HYMENOPTERA: FORMICIDAE) by Benjamin H

INTRASPECIFIC AGGRESSION IN THE DIFFICULT ANT, TECHNOMYRMEX DIFFICILIS (HYMENOPTERA: FORMICIDAE) By Benjamin H. Sollins Thesis Submitted to the Faculty of The Wilkes Honors College in Partial Fulfillment of the Requirements for the Degree of Bachelor of Arts in Liberal Arts and Sciences with a Concentration in Biology Wilkes Honors College of Florida Atlantic University Jupiter, Florida May 2010 INTRASPECIFIC AGGRESSION IN THE DIFFICULT ANT, TECHNOMYRMEX DIFFICILIS (HYMENOPTERA: FORMICIDAE) By Benjamin H. Sollins This thesis was prepared under the direction of the candidate’s thesis advisor, Dr. James Wetterer, and has been approved by the members of his supervisory committee. It was submitted to the faculty of The Honors College and was accepted in partial fulfillment of the requirements for the degree of Bachelor of Arts in Liberal Arts and Sciences. SUPERVISORY COMMITTEE: ____________________________ Dr. James K. Wetterer ____________________________ Dr. Michelle Ivey ______________________________ Dean Jeffery Buller, Ph.D. ____________ Date ii ABSTRACT Author: Benjamin Sollins Title: INTRASPECIFIC AGGRESSION IN THE DIFFICULT ANT, TECHNOMYRMEX DIFFICILIS (HYMENOPTERA: FORMICIDAE) Institution: Florida Atlantic University Wilkes Honors College Thesis Advisor: Dr. James Wetterer Degree: Bachelor of Arts in Liberal Arts and Sciences Concentration: Biology Year: 2010 One mechanism allowing ant species to successfully invade new areas at a rapid pace is unicoloniality, the formation of large networks connecting colonies over hundreds or even thousands of kilometers. These large networks of colonies, or “supercolonies” lack any form of intraspecific aggression, thus fighting between them is absent. I used aggression assays to study unicoloniality between colonies of the invasive difficult ant, Technomyrmex difficilis on the Florida Atlantic University Wilkes Honors College campus and a household located ~32 km northwest from the college. I found that for all trial combinations, no aggression took place among the ants. From these results, I conclude that T. difficilis does display unicoloniality in South Florida. iii Acknowledgements I gratefully thank Dr. Wetterer, Dr. Ivey, Curtis, and Jared who helped me on this thesis and all the ants who died to make this work possible. You will be remembered. iv TABLE OF CONTENTS Introduction………………………………………………………………………………………..1 Figure 1……………………………………………………………………………………………2 Materials and Methods…………………………………………………………………………….3 Figure 2……………………………………………………………………………………………3 Figure 3……………………………………………………………………………………………4 Figure 4……………………………………………………………………………………………4 Results……………………………………………………………………………………………..5 Discussion…………………………………………………………………………………………6 Works Cited……………………………………………………………………………………….8 v Introduction Exotic species are a major threat to the native population and can have drastic effects on the habitats where they are introduced, displacing native species and altering the structure and function of the ecosystem. They also are to blame, at least in part, for the decline of 68% of endangered species worldwide (Wilson 1992). Invasive tramp ants are non-native species usually associated with human disturbance; however, they can be equally disruptive to their native ecosystems as they become more abundant. The most common means for the spread of ant species is through human commerce (Williams 1994). One way in which invasive ant species dominate is by forming multiple-queen nests, called supercolonies (Wetterer and Wetterer 2006). Ants which belong to a supercolony display no aggressive behavior towards others of the same supercolony, regardless of spatial or genetic separation. This unicolonial behavior allows invasive ant species to grow to dense populations over time (Wetterer and Wetterer 2006). Without intraspecific competition, non-native populations rapidly become ecologically dominant. The most studied species of ant which displays unicoloniality is the red imported fire ant (Solenopsis invicta). Unicolonial populations of S. invicta can reach high densities, making them a successful invasive species; they do not fight with each other over territories, but instead establish massive supercolonies and outnumber any other species in the area. I wished to test whether the difficult ant, Technomyrmex difficilis, also displays unicoloniality. It is important to note that T. difficilis has often been misidentified since the early 1990’s as Technomyrmex albipes; commonly referred to as the white footed ant. These two ants look almost identical and can only be differentiated with the aid of a good microscope which can confirm the presence of a few erect hairs on the mesosoma (see Figure 1). 1 The earliest New World records of T. difficilis all come from Florida, where it was first collected in 1986 in Miami-Dade County (Wetterer 2008). Warner et al. (2005) reported that T. diffcilis was known to exist in 22 counties in Florida (Alachua, Brevard, Broward, Charlotte, Collier, Hendry, Hillsborough, Indian River, Lake, Lee, Martin, Miami-Dade, Monroe, Orange, Palm Beach, Pasco, Pinellas, Polk, St. Lucie, Sarasota, Seminole, and Volusia), as well as areas in South Carolina and Louisiana. This ant has recently become one of the most common arboreal ant species found in South Florida and has become a dominant arboreal ant on the Jupiter campus as well. O.5mm Figure 1. Lateral view of Technomyrmex difficilis. Photo courtesy of keys.lucidcentral.org 2 Materials and Methods With the assistance of Curtis Phillabaum, I collected Technomyrmex difficilis from two sites in Jupiter, Florida (colonies A and B) and one in Palm City, Florida (colony C). Colonies A and B are ~ 170 m apart and both are about 32 km from colony C (see Figures 2, 3 & 4). We collected the ants by disturbing the nests and aspirating them into 9 dram styrene vials. The top halves of the vials were coated with fluon to prevent the ants from escaping while loading them and a damp sponge was used as a cap to provide a humid environment. No food, dirt, water or any other resource was introduced to avoid resource competition. Figure 2. Colony sites; two in Jupiter and one in Palm City 3 Figure 3. Colony sites on the Jupiter campus Figure 4. Colony site in Palm City 4 We then evaluated intraspecific aggression among workers along with Jim Wetterer, Curtis Phillabaum, and Jared Leichner. We performed aggression assays in an air-conditioned room with natural sunlight as the light source in order to mimic the natural lighting which the ants are used to. Three ants from one of the colony sites were placed into one of the capped vials with three ants from either the same site or from another site. Without knowing which ants were from which colony, we assessed aggression in the vials between the workers using methods adapted from Holway et al. (1998), Lim et al. (2003), and Wetterer (2005). We allowed the workers to interact for five minutes before recording their behaviors numerically using Holway et al. (1998) levels of aggression. These levels are as follows: 0 = no apparent interest between workers, 1 = slight antennation between workers, 2 = physical contact resulting in workers retreating, 3 = aggressive lunging, biting or ripping off of legs and antennae, or 4 = prolonged aggression between workers, up to and including death of one or more ants. Any interactions scored as 3 or higher are considered aggressive while any scored as 2 or lower are considered unaggressive. After we recorded the behavior, the ants were discarded and none of them were used more than once. Three more replicates were performed with different combinations from colonies A and B. Three days later, we performed three more replicates using random combinations using all three colonies; I set up the experiments and Curtis assessed the aggression in the vials not knowing the combinations. Results Every single trial performed was scored as a one according to the aggression assay. The ants from like colonies and mixed colonies all displayed the same behavior: slight anntenation and no retreating. 5 Discussion We found no intercolony aggression in T. difficilis of South Florida. During the collection processes, we found T. difficilis in almost every single pine tree examined within a ~10 meter radius around the colony we collected from, which suggests that the arboreal community is dominated by T. difficilis. Even though this may be of little concern to humans at the moment, the results suggest that the ant will spread quickly to other counties in Florida and possibly become a major house pest in years to come. The possibility that T. difficilis may become a crop pest also warrants some concern for the agricultural businesses in the area. If the ant can successfully live in the trees and spread in mass quantities, then crops targeted by the ants will be destroyed; causing hundreds or even thousands of dollars worth in damage. Even though we only found T. difficilis in the trees, this does not suggest that there are none to be found on the ground. Some surveys were performed on the ground near the collection sites but not enough to conclude that T. difficilis also inhabited those areas. More in-depth surveys on the ground could be beneficial because it would let us know if the ant species is forced up into the trees or not. If no T. difficilis is found on the ground, then it is possible that they are forced into the trees, which would suggest that the ant is being pushed to flee to safety. If large colonies of T. difficilis are found on the ground, then it is possible

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