Parthenogenesis, a form of asexual reproduction, allows for the development of an embryo from an unfertilized egg. This phenomenon, sometimes referred to as “virgin birth,” occurs across the animal kingdom in various species, including insects, reptiles, and fish. While less common in more complex animals, the domestic turkey is a notable example of a bird capable of this reproductive strategy. This process enables a female to produce offspring without any genetic contribution from a male.
The Biological Mechanism in Turkeys
The process of parthenogenesis in turkeys is rooted in their sex-determination system. Unlike mammals (XX/XY), birds use a ZW system. Males possess two Z chromosomes (ZZ), while females have one Z and one W chromosome (ZW).
When a female turkey’s unfertilized egg begins to develop, it starts as a haploid cell containing only one sex chromosome (either Z or W). The developmental process initiates through the doubling of this cell. This conversion to a diploid state, with a full set of chromosomes, allows the embryo to grow.
An outcome of this process is that only certain chromosome combinations are viable. An egg that doubles a W chromosome (WW) will not develop. Consequently, only eggs that double the Z chromosome to become ZZ can develop into viable embryos. This means all offspring produced through parthenogenesis in turkeys are male. These resulting males are not clones of their mother.
Triggers and Prevalence
Parthenogenesis in turkeys is a rare event in nature, but its frequency can be influenced by several factors. The tendency for unfertilized eggs to begin development can be increased through selective breeding. For example, in some selectively bred flocks of the Beltsville Small White turkey, nearly half of all unfertilized eggs showed some embryonic development.
The exact triggers are not fully understood, but several factors are thought to play a role. The prolonged absence of males in a flock is considered a potential stimulus, allowing a female to perpetuate the species when no mates are available.
Another proposed trigger involves viral infections. Some scientific studies have suggested that certain viruses may be able to stimulate the egg to begin cell division, effectively initiating the parthenogenetic process. This stimulation provides a pathway for the embryo to start developing without the need for fertilization from a male’s sperm. While the precise mechanisms are still under investigation, these factors highlight the complex interplay between genetics and environment in this form of reproduction.
Viability of the Offspring
Although turkey hens can produce offspring without a mate, the viability of these young, known as parthenotes, presents a mixed picture. A large percentage of embryos that begin development through parthenogenesis die very early in the incubation period. Only a small fraction of these embryos survive to hatch. This high mortality rate underscores the challenges inherent in this reproductive method compared to sexual reproduction.
The poults that do successfully hatch and survive can grow into adult males that are often physically indistinguishable from those produced through traditional mating. They are capable of normal behaviors, including mating. This demonstrates that parthenogenesis can, in rare instances, produce a seemingly healthy, mature turkey.
However, these male turkeys often face underlying health and reproductive issues. Studies have shown that males produced via parthenogenesis may have slower growth rates and reach a smaller adult size than their sexually reproduced counterparts. Furthermore, they can exhibit reduced fertility, possessing smaller testes. These factors can limit their overall reproductive success and long-term contribution to the population.