Relative roles of jelly layers in successful fertilization of Bufo japonicus

The uterine eggs of Bufo japonicus are invested with four jelly layers, J₁, J₂, J₃, and J₄, from inner to outer, respectively. When eggs were inseminated with serially diluted sperm suspensions, a higher concentration of sperm was required for successful fertilization of dejellied uterine eggs in solubilized jelly preparation than fertilization of fully jellied uterine eggs. When the eggs taken from different portions of oviduct were inseminated, the eggs invested with J₁J₂J₃ were fertilized as effectively as fully jellied uterine eggs. Those with J₁J₂ were fertilized at lower frequency but those with J₁ and a thin J₂ were hardly fertilizable. Eggs artificially invested with J₃J₄ were less fertilizable than the J₁J₂ eggs, but addition of J₃J₄ to J₁ and a thin J₂ made eggs as fertilizable as the J₁J₂ eggs. Observations on the sperm penetrating the jelly indicated that these differences in fertilizability were dependent on two variables: an increased number of sperm penetrating into J₃ and J₄, and an increased rate of acrosome reacted sperm in J₁ and J₂. © 1993 Wiley‐Liss, Inc.