Long-Term Disease Dynamics for a Specialized Parasite of Ant Societies: A Field Study

Abstract

Many studies have investigated how social insects behave when a parasite is introduced into their colonies. These studies have been conducted in the laboratory, and we still have a limited understanding of the dynamics of ant-parasite interactions under natural conditions. Here we consider a specialized parasite of ant societies (Ophiocordyceps camponoti-rufipedis infecting Camponotus rufipes) within a rainforest. We first established that the parasite is unable to develop to transmission stage when introduced within the host nest. Secondly, we surveyed all colonies in the studied area and recorded 100% prevalence at the colony level (all colonies were infected). Finally, we conducted a long-term detailed census of parasite pressure, by mapping the position of infected dead ants and foraging trails (future hosts) in the immediate vicinity of the colonies over 20 months. We report new dead infected ants for all the months we conducted the census – at an average of 14.5 cadavers/month/colony. Based on the low infection rate, the absence of colony collapse or complete recovery of the colonies, we suggest that this parasite represents a chronic infection in the ant societies. We also proposed a “terminal host model of transmission” that links the age-related polyethism to the persistence of a parasitic infection.

Evidence for convergent evolution of host parasitic manipulation in response to environmental conditions

“…; Loreto et al. ), so we were able to estimate the abundance for those specific areas. This permitted us to confirm previous observations that most of the occurrence records for O. unilateralis s.l .…”

“…killed ants encountered was not recorded, but it is in excess of 10,000 samples based on 12 years of field work in the Atlantic rainforests of Brazil (Loreto et al. ), Amazonian forest of Brazil (Araujo et al. ), and Colombia (Sanjuan et al.…”

“…; Loreto et al. ) and parasite development is completed in a few months after it kills the host (Mongkolsamrit et al. ; Araujo et al.…”

“…), the epidemiological significance of behavioral manipulation (Loreto et al. ), and the ecological importance of manipulated hosts in the environment (Thomas et al. ; Sato et al.…”

“…; Loreto et al. ). The death of the ant, shortly after the manipulated biting behavior, is the end point of the manipulation and marks the transition for the fungus, from feeding parasitically on living tissue to feeding saprophytically on the dead tissue of its recently killed host (de Bekker et al.…”