Adaptive radiation

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.[1][2] Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits. The prototypical example of adaptive radiation is finch speciation on the Galapagos ("Darwin's finches"), but examples are known from around the world.

Darwin's finches.jpeg
Four of the 14 finch species found in the Galápagos Archipelago, which are thought to have evolved via an adaptive radiation that diversified their beak shapes, enabling them to exploit different food sources.


Four features can be used to identify an adaptive radiation:[2]

  1. A common ancestry of component species: specifically a recent ancestry. Note that this is not the same as a monophyly in which all descendants of a common ancestor are included.
  2. A phenotype-environment correlation: a significant association between environments and the morphological and physiological traits used to exploit those environments.
  3. Trait utility: the performance or fitness advantages of trait values in their corresponding environments.
  4. Rapid speciation: presence of one or more bursts in the emergence of new species around the time that ecological and phenotypic divergence is underway.


Adaptive radiation tends to take place under the following conditions:[3]

  1. A new habitat has opened up: a volcano, for example, can create new ground in the middle of the ocean. This is the case in places like Hawaii and the Galapagos. For aquatic species, the formation of a large new lake habitat could serve the same purpose; the tectonic movement that formed the East African Rift, ultimately leading to the creation of the Rift Valley Lakes, is an example of this. An extinction event could effectively achieve this same result, opening up niches that were previously occupied by species that no longer exist.
  2. This new habitat is relatively isolated. When a volcano erupts on the mainland and destroys an adjacent forest, it is likely that the terrestrial plant and animal species that used to live in the destroyed region will recolonize without evolving greatly. However, if a newly formed habitat is isolated, the species that colonize it will likely be somewhat random and uncommon arrivals.
  3. The new habitat has a wide availability of niche space. The rare colonist can only adaptively radiate into as many forms as there are niches.


Darwin's finches

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).[4] Darwin's finches are not actually finches in the true sense, but are members of the tanager family Thraupidae, and are derived from a single ancestor that arrived in the Galapagos from mainland South America perhaps just 3 million years ago.[5] Excluding the Cocos finch, each species of Darwin's finch is generally widely distributed in the Galapagos and fills the same niche on each island. For the ground finches, this niche is a diet of seeds, and they have thick bills to facilitate the consumption of these hard materials.[4] The ground finches are further specialized to eat seeds of a particular size: the large ground finch (Geospiza magnirostris) is the largest species of Darwin's finch and has the thickest beak for breaking open the toughest seeds, the small ground finch (Geospiza fuliginosa) has a smaller beak for eating smaller seeds, and the medium ground finch (Geospiza fortis) has a beak of intermediate size for optimal consumption of intermediately sized seeds (relative to G. magnirostris and G. fuliginosa).[4] There is some overlap: for example, the most robust medium ground finches could have beaks larger than those of the smallest large ground finches.[4] Because of this overlap, it can be difficult to tell the species apart by eye, though their songs differ.[4] These three species often occur sympatrically, and during the rainy season in the Galapagos when food is plentiful, they specialize little and eat the same, easily accessible foods.[4] It was not well-understood why their beaks were so adapted until Peter and Rosemary Grant studied their feeding behavior in the long dry season, and discovered that when food is scarce, the ground finches use their specialized beaks to eat the seeds that they are best suited to eat and thus avoid starvation.[4]

The other finches in the Galapagos are similarly uniquely adapted for their particular niche. The cactus finches (Geospiza sp.) have somewhat longer beaks than the ground finches that serve the dual purpose of allowing them to feed on Opuntia cactus nectar and pollen while these plants are flowering, but on seeds during the rest of the year.[4] The warbler-finches (Certhidea sp.) have short, pointed beaks for eating insects.[4] The woodpecker finch (Camarhynchus pallidus) has a slender beak which it uses to pick at wood in search of insects; it also uses small sticks to reach insect prey inside the wood, making it one of the few animals that use tools.[4]

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.[5] Once they occurred in sympatry, niche specialization was favored so that the different species competed less directly for resources.[5] This second, sympatric event was adaptive radiation.[5]

Cichlids of the African Great Lakes

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.[6][7][8] These lakes are believed to be home to about 2,000 different species of cichlid, spanning a wide range of ecological roles and morphological characteristics.[9] Cichlids in these lakes fill nearly all of the roles typically filled by many fish families, including those of predators, scavengers, and herbivores, with varying dentitions and head shapes to match their dietary habits.[8] In each case, the radiation events are only a few million years old, making the high level of speciation particularly remarkable.[8][7][6] Several factors could be responsible for this diversity: the availability of a multitude of niches probably favored specialization, as few other fish taxa are present in the lakes (meaning that sympatric speciation was the most probable mechanism for initial specialization).[6] Also, continual changes in the water level of the lakes during the Pleistocene (which often turned the largest lakes into several smaller ones) could have created the conditions for secondary allopatric speciation.[8][6]

Tanganyika cichlids

Lake Tanganyika is the site from which nearly all the cichlid lineages of East Africa (including both riverine and lake species) originated.[10] Thus, the species in the lake constitute a single adaptive radiation event but do not form a single monophyletic clade.[10] Lake Tanganyika is also the least speciose of the three largest African Great Lakes, with only around 200 species of cichlid;[7] however, these cichlids are more morphologically divergent and ecologically distinct than their counterparts in lakes Malawi and Victoria, an artifact of Lake Tanganyika's older cichlid fauna. 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.[7] Many of Tanganyika's cichlids live very specialized lifestyles. 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).[7] It is thought that giant cichlids spawn only a single time, breeding in their third year and defending their young until they reach a large size, before dying of starvation some time thereafter.[7] The three species of Altolamprologus are also piscivores, but with laterally compressed bodies and thick scales enabling them to chase prey into thin cracks in rocks without damaging their skin.[7] Plecodus straeleni has evolved large, strangely curved teeth that are designed to scrape scales off of the sides of other fish, scales being its main source of food.[7] Gnathochromis permaxillaris possesses a large mouth with a protruding upper lip, and feeds by opening this mouth downward onto the sandy lake bottom, sucking in small invertebrates.[7] A number of Tanganyika's cichlids are shell-brooders, meaning that mating pairs lay and fertilize their eggs inside of empty shells on the lake bottom.[7] Lamprologus callipterus is the most unique egg-brooding species, with 15 cm-long males amassing collections of shells and guarding them in the hopes of attracting females (about 6 cm in length) to lay eggs in these shells.[7] These dominant males must defend their territories from three types of rival: (1) other dominant males looking to steal shells; (2) younger, "sneaker" males looking to fertilize eggs in a dominant male's territory; and (3) tiny, 2–4 cm "parasitic dwarf" males that also attempt to rush in and fertilize eggs in the dominant male's territory.[7] These parasitic dwarf males never grow to the size of dominant males, and the male offspring of dominant and parasitic dwarf males grow with 100% fidelity into the form of their fathers.[7] A number of other highly specialized Tanganyika cichlids exist aside from these examples, including those adapted for life in open lake water up to 200m deep.[7]

Malawi cichlids

The cichlids of Lake Malawi constitute a "species flock" of up to 1000 endemic species.[8] Only seven cichlid species in Lake Malawi are not a part of the species flock: the Eastern happy (Astatotilapia calliptera), the sungwa (Serranochromis robustus), and five tilapia species (genera Oreochromis and Coptodon).[8] All of the other cichlid species in the lake are descendants of a single original colonist species, which itself was descended from Tanganyikan ancestors.[10] The common ancestor of Malawi's species flock is believed to have reached the lake 3.4 million years ago at the earliest, making Malawi cichlids' diversification into their present numbers particularly rapid.[8] Malawi's cichlids span a similarly range of feeding behaviors to those of Tanganyika, but also show signs of a much more recent origin. 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.[8] Males of most species display predominantly blue coloration when mating. 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.[8]

Victoria cichlids

Lake Victoria's cichlids are also a species flock, once composed of some 500 or more species.[6] The deliberate introduction of the Nile Perch (Lates niloticus) in the 1950s proved disastrous for Victoria cichlids, and the collective biomass of the Victoria cichlid species flock has decreased substantially and an unknown number of species have become extinct.[11] However, the original range of morphological and behavioral diversity seen in the lake's cichlid fauna is still mostly present today, if endangered.[6] These again include cichlids specialized for niches across the trophic spectrum, as in Tanganyika and Malawi, but again, there are standouts. Victoria is famously home to many piscivorous cichlid species, some of which feed by sucking the contents out of mouthbrooding females' mouths.[11] Victoria's cichlids constitute a far younger radiation than even that of Lake Malawi, with estimates of the age of the flock ranging from 200,000 years to as little as 14,000.[6]

Adaptive radiation in Hawaii

Iiwi on native mint - Hakalau Forest NWR
An ʻiʻiwi (Drepanis coccinea). Note the long, curved beak for sipping nectar from tubular flowers.

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.[12][13]

Hawaiian honeycreepers

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). The Hawaiian honeycreepers are known for their beaks, which are specialized to satisfy a wide range of dietary needs: for example, the beak of the ʻakiapōlāʻau (Hemignathus wilsoni) is characterized by a short, sharp lower mandible for scraping bark off of trees, and the much longer, curved upper mandible is used to probe the wood underneath for insects.[4] Meanwhile, the ʻiʻiwi (Drepanis coccinea) has a very long curved beak for reaching nectar deep in Lobelia flowers.[12] An entire clade of Hawaiian honeycreepers, the tribe Psittirostrini, is composed of thick-billed, mostly seed-eating birds, like the Laysan finch (Telespiza cantans).[12] In at least some cases, similar morphologies and behaviors appear to have evolved convergently among the Hawaiian honeycreepers; for example, the short, pointed beaks of Loxops and Oreomystis evolved separately despite once forming the justification for lumping the two genera together.[14] The Hawaiian honeycreepers are believed to have descended from a single common ancestor some 15 to 20 million years ago, though estimates range as low as 3.5 million years.[15]

Hawaiian silverswords

Young silverswords, Haleakala
A mixture of blooming and non-blooming Haleakalā silverswords (Argyroxiphium sandwicense macrocephalum).

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.[12] The Hawaiian silversword alliance consists of twenty-eight species of Hawaiian plants which, aside from the namesake silverswords, includes trees, shrubs, vines, cushion plants, and more.[15] The silversword alliance is believed to have originated in Hawaii no more than 6 million years ago, making this one of Hawaii's youngest adaptive radiation events.[15] This means that the silverswords evolved on Hawaii's modern high islands, and descended from a single common ancestor that arrived on Kauai from western North America.[15] The closest modern relatives of the silverswords today are California tarweeds of the family Asteraceae.[15]

Hawaiian lobelioids

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.[15] Today the Hawaiian lobelioids form a clade of over 125 species, including succulents, trees, shrubs, epiphytes, etc. Many species have been lost to extinction and many of the surviving species endangered.

Caribbean anoles

Anole lizards are distributed broadly in the New World, from the Southeastern US to South America. With over 400 species currently recognized, often placed in a single genus (Anolis), they constitute one of the largest radiation events among all lizards.[16] Anole radiation on the mainland has largely been a process of speciation, and is not adaptive to any great degree, but anoles on each of the Greater Antilles (Cuba, Hispaniola, Puerto Rico, and Jamaica) have adaptively radiated in separate, convergent ways.[17] On each of these islands, anoles have evolved with such a consistent set of morphological adaptations that each species can be assigned to one of six "ecomorphs": trunk–ground, trunk–crown, grass–bush, crown–giant, twig, and trunk.[17] Take, for example, crown–giants from each of these islands: the Cuban Anolis luteogularis, Hispaniola's Anolis ricordii, Puerto Rico's Anolis cuvieri, and Jamaica's Anolis garmani (Cuba and Hispaniola are both home to more than one species of crown–giant).[16] These anoles are all large, canopy-dwelling species with large heads and large lamellae (scales on the undersides of the fingers and toes that are important for traction in climbing), and yet none of these species are particularly closely related and appear to have evolved these similar traits independently.[16] The same can be said of the other five ecomorphs across the Caribbean's four largest islands. 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.

Other examples

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.[18] Madagascan mantellid frogs have radiated into forms that mirror other tropical frog faunas, with the brightly colored mantellas (Mantella) having evolved convergently with the Neotropical poison dart frogs of Dendrobatidae, while the arboreal Boophis species are the Madagascan equivalent of tree frogs and glass frogs. 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.[19][20] Older examples are known: the K-Pg extinction event, which caused the disappearance of the dinosaurs and most other reptilian megafauna 65 million years ago, is seen as having triggered a global adaptive radiation event that created the mammal diversity that exists today.[3]

See also


  1. ^ Larsen, Clark S. (2011). Our Origins: Discovering Physical Anthropology (2 ed.). Norton. p. A11.
  2. ^ a b Schluter, Dolph (2000). The Ecology of Adaptive Radiation. Oxford University Press. pp. 10–11. ISBN 0-19-850523-X.
  3. ^ a b Stroud and Losos (2016). "Ecological Opportunity and Adaptive Radiation". Annual Review of Ecology, Evolution, and Systematics. 47: 507–532. doi:10.1146/annurev-ecolsys-121415-032254.
  4. ^ a b c d e f g h i j k Weiner, Jonathan (1994). The Beak of the Finch: A Story of Evolution in Our Time. New York: Alfred A. Knopf, Inc. p. 207. ISBN 0-679-40003-6.
  5. ^ a b c d Petren, K.; Grant, P. R.; Grant, B. R.; Keller, L. F. (2005). "Comparative landscape genetics and the adaptive radiation of Darwin's finches: the role of peripheral isolation". Molecular Ecology. 14 (10): 2943–2957. doi:10.1111/j.1365-294x.2005.02632.x. PMID 16101765.
  6. ^ a b c d e f g Seehausen, Ole (1996). Lake Victoria Rock Cichlids: taxonomy, ecology, and distribution. Verduyn Cichlids. ISBN 90-800181-6-3.
  7. ^ a b c d e f g h i j k l m n Konings, Ad (2015). Tanganyika Cichlids in their natural habitat, 3rd Edition. El Paso, TX: Cichlid Press. pp. 8, 325–328. ISBN 978-1-932892-18-5.
  8. ^ a b c d e f g h i Konings, Ad (2016). Malawi Cichlids in their natural habitat, 5th edition. El Paso, TX: Cichlid Press. ISBN 978-1-932892-23-9.
  9. ^ Losos, Jonathan B (2010). "Adaptive Radiation, Ecological Opportunity, and Evolutionary Determinism". The American Naturalist. 175 (6): 623–639. doi:10.1086/652433. PMID 20412015.
  10. ^ a b c Salzburger; Mack; Verheyen; Meyer (2005). "Out of Tanganyika: Genesis, explosive speciation, key-innovations and phylogeography of the haplochromine cichlid fishes". BMC Evolutionary Biology. 5:17: 17. doi:10.1186/1471-2148-5-17. PMC 554777.
  11. ^ a b Goldschmidt, Tijs (1996). Darwin's Dreampond: Drama in Lake Victoria. Cambridge, MA: The MIT Press. ISBN 978-0262071789.
  12. ^ a b c d Olsen, Steve (2004). Evolution in Hawaii: A Supplement to Teaching about Evolution and the Nature of Science. Washington, D.C.: The National Academies Press. ISBN 0-309-52657-4.
  13. ^ Haines; Schmitz; Rubinoff (2014). "Ancient diversification of Hyposmocoma moths in Hawaii". Nature Communications. 5: 1–7. doi:10.1038/ncomms4502.
  14. ^ Reding, DM; Foster, JT; James, HF; Pratt, HD; Fleisher, RC (2009). "Convergent evolution of 'creepers' in the Hawaiian honeycreeper radiation". Biology Letters. 5 (2): 221–224. doi:10.1098/rsbl.2008.0589. PMC 2665804. PMID 19087923.
  15. ^ a b c d e f Baldwin, Bruce G.; Sanderson, Michael J. (1998). "Age and rate of diversification of the Hawaiian silversword alliance (Compositae)". Proceedings of the National Academy of Sciences. 95 (16): 9402–9406. Bibcode:1998PNAS...95.9402B. doi:10.1073/pnas.95.16.9402. PMC 21350.
  16. ^ a b c Losos, Jonathan (2009). Lizards in an Evolutionary Tree: Ecology and Adaptive Radiation of Anoles. Oakland, CA: University of California Press. ISBN 978-0520255913.
  17. ^ a b Irschick, Duncan J.; et al. (1997). "A comparison of evolutionary radiations in mainland and Caribbean Anolis lizards". Ecology. 78 (7): 2191–2203. doi:10.2307/2265955.
  18. ^ Reddy; Driskell; Rabosky; Hackett; Schulenberg (2012). "Diversification and the adaptive radiation of the vangas of Madagascar". Proceedings of the Royal Society B. 279:1735: 2062–2071.
  19. ^ "Where did all of Madagascar's species come from?". WebCite. October 2009. Archived from the original on 2011-03-19. Retrieved June 3, 2018.
  20. ^ Feng; Blackburn; Liang; Hillis; Wake; Cannatella; Zhang (2017). "Phylogenomics reveals rapid, simultaneous diversification of three major clades of Gondwanan frogs at the Cretaceous–Paleogene boundary". PNAS. 114 (29): 5864–5870.

Further reading


Anolis is a genus of anoles (US: (listen)), iguanian lizards in the family Dactyloidae, native to the Americas. With more than 425 species, it represents the world's most species-rich amniote tetrapod genus, although it has been proposed that many of these should be moved to other genera, in which case only about 45 Anolis species remain. Previously, it was classified under the family Polychrotidae that contained all the anoles as well as Polychrus, but recent studies place it under Dactyloidae.

Argyroxiphium grayanum

Argyroxiphium grayanum, commonly known as the greensword, is a species of flowering plant in the sunflower family, Asteraceae, and a member of the silversword alliance, a group of over 50 species which are diverse in morphology and habitat but are genetically closely related.The silversword alliance provides a convincing natural case study in evolution by adaptive radiation, with the greensword representing one extreme of the genus' plasticity. Some Argyroxiphium, including the well-known Haleakala and Mauna Kea silverswords, live in harsh alpine desert-like conditions of heat, sun, wind, and aridity, and are drought-adapted plants capable of storing water as a gel in leaf structures which are normally air pockets in other plants. However, A. grayanum is a bog plant adapted to very different conditions – excessive moisture, lack of regular sunlight, and cool temperatures, and its leaves are non-succulent like those of the related genus Dubautia.


Asymphorodes is a gelechioid moth genus in subfamily Agonoxeninae of the palm moth family (Agonoxenidae), whose taxonomic status is disputed. Alternatively, the palm moths might be a subfamily of the grass-miner moth family (Elachistidae), with the Agonoxeninae becoming a tribe Agonoxenini.Formerly, this genus was included in the cosmet moths (Cosmopterigidae). They are found in southern Polynesia as well as the Hawaiian and the Solomon Islands, and are notable for their adaptive radiation on the Marquesas Islands.


Cyclorrhapha is an unranked taxon within the infraorder Muscomorpha. They are called "Cyclorrhapha" ('circular-seamed flies') with reference to the circular aperture through which the adult escapes the puparium. This is a circumscriptional name that has significant historical familiarity, but in the present classification, this name is synonymous with the more recent nt "Muscomorpha";Cyclorrhapha underwent major adaptive radiation that led to the creation of over 72 000 species. These species share multiple attributes such as the 360-degree rotation of the male terminalia.

Depauperate ecosystem

A depauperate ecosystem is one which is lacking in numbers or variety of species, often because it lacks enough stored chemical elements required for life. Thus, depauperate ecosystems often cannot support rapid growth of flora and fauna, high biomass density, and high biological diversity. An urchin barren is an example of a depauperate ecosystem.

An ecosystem is a biological community of interaction organisms and their actual physical environment. In Ecology, depauerate is an area that is so poor in species quantities and diversity. It lacks in numbers or a variety of species. Basically, a plant or animal is imperfectly developed. The reasons why there are depauperate areas are because the species do not have many competitors to fight with. Also, they have fewer resources causing the species not to survive without any protein or nutrients. Because these species lack the basic life necessities that they need, it’s hard for them to continue to carry on with life. ( The ecology of Adaptive Radiation). Therefore they aren’t reproducing the way that they are supposed to. In some cases, the species will actually start inbreeding. And because of that there are the same species everywhere. Therefore, competing with themselves, which can cause them to die. So, the area ends up falling short of the natural developmental size.

Dolph Schluter

Dolph Schluter (born May 22, 1955) is a professor of Evolutionary Biology and a Canada Research Chair in the Department of Zoology at the University of British Columbia. Schluter is a major researcher in adaptive radiation and currently studies speciation in the three-spined stickleback, Gasterosteus aculeatus.

Schluter received his Bachelor of Science from the University of Guelph in 1977, and his Doctor of Philosophy from the University of Michigan in 1983, both in Ecology and Evolution. Schluter's early research was done on the evolutionary ecology and morphology of Darwin's finches.Schluter is the author of The Ecology of Adaptive Radiation, 2000, Oxford University Press, and The Analysis of Biological Data, 2009 (and 2015), with Michael Whitlock, and an editor with Robert E. Ricklefs of Species Diversity in Ecological Communities: Historical and Geographical Perspectives, 1993, Chicago University Press.

In 1999, he was elected as a fellow of the Royal Society of London. In 2001, he was elected as a fellow of the Royal Society of Canada. In 2017, he was elected as a Foreign Fellow of the US National Academy of Sciences.


Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including the sharks (superorder Selachii) and the rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.

The earliest elasmobranch fossils came from the Devonian and many surviving orders date back to the Cretaceous, or even earlier. Many species became extinct during the Permian and there was a burst of adaptive radiation during the Jurassic.

Evolution of birds

The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. Birds are categorized as a biological class, Aves. For more than a century, the small theropod dinosaur Archaeopteryx lithographica from the Late Jurassic period was considered to have been the earliest bird. Modern phylogenies place birds in the dinosaur clade Theropoda. According to the current consensus, Aves and a sister group, the order Crocodilia, together are the sole living members of an unranked "reptile" clade, the Archosauria. Four distinct lineages of bird survived the Cretaceous–Paleogene extinction event 66 million years ago, giving rise to ostriches and relatives (Paleognathae), ducks and relatives (Anseriformes), ground-living fowl (Galliformes), and "modern birds" (Neoaves).

Phylogenetically, Aves is usually defined as all descendants of the most recent common ancestor of a specific modern bird species (such as the house sparrow, Passer domesticus), and either Archaeopteryx, or some prehistoric species closer to Neornithes (to avoid the problems caused by the unclear relationships of Archaeopteryx to other theropods). If the latter classification is used then the larger group is termed Avialae. Currently, the relationship between dinosaurs, Archaeopteryx, and modern birds is still under debate.

Evolutionary radiation

An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment, they are termed adaptive radiations.

Flores long-nosed rat

The Flores long-nosed rat, also known as Paula’s long-nosed rat, (Paulamys naso) is a species of rodent endemic to Flores Island, Indonesia. This species was first described from subfossil fragments collected in the 1950s by Theodor Verhoeven, who named it Paula’s long-nosed rat, and was named Floresomys naso by Guy Musser in 1981. Since Floresomys was preoccupied, Musser changed the name to Paulamys, after Verhoeven's life partner Paula Hamerlinck. A living specimen was reported from the montane forest of western Flores in 1989. It is recorded as common between 1,000 and 2,000 m above sea level on the volcanic mountain Gunung Ranakah, but is believed to be threatened by habitat destruction. It is the only known member of the genus Paulamys . The genera Papagomys, Komodomys and Paulamys are closer related to each other than to other murids, suggesting an adaptive radiation.


The haplochromine cichlids are a tribe of cichlids in subfamily Pseudocrenilabrinae called Haplochromini. This group includes the type genus (Haplochromis) plus a number of closely related genera such as Aulonocara, Astatotilapia, and Chilotilapia. They are endemic to eastern, southern and northern Africa, except for Astatotilapia flaviijosephi in the Middle East. A common name in a scientific context is East African cichlids – while they are not restricted to that region, they are the dominant Cichlidae there. This tribe was extensively studied by Ethelwynn Trewavas, who made major reviews in 1935 and 1989, at the beginning and at the end of her career in ichthyology. Even today, numerous new species are being described each year.

The haplochromines were in older times treated as subfamily Haplochrominae, However, the great African radiation of pseudocrenilabrine cichlids is certainly not monophyletic without them, and thus they are today ranked as a tribe therein. They do include, however, the type genus of the subfamily, Pseudocrenilabrus. Since taxonomic tribes are treated like genera for purposes of biological nomenclature according to the ICZN, the Haplochromis is the type genus of this tribe, and not the (later-described) Pseudocrenilabrus, even though the tribe name Pseudocrenilabrini was proposed earlier.

In the African Great Lakes, there has been an amazing adaptive radiation of Haplochromini. Many have interesting behavior (e.g. mouthbrooding in Astatotilapia burtoni or the "sleeper" ambushes of Nimbochromis), and brilliant colours are also widespread. Males and females are often strikingly sexually dichromatic. In the aquarium hobby, these fishes are popular for these reasons. They are often aggressive and demand rather unusual water parameters, making them generally unsuited for beginners or community tanks. There are some informal names used among aquarists for Haplochromini. Generally, any and all (as well as some similar-looking Pseudocrenilabrinae) may be referred to haplos, haps or happies. More specific terms are mbuna ("rock-dwelling browser") and utaka ("free-roaming hunter"), which are Bantu terms for these two ecological groups.

Haplochromines inhabit both rivers and lakes, but it is the lake species that have been most closely studied because of the species flocks known from some of the larger lakes, such as Lake Malawi. In the aquarium hobby, the "happies" are conveniently divided into four groups:

Riverine species and those endemic to the northern Great Lakes such as Lake Kivu and Lake Victoria

Mbuna, endemic to Lake Malawi

Utaka and other non-mbuna species endemic to Lake Malawi

Species endemic to Lake TanganyikaLake Victoria's trophic web was thoroughly upset in the second half of the 20th century, after Nile Perch (Lates niloticus) were introduced to the lake. Among the haplochromines found there, there have been many extinctions, and a number of other species only survive in aquaria. One monotypic genus, Hoplotilapia, is believed to be entirely extinct at least in the wild.

Hawaiian honeycreeper

Hawaiian honeycreepers are small, passerine birds endemic to Hawaiʻi. They are closely related to the rosefinches in the genus Carpodacus. Their great morphological diversity is the result of adaptive radiation in an insular environment.Before the introduction of molecular phylogenetic techniques, the relationship of the Hawaiian honeycreepers to other bird species was controversial. The honeycreepers were sometimes categorized as a family Drepanididae, other authorities considered them a subfamily, Drepanidinae, of Fringillidae, the finch family. The entire group was also called "Drepanidini" in treatments where buntings and American sparrows (Passerellidae) are included in the finch family; this term is preferred for just one subgroup of the birds today. Most recently, the entire group has been subsumed into the finch subfamily Carduelinae.


Microlophus is a genus of tropidurid lizards native to South America. There are around twenty recognized species and six of these are endemic to the Galápagos Islands where they are popularly known as lava lizards (they are sometimes placed in Tropidurus instead). The remaining, which often are called Pacific iguanas, are found in the Andes and along the Pacific coasts of Chile, Peru, and Ecuador.

The distribution of the lava lizards and their variations in shape, colour and behaviour show the phenomenon of adaptive radiation so typical of the inhabitants of this archipelago. One species occurs on all the central and western islands, which were perhaps connected during periods of lower sea levels, while one species each occurs on six other more peripheral islands. All have most likely evolved from a single ancestral species. However, as usual for Tropiduridae they can change their colour individually to some extent, and members of the same species occurring in different habitats also show colour differences. Thus animals living mainly on dark lava are darker than ones which live in lighter, sandy environments.


Neognaths (Neognathae) (from Ancient Greek neo- "new" + gnáthos “jaw”) are birds within the subclass Neornithes of the class Aves. The Neognathae include virtually all living birds; exceptions being their sister taxon (Palaeognathae), which contains the tinamous and the flightless ratites. There are nearly 10,000 species of neognaths.

The earliest fossils are known from the very end of the Cretaceous but molecular clocks suggest that neognaths originated sometime in the first half of the Late Cretaceous about 90 million year ago. Since then, they have undergone adaptive radiation producing the diversity of form, function, and behavior that we see today. It includes the order Passeriformes (perching birds), the largest clade of land vertebrates, containing some 60% of living birds and being more than twice as speciose as rodents and about five times as speciose as Chiroptera (bats), which are the largest clades of mammals. There are also some very small orders, usually birds of very unclear relationships like the puzzling hoatzin.

The neognaths have fused metacarpals, an elongate third finger, and 13 or fewer vertebrae. They differ from the Palaeognathae in features like the structure of their jawbones. "Neognathae" means "new jaws", but it seems that the supposedly "more ancient" paleognath jaws are among the few apomorphic (more derived) features of the Palaeognaths, meaning that the respective jaw structure of these groups is not informative in terms of comparative evolution.

Partula (gastropod)

Partula is a genus of air-breathing tropical land snails, terrestrial pulmonate gastropod mollusks in the family Partulidae. Many species of Partula are known under the general common names "Polynesian tree snail" and "Moorean viviparous tree snail". Partulids are distributed across 5,000 sq mi (13,000 km2) of Pacific Ocean islands, from the Society Islands to New Guinea.Once used as decorative items in Polynesian ceremonial wear and jewelry, these small snails (averaging about one-half to three-quarters of an inch in length) gained the attention of science when Dr. Henry Crampton (along with Yoshio Kondo) spent 50 years studying and cataloging partulids, detailing their remarkable array of morphological elements, ecological niches, and behavioral aspects that illustrate adaptive radiation.


Scalesia is a genus in the family Asteraceae endemic to the Galapagos Islands. It contains fifteen species that grow as shrubs or trees. This is unusual, because tree species are uncommon in Asteraceae. The genus Scalesia resulted from a blunder by Arnott who named it in honour of "W. Scales Esq., Cawdor Castle, Elginshire" but discovered after publication that the name should have read 'Stables', after Scottish botanist, William Alexander Stables (1810–1890).All of the species have soft, pithy wood. Scalesia species have been called "the Darwin's finches of the plant world" because they show a similarly dramatic pattern of adaptive radiation.

One of the largest and most widespread species is Scalesia pedunculata – a large tree which grows up to 15 to 20 metres tall, reaching maturity in a few years time. These trees typically grow in dense stands of the same species and age. They die around the same time, and then a new generation of seedlings grows up in the same place. The largest stands of Scalesia pedunculata are found on the humid windward sides of Santa Cruz, San Cristóbal, Santiago and Floreana islands, at an altitude of 400–700 m. The best known and most visited stand is on Santa Cruz Island, and is crossed by a road.

Scalesia atractyloides and S. stewartii are two small tree species, very similar to each other.


Setophaga is a genus of birds of the New World warbler family Parulidae. It contains at least 33 species. The males in breeding plumage are often highly colorful. The Setophaga warblers are an example of adaptive radiation with the various species using different feeding techniques and often feeding in different parts of the same tree.

Most Setophaga species are long-range migrants, wintering in or near the New World tropics and seasonally migrating to breed in North America. In contrast, two Setophaga species, the palm warbler and yellow-rumped warbler, have winter ranges that extend along the Atlantic coast of North America as far north as Nova Scotia.

Silversword alliance

The silversword alliance, also known as the tarweeds, refers to an adaptive radiation of around 30 species in the composite or sunflower family, Asteraceae. The group is endemic to Hawaii, and is derived from a single immigrant to the islands. For radiating from a common ancestor at an estimated 5.2±0.8 Ma, the clade is extremely diverse, composed of trees, shrubs, subshrubs, mat-plants, cushion plants, rosette plants, and lianas.The silversword alliance is named for its most famous and visually striking members, the silverswords. The species of the clade break down into three genera: Wilkesia, Argyroxiphium, and Dubautia. There are three species of silverswords and two greenswords in the genus Argyroxiphium, confined to the islands of Maui and Hawaiʻi, and two species of Wilkesia (iliau) on Kauaʻi. The bulk of the species are placed in the genus Dubautia, which is widespread on all the main islands.

The genus Dubautia contains a wide variety of forms, including cushion plants, shrubs, trees, and lianas.

Similar species frequently occur in the same habitat and are often difficult to tell apart. Hybrids frequently occur between Dubautia species, and between Dubautia and Argyroxiphium. As a result, there is some disagreement over the number of species, with modern sources giving between 28 and 33 species.

Thomas J. Givnish

Thomas Joseph Givnish (born May 14, 1951) is an American botanist, ecologist, and evolutionary biologist, holder of the Henry Allan Gleason Chair in Botany and Environmental Studies at the University of Wisconsin. He has written extensively on speciation, adaptive radiation, and determinants of diversity in several plant groups, including Bromeliaceae, Rapateaceae, Orchidaceae as well as the Hawaiian lobeliads.


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