Variability in the size of the nucleus in spermatozoa from Houbara bustards, Chlamydotis undulata undulata

Semen collected from 3-year-old male Houbara bustards contained large proportions (6-40%) of spermatozoa with large nuclei. In these spermatozoa, the length of the nucleus was up to twice the mean length of the nucleus in normal spermatozoa. The lengths of the acrosome, midpiece and flagella were all normally distributed, but the length of the nucleus formed a bimodal distribution. The proportion of spermatozoa with large nuclei varied among males, but not among different semen samples collected from the same male throughout the breeding season. The proportion of motile spermatozoa with large nuclei was half that of normal spermatozoa, but their velocity was significantly greater. After insemination into females, spermatozoa with large nuclei were observed in the outer perivitelline layer of eggs laid, indicating that they were stored and transported within the oviduct and reached the egg at about the time of fertilization. Furthermore, there was no difference in the ability to produce viable progeny in females that were mated with males producing greater proportions of spermatozoa with large nuclei compared with those producing 'normal' spermatozoa. Thus, the abnormal spermatozoa did not appear to impede fertility. There were no signs of triploidy in the males that produced spermatozoa with large nuclei, or in their progeny, as demonstrated by the size of erythrocytes. Therefore, it appears that the spermatozoa with large nuclei were the result of aberrant spermatogenesis.