How to Make a Beetle Out of Wood: Multi-Elemental Stoichiometry of Wood Decay, Xylophagy and Fungivory

Abstract

The majority of terrestrial biomass is wood, but the elemental composition of its potential consumers, xylophages, differs hugely from that of wood. This causes a severe nutritional imbalance. We studied the stoichiometric relationships of 11 elements (C, N, P, K, Ca, Mg, Fe, Zn, Mn, Cu, Na) in three species of pine-xylem-feeding insects, Stictoleptura rubra, Arhopalus rusticus (Coleoptera, Cerambycidae) and Chalcophora mariana (Coleoptera, Buprestidae), to elucidate their mechanisms of tissue growth and to match their life histories to their dietary constraints. These beetles do not differ from other Coleoptera in their absolute elemental compositions, which are approximately 1000 (N), 100 (P, Cu) and 50 (K, Na) times higher than in dead but undecayed pine wood. This discrepancy diminishes along the wood decay gradient, but the elemental concentrations remain higher by an order of magnitude in beetles than in highly decayed wood. Numerical simulation of the life history of S. rubra shows that feeding on nutrient-poor undecayed wood would extend its development time to implausible values, whereas feeding on highly decomposed wood (heavily infected with fungi) would barely balance its nutritional budget during the long development period of this species. The changes in stoichiometry indicate that the relative change in the nutrient levels in decaying wood cannot be attributed solely to carbon loss resulting from decomposer respiration: the action of fungi substantially enriches the decaying wood with nutritional elements imported from the outside of the system, making it a suitable food for wood-eating invertebrates.

Biofilm feeding: Microbial colonization of food promotes the growth of a detritivorous arthropod

“…The nutritional contribution of leaf litter biofilm has been generally attributed to the degradation of cellulose (Voriskova and Baldrian 2013; Zimmer and Topp 1997; 1999). Alternatively, the biofilm community may also provide limiting nutrients (Filipiak and Weiner 2014; Thompson et al 2002; Zimmer and Topp 1998) or increase the consumption rate of feeding animals through indicating high-quality food sources (Zimmer et al 2003). In our study, the greater mass increase of individuals feeding on diets with a high amount of biofilm suggests that the biofilm community improves the nutritional value of the primary food source.…”

“…While herbivores may not obtain enough nitrogen by feeding on living plants (Pierce and Berry 2011), the nutrient content of dead plant material is even lower for detritivorous species (Zimmer 2002a). Nevertheless, many herbivores and detritivores successfully consume plant material, but how they actually meet their nutritional requirements is still an unresolved question (but see Filipiak and Weiner 2014). Animals have employed different strategies to compensate for low-quality diet by simply processing more food per unit time (Woods 1999) or aggregate in social groups to have better access to food (Lihoreau et al 2015).…”

“…aphids and amino acid requirements, Gunduz and Douglas 2009), and detritivorous species may profit from microbial colonization of dead plant material (Kautz et al 2002; Zimmer 2002a; Zimmer et al 2003). Another strategy used by wood boring beetles promotes a significant nutritional contribution of fungi that are ingested along with decomposed wood (Filipiak and Weiner 2014; Tanahashi et al 2009). Beetles thus may cover their nutritional needs by feeding on an organism that itself lives on plant material.…”

Plant–insect interactions: the role of ecological stoichiometry

“…Lemoine et al [33] compared the C:N:P resourceconsumer stoichiometry within an entirely terrestrial community, and the results suggest that the colimitation of herbivore development is a result of N and P scarcity in plant tissues. Multielemental colimitation has been demonstrated to shape the life histories and feeding strategies of woodboring beetles [71][72][73], and such a limitation may influence growth, development, and feeding strategies of detritivores [74]. Possible mechanisms that might connect ecological stoichiometry with plant-animal interactions in land ecosystems have been described by Mulder et al [75], who focused on understanding the biodiversity-ecosystem functional relationship and considered stoichiometry an important treat that shapes within-ecosystem relationships.…”

“…Therefore, the TSR index serves as a conservative but convenient tool that facilitates the detection of elements that colimit development and comparisons of the severity of the limitations imposed by various foods on different consumers. On that basis, testable hypotheses can be generated to better understand both (i) the biomass and nutrient flow within and between ecosystems and (ii) the nutritional ecology of organisms and the relationship between organisms and their various food sources, including plant-insect interactions (e.g., [71][72][73][74]). …”