No abstract

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.

Invasive plant species may benefit from a reduction in herbivory in their introduced range. The reduced herbivory may cause a reallocation of resources from defence to fitness. Here, we evaluated leaf herbivory of an invasive tree species (Ligustrum lucidum Aiton) in its native and novel ranges, and determined the potential changes in leaf traits that may be associated with the patterns of herbivory. We measured forest structure, damage by herbivores and leaf traits in novel and native ranges, and on the basis of the literature, we identified the common natural herbivores of L. lucidum. We also performed an experiment offering leaves from both ranges to a generalist herbivore (Spodoptera frugiperda). L. lucidum was more abundant and experienced significantly less foliar damage in the novel than in the native range, in spite of the occurrence of several natural herbivores. The reduced lignin content and lower lignin : N ratio in novel leaves, together with the higher herbivore preference for leaves of this origin in the laboratory experiment, indicated lower herbivore resistance in novel than in native populations. The reduced damage by herbivores is not the only factor explaining invasion success, but it may be an important cause that enhances the invasiveness of L. lucidum.