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

1. Phalangiumopilio’s ability to overcome obstacles without changing from it’s tripod gait Betty J. RossieDepartment of Biology, McDaniel College, Westminster, Maryland, 21157 Natural History Results Objectives • Why do we care? • One of the things this may tell us is optimal habitat for harvestmen living within areas that are most easy to escape in. • 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 determine which is the preferred angulationand if there is a change when holes are cut in the screen making more obstacles for the specimen to overcome. • 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. What Looks Like a Spider but isn’t? A relative of the spider, Daddy LongLegs, Harvestman, or their family name Opiliones, they have similar characteristics. 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. Order Arachnida Methods • In order to perform laboratory trials, I had to first locate and collect specimens. After spending many evenings in the woods of Hashawa Nature Center, I encountered and collected a variety of species. • 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. Figure 1. Phylogenetic tree for order Arachnida (Shultz, 1990) Opiliones are a seldom studied group of terrestrial Arachnids that occur in most areas of the planet. They are a varied in appearance, but their main features are recognizable to most cultures. There are over 3,200 species (and counting), 200 of which are native to the United States. Unlike a spider, a harvestman has long, stiltlike legs and a segmented abdomen, and lacks silk glands. The legs each have seven joints, making them highly flexible and allowing the animal to run rapidly over leaves and grass. Harvestmen feed on small insects, decayed animal matter, and the juices of fruits and vegetables. 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). Speed of specimens walking over screen at a 90º and 45º angles from the countertop. n=12; 6males, 6 females. 1 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 not forfeit 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 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. All were local native species such as Leiobunumvittatum (1), Leiobunumpolitum (2), Leiobunumserratipalpe (3), Leiobunumverrucosum (4), Hadrobunusgrandis (5). The easiest to catch and maintain in the laboratory were Phalangiumopilio (6) collected in the yard of my home in Finksburg, MD. Because of that, I decided to use Phalangiumopilio for my trials. All of the specimens were approximately the same size and weight (n=12, 6 males and 6 females) In order 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. Phalangiumopilio adult male Terrestrial Locomotion and Escape Behaviour Normal harvestman behavior is cryptic and often their most of their actions occur during the night are not always easily observed. When escaping in nature the ideal movement was observed to be horizontal running over substrate and around tree trunks or as simple as moving from the surface of the leaf to the underside of the leaf (personal field observation). In the lab however, the escape maneuver was flat out running to escape, regardless of direction. Similar to insects with 6 legs, Phalangiumopilio, as with all species of Opliones, utilizes 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). Figure 6. Screen 44.45cm x 22.86 cmat 90º angle from flat countertop It was determined that the ideal setup would be for the specimen to travel across the screen at a 45º from the countertop Figure 7. Multi-cut screen at 45º angle from flat countertop  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. 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, Leiobunumvittatum(Opiliones). Jrl of Arachnology 34:627-633. Shultz, J.W. 1990. Evolutionary morphology and phylogeny of Arachnida. Cladistitcs 6: 1-38. All specimens were housed in terrariums prepared with a base of small rocks, layer of sand and dirt. Phalangiumopilioadult female tripod stance indicated: L1, L3, R4 R1, R3, L4 Acknowledgements Visual observations were made at the time of the trials as well as the review of the videos recorded using a Nikon CoolPix L18 digital camera with the help of a tripod. The videos were reviewed using Windows Media Player, frame by frame to observe any change of gait as well as timed at full speed. The timing was done on the continuous movement of the specimen with no further prompting other than the initial. 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 HashawaNature Center – Westminster, MD Adam Hudson – McDaniel College – Exelguru/lab mate John Rossie – my understanding husband/arachnophob; Nick Minkowski – my lab asst/son