Effects of host colony size and hygiene behaviours on social spider kleptoparasite loads along an elevation gradient

Abstract

Abstract Group living animals are likely to attract more parasites than solitary ones. Parasite loads, however, should also depend on environmental conditions and on host characteristics and behaviours. Previous work has found that social spider colonies harbour communities of kleptoparasitic spiders that forego building their own web and, instead, steal prey from their social host. We examined kleptoparasite loads and host hygiene behaviours in colonies of social and subsocial spiders in the genus Anelosimus along an elevation gradient in eastern Ecuador. We found that kleptoparasite loads declined dramatically with increasing elevation. Host hygiene behaviours, such as debris removal, web repair and interactions with the parasites, also declined with elevation. Within elevations, species with more frequent hygiene behaviours appeared more successful at keeping parasites at bay. Contrary to our predictions, parasite density declined with host nest and colony size. The decline in parasite loads at higher elevations likely reflects a lower rate of energy exchange between colonies and their environments, where colder temperatures mean fewer and smaller prey for colonies to process. The decline in parasite density with host colony size may reflect a decline in the number of accessible prey in larger host colonies, as larger colonies should capture fewer but larger insects due to scaling properties of their three‐dimensional webs. Social immunity, whereby a social host uses social behaviour to fight against parasites, has been studied in eusocial and non‐eusocial insects. This study opens up social spiders as a novel system in which to study how host characteristics interact with environmental factors to affect parasite loads. It also introduces the concept of group‐level immunity to social spiders and suggests a role for colony‐level metabolism in determining ecological patterns in parasitism. A plain language summary is available for this article.