Graveyards on the Move: The Spatio-Temporal Distribution of Dead Ophiocordyceps-Infected Ants

Abstract

Parasites are likely to play an important role in structuring host populations. Many adaptively manipulate host behaviour, so that the extended phenotypes of these parasites and their distributions in space and time are potentially important ecological variables. The fungus Ophiocordyceps unilateralis, which is pan-tropical in distribution, causes infected worker ants to leave their nest and die under leaves in the understory of tropical rainforests. Working in a forest dynamic plot in Southern Thailand we mapped the occurrence of these dead ants by examining every leaf in 1,360 m2 of primary rainforest. We established that high density aggregations exist (up to 26 dead ants/m2), which we coined graveyards. We further established that graveyards are patchily distributed in a landscape with no or very few O. unilateralis-killed ants. At some, but not all, spatial scales of analysis the density of dead ants correlated with temperature, humidity and vegetation cover. Remarkably, having found 2243 dead ants inside graveyards we only found 2 live ants of the principal host, ant Camponotus leonardi, suggesting that foraging host ants actively avoid graveyards. We discovered that the principal host ant builds nests in high canopy and its trails only occasionally descend to the forest floor where infection occurs. We advance the hypothesis that rare descents may be a function of limited canopy access to tree crowns and that resource profitability of such trees is potentially traded off against the risk of losing workers due to infection when forest floor trails are the only access routes. Our work underscores the need for an integrative approach that recognises multiple facets of parasitism, such as their extended phenotypes.

The Regulation of Filamentous Growth in Yeast

“…The filamentation response is highly variable among species, ranging from mycelial mat or hyphal formation in true filamentous fungi to subtle changes in cell shape in yeasts. The biology that attends this response is fascinating and mysterious and ranges from contact-responsive hyphal growth (Kumamoto 2005) to behavior modification of insect species, such as the erratic behavior exhibited by "zombie ants" infected with Ophiocordyceps (Pontoppidan et al 2009), to the formation of lasso-type structures in Nematode-trapping parasites (Wang et al 2009a). Some species, like the extensively studied fission yeast Schizosaccharomyces pombe, have only recently be shown to undergo filamentous growth as part of their life cycles (Amoah-Buahin et al 2005).…”

Mycosphere Essay 19. Cordyceps species parasitizing hymenopteran and hemipteran insects

“…Twenty two Ophiocordyceps species parasitize Camponotus ants (Table 2). Among them, O. unilateralis parasitizes multiple Camponotus species, such as C. atriceps (Fawcett 1886) and C. sericeiventris (Evans & Samson 1984) in South America, C. brutus and C. vividus in Africa (Evans 1974), C. pennsylvanicus (Bequaert 1922) and C. americanus (Mains 1940) in North America, C. leonardi (Pontoppidan et al 2009) and C. saundersi (Luangsa-Ard et al 2011) in Asia, and C. ligniperdus (Bequaert 1922) in Europe and North America (Table 2). Similarly, O. formicarum parasitizes Camponotus obscuripes (Kobayasi 1939b) and C. japonicus (Kawamura 1955) in Asia (Table 2).…”

Field Trial of Aqueous and Emulsion Preparations of Entomopathogenic Fungi Against the Asian Citrus Psyllid (Hemiptera: Liviidae) in a Lime Orchard in Mexico

“…1) (Andersen et al 2009;Pontoppidan et al 2009). Hirsutella citriformis could use of the host as a vehicle for dispersion.…”