The Interaction s of h erbivory , ant species and MÃ¼llerian body production in Cecropia obtusifolia (Cecropiaceae) Laura Hurley Department of Fisheries, Wildlife and Conservation Biology, University of Minnesota RESUMEN El mutualismo es prevalente en todos los ecosistemas. La interacciÃ³n Cecropia Azteca es un ejemplo de un mutualismo prominente muy bien estudiado en los trÃ³picos del nuevo mundo. Las hormigas Azteca actÃºan como defensores biÃ³ticos atacando herbÃvoros y lianas que atacan los Ã¡rboles. En retorno, reciben nutrientes de la planta en la forma de cuerpos Mullerianos (CM) en forma de proteÃna y un lugar para vivir en el tallo hueco del Ã¡rbol. No es un mutualismo especialista, y mientras las especies muestran una preferencia por condiciones ambientales, varias especies de hormigas son capaces de vivir en una especie de Cecropia. Diferentes especies de hormigas tienen diferentes comportamientos que les dan diferentes respuestas por la planta. Este estudio exami na el grado de herbivorÃa y la producciÃ³n de CM en C. obtusifolia dependiendo de las especies de hormigas asociadas. Se muetrearon 40 individuos de C. obtusifolia en la regiÃ³n de Monteverde en Costa Rica. Cuando las hormigas estÃ¡n presente se colectaron e identificaron. Cuando hay hormigas presentes, existe cerca de 60% menos herbivorÃa que cuando no hay hormigas. El grado de herbivorÃa no difiere entre especies y no esta relacionado con la producciÃ³n de CM, sugiriendo que la presencia de hormigas disuad e la herbivorÃa pero ninguna especie es mejor que la otra. Existen diferencias en la producciÃ³n de CM de acuerdo con la especie de hormiga asociada a la planta, plantas con A. xanthochroa producen menos CM que cuando no hay hormigas presentes en las plantas y menos que otros Ã¡rboles con diferentes especies de hormigas. Atribuyo esto a la predicciÃ³n que los comedores de floema que las hormigas mantienen dentro de las plantas, lo cual requir e una mayor inversiÃ³n energÃ©tica por parte de la planta y por lo tanto menor producciÃ³n de CM, son mÃ¡s abundantes en Ã¡rboles hÃ¡bitados por A. xanthochroa. Cecropia obtusifolia sin hormigas producen mÃ¡s CM que los Ã¡rboles con hormigas, lo cual se puede debe r a que los Ã¡rboles tratan de reclutar colonias de hormiga para la defensa. La relaciÃ³n Cecropia hormiga no es tan simple como la presencia o ausencia de hormigas, la respuesta de las plantas varÃa de acuerdo a las especies y el comportamiento de las mism as. ABSTRACT Mutualisms are prevalent in every ecosystem. The Cecropia Azteca interaction is an example of a well studied and promin ent mutualism in the neotropics. Azteca ants act as biotic defenders by attacking herbivores and vines that assault the tree. In return, they receive nutrients from the Cecropia in the form of protein rich MÃ¼llerian bodies (MBs) and a place to live in the hollow stem of the tree. It is not a specialist mutualism, and while species show some preference to environmental con ditions, multiple species of ants are able to live in one species of Cecropia. Different species of ants have different behaviors which elicit responses from the tree. This study examined how herbiv ory and rate of MB production of C. obtusifolia varied with ant presence and species. Forty C. obtusifolia in the Monteverde region of Costa Rica were sampled. When ants were present they were collected and identified. Herbivory was calculated for each tree as was rate of MB production. When ants were present, there was about 60% less herbivory than when ants were not present. Herbivory did not differ between species and w as not related to MB production, suggesting that the presence of ants deters herbivores but one species is not a be tter defender than another. There were differences in MB production according to species. C. obtusifolia inhabited by A. xanthochroa produced significantly fewer MBs than when no ants were present on the tree and fewer than other trees with different ant species. I attribute this to the prediction that phloem feeding coccids that Azteca farm on the inside of
the Cecropia , w hich require the tree to invest more energy in repair and less in MB production , are more abundant in trees inhabited by A. xanthochr oa . Cecropia obtusifolia without ants produced more MBs than trees with ants, which could also be due to trees trying to recruit ant colonies for biotic defense. The Cecropia ant relationship is not as simple as the presence or absence of ants; tree resp onses vary according to ant species and their behavior. INTRODUCTION Interspecies relationships are ubiquitous and fundamental to the functioning of an ecosystem (Herre et al . 1999 ). Mutualisms, simply described as reciprocally beneficial relationships between organisms, are one of the most prominent and important of these re lationships (Rutter & Rausher 2 004). Examples of m utualisms can include pollinators that increase the sexual reproduction of a plant, zooxanthellae that allow for the survival of reef building corals, and mycorrhizal fungi that provide plants with increased nutrients (Herre et al . 1999 ). In order for these mutualisms to evolve, the resource benefit to both parties must be greater than the cost of the relationship (Rutt er & Rausher 2004). In the tropics, many plants develop mutualisms with insects that protect the plant from herbivores in order for the plant to decrease its investment in defensive chemical compounds in the leaves (Janzen 1969). Janzen (1966) demonstrat ed that many ant plant interactions are examples of these co evolved mutualisms. The ant loving plants, termed myrmecophytes, gain herbivore and climber protection while the ants generally gain both domatia and nutrients produced by the plant (Longino 199 1a). The Cecropia and Azteca relationship is a prominent and thoroughly studied neotropical ant plant mutualism (Longino 1989). Cecropia is a pioneer species often found along roads, in pastures, and in tree fall gaps in the forest (Longino 1989). There are four species of Cecropia in Costa Rica, three of which are inhabited by Azteca ants (Burger 1977). Four Azteca species that reside i n Cecropia are present in the Monteverde region, along with three species of Cecropia , one of which, C. angustifolia , does not house ants (Loope 2008). The ant housing Cecropia are inhabited by a founding queen, which enters through the thin prostoma on e ither side of a hollow internode when the Cecropia is less than 1m tall (Janzen 1973). Saplings are usually colonized by multiple species of Azteca queens, each of which produces a small worker force. However, by the time the tree reaches 3 4m in height, there is usually one dominant colony which will soon out compete any other colony present (Longino 1991a). Along with a hollow site to nest in, myrmecophytic Cecropia provide Azteca with glycogen rich MÃ¼llerian bodies which are produced by the trichilium to be harvested by the ants (Janzen 1969, Schupp 1986). Azteca ants provide rigorous defensive behavior when herbivores or climbing vines come into contact with a host Cecropia . Ants will attack insect herbivores and prune encroaching vines, releasing t he Cecropia of these pests and reducing the amount of chemical defenses the tree must produce on its own ( Davidson 2005 ). The presence of this biotic defense dramatically increases the success of the Cecropia (Longino 1991a). Azteca also exhibit behaviors that are detrimental to their host. For example, they farm scale insects on the hollow inside of the tree. These cocc ids feed on the phloem of the Cecropia and provide sugars to the ants in the form of honeydew (Rico Gray & Oliveir a 2007). I mpacts of coccids on the Cecropia are d amaging , but it is yet unstudied how the tree responds to their presence and whether their abundance changes according to ant species (Hunt 2003). According to Longino (1989), Azteca and Cecropia are not considered a specialist mutualism. Multiple species of Azteca are able to inhabit multiple Cecropia species, with the exception being C. angustifolia. In fact, Azteca are not the only ant species that colonizes Cecropia. Many other genera, such as Crema togaster and Pachycondyla, seek out Cecropia as
well ; however, it is unknown whether they participate in a mutualistic relationship with the plant as well or if they simply use the plant for protection and nutrients , essentially acting as a parasite rather than a mutualist (Longino 1991b). Crematogaster and Azteca species do show some differential preference to the environmental conditions that different species of Cecropia inhabit ( Rico Gray & Oliveira 2007, Longino 1989). Furthermore, A. xanthochroa and A. constructor seem to provide better protection for Cecropia than other species of Azteca ( Longino 1991b ). Cecropia obtusifolia relies heavily on ant protection and is therefore especially susceptible to herbivor y and vine encroachment during success ion . Azteca xanthochroa and A. constructor are more aggressive in their defense of their host tree as they are known to defend their tree first and inves t energy in colony reproduction secondaril y ( Longino 1991b ). Therefore, C. obtusifolia inhabited by species of Azteca other than A. xanthochroa and A. constructor have been shown to have a higher mortality rate . Longino (1991a) measured aggressiveness of Azteca species by their speed of response to disturbance, amount of herbivore damage to and presence of patrolling and defensive biting. He found that A. constructor is the most aggressive of Costa Rican Azteca species, followed closely by A. xanthochro a. A. coeruleipennis is thought to be the least aggressive , and A. alfari , showed a combination of aggressi ve and non aggressive behaviors (Longino 1991a). So, if some ant species are better defenders of their host plant , how do es Cecropia respond to these differences? Varying degrees of aggression within the Cecropia inhabiting ants could lead to differences in herbivory, presumably with the less aggressive species allowing more herbivory on the leaves of the tree . However, when determining the response of the tree to the ant species, the detrimental effects that Azteca have on Cecropia, such as the coccids they farm , must also be taken into account. MÃ¼llerian body (MB) production varies in Cecropia (Rico Gray & Oliveira 2007) , but i t is unknown whether this is due to the species of Az teca which inhabits the tree. This study investigate d the rate of MÃ¼llerian body production and herbivory according to the ant species inhabiting trees of C. obtusifolia . METHODS Study Sites This study took place in the Cerro Plano, Santa Elena and CaÃ±itas areas with in the Monteverde zone of Costa Rica during April and May of 2011. Because Cecropia require plenty of light to grow, they usually occur along the sides of roads, trails, and pastures and in light gaps in the forest (Loope 2008) . Thi s study used C . obtu s ifolia trees found in these types of locations as well as in gardens and overgrown pastures located in the CaÃ±itas area. All study sites were open to sunlight, though sites at Bajo del Tigre and trails behind the Butterfly Garden had more shade cover as they occurred along trails within secondary forest growth. All sites were located within the elevational range of C. obtusifolia, from 1000 1400 meters (Janzen 1973).
Cecropia obtusifolia All trees sampled were of the Cecropia obtusifolia species and were 2 4 meters in height . This species was chosen because multiple Azteca species are known to inhabit it and it was prevalent within the given study area. A total of 40 C. obtusifolia were sampled, and were identified in the field b y the presence of 10 13 lobes, the longest leaf having about 30 pairs of secondary veins, and, when present, inflorescences longer than 10cm (Burger 1977). Trees sampled had at least 3 branches because leaves from three separate branches we re tested for herbivory. C. obtusifolia of the pro per height with and without ant inhabitants were used (Fig. 1) . FIGURE 1: Cecropia obtusifolia in a sunny field with overgrowth on the side of the road in CaÃ±itas . Many C. obtusifolia were sampled in this overgrown field and all except for one were occupied by Azteca ant colonies. This particular tree was occupied by A. xanthochroa, had little herbivory, and produced many MBs. Ant Samplings To det ermine if ants were present, C. obtusifolia tree s were shaken vigorously for 1 2 minutes or until ants emerged. If no ants emerged, it was deemed that there was no ant colony occupying that individual tree . Ant species were collected from 28 C. obtusifolia by hand and placed in samp le bags containing ethanol. Two different genera of ants, Azteca and Crematogaster, were found inhabiting the sampled trees. Ants could not be identified in the field so were identified to species in the lab at a later date using the Ants of Costa Rica o nline key compiled by John Longino found at http://academic.evergreen.edu/projects/ants/genera . M Ã¼ llerian Bodies R ate of MÃ¼ llerian B ody (MB) production in C. obtusifoli a was measure d for all but four of the 40 sampled trees. Those four trees were too tall to reach the MB producing trichilia. To measure MB production on the remaining trees, I removed present MBs from 2 trichilia per plant. The newest trichilia (those nearest the top of the tree), produce the most MBs so these were the trichilia I used for sampling on each individual tree . I then encircled the trichilia with Vaseline and covered them with mesh netting to ensure that no ants or outside insects were able to remove newl y pr oduced MBs (Fig. 2 ) . I returned 24 h ours later to remove the mesh and Vaseline and count the MBs produced by each trichilia of the Cecropia.
FIGURE 2 : Trichilium of C. obtusifoli a with newly produced MÃ¼llerian bodies 24 hours after being surrounded by Vaselin e and covered with mesh netting to keep ants and other insects from harvesting MÃ¼llerian bodies. Herbivory Three l eaves were collected from each C. obtusifolia (N=40) to mea sure the amount of herbivory. Since the leaves of most trees were of a reachable height, a knife was used to cut the leaves. For leaves not within reach , a wendii was used. Three different leaves from each plant , all of different ages (young, medium, and old) , were measured for herbivory . This was done to calculate an accurate average since herbivory tends to be greatest on oldest leaves and least on new leaves. The top most full leaf of the plant represented a young leaf, the 2 4 leaf was of intermediate age, and the second leaf from th e bottom represented an old leaf. A 1cm x 1cm grid was used to measure the amount of herbivory on each leaf. Entire leaves were traced on the grid to measure the total amount of squares covered by the leaf. Squares missing more than 25% of their leaf matter were counted as having herbivory. In this manner, total herbivory per leaf was recorded. RESULTS Ants Two species of Azteca , A. xanthochroa and A. constructor, and one species of Crematogaster, C. nigropilosa, were found inhabiting C. obtusifo lia . C rematogaster nigropilosa was only found inhabiting C. obtusifolia that experienced shading from taller canopy trees. However , colonies of both species of Azteca were found in C. obtusifolia in very large and sunny gaps and in more shaded areas along trails. Both A. xanthochroa and A. constructor exhibited aggressive behavior during collection. A zteca constructor colonies usually swarmed the outside of the Cecro pia upon disruption. They were very fast and seen patrolling leav es on occasion. A zteca xanthochroa colonies were often very large, larger than A. constructor colonies, and the ants were very aggressive in their attack, usually biting for defensive purposes. C rematogaster nigropilosa were not aggressive at all and were never observed collecting the MBs on the Cecropia . They were often seen sitting on the leaves or trunk of the Cecropia but were not
disturbed at all when the plant was shaken . In addition, Crematogaster colonies were always extremely small, with nev er more than 5 ants seen on the outside of a single C. obtusifolia. In general, a nts on smaller trees usually attacked less quickly, if at all, and with far less force than colonies of larger trees. M Ã¼ llerian Bodies M Ã¼ llerian body production was significantly different depending on the ant species inhabiting the C. obtusifolia individual (One Way ANOVA, F 4,69 =2.97, P = 0 .0257). Cecropia obtusifolia colonized by A. xanthochroa produced fewer MBs than trees without ants, w ith an average of SD test, P < 0.05). Trees inhabited by A. constructor, C. nigropilosa or no ants did not differ significantly in their MB production, producing an average of 3 5.9, 35.5 and 48.8 MBs per day test, P > 0.05; Fig. 3 ) . However, trees with no ants did produce an average of 12 more MBs per day than those inhabited by A. constructor and C. nigropilosa. FIGURE 3 : Average Mullerian body production per day of 36 C. obtusifolia. Twelve Cecropia without ants, 8 A. constructor inhabited, 7 C. nigropilosa inhabited , and 9 A. xanthochroa inhabited Cecropia were sampled. Error bars represent Â± one standard error of the mean . Herbivory In contrast to M Ã¼ llerian body production versus ant species, herbivory on C. obtusifolia was not related to the ant species inhabiting the plant (One Way ANOVA, F 4,122 =1.65, P =0.1659). Azteca constructor inhabited trees, which had 4.7% average herbivory, was very similar to A. xanthochroa and C. nigropilosa inhabited trees , which showed 5.4 % and 4.9% average herbivory, respectively. When no ants were present, the most damage was done by herbivores on C. obtusifolia trees , with an average of 8.4% herbivory on leaves (Fig. 4 ) . The difference between Cecropias with no ants and trees with ants was not enough to be s tatistically significant, but the results show that there was about a 60% increase in herbivory when ants were not present. 0 10 20 30 40 50 60 None A. constructor C. nigropilosa A. xanthochroa Average MB Production/day Ant Species
FIGURE 4 : Difference in % average herbiv ory on C. obtusifolia according to ant species inhabiting the plant . Forty C. obtusifolia total were sampled; 12 Cecropia without ants, 11 A. xanthochroa inhabited, 7 C. nigropilosa inhabited, and 10 A. constructor inhabited . Herbivory did not noticeably differ according to ant species but was much higher when ants were not present. Error bars are Â± one standard error of the mean . DISCUSSION Multiple species of ants were found inhabiting C. obtusifolia . Crematogaster w ere always found in shaded sites , and were very docile ; they showed almost no defensive behaviors and unlike the Azteca ants were not at all bothered when the MBs were being removed or covered. This could be because ants that are not obligate Cecropia ass ociates , such as Crematogaster, tend not to recognize MBs as a food source and therefore do not defend them (Davidson 2005) . A zteca xanthochroa and A. constructor were the only Azteca species sampled on C. obtusifolia, presumably because C. obtusifolia in open areas require aggressive ant defenders (Longino 2005 ). Even though A. alfari are also found in the area studied, they are not often present on C. obtusifolia , and are more common on C. obtusifolia in the lower part of their range (~1000masl) where I did not sample . These differences in environment show that different species of ants have distinct habitat affiliations when choosing Cecropia trees. Regardless of habitat preference, all ants offered some protection from herbivores to C. obtusifoli a . Schupp (1986) demonstrated that when its ant inhabitants were removed, C. obtusifolia experienced higher herbivory, increased vine cover, and signi fi cantly stunted growth . My results and observations support this finding, although growth rate was not measured. C. obtusifolia almost always had more herbivory when ants were not present, especially on their intermediate age and youngest leaves. However, herbivory did not di ffer according to ant species. This implies that degree of herbivory relies on the presence of ants, but their level of aggression does not make them better or worse defenders. The only variation in ant colony that causes a difference in herbivory is the size of the colony. Larger colonies are better defenders as they have more ants to designate to defense (Longino 2005). A nt presence on C. obtusifolia causes a decline in herbivory, but this herbivory is not linked to rate of MÃ¼llerian body production . However, the presence of ants and the ant species 0 2 4 6 8 10 12 None A. xanthochroa C. nigropilosa A. constructor % Average Herbivory Ant Species
do have an effect on MB production. Trichilia on un inhabited Cecropia were observed to have over a hundred MBs on a single t richilium. This could be due to MBs collecting over a number of da ys because they were not being harvested; however, when MBs were removed from these trichilia and newly produced MBs were counted 24 hours later, C. obtusifolia without ants produced more MBs than C. obtusifolia with ants. According to Agrawal and Dubi n T hauer (1999) it is not clear if the ants or the plants regulate the induct ion of t he ant colony. My data suggest that trees are producing an abundance of MBs in order to attract ant colonies, meaning the plants are regulating the induction of the ant colony. Once an ant colony has inhabited a Cecropia, however, it may be the behavior of the ant species that regulat es the MB production. C. obtusifolia inhabited by an A. xanthochroa colony produced fewer MBs than trees with other species of ants. Since there was no difference in herbivory allowed by ant species, assuming there was also no difference in energy invest ed in leaf repair by the plant, this variance must be acc ounted to a damaging effect A. xanthochroa has on C. obtusifolia that is less for other species and absent when ants are not present. I believe this difference is due, at least in part, to the cocci ds that Azteca ants farm on the inside of hollow Cecropia. These scale insects act as herbivores as they feed on the phloem of the Cecropia, damaging the tree and causing it to invest more energy in repair (Rico Gray & Oliveira 2007) . Because C. obtusifolia inhabited by A. xanthochroa invest less energy in MB production, I propose that this is because A. xanthochroa rely more heavily on coccids for sugar than other Azteca species and therefore farm larger colonies of them, causing mor e damage to the tree. Furthermore, in my observations larger trees with larger ant colonies often produced very few MBs, plausibly because larger colonies of scale insects were present and feeding on the Cecropia , causing the tree to invest less energy in MB production and more in self repair. Plant defense is costly and employing a biotic defense can be a good strategy to reduce some of those costs. However, biotic defenses have associated costs as well. All myrmecophytic Cecropia invest energy in pro ducing M Ã¼ llerian bodies for their ants (Davidson 2005 ). Furthermore, Azteca are known to farm scale insects that feed on the Cecropia, which may affect the rate of Mullerian body production by the Cecropia . Plant defense by ants is not as simple as the presence or absence of ants; the diversity of behavior between ant species is an important factor in their effectiveness as defenders (Davidson 2005 ). More research needs to be done into the cost/benefit relationships that varying ant species present their host Cecropia with. Cecropia that have ants show little difference in herbivory according to species, but their rate of MB production is significantly different. This points to variation in behaviors other than protection and suggests that Cecropia adapt to the combined effects of inhabiting sp behaviors, and not just their quality of defense.
ACKNOWLEDGMENTS Thank you to Moncho CalderÃ³n for helping me collect ants and realize that I needed shorter Cecropias . Thank you to my host family for thinking my obsession with leaves and ants was comical. LITERATURE CITED Agrawal, A.A. and B.J. Dubin Thaler. 1999. Induced responses to herbivory in the Neotropical antplant association between Azteca ants and Cecropia trees: response of ants to potential inducing cues. Behavioral Ecology and Sociobiology 45: 47 54. Burger, W. 1977. Mo raceae, In . W. Burger (Ed.). Flora Costaricensis, Fieldiana, Botany 40: 94 215. Davidson, D.W. 2005. Cecropia and its biotic defenses. In : Flora Neotropica , C.C. Berg & Franco Rosselli ( ed s.) Vol. 94, New York Botanical Garden, NY, pp. 214 226. Herre, E.A., N. Knowlton, U.G. Mueller, and S.A. Rehner. 1999. The evolution of mutualisms: exploring the paths between conflict and cooperation. TREE 14: 49 53. Hunt, J. 2003. Cryptic herbivores of the rainforest canopy. Science 300: 916 917. Ja nzen, D. H. 1966. Coevolution of mutualism between ants and acacias in Central America. Evolution 20: 249 275. Janzen, D. H. 1969. Alleopathy by Myrmecophytes: the ant Azteca as an alleopathic agent of Cecropia . Ecology 50: 147 150. Janzen, D.H. 1973. Dissolution of mutualism between Cecropia and its Azteca ants. Biotropica 5: 15 28. Longino, J . 1989. Geographical Variation and Community Structure in an Ant Plant Mutualism: Azteca and Cecropia in Costa Rica. Biotropica 21: 126 132 . Longino, J . 1991a. Azteca ants in Cecropia Trees: Taxonomy, Colony Structure, and Behaviour. In: Ant plant interactions, C. Huxley & D. Cutler (eds.), Oxford University Press, Oxford, UK, pp. 271 288. Longino, J. 1991b . Taxonomy of Cecropia inhabiting Azteca ants. Journal of Natural History 25: 1571 1602. Longino, J. 2005, September 22 . The Cecropia Azteca association in Costa Rica. Retrieved May 8, 2011, from http://academic.evergreen.edu/projects/ants/antplants/CECROPIA/Cecropia.html . Loope, G . 2008. Range change in Cecropia and Azteca : the effects of climate change on m utualistic part ners in Monteverde, Costa Rica. CIEE Spring. Monteverde, Costa Rica. Rico Gray, V., and P. Oliveira. The Ecology and Evolution of Ant Plant Interactions. University of Chicago Press, Chicago, pp. 107 109. Rutter, M. T., an d M. D. Rausher. 2004. Natural selection on extrafloral nectar production in Chamaecrista fasciculate : the costs and benefits of a mutual ism trait. Evolution 58: 2657 2668.
Schupp, E. W. 1986. Azteca protection of Cecropia : ant occupation benefits juvenile trees. Oecologia 70: 379 385.
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Las interacciones de herbvoros, las especies de hormigas y la obtencin de Muller en Cecropia obtusifolia (Cecropiaceae)
The interactions of herbivory, ant species and Mullerian body production in Cecropia obtusifolia (Cecropiaceae)
Mutualisms are prevalent in every ecosystem. The Cecropia-Azteca interaction is an example of a well-studied and prominent mutualism in the neotropics. Azteca ants act as biotic defenders by attacking herbivores and vines that assault the tree. In return, they receive nutrients from the Cecropia in the form of protein rich Mllerian bodies (MBs) and a place to live in the hollow stem of the tree. It is not a specialist mutualism, and while species show some preference to environmental conditions, multiple species of ants are able to live in one species of Cecropia. Different species of ants have different behaviors which elicit responses from the tree. This study examined how herbivory and rate of MB production of C. obtusifolia varied with ant presence and species. Forty C. obtusifolia in the Monteverde region of Costa Rica were sampled. When ants were present they were collected and identified. Herbivory was calculated for each tree as was rate of MB production. When ants were present, there was about 60% less herbivory than when ants were not present. Herbivory did not differ between species and was not related to MB production, suggesting that the presence of ants deters herbivores but one species is not a better defender than another. There were differences in MB production according to species. C. obtusifolia inhabited by A. xanthochroa
produced significantly fewer MBs than when no ants were present on the tree and fewer than other trees with different ant species. I attribute this to the prediction that phloem-feeding coccids that Azteca farm on the inside of the Cecropia, which require the tree to invest more energy in repair and less in MB production, are more abundant in trees inhabited by A. xanthochroa. Cecropia obtusifolia without ants produced more MBs than trees with ants, which could also be due to trees trying to recruit ant colonies for biotic defense. The Cecropia-ant relationship is not as simple as the presence or absence of ants; tree responses vary according to ant species and their behavior.
El mutualismo es prevalente en todos los ecosistemas. La interaccin Cecropia-Azteca es un ejemplo de un mutualismo prominente muy bien estudiado en los trpicos del nuevo mundo. Las hormigas aztecas actan como defensores biticos atacando herbvoros y lianas que atacan los rboles. En retorno, reciben nutrientes de la planta en la forma de cuerpos Mullerianos (CM) en forma de protena y un lugar para vivir en el tallo hueco del rbol. No es un mutualismo especialista, y mientras las especies muestran una preferencia por las condiciones ambientales, varias especies de hormigas son capaces de vivir en una especie de Cecropia. Las diferentes especies de hormigas tienen diferentes comportamientos que les dan diferentes respuestas por la planta. Este estudio examina el grado de herbivora y la produccin de CM en C. obtusifolia dependiendo de las especies de hormigas asociadas. Se muestrearon 40 individuos de C. obtusifolia en la regin de Monteverde en Costa Rica. Cuando las hormigas estn presentes se colectaron e identificaron. Cuando hay hormigas presentes, existe cerca de un 60% menos herbivora que cuando no hay hormigas. El grado de herbivora no difiere entre las especies y no est relacionado con la produccin de CM, sugiriendo que la presencia de las hormigas disuade a la herbivora pero ninguna especie es mejor que la otra. Existen diferencias en la produccin de CM de acuerdo con la especie de hormiga asociada a la planta, las plantas con A. xanthochroa producen menos CM que cuando no hay hormigas presentes en las plantas y menos que otros rboles con diferentes especies de hormigas. Atribuyo esto a la prediccin que los comederos de floema que las hormigas mantienen dentro de las plantas, lo cual requiere una mayor inversin energtica por parte de la planta y por lo tanto menor produccin de CM, son ms abundantes en rboles habitados por A. xanthochroa. Cecropia obtusifolia sin hormigas producen ms CM que los rboles con hormigas, podra ser porque los rboles tratan de reclutar colonias de hormigas para la defensa. La relacin Cecropia-hormiga no es tan simple como la presencia o ausencia de hormigas, la respuesta de las plantas vara de acuerdo a las especies y el comportamiento de las mismas.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Spring 2011
Mllerian body production
Ecologa Tropical Primavera 2011
Produccin del cuerpo Mulleriano
t Monteverde Institute : Tropical Ecology