Meeting Abstract

P3.91  Friday, Jan. 6  Characterization of Midgut Morphology in Manduca sexta and the Development of a Model of Digestion CONNELL, K. P.*; RAITHEL, S. J.; KERKOFF, A. J.; ITAGAKI, H. ; Kenyon College; Kenyon College; Kenyon College; Kenyon College connellk@kenyon.edu

We aimed to characterize the growth and change in the midgut of larval Manduca sexta and see how changes in morphology affected digestive processes by utilizing a simplified model. We sampled from each of the five instars and measured changes in midgut perimeter over development. Our results so far demonstrate that the perimeter of the midgut scales as weight to the 0.48 power (r2 = 0.8651, ANOVA p=0.00). This value indicates that the perimeter is increasing at a greater rate than by isometric growth, which would predict an exponent of 0.33. Observation of the morphology suggests that the increase in the level of infolding of the gut wall is responsible for the greater perimeter. This increase can have a huge impact on an organism’s digestive capabilities and feeding behavior. To explore this, we characterized the midgut of Manduca sexta as a plug flow chemical reactor and parameterized the gut with our data to see how different sizes affected reactor performance. Based on our model, we made predictions about how maximal absorption rate, optimal consumption rate, optimal gut content flow rate, gut passage time, and absorption efficiency scale with weight. The predicted optimal consumption rate scaled as weight to the 0.89 power, a good approximation of third, fourth, and fifth instar caterpillar food intake. The predicted maximal amino acid absorbance rate scaled as weight to the 0.74 power, which overestimated the observed amino acid assimilation to an increasing degree as the caterpillar grew. However, the observed dry growth scaled as weight to the 0.88 which was very close throughout ontogeny to the predicted maximal absorbance rate. This model offers insights into digestion in this insect; we believe our results support the hypothesis that Manduca optimize their behavior to maximize absorbance given their gut morphology.