Parthenogenesis or ‘virgin birth’ is embryonic development in unfertilized eggs. It is a routine means of reproduction in many invertebrates. However, even though parthenogenesis occurs naturally in even more advanced vertebrates, like birds, it is mostly abortive in nature. In fact, multiple limiting factors, such as delayed and unorganized development as well as unfavorable conditions developing within the unfertilized egg upon incubation, are associated with termination of progressive development of parthenogenetic embryos. In birds, diploid parthenogenesis is automictic and facultative producing only males. However, the mechanisms controlling parthenogenesis in birds are not clearly elucidated. Additionally, it appears from even very recent research that these mechanisms may hinder the normal fertilization process and subsequent embryonic development. For instance, virgin quail and turkey hens exhibiting parthenogenesis have reduced reproductive performance following mating. Also, genetic selection and environmental factors, such as live virus vaccinations, are known to trigger the process of parthenogenesis in birds. Therefore, parthenogenesis has a plausible negative impact on the poultry industry. Hence, a better understanding of parthenogenesis and the mechanisms that control it could benefit commercial poultry production. In this context, the aim of this review is to provide a complete overview of the process of parthenogenesis in birds.
A technique was developed to determine the total number of spermatozoa stored in the uterovaginal junction of hens. After insemination of spermatozoa treated with the nuclear fluorescent dye bisbenzimide, oviductal tissue was collected from hens and homogenized. Samples of homogenate were dried, and the number of spermatozoa mm−2 was determined with the use of a fluorescence microscope. When spermatozoa were added to excised uterovaginal junction tissue before homogenization, results indicated a 1:1 linear relationship between actual numbers of spermatozoa added to the tissue and calculated numbers of spermatozoa added to the tissue. This new technique was used to show that insemination of hens with 25, 50 or 100 × 106 spermatozoa resulted in a linear increase in the number of spermatozoa stored in the uterovaginal junction. Insemination of hens with 328 × 106 spermatozoa produced no increase in uterovaginal junction storage of spermatozoa over insemination with 100 × 106 spermatozoa. At the maximum sperm storage tubule filling dose of 100 × 106 spermatozoa, only 0.22% of the spermatozoa inseminated were found in the uterovaginal junction 24 h after insemination. Treatment of spermatozoa with bisbenzimide had no detrimental effects on fertility or penetration rates when compared with untreated (control) spermatozoa. However, when spermatozoa were treated with bisbenzimide hatchability of fertile eggs was reduced. In conclusion, this new fluorescence technique appears to be valuable in determining the total number of spermatozoa stored in the uterovaginal junction of hens.