Dynamic environments of fungus‐farming termite mounds exert growth‐modulating effects on fungal crop parasites

Abstract

This study investigated for the first time the impact of the internal mound environment of fungus-growing termites on the growth of fungal crop parasites. Mounds of the termite Odontotermes obesus acted as (i) temperature and relative humidity (RH) 'stabilisers' showing dampened daily variation and (ii) 'extreme environments' exhibiting elevated RH and CO levels, compared to the outside. Yet, internal temperatures exhibited seasonal dynamics as did daily and seasonal CO levels. During in situ experiments under termite-excluded conditions within the mound, the growth of the crop parasite Pseudoxylaria was greater inside than outside the mound, i.e., Pseudoxylaria is 'termitariophilic'. Also, ex situ experiments on parasite isolates differing in growth rates and examined under controlled conditions in the absence of termites revealed a variable effect with fungal growth decreasing only under high CO and low temperature conditions, reflecting the in situ parasite growth fluctuations. In essence, the parasite appears to be adapted to survive in the termite mound. Thus the mound microclimate does not inhibit the parasite but the dynamic environmental conditions of the mound affect its growth to varying extents. These results shed light on the impact of animal-engineered structures on parasite ecology, independent of any direct role of animal engineers.

Bi-layered architecture facilitates high strength and ventilation in nest mounds of fungus-farming termites

“…The enhanced porosity of the periphery may allow termite mounds to act as temperature and relative humidity 'stabilisers' maintaining high relative humidity (> 98%), high levels of CO 2 and moderate temperatures compared to the outside 13 . These conditions are crucial for the survival of O. obesus termites and their fungal gardens 13 . We have previously shown that termites manipulate soil in the presence of moisture for manufacturing bricks (boluses) which they use for mound construction 9 .…”

“…S1 online) 4 , 9 . Moreover, mounds also maintain elevated relative humidity (> 98%), extremely high CO 2 concentrations (< 1–6%) 4 , 13 , and dampened temperature variations relative to the external environment 12 . This is crucial for the survival of the fungus garden that termites cultivate for food 6 .…”

Moisture alone is sufficient to impart strength but not weathering resistance to termite mound soil

“…The interior of the mound is characterized by high humidity (approx. 98%), high CO 2 (up to 4%) and with dampened temperature fluctuations compared to the exterior [ 9 ]. We did not attempt to mimic these conditions.…”

“…This study was conducted on O. obesus termites at the Indian Institute of Science campus in Bangalore, India. Odontotermes obesus is widely distributed in India [ 36 ], cultivates fungus [ 9 ] and constructs mounds that can be up to 2.5 m tall [ 30 ] and that have been observed to last for more than 10 years [ 30 ]. The study region has red soil dominated by the clay minerals kaolinite and montmorillonite, and the non-clay minerals quartz, mica and feldspar [ 37 ].…”

“…Soil and marine sediments have been used for the construction of various structures by humans and non-human animals. These structures provide shelter [ 1 ], protection from predators [ 2 – 4 ], help in prey capture [ 5 ], thermoregulation [ 6 ] and mate attraction [ 7 , 8 ], and act as incubators for fungus cultivation [ 1 , 9 ]. Different materials can be employed, e.g.…”