A MORPHOLOGICAL EXAMINATION OF SPERM-EGG INTERACTION IN THE FRESHWATER PRAWN,<i>MACROBRACHIUM ROSENBERGII</i>

Abstract

Eggs, covered by a bilayered investment composed of a 0.5µm protein outer layer and a 2.5 µm mucopolysaccharide inner layer, are spawned through an externally held spermatophore following a female's ovigerous molt and mating. Mature sperm resemble everted umbrellas and consist of a cupped base with a single spike projecting from the convex surface. These sperm (<5/egg) attach base-first with the spike oriented perpendicularly to the investment. Within 15 seconds, the spike of the sperm bends at the base and contacts the investment. The spike penetrates the investment, the base is inverted, and fertilization occurs within two minutes. The spike remains briefly as a central core in the fertilization cone. The meiotic division of the egg resumes at this stage. First karyokinesis is completed approximately 6 hours post fertilization, but cytokinesis is suppressed until following the second karyokinesis at 8 hours postfertilization. First and second cytokinesis are simultaneous, and at 9 h the egg cleaves to the four cell stage.