Variation in sperm morphology of a murine rodent from South-East Asia: the Greater Bandicoot Rat, Bandicota indica

Abstract

In most mammals the male gamete, the spermatozoon, has a fairly consistent, species-specific shape although in a few species some variability is evident. The present study set out to determine the extent of sperm variability in a population of a South-East Asian murine rodent, Bandicota indica, that was sampled during both the breeding and non-breeding periods. We found that, regardless of the time of year when the animals were obtained, males had sperm present in the cauda epididymides but a high degree of variability was always evident including the presence of some grossly abnormal forms. The abundance of abnormal sperm tended to be greater during the non-breeding period. These animals also have relatively small testes, thus the occurrence of the variable sperm populations is consistent with the hypothesis that depressed levels of intermale sperm competition result in a relaxation of the genetic control of male germ cell maturation during spermiogenesis and thus the production of polymorphic sperm populations.