The Acrosome Reaction of Sperm from Paphia undulata

Abstract

Acrosome reaction (AR) of the sperm from Paphia undulata, the short-necked or baby clam, was induced with high calcium-artificial seawater (containing 0.3 M calcium chloride). Scanning electron microscopy revealed the occurrence of an average of 41.6 % ± 10.6 sd acrosome-reacted sperm upon the induction. The head of the acrosome-intact sperm consisted of a conical shaped acrosome (0.29 µm ± 0.02 sd long and 0.58 µm ± 0.05 sd diameter) and a conical shaped nucleus (1.29 µm ± 0.08 sd long and 1.28 µm ± 0.05 s.d. diameter). The AR was marked by the initial elongation of the anterior end of the acrosome followed by the rupture of the tip exposing an axial, rod-like, acrosomal process (AP). At the completion of the AR, the fully extended AP (0.51 µm ± 0.04 sd long and 0.16 µm ± 0.01 sd diameter) with a slightly wider base (0.28 µm ± 0.03 sd diameter) surrounded by the empty hull of the acrosome was formed.