Speciation is a term used in evolutionary biology to refer to the process by which a new species emerges in a group that has isolated itself from other members of an ancestral population and has evolved unique traits. In most cases, this process is a relatively slow one, occurring over many generations and thousands or even millions of years. The formation of a new species typically happens after individuals become geographically isolated from their original population, and the two groups lose their ability to exchange genetic material and generate viable offspring with each other. But in some circumstances, new species can form before a group of individuals becomes physically separated from, or genetically incompatible with, its ancestral population.<\/p>\n
A study published March 25 in Science<\/em> suggests that the emergence of minor physical or behavioral traits, such as distinctive plumage or song patterns, is sufficient to stimulate the emergence of new species of capuchino seedeaters, a group of small birds of the genus Sporophila<\/em> that includes more than 40 species occurring primarily in open-field environments in South America. Capuchino seedeaters are about 10 centimeters long, weigh less than 10 grams, and are appreciated for their beautiful song.<\/p>\n The study, conducted by an international team of biologists and ornithologists, found that two species in this group\u2014the Ibera seedeater (Sporophila iberaensis<\/em>) and the tawny-bellied seedeater (Sporophila<\/em> hypoxantha<\/em>)\u2014share the same habitat (the north portion of Esteros del Iber\u00e1, a wetland area in central Argentina), have nearly identical genomes, and are able to produce fertile hybrids, as demonstrated in captive breeding experiments. They have neighboring nesting territories, breed in the same season, and forage together on the same grasses. Yet, based on experiments in the field and genetic analyses, females nearly always mate with males of the same species and avoid suitors of the neighboring species. In the study, researchers analyzed the DNA of 37 male and female individuals of the two species.<\/p>\n According to the authors of the paper, females discern the species of their mating partners by their plumage coloring and song. Over time, this sexual preference is believed to have caused the two seedeater species to diverge. \u201cThe study shows that species can emerge and diverge rapidly through variation in traits such as plumage and song; it also indicates that genetic separation can take much longer to arise,\u201d says Lu\u00eds F\u00e1bio Silveira, curator of the ornithology department at the University of S\u00e3o Paulo Zoology Museum (MZ-USP) and one of the authors of the paper. Silveira is currently heading a FAPESP-funded research project to study species endemic to Atlantic Forest patches in the Northeast, including several seedeater species. \u201cMorphological and behavioral isolation occurs long before genetic isolation does, and this could be a major factor in the emergence of new species.\u201d<\/p>\n Three key criteria are currently used to discern new bird species: morphology, genetic material, and song. For some authors, a difference in one only one of these parameters is sufficient to claim the existence of a new species, while others are more conservative and will only make such claims when at least two parameters differ.<\/p>\n<\/div>