ZenToks Publication

Chapter 13

Neurosecretory Responses of Native, Endogeic Earthworm Metaphire posthuma (Vaillant, 1868) to Sub-acute Hyperthermic and Hypothermic Stress

Abstract/Preface

Temperature is regarded as an important factor that influences the growth and reproduction of earthworms. During summer, earthworms experience hyperthermic stress, while in winter, they undergo hypothermic stress. Topsoil, endogeic, native earthworm Metaphire posthuma [1], when subjected to sub-acute hyperthermic stress (35◦C) as well as hypothermic stress (4◦C), both types of neurosecretory cells (NSCs; A and B cells) show significant neurosecretory changes. Under sub-acute hyperthermic stress, exudation of profuse mucus and coelomic fluid from the earthworm’s body was noticed, leading to decreased body weight. The sub-acute hyperthermic stress also exerted the presence of cytoplasmic vacuolation as well as depletion of neurosecretory materials (NSM) in both types of NSCs, followed by axonal transport of NSM to the ”zone of accumulation”. Under hypothermic stress, exudation of a small amount of mucus and ejection of scanty coelomic fluid were noticed. The hypothermic stress exerted an increase in the number of deeply stained Type A cells in the cerebral ganglia, besides having partial depletion of nuclear volumes and retarded axonal transport. Accumulation of NSM in the NSCs was also noticed, while the zone of accumulation showed scanty distribution of NSM. The results indicate that the impact of thermal fluctuations is mediated through supra-oesophageal ganglionic NSCs (both type A and type B cells) of Metaphire posthuma [1] as evidenced by histo-morphic variations and changes in secretory dynamics, furnishing a working hypothesis for their ’adaptive value’ to thermal gradient.