Body mass and growth rates predict protein intake across animals

Abstract

Organisms require dietary macronutrients in specific ratios to maximize performance, and variation in macronutrient requirements plays a central role in niche determination. Although it is well-recognized that development and body size can have strong and predictable effects on many aspects of organismal function, we lack a predictive understanding of ontogenetic or scaling effects on macronutrient intake. We determined protein and carbohydrate intake throughout development on lab populations of locusts and tested whether lab responses can predict results for field populations. Self-selected protein:carbohydrate targets declined dramatically through ontogeny, due primarily to declines in mass-specific protein consumption rates which were highly correlated with declines in specific growth rates. Importantly, lab results for protein consumption rates predicted results for field-collected locusts. However, field locusts consumed nearly double the carbohydrate, likely due to higher activity and metabolic rates. Combining our results with the available data for animals, both across species and during ontogeny, protein consumption scaled predictably and hypometrically, demonstrating a new scaling rule key for understanding nutritional ecology.

How Nutrients Mediate the Impacts of Global Change on Locust Outbreaks

“…Grasshoppers tend to be tight regulators, and a given population will consistently select the same ratio. Most studies have measured ITs in finalinstar juveniles or adult grasshoppers and show interspecific variation spanning from the most protein-biased 1p:0.6c ratio (Melanoplus femurrubrum) (9) to the most carbohydrate-biased 1p:2.5c ratio (Schistocerca cancellata) (130). There can even be substantial variation within a genus.…”

“…For all consumers, protein is the main building block for growing tissues, and carbohydrates (and/or lipids) are the primary energy fuel. Vertebrate studies suggest that protein requirements are generally higher in early ontogeny, matching higher specific growth rates (for a review, see 130). A study of South American locusts (S. cancellata) measuring ITs for each developmental stage from hatchlings to adults demonstrated that mass-specific protein intake decreases in a predictable way with development and decreased growth rate, representing a fourfold decrease…”

“…Beyond the availability of green vegetation, plant nutrients play a significant role in regulating grasshopper population dynamics (23,144). Research over the past decade has revealed connections between low-N environments and locust outbreaks (23,26,78,80,82,83,129,130,134,146). Most plant N is found in the form of protein, an excess of which can limit consumption of other key macronutrients, including digestible carbohydrates (31).…”

“…For locusts who are long-distance migrators with high metabolism, low-N environments can support carbohydrate-loading and heightened survival, egg production, and migration (25,82,129,131). However, the relationships between plant nutrients and locusts can vary through ontogeny and with field conditions (130).…”

Optimum ratio of dietary protein and carbohydrate that maximises lifespan is shared among related insect species

“…Comparative nutrition has long been recognised as a powerful approach to uncover how nutritional needs have evolved (Baker & Czarnecki‐Maulden, 1991 ; Mitchell, 1962 ; Payne & Wheeler, 1968 ). It was used to provide insights into the effects of both macro‐ and micronutrients on health (see Baker & Czarnecki‐Maulden, 1991 ; Lei et al., 2022 , references therein), including the effects of protein on morphological and reproductive traits (Swanson et al., 2016 ; Talal et al., 2023 ). Comparative nutrition studies are few because it is difficult to obtain a single dataset that maps the effects of specific nutrients to life‐history traits, such as lifespan or reproduction.…”