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Adaptive Radiation in BirdsDiamos, GuevarraFebruary 24, 20141Adaptive Radiation An adaptive radiation is a clade (group of related species) that has diversified rapidly into a multitude of new forms Adaptive RadiationBrought about by a change in the environmentOpportunityInnovationA characteristic example of cladogenesisAdaptive radiation is facilitated by a rugged adaptive landscape, where fitness peaks correspond to trait values that enhance the use of distinct resources. Different species are thought to occupy the different peaks, with hybrids falling into low-fitness valleys between them.Adaptive radiationis a process in which organisms diversify rapidly into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges and opens environmental niches.Starting with a recent single ancestor, this process results in thespeciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits with which they can exploit a range of divergent environments.

Opportunity- Adaptive radiations often occur as a result of an organism arising in an environment with unoccupied niches, such as a newly formed lake or isolated island chain. The colonizing population may diversify rapidly to take advantage of all possible niches.*Extinctions are opportunities for adaptive radiations because extinctions open or re-open niches for new species to invade and occupy

Innovation- The evolution of a novel feature may permit a clade to diversify by making new areas of morphospace accessible.

Adaptive radiation, a characteristic example ofcladogenesis

Adaptive radiation in mammals: generalizationAdaptive Radiation in birds: Specialization2 Adaptive Radiation: GeneralizationDefinition: Adaptation of a species to a wide range of environmental niches

Examples: Mammals spread after the disappearance of dinosaurs 65 million years ago and occupied innumerable niches Monkeys with a mixed diet occupied diverse arboreal habitats; displaced the prosimians Humans: from frozen north to tropical rainforest or desert- Most generalized primate (because of culture)

Innumerable niches: from grassland (ungulates) to trees (bats)

Prosimiansare a type of primatethat include lemurs, lorises, bushbabies, and tarsiers, but not simians, e.g. Monkeys, and apes(including humans). They are considered to have characteristics that are more primitive than those of monkeys and apes.3 Adaptive Radiation: SpecializationDefinition: Adaptation of a species to a narrow range of environmental niches

Examples: Darwins finches on Galpagos Islands Medium ground finch was nearly wiped out in the 1977 droughtSudden change could eliminate this or others of these genera and species of finches Example: Prosimians adapt in habitats afforded by Madagascar and are close to extinction

Adaptive Radiation: BirdsMain Cause: Evolution of a key innovation

Birds radiate after the evolution of flapping flightHypotheses:From the trees downFrom the ground upWAIRPouncing Proavis

"from the trees down", that birds' ancestors first glided down from trees and then acquired other modifications that enabled true powered flight"from the ground up", that birds' ancestors were small, fast predatory dinosaurs in whichfeathersdeveloped for other reasons and then evolved further to provide first lift and then true powered flight5 Adaptive Radiation: Birds

Characteristics for birds leading to radiation:Removal of a species from an area of interspecific selection

Paradisaea rudolphiSemioptera wallaciiLoss of emphasis on species recognition marks6 Adaptive Radiation: Birds

Characteristics for birds leading to radiation :Any life requirement where there is competition and interaction among species

Feeding adaptationsNest foragingFlock signalsFood allocation

High rate of interspecific hybridization

Adaptive Radiation: Darwins Finches

Henry Fairfield OsbornThe birds vary in size from 10 to 20cm and weigh between 8 and 38grams

Developmental research in 2004 found thatbone morphogenetic protein 4(BMP4), and its differential expression during development, resulted in variation of beak size and shape among finches. BMP4 acts in the developing embryo to lay down skeletal features, including the beak.[24]The same group showed that the different beak shapes of Darwin's finches develop are also influenced by slightly different timing and spatial expression of a gene called calmodulin (CaM)8

Hawaiian Honeycreepers

Hawaiian honeycreepersOf Hawaiis birds, the honeycreepers (Drepanidinae) are most famousAn explosion of species from a single unspecialized ancestor to at least 54 species - dwarfs the famed radiation of Darwins 14 Galapagos finchesSmall to medium-sized passerines (perching birds, less accurately called songbirds) with very varied morphotypes; some dull olive-green, others bright red or yellow.

One of the most strikingly diverse and endangered bird families in the world

Of Hawaii's birds, the honeycreepers (Drepanidinae) are most famous, having put on what is arguably the world's most dazzling display of adaptive radiation--an explosion of species from a single unspecialized ancestor to at least 54 species that filled available niches in the islands' habitats. In fact, speciation in the Hawaiian honeycreepers dwarfs the famed radiation of Darwin's 14 Galapagos finches

There were once more than 50 species of these colourful songbirds that were so diverse that historically it was unclear that they were all part of the same group.

Small to medium-sized passerines (arrangement of their toes (three pointing forward and one back) which facilitates perching) with very varied morphotypes; some dull olive-green, others bright red or yellow.

11Ancestor arrived three to four million years ago; others put the arrival farther back, at closer to seven million years ago- This ancestor, one colonizing species of finch, started what proved to be an evolutionary snowball- "There must have been a lot of open niches, and the birds hit the islands and speciated very rapidly,- R. Fleischer, National Zoos Molecular Genetics Laboratory

Hawaiian honeycreepersThought to be within the first 200,000 to 300,000 years after the first finch touch-down

Robert Fleischer, Cheryl Tarr, and Carl McIntosh at the National Zoo's Molecular Genetics Laboratory estimate that the honeycreepers' ancestor arrived three to four million years ago; others put the arrival farther back, at closer to seven million years ago. This ancestor--one colonizing species of finch, possibly a Eurasian rosefinch (Carpodacussp.) or, less likely, the North American house finch (Carpodacus mexicanus)--started what proved to be an evolutionary snowball. "There must have been a lot of open niches, and the birds hit the islands and speciated very rapidly," says Fleischer, who studies the genetics of fossil and living Hawaiian birds. Rapidly, in terms of geologic time, is thought to be within the first 200,000 to 300,000 years after the first finch touch-down.12Hawaiian honeycreepers

Figure 1.Gradualism provides a plausible explanation for the origin of different bill shapes in the Hawaiian honeycreepers shown here..Nectar-feeding honeycreepers with dramatically curved bills Insectivorous honeycreepers with thin, warbler-like bills Honeycreepers probably represent the most impressive example of an adaptive radiation in vertebrates that has led to a number of beak shapes unique among birds.

Nectar-feeding honeycreepers evolved dramatically curved bills designed for probing and extracting the nectar from the flowers of Hawaii's endemic lobelias and other plants. Insectivorous honeycreepers developed thin, warbler-like bills for picking insects from the foliage.

Gradualism states that the large differences in anatomical traits that characterize different species originate through the accumulation of many small incremental changes over very long periods of time. This theory is important because genetic changes having very large effects on organismal form are usually harmful to the organism. It is possible, however, that some genetic variants that have large effects on the organism are nonetheless sufficiently beneficial to be favored by natural selection. Therefore, although gradual evolution is known to occur, it may not explain the origin of all structural differences that we observe among species (Figure 1-14). Scientists are still actively studying this question.

13Hawaiian Islands part of a conveyor belt of island formation due to volcanic activityEach island that forms represents a blank slate for evolutionEnabled scientists to tie a biological system to geological formation

How did this incredible diversity evolve over time?

Seed-eaters developed stouter, stronger bills for cracking tough husks. Some species probed or cracked bark with strong hooked bills seeking wood-boring insects, thereby filling a niche woodpeckers do elsewhere.

The answer is unique to the Hawaiian Islands, which are part of a conveyor belt of island formation due to volcanic activity, with new islands popping up as the conveyor belt moves northwest. Each island that forms represents a blank slate for evolution, so as one honeycreeper species moves from one island to a new island, those birds encounter new habitat and ecological niches that may cause them to adapt and branch off into distinct species. The researchers examined the evolution of the Hawaiian honeycreepers after the formation of Kauai-Niihau, Oahu, Maui-Nui and Hawaii.

The largest burst of evolution into new species, called a radiation, occurred between 4 million and 2.5 million years ago, after Kauaii-Niihua Oahu formed but before the remaining two large islands existed, and resulted in the evolution of six of 10 distinct types of species.

Co-author Helen James, a research zoologist at the Smithsonian National Museum of Natural History "This radiation is one of the natural scientific treasures that the archipelago offers out in the middle of the Pacific. It was fascinatingto be able to tie a biological system to geological formation and allowed us to become the first to offer a full picture of these birds' adaptive history."14

Shared the islands with an array of other unique bird speciesAn almost mythical world where birds, not mammals, dominatedIsolation left Hawaiis flora and fauna ill-equipped to deal with the arrival of humans- flightless and ground-nesting species were wiped out

* 15 genera, 23 species, 24 taxa.* 18 species threatened; 3 of these, and 3 currently unassessed species, possibly extinct; at least 16 other species extinct since 1600Hawaiian honeycreepers

Honeycreepers shared the islands with an array of other unique bird species. In 1991, Storrs L. Olson and Helen F. James of the Smithsonian's National Museum of Natural History described for the first time 32 extinct species they identified from bones found in lava tubes, sinkholes, dunes, and excavated Polynesian refuse piles (middens) on the main Hawaiian Islands over the past 19 years. Three others had been previously described. When their analyses are through, at least 20 more species will likely be added. These recent findings conjure up a vision of an almost mythical world where birds, not mammals, dominated. Large flightless waterfowl called moa nalos were the islands' large herbivores. A harrier, a hawk, an eagle, and four owls topped the food chain as predators. No mammals patrolled the ground (Hawaii's only native land mammal is a bat), and, with the need to fly gone, many of the castaway bird species, such as endemic ducks, ibis, and rails, lost their powers of flight.

But splendid isolation left Hawaii's flora and fauna ill-equipped to deal with the arrival of humans, and, as on most other isolated islands, endemic species quickly disappeared, or declined, onceHomo sapienshit the shores and wiped out flightless and ground-nesting species.

The diversity of Hawaiian honeycreepers has taken a huge hit, with more than half of the known 56 species already extinct. The researchers focused on the 18 surviving honeycreeper species but of those, six are considered critically endangered by the International Union for Conservation of Nature, four are considered endangered and five are vulnerable.15ConclusionAdaptive radiation is a rapid diversification of a clade due to several reasons. Darwins finches...Morphological innovations under specific ecological conditions have fuelled radiations like those of the drepanidine Hawaiian honeycreepersHumans definitely affect the course of evolution for the mentioned species- may drive speciation, or extinction