Non-Seasonal Breeding in a Porcellionid Isopod

Abstract

Female Porcellio laevis (Latreille) raised in the laboratory first reproduced when 7 months old and can breed up to 7 times during their life time irrespective of season. In that, this species differs from most other isopod species studied so far. After a single mating, a female can breed several times without the presence of a male presumably because she stores sperm. Females known to be virgins never became gravid, thus there is no evidence of parthenogenesis. Males are therefore essential for reproduction in P. laevis. Sex ratio in the laboratory population was found to be 1 male to 2.5 females. The average time intervals between consecutive broods is 7.7 weeks. Most females reproduce 3 or 4 times in their lifetime (e.g., until the age of about 1 year). The average number of broods is 3.1. Number of mancas in the brood is positively correlated to weight of the mother. The average number of mancas in a brood is 66.6. The average survival of mancas until they are 7 or 8 months old is 44.7%. The ovary of P. laevis is typical of an iteroparous isopod in that it contains both large and small oocytes. However, it differs from that known for all other isopod species by having a few large oocytes persisting in the ovaries at all times. Apparently, oocyte cohorts do not mature simultaneously as indicated by the fact that some large oocytes were present at all times but move a few at a time into the brood pouch at a continuous rate.