Remodeling of the intestine during metamorphosis of Microhyla berdmorei (Anura: Microhylidae)

Abstract

Remodeling of the intestine of a microhylid frog, Microhyla berdmorei along with changes in diets between larval stages and adult stage was studied for the first time from pre-metamorphic to metamorphic climax. Elongation of the intestine from Gosner stage 25 to stage 40 significantly correlated with the elongation of the larval body. From stage 40 to stage 46, the lengths of tadpole and intestine abruptly reduced, showing perfect negative correlation between Gosner stage with that of total body length and gut length. Whereas Gosner stages 25 to 46 revealed non-significant relationship with total tadpole length and gut length. Within 10 – 17 days (during spontaneous metamorphosis), reduction of the length of Microhyla berdmorei tadpole intestine (from Gosner stage 40 – stage 46) by about 82% was observed. Light microscopic and transmission electron microscopic (TEM) studies showed that the primary epithelium (PE) of the larval intestine was replaced by the secondary epithelium (SE) at stage 46 where the intestinal folds (IF) appeared as several circular folds lined by mucus membrane with elaborate connective tissue and muscles. The columnar epithelial cells of the mature animal differed in their fine structural organization from their larval precursors. The present study indicated that the long small intestine with a single tubular layer of larval epithelium lined by a very little connective tissue or muscle of an omnivorous tadpole transformed into a carnivorous frog possessing the adult type of complex organ comprising of a multiple folded epithelium with elaborate connective tissue and muscle, accompanied by the programmed cell death of larval epithelium by metamorphosis.