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The insect herbivore gut as a series of chemical reactors: Mathematical modeling and empirical evaluation
Abstract
A mathematical model of digestion for an insect herbivore is developed as a combination of semibatch and plug-flow chemical reactors and tested based on gut morphology, digestive physiology, and feeding behavior. The crop is modeled as a semibatch reactor with periodic input as food; continuous output passes the partially digested food to the midgut. The midgut is modeled as a plug-flow reactor with continuous, variable input described by the crop function. If an insect herbivore maximizes the rate of gain for some limiting dietary component, the model predicts the digestive responses to variable food quality and body size. When food quality or body size decreases, the animal should construct and maintain a relatively larger gut to increase digestive capacity, shorten food residence time (FRT) to process more food, and/or increase digestibility rate (digestibility per food residence time), to increase the time rate of digestive efficiency. In addition, relative gut volume should decrease with increased body weight. Empirical results generally support the model predictions. Melanoplus differentialis (Thomas) (Orthoptera: Acrididae), manipulated gut sizes and FRT as digestive compensatory means to meet their energetic and nutritional requirements in response to changes in food quality and body size. When food quality decreased, the proportion of gut dry weight to body dry weight (G/B) increased linearly while FRT decreased linearly. Faster food passage increased food consumption by grasshoppers; individuals fed more frequently with equal meal length. Compared with three-day-old adults, three-day-old sixth-instar nymphs weighed half as much, but allocated 20% more to their digestive tract, shortened FRT by 16.3%, and spent 38.7% more time on feeding by more frequent, longer meals. In general, 29 species of grasshoppers representing a range of body sizes and life styles, exhibited a quadratic gut-body size relationship. Contrary to the model predictions, digestibility rate did not increase with reduced food quality or decreased body size, suggesting that digestive tactics other than FRT and gut volume can also significantly influence digestion rate.
Subject Area
Ecology|Entomology|Anatomy & physiology|Animals
Recommended Citation
Yang, Yuelong, "The insect herbivore gut as a series of chemical reactors: Mathematical modeling and empirical evaluation" (1993). ETD collection for University of Nebraska-Lincoln. AAI9331436.
https://digitalcommons.unl.edu/dissertations/AAI9331436