through all developmental stages but that the effectiv eness of different defense behaviors would vary. Thus my prediction was that the frequency of de fensive behavior types would differ as the nymphs aged. My prediction was confirmed in this experiment, thus supporting my hypothesis. As predicted, fema le parents guarded their brood through all stages of development. This is explained by the fact that the mother is semelparous and the survival of the young depends on her. In treehopper species that lay only one clutch, the cost of remaining with the brood are expect ed to be so minimal that the female should always display extended care (Zink 2003). I also found that the mothers behaviors varied throughout nymphal developmental stages because some behaviors were more effective than others in deterring predators. For example, c overing is not as effective of a behavior for fourth instars as it is for s econds because the nymphs at this age are too large, making it difficult and time consuming for the mother to carry out this behavior. Although the frequency of different behavi ors changed with th e age of the nymphs, kicking was the most co mmon behavior overall. In this study, I found that females with eggs showed the least amount of response and movement when approached by a predator. In the case of U. crassicornis Wood (1983) believes that lack of movement e nhances cryptic coloration and reduces the vulnerability of parent females while guard ing eggs. The main behavior exhibited by mothers with eggs proved to be kicking, with some fanning. The frequency of behaviors shown in this age group is likely due to their position on the branch. In the later stage, mothers with second in stars proved to be very aggressive. They favored kicking over other behaviors follo wed by covering and then fanning. Mothers with second instars were the only groups to exhibit covering behavior multiple times during a single test. This change in frequency can be attributed to the effectiveness of behaviors used. Although kick ing is the most effective wh en the predator is nearby, when the predator is not within reach, other behaviors must be used. Due to the size and vulnerability of nymphs at th is age, covering appears to be a quite effective and easily accomplished way of protecting the brood from predator invasion. The final groups, fourth instars are uni que in that they too act to defend themselves against predators, mostly by til ting. However, when looking solely at maternal defensive behavior, I found that as with other groups, mo thers chose to kick 5

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more than anything else. The next highest frequency of behavior observed was fanning. This can be explained using a study on U. crassicornis, which found direct movement to be the most effective, followed by fanning, which provides defense without movement toward the predator (Wood 1974). Based on this evidence, it can be concluded that mothers show varied defensive behaviors to be effective at deterring predators. My study is unique in that is the first to compare behavior between developmental stages in Umbonia Similarly, it is the first to test for different responses toward predators of different types. Although significant results were not found for a change in frequency of behavior between predators, the females prove to be more aggressive toward the black wasp; although it is unknown exactly why. Some types of black wasps in Monteverde are known to be parasites, though the ones used in the study are not. It is possible that the females act more aggressive ly because they perceive these wasps as being parasitic, however, this pr oposal is extremely difficult to prove. In future studies, it would be interesting to include reduuvid bugs as predators. Unlike wasps, which approach from the air, these insects approach the group by walking toward them on the branch. Also, if time allowed, it would be helpful to track the same groups throughout developmental stages to see how behavior ch anged for that specific female. These kind of data would allow for a more detailed anal ysis, although similar results would likely be obtained. ACKNOWLEDGEMENTS I would like to first of all thank Karen Master s for suggesting this idea for a project. Her assistance, encouragement, motivation and common love for this unique insect have helped to guide me through the research process and allowed me to be successful with my project. At times when I was frustrated and ready to gi ve up, she pushed me to keep going and try harder. Without th is I would not have made the progress I did in this short span of time. I also want to thank Alan Masters for supporting my ideas and talking me through my frustrations. Next, I would lik e to thank Tom and especially Camryn for being awesome TAs and helping me work th rough issues with research, proposals and figures. Your help is extremely appreciated and without it I woul d have lost endless hours of my life attempting to sort through the inter-workings of Excel and Stat-View. Finally, I want to thank my be st friend Katie Korus for always being supportive. Without her constant willingness to listen and lend a hand or a hug, I never would have made it through all of this. LITERATURE CITED Chung-Ping, Lin, Danfourth, Bryan N. & Wood, Thomas K. 2004. Molecular phylogenetics and evolution of matern al care in membracid treehoppers. Systematic Biology 53:400-426. Cocroft, Reginald B. 1998. Offspring pare nt communication in a subsocial treehopper (Hemiptera: Membracidae: Umbonia crassicornis). Behavior 136:1-21. Cocroft, Reginald B. 2002. Antipredator defens e as a limited resource: unequal predation risk in broods of an insect with maternal care. Behavioral Ecology 13:125-133. 6

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Hernick, Charles A. 2001. Distribution of Host Species Ranges of Umbonia ataliba and Umbonia crassicornis and the Potential for Interspecific Competition. In CIEE Fall 2001 Tropical Ecology and Conservation pp. 25-33. Masters, Karen L., Masters, Alan R. & Fors yth, A. 1994: Female-biased sex ratios in the neotropical treehopper Umbonia ataliba (Homoptera: Membracidae). Ethology 96: 353-366. Masters. Karen L. 2000. Sex and Social Life of Umbonia Treehoppers. In: Monteverde: Ecology and Conservation of a Tropical Cloud Forest Nadkarni, N.M. and N.T. Wheelwright eds. Oxford University Press, New York, New York, pp. 103-104. Tallamy, Douglas W. 1983. Insect Parental Care. BioScience 34:20-24. Tallamy, Douglas W. and Wood, Thomas K. 1986. Convergence patterns in subsocial insects. Annual Reviews of Entomology 31:361-390. Wood, T.K. 1973. Aggregating Behavior of Umbonia crassicornis (Homoptera: Memracidae). Canadian Entomologist 106:169-173. Wood, T.K. 1974. Alarm Behavi or of Brooding Female Umbonia crassicornis (Homoptera: Memracidae). Annals of the Entomological Society of America 69:340-344. Wood, T.K. 1983. Umbonia crassicornis (Bicho Espino, Thorn Bug, Treehopper). In: Costa Rican Natural History D.H. Janzen, ed. The University of Chicago Press. Chicago, Illinois, pp. 773-775. Zink, Andrew G. 2003. Quantifying the costs and benefits of parental care in female treehoppers. Behavioral Ecology 14:687-69 7

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0 20 40 60 80 100 120 140 160 180 kicking fanning coveringBehavior Types Mom with eggs Mom with 2nd Mom with 4th 0 20 40 60 80 100 120 140 160 kicking fanning coveringBehavior Types Mom with eggs Mom with 2nd Mom with 4th Figure 1: The frequency of defensive behavi ors (kicking, fanning a nd covering) exhibited by the mother in response to the black wasp (A) and the yellow wasp (B) across three developmental stages. Asterisks indicate a observed behavior which deviated from random ** * * ** * B A 8

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0 50 100 150 200 250 300 350 400 450 500 Mom w/eggsMom w/2ndMom w/4th Developmental Stages covering fanning kicking Figure 2: The frequency of be havioral occurrences between developmental stages. This graph demonstrates the aggressiveness of mo thers with second inst ar nymphs compared to other developmental age groups. 0 100 200 300 400 500 600 700 800 kicking fanning covering Defensive Behaviors Mom w/4th Mom w/2nd Mom w/eggs Figure 3: The frequency of observed behavi ors occurring across developmental stages. This graph demonstrates that the most common observed behavior is kickin 9

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0 100 200 300 400 500 600 Black wasp Yellow wasp Predator type # of defensive behaviors Figure 4:The total number of observed mate rnal defensive behaviors exhibited in response to black and yellow wasps. Females showed more aggressive behaviors toward the black wasps than the yellow wasps. Table 1: Descriptions of defensive behavior types Behavior Description Kicking Fanning Running Covering Tilting Took place when the mother was close enough to the predator to touch th e wasp with one of her hind legs Took place at various proximities, consisted of mother aggressively fluttering her wings Took place when the wasp was to on the opposite side of mother, and she quickly move from the terminal end of the branch toward it Took place when predator was out of range for physical contact, consisted of her inching along the branch, positioning herself on top of the nymphs Took place when nymphs attempted to defend themselves by lifting their abdomens in a synchronized wave 10

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11 Table 2: Tilting behavior examined over thr ee developmental stages with two predator types (Yellow and Black wasps). Eggs Black Seconds Black Fourths Black Eggs Yellow Seconds Yellow Fourths Yellow Tilting 0 2 58 0 4 62


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A population of Umbonia ataliba (Homoptera: Membracidae) located between 1300 and 1500 m in Monteverde, Costa Rica was studied from October to November 2006. The maternal defensive behavior exhibited by these subsocial insects toward nymphs of different developmental stages was experimentally investigated. The purpose of my study was to determine how the defensive behavior changed from eggs to adults and in response to two different predator types. I attached dead wasps to long wooden sticks and then simulated predator approaches toward family groups of eggs, second instar and fourth instars nymphs. I found that the defensive behavior by females guarding nymphs of different ages differed from random in type and frequency. I determined that female parents with second instars were the most aggressive, and that the most common behavior type among all groups proved to be kicking. In regards to the behavior changes exhibited against predator types, females were generally more aggressive when approached with the black wasp, but there was no significant change in the frequency of behaviors.
Estudie de octubre a noviembre del 2006 una poblacin de Umbonia ataliba (Homoptera: Membracidae), ubicado entre los 1300 y 1500m en Monteverde, Costa Rica. Estudie la conducta defensiva maternal en las diferentes etapas de desarrollo de las ninfas. El propsito de mi estudio fue determinar como la conducta defensiva cambia de los huevos a adultos y en respuesta a dos tipos diferentes de depredadores.
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