Strong seasonality and clear choice of resting plant in a Neotropical harvestman (Arachnida: Opiliones)

Preliminary observations suggested that the Neotropical harvestman Jussara sp. (Sclerosomatidae, Eupnoi) had a patchy distribution and a marked seasonality, comparable to species in the Northern hemisphere. This would be an unusual pattern, since conditions of temperature and humidity are very different between tropical and temperate environments. Using a mark-recapture method, we investigated the phenology, habitat use and individual movement of Jussara sp. in a tropical rainforest in southern Brazil. We found a very marked seasonality in the population of adults, with a positive correlation between temperature, humidity and number of adults found. Adults were found only in the wet and warm months and significantly preferred the plant Psycothria suterella (Rubiaceae) as a resting substrate, spending the days motionless on its leaves, often in groups. The same individuals were found for a maximum of three months after their first capture, 30 m from their original site of capture. At night, the harvestmen would descend from the plants, forage and interact with conspecifics on the leaf litter. In this first long term behavioral study with a representative of the suborder Eupnoi in Brazil, we provide quantitative evidence that, despite the milder climate, Neotropical harvestmen may show a seasonality similar to the seasonality shown by related species in temperate regions.