Parental Nitrogen Transfer and Apparent Absence of N₂ Fixation during Colony Foundation in Coptotermes formosanus Shiraki

Abstract

Colony foundation and early growth is a critical period in the life-cycle of a termite colony, as the initial family unit is resource limited. One such resource is nitrogen, which is essential for initial colony growth. This study examined the whole-colony nitrogen inventory during foundation and early growth of Coptotermes formosanus Shiraki colonies. It was hypothesized that termite colonies would go through an initial period of parental investment, representing a transfer of nitrogen to the first brood, and that once a functional worker caste was present, further provisioning in the form of intrinsic N₂ fixation would occur. Our results showed that, when in nitrogen-poor rearing conditions, the king and queen initially transferred half of their nitrogen reserves to their first brood. However, the total nitrogen content in colonies did not increase over a 12 month period, despite the presence of functional workers. Furthermore, colonies did not increase their biomass beyond the initial parental investment. Together, these results imply that nitrogen acquisition in incipient C. formosanus colonies relies on environmental or dietary sources, rather than the putative fixation through symbiotic diazotrophs.

Keywords: brood care; dinitrogen; parental investment.

Figure 1

Representatives of three termite families, showing first or second instar larvae with transparent bodies and no evidence of food in the form of wood in the gut. (A) Neocapritermes sp. (Termitidae), (B) Neotermes sp. (Kalotermitidae), (C) Microcerotermes sp. (Termitidae), (D) Coptotermes. (A–C) photo credit: Rudolf Scheffrahn, University of Florida FL-REC.

Figure 2

Nitrogen calculated in incipient colonies of Coptotermes formosanus during the first year of development. All data points (circles, triangles, and squares) represent means ± SE of 10 colonies. Total nitrogen (circles) represents the total mg of nitrogen present in all termite biomass of each colony. Ingested nitrogen (squares) represents the cumulative dietary nitrogen mg ingested from the wood diet provided to the colonies. Net nitrogen (triangles) represents the dietary nitrogen mg consumed from wood subtracted from the total nitrogen mg in termite biomass for each colony.

Figure 3

Distribution and transfer of total nitrogen by age and instar in incipient colonies of Coptotermes formosanus. Letters (A, B, C) in columns represent significant differences in nitrogen present in the reproductive caste (ANOVA α = 0.05, p < 0.001, post hoc Tukey’s HSD).