MADRID, 13 (EUROPA PRESS)
New evidence shows that sex reversal is more common in wild birds than previously thought, with potential implications for endangered species.
In a study of nearly 500 birds from five Australian species—including magpies, kookaburras, pigeons, and lorises—researchers at the University of the Sunshine Coast found that up to 6% had the physical characteristics of one sex but the genetic makeup of the other.
"This indicates that sex determination in wild birds is more fluid than we thought and can persist into adulthood," said Dominique Potvin, associate professor and co-author of the study, published in Biology Letters, in a statement.
GENETICALLY FEMALES WITH MALE REPRODUCTIVE ORGANS
The birds were examined postmortem after being admitted to wildlife hospitals in southeast Queensland with unrelated injuries or illnesses. Researchers identified their reproductive organs and analyzed their DNA to determine their genetic sex. "One of the key findings was that 92% of the sex-reversed birds were genetically female but had male reproductive organs," explained Dr. Potvin.
We also discovered a genetically male kookaburra with reproductive activity, large follicles, and a distended oviduct, indicating recent egg production.
While sex reversal is known in fish, amphibians, and reptiles, it is rarely documented in wild birds and mammals. This study provides a foundation for understanding this phenomenon in Australian bird populations.
"Understanding how and why sex reversal occurs is vital for conservation and for improving the accuracy of bird research," said Dr. Potvin.
Lead author Dr. Clancy Hall noted that the presence of sex-inverted individuals could affect reproductive success in wild populations, raising concerns about the impact on endangered species.
"This can lead to skewed sex ratios, reduced population sizes, altered mate preferences, and even population decline," said Dr. Hall, who co-led the study as part of her doctoral research at UniSC.
The presence of these sexually ambiguous birds also challenges traditional methods for identifying bird sex, such as genetic markers, plumage, or behavior.
"The ability to unequivocally identify the sex and reproductive status of individuals is crucial in many fields of study," said Dr. Hall. "We've established that DNA testing doesn't always reflect the suspected sex."
Bird researchers often take small DNA samples from blood or feathers and make decisions based on the results indicating male or female, but this can be wrong in up to 6% of cases.
For the study, sex-reversed birds were classified as genetic males with a complete female phenotype, genetic females with a complete male phenotype, and those showing a combination of testicular and ovarian characteristics.
The causes of sex reversal in birds are unclear, and researchers say more studies are needed to better understand the environmental triggers and the potential impact on endangered species.
They claim that environmental factors, such as endocrine-disrupting chemicals and high levels of stress hormones, may influence sexual development in birds.
For example, the reproductively active and genetically male kookaburra was found in a peri-urban agricultural area, where such chemicals can accumulate.
