May 9, 2024 — Foods are complex mixtures of chemical compounds provided in various levels of digestibility that humans and animals ingest for nutritional support. Often, animals need to ingest several food types in order to fulfill their multidimensional nutritional needs and may suffer health consequences by not eating the needed nutrients in specific quantities and ratios. Understanding what considerations influence dietary choices is, thus, a very important but extremely challenging question to study. The authors addressed this challenge by focusing on the simple but mysterious diet of the desert isopods—an interesting species of pill-bug that eats dry leaves and large quantities of nutritionally poor biological soil crust (the upper layer of desert soils that harbor many microorganisms).

The researcher fed isopods with natural and artificial foods and found that when allowing a choice, isopods can tightly regulate their food consumption to meet a very specific ratio of proteins, sugars, and calcium. Isopods receive most of their proteins and sugars from dry leaves and eat soil crust to meet their very high calcium needs. The exoskeleton of isopods is made of calcium carbonates that they must consume in large quantities to grow. However, when isopods could supplement leaf litter with artificial sources of calcium, they successfully met their exact calcium needs but suffered reduced growth. The authors used gamma-radiation to kill the microorganisms of the soil crust while maintaining its nutritional value. They measured the isopods’ food assimilation efficiency and growth rate in comparison to isopods that ate the untreated crust. The authors found that isopods eat the crust to incorporate live microorganisms into their digestive system. Those microbes assisted in improving the digestion of fibrous plant litter. The authors concluded that isopods eat foods that allow them to meet their nutritional needs by providing nutrients but also by helping them to digest. These revolutionary findings may shed new light on how different animals and humans choose their diet by considering the food’s nutrients and the existence of digestive assisting agents. Humans do not eat soil crust but may think about the general insights of this interesting study during their next visit to the local grocery shop.

Animals optimize their fitness by assimilating specific quantities and ratios of macronutrients and mineral nutrients. To understand this phenomenon, the team conducted extensive field and laboratory experiments focusing on the dietary preferences of desert isopods. Contrary to expectations, wild isopods exhibited a preference for macronutrient-poor biological soil crust (BSC) over plant litter, consuming three times more of the former.

The research revealed that desert isopods rigorously regulate their intake of macronutrients and calcium, with phosphorus intake remaining unaffected. Moreover, the team observed that despite equivalent calcium ingestion, isopods thrived better when consuming BSC compared to artificial foods. Notably, isopods consuming gamma-radiation-sterilized BSC exhibited increased consumption but slower growth rates compared to those consuming live BSC, suggesting the crucial role of ingested microorganisms in facilitating litter digestion.

Dr. Moshe Zaguri, the study’s lead researcher, commented, “Our findings underscore the complexity of dietary decision-making among desert isopods and highlight the importance of considering multifaceted factors in understanding trophic interactions.”

Understanding the complex nutritional and functional considerations driving the dietary choices of desert isopods is crucial for advancing our knowledge of ecological dynamics. This research sheds light on how these animals optimize their fitness by regulating nutrient intake and preferring specific food sources. By uncovering the role of ingested microorganisms in facilitating digestion and growth, the study emphasizes the interconnectedness of organisms and their environment.

The research paper titled “Dust you shall eat”: the complex nutritional and functional considerations underlying a simple diet” is now available in Dryad and can be accessed at https://doi.org/doi:10.5061/dryad.tdz08kq57