Soil organic matter is essential for colony growth in subterranean termites

Abstract

Intrinsic dinitrogen (N2) fixation by diazotrophic bacteria in termite hindguts has been considered an important pathway for nitrogen acquisition in termites. However, studies that supported this claim focused on measuring instant N2 fixation rates and failed to address their relationship with termite colony growth and reproduction over time. We here argue that not all wood-feeding termites rely on symbiotic diazotrophic bacteria for colony growth. The present study looks at dietary nitrogen acquisition in a subterranean termite (Rhinotermitidae, Coptotermes). Young termite colonies reared with wood and nitrogen-rich organic soil developed faster, compared to those reared on wood and inorganic sand. More critically, further colony development was arrested if access to organic soil was removed. In addition, no difference of relative nitrogenase expression rates was found when comparing the hindguts of termites reared between the two conditions. We therefore propose that subterranean termite (Rhinotermitidae) colony growth is no longer restricted to metabolically expensive intrinsic N2 fixation, as the relationship between diazotrophic bacteria and subterranean termites may primarily be trophic rather than symbiotic. Such reliance of Rhinotermitidae on soil microbial decomposition activity for optimal colony growth may also have had a critical mechanistic role in the initial emergence of Termitidae.

Eusociality and the transition from biparental to alloparental care in termites

“…Nitrogen availability is a primary limiting factor in initial termite colony growth (Mullins et al, 2021). The net nitrogen content of queens and kings closely followed the loss patterns observed of their respective dry weights, with a similar ~40 days delay in kings, by progressively decreasing during the first 110–120 days post‐foundation and maintaining a minimal nitrogen content until ~150 days (Figure 3e,f, Weibull models).…”

“…Specifically, wood-feeding termites have limited access to dietary nitrogen, especially during colony foundation where the limited alates' nitrogen-carrying capacity constrains initial colony growth (Mullins & Su, 2018). This set of observations raises a series of questions on how the transition to alloparental care was optimized during termite evolution (Chouvenc, 2019;Husseneder et al, 2012;Inagaki et al, 2020;Li et al, 2021) within the context of limited access to environmental nitrogen resources during colony foundation (Mullins et al, 2021;Nalepa, 2015). Using Coptotermes as a termite model, this study investigates the following questions: first, what is the timing of the transition from biparental to alloparental care and how does it relate to the emergence of the first few workers?…”

Understanding global and regional patterns of termite diversity and regional functional traits

“…Our data reveal large termite body sizes in the southern China, and these regions have low soil organic carbon density, 25 which could supply basic resources for termites and drive bigger body sizes. 26 Meanwhile, termite species specialized toward foraging sites rich in soil organic matter to enhance nutrient intake, 27 which probably explains why soil factors influence termite body size.…”

Termite nest evolution fostered social parasitism by termitophilous rove beetles

“…The distinction between one-piece nesters and foragers is blurred by the existence of species with intermediate nesting behaviors. Some species classified as one-piece nesters have the potential to come out of their nesting piece of wood to colonize neighboring wood items (Bourguignon et al 2016;Mizumoto and Bourguignon 2020) or to access soil particles as nutrient resources (Mullins et al 2021). All foraging species of termites have access to soil (Chouvenc et al 2021), providing additional opportunities for termite colonies to be infected by termitophiles.…”

“…2016; Mizumoto and Bourguignon 2020) or to access soil particles as nutrient resources (Mullins et al. 2021). All foraging species of termites have access to soil (Chouvenc et al.…”