Metazoan inhabitants of extreme environments typically evolved from forms found in less extreme habitats. Understanding the prevalence with which animals move into and ultimately thrive in extreme environments is critical to elucidating how complex life adapts to extreme conditions. Methane seep sediments along the Oregon and California margins have low oxygen and very high hydrogen sulfide levels, rendering them inhospitable to many life forms. Nonetheless, several closely related lineages of dorvilleid annelids, including members of Ophryotrocha , Parougia , and Exallopus , thrive at these sites in association with bacterial mats and vesicomyid clam beds.
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In evolutionary biology , adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches. The prototypical example of adaptive radiation is finch speciation on the Galapagos " Darwin's finches " , but examples are known from around the world. Four features can be used to identify an adaptive radiation: .
Adaptive radiation tends to take place under the following conditions: . Darwin's finches are an often-used textbook example of adaptive radiation. Today represented by approximately 15 species, Darwin's finches are Galapagos endemics famously adapted for a specialized feeding behavior although one species, the Cocos finch Pinaroloxias inornata , is not found in the Galapagos but on the island of Cocos south of Costa Rica.
For the ground finches, this niche is a diet of seeds, and they have thick bills to facilitate the consumption of these hard materials. The other finches in the Galapagos are similarly uniquely adapted for their particular niche. The cactus finches Geospiza sp. The mechanism by which the finches initially diversified is still an area of active research.
One proposition is that the finches were able to have a non-adaptive, allopatric speciation event on separate islands in the archipelago, such that when they reconverged on some islands, they were able to maintain reproductive isolation. The haplochromine cichlid fishes in the Great Lakes of the East African Rift particularly in Lake Tanganyika , Lake Malawi , and Lake Victoria form the most speciose modern example of adaptive radiation. Lake Tanganyika is the site from which nearly all the cichlid lineages of East Africa including both riverine and lake species originated.
Lake Tanganyika itself is believed to have formed 9—12 million years ago, putting a recent cap on the age of the lake's cichlid fauna.
The giant or emperor cichlid Boulengerochromis microlepis is a piscivore often ranked the largest of all cichlids though it competes for this title with South America's Cichla temensis , the speckled peacock bass. The cichlids of Lake Malawi constitute a "species flock" of up to endemic species. For example, all members of the Malawi species flock are mouth-brooders, meaning the female keeps her eggs in her mouth until they hatch; in almost all species, the eggs are also fertilized in the female's mouth, and in a few species, the females continue to guard their fry in their mouth after they hatch.
However, a number of particularly divergent species are known from Malawi, including the piscivorous Nimbochromis livingtonii , which lies on its side in the substrate until small cichlids, perhaps drawn to its broken white patterning, come to inspect the predator - at which point they are swiftly eaten.
Lake Victoria's cichlids are also a species flock, once composed of some or more species. Victoria is famously home to many piscivorous cichlid species, some of which feed by sucking the contents out of mouthbrooding females' mouths. Hawaii has served as the site of a number of adaptive radiation events, owing to its isolation, recent origin, and large land area.
The three most famous examples of these radiations are presented below, though insects like the Hawaiian drosophilid flies and Hyposmocoma moths have also undergone adaptive radiation.
The Hawaiian honeycreepers form a large, highly morphologically diverse species group that began radiating in the early days of the Hawaiian archipelago. While today only 17 species are known to persist in Hawaii 3 more may or may not be extinct , there were more than 50 species prior to Polynesian colonization of the archipelago between 18 and 21 species have gone extinct since the discovery of the islands by westerners.
Adaptive radiation is not a strictly vertebrate phenomenon, and examples are also known from among plants. The most famous example of adaptive radiation in plants is quite possibly the Hawaiian silverswords , named for alpine desert-dwelling Argyroxiphium species with long, silvery leaves that live for up to 20 years before growing a single flowering stalk and then dying.
Hawaii is also the site of a separate major floral adaptive radiation event: the Hawaiian lobelioids. The Hawaiian lobelioids are significantly more speciose than the silverswords, perhaps because they have been present in Hawaii for so much longer: they descended from a single common ancestor who arrived in the archipelago up to 15 million years ago.
Many species have been lost to extinction and many of the surviving species endangered. With over species currently recognized, often placed in a single genus Anolis , they constitute one of the largest radiation events among all lizards.
Much like in the case of the cichlids of the three largest African Great Lakes, each of these islands is home to its own convergent Anolis adaptive radiation event. Presented above are the most well-documented examples of modern adaptive radiation, but other examples are known.
On Madagascar, birds of the family Vangidae are marked by very distinct beak shapes to suit their ecological roles. The pseudoxyrhophiine snakes of Madagascar have evolved into fossorial, arboreal, terrestrial, and semi-aquatic forms that converge with the colubroid faunas in the rest of the world. These Madagascan examples are significantly older than most of the other examples presented here: Madagascar's fauna has been evolving in isolation since the island split from India some 88 million years ago, and the Mantellidae originated around 50 mya.
From Wikipedia, the free encyclopedia. A process in which organisms diversify rapidly from an ancestral species. For a more general term to describe any radiation, see Evolutionary radiation. Darwin's finches by John Gould. Key topics. Introduction to evolution Evidence of evolution Common descent Evidence of common descent. Processes and outcomes. Natural history.
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Our Origins: Discovering Physical Anthropology 2 ed. The Ecology of Adaptive Radiation. Oxford University Press. Annual Review of Ecology, Evolution, and Systematics. New York: Alfred A. Knopf, Inc. Molecular Ecology. Lake Victoria Rock Cichlids: taxonomy, ecology, and distribution. Verduyn Cichlids. Tanganyika Cichlids in their natural habitat, 3rd Edition. Malawi Cichlids in their natural habitat, 5th edition. The American Naturalist.
BMC Evolutionary Biology. Darwin's Dreampond: Drama in Lake Victoria. Washington, D. Nature Communications. Biology Letters. Proceedings of the National Academy of Sciences. Bibcode : PNAS Proceedings of the Royal Society B. October Archived from the original on Retrieved June 3, Categories : Speciation Evolutionary biology terminology.
Social implications Evolution as fact and theory Social effects Creation—evolution controversy Objections to evolution Level of support. Wikimedia Commons has media related to Adaptive radiation.
Phylogeny and Adaptive Radiation
We have loaded Previous years questions with explanations Like and Follow us on Facebook and Telegram for latest updates Polychaeta is the largest class of phylum Annelida. This class shows greatest diversity in Phylum Annelida. Majority of the species of polychaetes are marine and exhibit a variety of habits and habitats. And accordingly they show great adaptive diversity.
Chaetopteridae . Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae , which are made of chitin. More than 10, species are described in this class. Common representatives include the lugworm Arenicola marina and the sandworm or clam worm Alitta. Polychaetes as a class are robust and widespread, with species that live in the coldest ocean temperatures of the abyssal plain , to forms which tolerate the extremely high temperatures near hydrothermal vents.