Phalangium opilio’s ability to overcome obstacles without changing from its tripod gait

1. Phalangiumopilio’s ability to overcome obstacles without changing from its tripod gait Betty J. RossieDepartment of Biology, McDaniel College, Westminster, Maryland, 21157 Natural History Results Objectives • One of the things this may tell us is optimal habitat for harvestmen living within areas that are most easy to escape in. Current robotics research is highly focused on the stability of insect locomotion • Observe the locomotion of the harvestmen (Phalangiumopilio) when maneuvering over unnatural surfaces (premade screens).The comparison of the speed with • which the specimen moves across the area will show preference for angle of escape. • Determine, by physical trials, the ability of the harvestmen to maneuver over obstacles without changes to normal hexapodal locomotion with tripod gait when encountering holes in the unnatural surfaces. A relative of the spider, Daddy LongLegs, Harvestman, or members of the family Opiliones, they have similar characteristics (fig. 1). The specimens traveled over the screens an average of 4.2 cm/sec up the screen set at a 90 angle. The average speed of the specimens traveling over the screen set at a 45 angle was almost the same for the screen with no holes and the screen with holes at 5.3 cm/sec and 5.2 cm/sec respectively (Fig. 2). Order Arachnida Methods Figure 1. Phylogenetictree for order Arachnida (Shultz, 1990) • Phalangiumopiliowere the easiest to catch and maintain in the lab, so I decided to use them for the experiments. • All specimens were hand collected using a small fish net and a plastic 20 oz. soda bottle with the top cut off at the neck. Opiliones are a seldom studied group of terrestrial Arachnids that occur in most areas of the planet. 3,200 species + (and counting), 200 native to the United States (Pinto-da-Rocha, 2007). Varied in appearance, but main features recognizable to most cultures. Unlike a spider, a harvestman has 8 long, stiltlikelegs, segmented abdomen, and lacks silk glands. Thought to be introduced in Maryland they are not currently considered invasive, but have been observed cannibalizing their own species and other species. One of the most common Opilionid encounter in human areas are Phalangiumopilio. 1 Figure 2.Speed of specimens walking over screen at a 90º and 45º angles from the countertop. n=12; 6males, 6 females. Leiobunumvittatum, male Conclusion Based on visual observations and video review, there appeared to be a difference in the preferred angle of either 0º or 90º however, there was no significant difference between the angles nor the obstacles in the screens based on the post hoc test performed. The 45º angled screens were thought to present the most difficult obstacles to overcome but statistically there was no significant adjustment of speed or maneuvering regardless of the direction or obstacle. The tripod stance is maintained when maneuvering around obstacles, specimensutilize the second set of limbs for sensing and not for walking over all surfaces only at rest are those limbs used as part of stabilization and weight balance. This did lead to some discussion as to whether different, more natural obstacles would make a difference to the results. It is possible that a larger population or longer distance might make a difference in the outcome. It is curious also whether this allows for more adaptability in changing habitats. 6 Phalangiumopilio adult male Leiobunumaldrichi, male All of the specimens were approximately the same size and weight (n=12, 6 males and 6 females) To determine if there is a change in the locomotion when encountering obstacles (cuts in the screens and surface angle shifts), I began with homemade screens made from balsa wood and 18 sq/in window screening. A pair of glands in the carapace secrete an unpleasant-smelling substance that deters predators. Harvestmen do not bite, so they are harmless to people. (Pinto-da-Rocha, 2007). Further Research: It would be interesting to determine if there is a difference between species and whether or not there is a difference between the length of the limbs and total body weight. Also a closer look at the differences between the age of the specimens. Screen44.45cm x 22.86 cm at 90º angle from flat countertop Terrestrial Locomotion and Escape Behavior Each leg has seven joints, making them highly flexible and allowing the animal to run rapidly over leaves and grass. During a field study, I observed a variety of escape behavior, horizontal running over substrate, around tree trunks, and moving to the underside of a leaf. Phalangiumopilioutilizes an alternating sets of tripods, legs L1, L4, R3 and L3, R4, R1 for locomotion. The second pair of limbs are most commonly used as tactile organs and so are not included in the tripodal stance, however, if needed for extra support these limbs are used (Sensing, 2006). Multi-cut screen at 45º angle from flat countertop PhalangiumOpilio 2 weeks from hatching ~2mm body length I housed all specimens in terrariums that I prepared with a base of small rocks, layer of sand and dirt. Literature Cited Pinto-da-Rocha, R., Machado, G., & Giribet, G. eds.,2007. The Biology of Opiliones. Harvard University Press, Cambridge, Massachusetts:chpts 1,7. Sensing, A.T. and Shultz, J.W., 2006 (2007). Mechanical energy oscillations during locomotion in harvestmen, Leiobunum vittatum(Opiliones). Jrl of Arachnology 34:627-633. Shultz, J.W. 1990. Evolutionary morphology and phylogeny of Arachnida. Cladistitcs 6: 1-38. Phalangiumopilio adult female tripod stance indicated: L1, L3, R4 R1, R3, L4 I made visual observations at the time of the trials as well as the reviewed the videos recorded using a Nikon CoolPix L18 digital camera with the help of a tripod. Using Windows Media Player, frame by frame I reviewed the videos to observe any change of gait. I timed the continuous movement of the specimen with no further prompting other than the initial prompt. Acknowledgements I would not have been able to perform this research if not for the following: Dr. Brett McMillan – McDaniel College – my advisor Dr. Jeffery Shultz – University of Maryland College Park Adam Hudson – McDaniel College – Excel guru/lab mate John Rossie – my understanding husband/arachnophobe; Nick – my lab asst/son