Losing legs and walking hard: effects of autotomy and different substrates in the locomotion of harvestmen in the genus Prionostemma

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Altamirano, CAC
Bernaola, VV
Bolanos, LFB
Dionisio, OM
Garcia, MC
Leonardo, D
Lopez, CB
Meza, EP
Monsalve, LAB
Passiuri, IC
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Bio One
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Autotomy, the strategy of voluntarily releasing a leg during an encounter with a potential predator or in agonistic interactions between conspecifics, is common in animals. The potential costs of this behavior have been scarcely studied. In addition, locomotion and substrate-dependent performance might be affected by autotomy. We did a comparative and observational study to investigate whether losing legs affects the escape speed and trajectory of harvestmen in the genus Prionostemma Pocock, 1903 (Eupnoi: Sclerosomatidae) on different substrates: soil (the least roughened), smooth bark and mossy bark (the most roughened) in a tropical premontane forest in Costa Rica. We observed that 71% of the individuals found were missing at least one leg. Harvestmen, regardless of leg condition, walked faster and made fewer turns in their trajectory in the soil. While climbing, they were faster on smooth bark than in moss. On all substrates, autotomized individuals were slower and had a more erratic trajectory than intact ones. The type of missing legs (sensory or locomotor) had no influence on the speed or trajectory. We experimentally induced autotomy and found that walking speed on soil decreases if individuals lose a leg. Our findings confirm that losing legs affects locomotion, and we provide novel insights on how locomotion in these harvestmen depends on surface roughness. Our data suggest that moss could be a type of substrate that requires more elaborate skills in balance, orientation and texture recognition than smooth bark.
We thank A.G. Farji-Brener, F. Chinchilla, and G. Barrantes for their assistance in the design, analysis and interpretation of this project. E. Triana provided great suggestions to improve the project, as well as field assistance. We thank the Organization for Tropical Studies and Las Cruces Biological Station for providing housing, logistics, transportation and financial support during this project. V.R. Townsend, Jr., Joel Wixson, Elizabeth C. Braun, and two anonymous reviewers provided useful comments to improve this project. The Biology Department of the UPR at Rio Piedras provided financial support to CF. The Universidad de Antioquia, Colombia provided financial support to DG-R, and the Center For Conservation Education and Sustainability, Smithsonian Conservation Biology Institute and CONCYTEC for the financial support to FC-R.
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Sclerosomatidae, Costa Rica, Eupnoi, Opiliones