Ultrastructure of seminal receptacle and sperm storage in Armadillidium granulatum Brandt (Isopoda: Oniscidea)

Abstract

The aim of this study was to evaluate the efficacy of sperm storage in the seminal receptacle in females of Armadillidium granulatum after the first mating and in the absence of further mating. Females of A. granulatum were bred in the laboratory, isolated from males, until they were sexually mature, and then they were allowed to mate. They were then isolated again from the males and observed to evaluate their reproductive behaviour until their natural death. Some females were sacrificed at various time intervals to carry out ultrastructural observations of the seminal receptacle and of the spermatozoa inside. All the females had the first brood at about 20 days after mating; a little less than 50% of the females had a second brood during the first reproductive season; only 10% of the females had another brood during the second reproductive season. The average number of juveniles produced by each female was about 25 at the first brood, but fall with the successive broods; the sex ratio of juveniles was about 1 male : 4 females. The ultrastructural observations showed some variations in the seminal receptacle wall over time with respect to reproductive activity while there was no appreciable modification as regards the spermatozoa present in the organ, the number of which progressively decreased during the period of reproductive activity.