Tiaris obscura

Dull-colored Grassquit

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Habitat and Adaptations

Tiaris obscura is distributed throughout Venezuela, Colombia, Ecuador, Peru, Bolivia and Argentina. (32) Its habitat differs from humid forests, through scrub, to open areas of woodland and farmland, and from lowlands to altitudes of 2000 meters in the Andes Mountains. Its primary source of food is seed, and feeds either alone or in pairs. (32) Its main predators are other larger birds such as eagles or falcons in addition to the threat that humans propose. It has adapted from Darwin's Finches to have a small, thick beak which fullfils its purpose of obtaining food.(29)

Ancestry

The Tiaris obscura is the closest living species (genetically) to the 15 Darwin's Finches.(28) T. obscura has evolved to have a small body frame as well as a small, thick beak. All of Darwin's Finches are closely related to one another and have basic common characteristics such as cone-shaped bills, and are all mainly seed-eating finches.(20) Through simple observation, the Vegetarian Tree Finch is thought to be a direct descendant of Tiaris obscura, as both have a small body, short and thick beak and the diets of the two are essential the same. The first finch (common ancestor) was a ground finch who was seed-eating. Through adaptive radiation, 3 new species of ground finch, 3 new species who ate cacti and seeds, one living in trees and eating seeds, and 7 insect-eating, tree-dwellers.(29)(22) The prominent difference in all of these species is the variation of beak size and shape.(1) For example, compared to the small, thick beaks of Tiaris obscura, the tree-dwelling, insect-eating finches had much longer and skinnier beaks. Since the ancestral finch(of Darwins Finches) was a ground finch, its beak was most likely short, squat and thick. As evolution progresses, the possibility of a species without the ability to fly arises. With that in mind, the wings of the finch would then be vestigial for flying, but could aid the finch in other scenarios. (30) However, these vestigial structures would still be visible and could lead one to hypothesize that these finches originally were derived from a species of finch that had the ability to fly.(30)


Clade(s) of Tiaris obscura

Tiaris obscura is a part of a clade which includes Caribbean genera, Bannaquit, and Darwins Finches (Certhidea, Platyspiza, Pinaroloxias, Camarhynchus, and Geospiza) (14) The Caribbean genera is thought to be of similar descent as Darwin's Finches, but it has not been proven yet. All of the different species have some similarity between them, whether physical or genetical. For example, the Geospiza difficilis varies from the Tiaris obscura in that it has a sharp, short beak, while Tiaris has a blunt, short beak.(32) Also, the Warbler finches (Certhidea) differ in that they have short, thin beaks to the Tiaris' short, thick beaks.(33) The Pinaroloxias is the only finch of the Darwin's Finches not to have originated on the Galapagos Islands. Its beak is long and thin to supplement its diets of insects.(34)

Proof of Evolution?

Darwin's Theory of Evolution by Natural Selection is a battleground for science and religion. His theory is a highly controversial one, yet proof exists that species continue to grow and evolve (into different species) over time. Darwin's Finches are a textbook example of evolution. However, even they had to have evolved from a species(Common ancestor). Through geographic distribution and isolation as well as reproductive isolation, Darwin's Finches are believed to have originated from the Tiaris family.(37)(22)(20). Darwin's Finches diverged soon after the Tiaris family diverged from one another as well. Some members of Tiaris obscura were spread throughout the Caribbean, and underwent adaptive radiation.(22) Then, they spread to South America, which there, through adaptive radiation as well as geographic distribution (isolation) and reproductive isolation, the Tiaris obscura came to be.(20)(22) However, the Tiaris family also diverged to the Galapagos Islands and there through geographic isolation, came to be Darwin's Finches.(22)(20) Today, with modern technology, scientists are able to decipher through the DNA of organisms and find links to one another, thus proving that species B was a result of evolution from species A. In the case of Tiaris obscura, scientists have proven that it is the closest living species to the original Darwin's Finches. Through observation of diet, scientists assume that the Vegetarian Tree Finch is (could be) a direct descendent of Tiaris obscura.(22)(37) To prove relation between Darwin's Finches, assumed to be descendants of Tiaris obscura, scientists used two mitochondrial DNA segments and two nuclear markers to identify the most closely related species to Darwin's Finches. The study showed that the most closest related organism to Darwin's Finches was the species known as Tiaris obscura.(22)(20) As well as genetic similarity, Darwin's Finches and Tiaris are both similar in morphologies. There is especially similarity in the Vegetarian Tree Finch and Tiaris obscura. Both have a small body frame, and both have short, thick beaks. Also, it could be hypothesized that the insectivorous tree finch diverged from Tiaris because its beak is not short and thick but rather thin and long, to supplement its diet of insects.(37) Also, the use of fossils and fossil records can help support Darwin's Theory of Evolution by Natural Selection. For example, it is through fossils can we make the assumption that birds have evolved from winged dinosaurs. (38) Alvarezsauridae was the first dinosaur believed to have the ability to fly or at least, glide. Then, throughout different species, it is observed that the arms begin to get shorter and shorter until in Ichthyomis, the forearms disappear completely. Then, in Aves, the appearance of wings takes form. From then which evolves the modern bird. (38)(39)