Abstract

Fungus-growing termites of the genus Macrotermes cultivate symbiotic fungi (Termitomyces) in their underground nest chambers to degrade plant matter collected from the environment. Although the general mechanism of food processing is relatively well-known, it has remained unclear whether the termites get their nutrition primarily from the fungal mycelium or from plant tissues partly decomposed by the fungus. To elucidate the flows of carbon and nitrogen in the complicated food-chains within the nests of fungus-growing termites, we determined the stable isotope signatures of different materials sampled from four Macrotermes colonies in southern Kenya. Stable isotopes of carbon revealed that the termite queen and the young larvae are largely sustained by the fungal mycelium. Conversely, all adult workers and soldiers seem to feed predominantly on plant and/or fungus comb material, demonstrating that the fungal symbiont plays a different nutritional role for different termite castes. Nitrogen stable isotopes indicated additional differences between castes and revealed intriguing patterns in colony nitrogen cycling. Nitrogen is effectively recycled within the colonies, but also a presently unspecified nitrogen source, most likely symbiotic nitrogen-fixing bacteria, seems to contribute to nitrogen supply. Our results indicate that the gut microbiota of the termite queen might be largely responsible for the proposed nitrogen fixation.

Highlights

  • Fungus-growing termites of the genus Macrotermes cultivate symbiotic fungi (Termitomyces) in their underground nest chambers to degrade plant matter collected from the environment

  • Termites collect plant litter from the nest surroundings and provide it for the fungal symbiont that effectively decomposes lignocellulose in specific compost structures that serve as a type of ‘external rumen’ for the insect hosts[8]

  • In this study we explored stable isotope signatures of carbon and nitrogen to elucidate the nutritional role of the Termitomyces fungus for different termite castes and age-groups of two Kenyan Macrotermes species (M. michaelseni and M. subhyalinus)

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Summary

Introduction

Fungus-growing termites of the genus Macrotermes cultivate symbiotic fungi (Termitomyces) in their underground nest chambers to degrade plant matter collected from the environment. The role of Termitomyces has been suggested to be differently balanced between these two functions within different termite genera: in the genus Macrotermes the primary role of the fungal symbiont has been suggested to be lignin degradation, making plant material more digestible for the insects, whereas in several other genera of Macrotermitinae the highly nutritious fungal mycelium itself is believed to represent a primary food source for the termites[26]. As the collective food processing of fungus-growing termites, is highly complex, and includes several different termite castes each with different roles and functions[27], more detailed studies on nest internal nutrient fluxes are needed to comprehensively understand the significance of the symbiotic fungus for colony nutrition

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