Lack of costs associated with nest-related behaviors in an arachnid with exclusive paternal care

Nest-related behaviors may benefi t males by increasing off spring survival and their attractiveness to females, but may also limit males ’ foraging activity, increase their metabolic expenses, and expose them to increased mortality during nest attendance. Although intensively studied among birds and ectothermic vertebrates, the costs of nest-related behaviors in arthropods remain poorly explored. Females of the Neotropical harvestman Zygopachylus albomarginis (Arachnida: Opiliones) lay eggs exclusively inside mud nests that are built, repaired, cleaned and defended by males, which may remain stationary and associated with the nest for up to fi ve months. To assess energetic and survival costs of nest-related behaviors in this arthropod species, we measured body condition of nesting and non-nesting males and conducted a fi eld capturemark-recapture study to estimate their survival rates. Despite the long period of nest attendance, nesting males sustained good body conditions and presented higher survival rates than non-nesting males and females. Two ecological conditions may play an important role modulating the costs of nest attendance in the species. First, high food supply in tropical rainforests may provide males with frequent access to food in the vicinity of their nests, reducing or eliminating the costs related to limited foraging opportunities. Second, predation pressure seems to be directly mostly to vagrant individuals, so that the more they move, the more likely they are to be singled out by predators. Taken together, our fi ndings indicate that nest and off spring defense in Z. albomarginis provide numerous benefi ts, surprisingly imposing no evident cost to the males.