Comparative Morphology Of The Digestive Tract In Formicidae (Hymenoptera)

Morphology and structures of digestive system and proventriculus of 11 ant species representing three subfamilies(Formicinaeae,Myrmicinae and Ponerinaeae)in north China were studied by optical microscopes,scanning electron microscope(SEM)and transmission electron microscope(TEM),aiming to reveal the role of morphological and structural differentiation of digestive tract in the evolution and feeding differentiation in Formicidae.The main results are as follows:1.The digestive tract of the 11 ant species is very similar in overall structure,composed of esophagus,crop,proventriculus,midgut and hindgut(ileum and rectum).There are some differences in the morphology of proventriculus,rectum,and the number and length of malpighian tubules among three subfamilies.(1)Formicinaeae: The crop is milky,the proventriculus is funnel-shaped with four yellowish brown sepals,followed by the bulb,neck and stomodeal valve.The surface of the midgut is slightly rough,with white dots,the anterior part is wide and the posterior part is narrow.The malpighian tubulesare located at the junction of the midgut and the hindgut,the number are 12~18,and the length is about 1.65~2.11 mm.The ileum is slender,and the rectum is dilated in a transparent form,with five rectum pads on the rectum.(2)Myrmicinae: The anterior part of the crop is yellowish and gradually becomes transparent white in the posterior part.The proventriculus is globular or mushroom shaped,and its posterior part located inside the midgut.The midgut is cylindrical.The malpighian tubule is located at the end of the midgut,its number are 6~10,and the length is 1.46~1.96 mm,about 2-3 times longer than midgut.The ileum is slender.The rectum is dilated and translucent,but cannot find the rectum pad.(3)Ponerinaeae: The crop is yellowish or creamy white,with a thicker crop wall.The proventriculus is slender and its rod-shaped reach into the midgut;the midgut is cylindrical.The malpighian tubule is located at the end of the midgut,its number are 20~24,and the length is 3.05~3.18 mm,about 1.5 times longer than midgut.The ileum was larger and thicker,there are 6 rectal pads.2.There were significant differences in the morphology and structure of the proventriculus in ants from different subfamilies,and there were also slightly differences among species in the same subfamilies:(1)Formicinaeae: The proventriculus is like a funnel,including the sepals,the bulb,the neck and stomodeal valve from top to bottom.There are four sepals in the proventriculus,with a narrow passage in the center of each sepal;the external surface of the sepal wall is limited by a layer of striate muscles,and the inner surface is spiny,toothlike,or striate.There is a "ten" opening at the junction between the bulb and the sepals,forming four channel in the bulb.(2)Myrmicinae: The proventriculus is mushroom shaped or globular,the external surface of the proventriculus is folded to different degrees,the central channel of the proventriculus is the deepest,scattered around,and tends to be flat at the top.(3)Ponerinaeae: The proventriculus is elongated,the top is slightly enlarged,the external surface is a regular and neat wrinkle texture,and the inner surface is also pleated,with several grooves in the central channel.3.The midgut epithelium is composed of two kinds of cells: digestive cells and regenerative cells.There are the apical microvilli and a large number of mitochondria in the digestive cells.The digestive cells have nuclear,rough endoplasmic reticulum,mitochondria,Golgi body,lysosome,lipid granules,polyribosome,etc.The peripheral muscles of the basement membrane are the longitudinal muscle and the ring muscle,respectively.Bacteria and fungi were found between microvilli and in the midgut cells of two species ants.4.The ileum of the ants was slender and has thick cuticle,thin basement membrane,large number of long mitochondria.The cytoplasmic membrane was trapped in the outer wall of the intestine,and a layer of circular muscle and longitudinal muscle were wrapped in the outer part of the intestinal wall.The rectum has thin epithelium,underdeveloped muscles,tissue basement membrane invagination,interlaced cytoplasmic membrane and basal labyrinth with a large number of mitochondria.Based on the comparative morphological study of digestive system of three subfamilies ants,the results showed that the morphology and functional differentiation of digestive tract are closely related to their feeding habits,biological and behavioral characteristics.The morphological characteristics not only provide important evidences for the monophyly of various species of ants,but also provide new information for further exploring the systematic evolution history of the ants from the aspects of behavior,biology and so on.