Get acquainted with the sex lives of white-throated sparrows if you think navigating the human dating scene is challenging (Zonotrichia albicollis). Any one of these birds can only mate with one-fourth of the species. Why? for the reason that they chose to evolve two additional sexes on top of the two that they already had.
Biologists in Canada, where the white-throated sparrow is native, Elaina Tuttle and Rusty Gonser, discovered the genetic anomaly. Together, they discovered that the species had undergone a genetic mutation that resulted in the flipping of a sizable portion of the bird’s chromosome, giving rise to four genotypes that could only successfully reproduce when mixed with other genotypes of the same species.
According to Nature, “This bird acts like it has four sexes.” Evolutionary biologist Christopher Balakrishnan from East Carolina University in Greenville, North Carolina, said. He worked with Tuttle and Gonser. “Only 25% of the population can mate with one individual. Sexual systems with more than two sexes are rare.
A species is broadly defined as an animal that can reproduce successfully to produce viable offspring, i.e., children who can have children. Strangely, the two chromosomes of the species have evolved into distinct subtypes that determine which birds can successfully mate with whom, and the white-throated sparrow has evolved to make this a little more challenging for itself.
There are two morphs of white-throated sparrows in North America: those with white stripes on their heads and those with tan stripes. Although The White Stripes (not the band) are good singers, they are also aggressive and promiscuous, showing little sign of parental nurturing behaviors. The tan stripes, on the other hand, are monogamous, decent parents, but terrible singers.
Despite their differences, tan stripes and white stripes can only mate. What does the adage “opposites attract” mean?
The odd division within the one species can be explained by the fact that white stripes have several inversions where portions of the genome have effectively been cut off and reversed while tan stripes have two identical copies of each chromosome.
Tuttle and Gonser conducted additional research on these inversions and discovered that they essentially mixed up the genes to produce the two morphs. The XX and XY chromosomes in mammals, which determine mammalian sex, and the ZW sex-determination system, which determines a bird’s sex, are both products of inversions; however, the white-throated sparrow is unusual in having created two extra chromosomes to effectively give itself four sexes.
Gonser remarked, “There may be many more species with peculiar sex chromosomes, and we’ve simply never bothered to look.