Chimpanzees and bonobos, the closest human species, are known to have diverged about 6 million years ago. At some point, groups of the same ancestor became different servants. There is still no clear answer to how this specification occurs. There are only several theories that do not cross each other because they are geographically separated from each other, and that occurs in the process of accumulating different mutations in each group, or that different natural selection or sex selection occurs depending on the group. Even more enigmatic, speciation sometimes occurs between groups with overlapping habitats. A recent study published in science is based on the analysis of the two birds'Sporophila iberaensis and'Sporophila hypoxantha, which live in Argentina's Ibera National Park. It has been reported that speciation in habitats appears to occur through two sequestration stages, with pre-reproductive sequestration first, followed by post-reproductive sequestration, by accumulating intrinsic mutations in the genome over the course of millions of years thereafter.
Both the Ivera planters and the tan pear planters belong to the southern capuchino seedeater family'. The southern cappuccino planter is one of the fastest species of birds, and over the past million years, more than 10 species have diverged within the same habitat. There is not much difference in ecology or genomics between divergent species, which can be distinguished by the color of the male's feathers or the sound of a song. And it is known that hybrids that can reproduce between species are easily made. The researchers monitored 128 nests of both species during the two breeding seasons. In addition, genomic analysis and behavioral experiments were conducted on 80 freshly hatched baby birds and 126 adults. The effect of the selective crossing of these two species on the maintenance of the species, phenotypic characteristics that lead to the identification of self and homogeneity, the underlying genomic information, and where the genetic information originates were analyzed.
Unlike males, females of these two species are similar in appearance, making it difficult to distinguish with the naked eye, but the researchers conceived that birds can see colors in the ultraviolet region outside the human visible region. And in the bird's field of view, we checked whether the females' feather colors were different, but it wasn't very different. On the other hand, the results of analyzing the genomes of paired females and males revealed that the birds were paired with the same species. Birds often breed with unpaired individuals, so the researchers also tested the paternity of the hatched offspring. 52% of the males were fathers, but all males of the same kind were fathers. All of these results, the researchers interpret, suggest that they choose to mate. The two species have consistent habitats, consistent breeding seasons, and pecking together on the same grass, with selective mating taking place.
If so, the difference between the Ibera planter and the tan pear planter is the male feather color and the unique song they sing. To see if these traits are signals of selective mating, the researchers experimented with two male species with varying feather colors and multiple species of singing. As a result, it can be seen that males react most aggressively when they hear the same kind of male feathers and singing. It was implied that competing for mating were other males of their kind, and their feathers and vocalizations were the clues to distinguish them. The difference in feather color is likely to be based on genetic differences, and species-specific vocalization is directly culturally learned while growing, but in addition to this, it is likely to have a genetic element. To investigate this, the researchers analyzed their genome. As a result, the researchers first reported that their genomes were not significantly different, as expected. However, twelve genes showing a large genetic difference between the two species were identified, including genes TYRP1, OCA2, and HERC2 related to melanin pigments. These genes are likely to be related to species-specific male feather color.
Based on these results, the researchers found that when speciation occurs within the same habitat, characteristics such as the color of the feathers and the singing sound that act in the pre-mating stage change first, and based on this, when selective mating continues for a long time, gradually. As genetic changes accumulate within each group, it seems that the differentiation of the genome occurs along with it, he explained. This study presents two steps to explain speciation within a seemingly enigmatic habitat.