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Adaptive Radiations

The presentation discusses adaptive radiations, defined as the rapid evolutionary diversification of a single lineage into various specialized forms suited to different environmental niches. Key factors include the opening of ecological space, the evolution of key innovations, and reduced competition, often occurring after mass extinctions or colonization of new habitats. Examples include Darwin's finches, cichlid fish, and Anolis lizards, illustrating how species can quickly adapt to new environments and evolve distinct characteristics.

Science◦
Presentation on : Adaptive radiations Presented by : Rabia Shehzadi Presented to : Dr. Shumaila Msc.II
Adaptive radiations
Introduction Adaptive radiation is one of the most important outcomes of the process of evolution. The term itself was first used by H. F. Osborn. parallel adaptations convergence of species groups on different land masses.
Parallel adaptations Parallel evolution -wherein two or more species in the same environment develop similar adaptation or characteristics.  Parallel evolution is similar to convergent evolution in a way that two unrelated species evolved similar traits
Definition The evolutionary diversification -single ancestral lineage into various forms. Each adaptively specialized to a specific environmental niche.  Adaptive radiation generally proceeds most rapidly in environments.  where there are numerous unoccupied niches competition for resources is minimal.
Factors underlying adaptive radiations The most widely recognized “trigger” for adaptive radiation is the opening up of ecological space.  This may occur following evolution of a key innovation or when climatological or geological changes lead to the appearance of novel environments.
Islands of all types including in such dynamic environment contribute to the emergence of novel evolutionary changes.
Key innovations 1. 1. The term was first used in 1949 by H.F Osborn who defined it as "key adjustments in the morphological and physiological mechanism which are essential to the origin of new major groups 2. A key innovation is an evolutionary change in individual traits that is causally linked to an increased diversification rate in the resulting clade.
3.Adaptive breakthrough or key adaptation, is a novel phenotypic trait that allows subsequent radiation and success of a taxonomic group. 4.Typically they bring new abilities that allows the taxa to rapidly diversify and invade niches that were not previously available. 5.The phenomenon helps to explain how some taxa are much more diverse and have many more species than their sister taxa.
Examples 1.Darwin Finches Common ancestor –Galapagos  About two million years ago. Evolved into 15 recognized species differing in body size, beak shape, song and feeding behavior. Changes in the size and form of the beak Utilize different food resources such us insects, seeds, nectar from cactus flowers all driven by Darwinian selection.
2.Cichlid fish genome -adaptive evolution, Stanford scientists Roughly 40 million years ago, a handful of species of fish Nile River went into three lakes in Africa and experienced an Unusual flurry of evolution. In one of these lakes as many as 500 new species emerged in fewer than 100,000 years.
Adapted to eat the scales of other fish. Others have adaptations that allow them to live among rocks and eat prey, shells included.  Reproduction purposes  To get at how this spectacular "adaptive radiation" – the process by which multiple species evolve from an ancestor through adaptation – occurred so quickly among Cichild fish.  The scientists analyzed the genomes of these five species, starting with the Nile which represented the ancestral lineage.
3.Anolis Lizards In both adaptive radiation and convergent evolution. These divergences in habitat are accompanied by morphological changes primarily related to moving having short limbs, while trunk ecomorphs have long limbs.
In addition, these patterns repeat on numerous islands, with animals in similar habitats converging on similar body forms repeatedly. This demonstrates adaptive radiation can actually be predictable based on habitat encountered.
Factors promote adaptive radiations 1.Generally speaking, adaptive radiations occur when new, unoccupied ecological niches become accessible to a founder population. This can happen after a mass extinction during which the previous occupiers of those niches died out.
2. It can also happen when a colonizing species arrives at an island. (For instance the ancestor of the honeycreepers in Hawaii, or of Darwin's "finches" in the Galapagos) Honey creeper Change feeding habitat At least 56 species of Hawaiian honeycreepers known to have existed, although all but 18 of them are now extinct.
3. It can also happen when a founding population evolves some physiological innovation that brings it within reach of new niches. Examples would include the bird or bat wing, or the flower as a means of attracting insects for pollination.
4.Lack of competition. When a species enters an adaptive zone, it is poorly equipped to compete with species that have become adapted to the same niche. For example, mudskippers are fish that are making a living on land, but they are marine fish and they don't have to compete against frogs and salamanders, which are restricted to fresh water. That is why we don't see freshwater mudskippers.
process of adaptive radiation Ecological Release  Ecological release has been inferred to occur at the outset of adaptive radiation. This sort of release is the expansion of range, habitat or resource usage by an organism when it reaches a community from which competitors, predators or parasites may be lacking.
Colonization of species. Taxon cycle Habitat varying as population expand- species dispersal.
Adaptive plasticity Phenotypic plasticity(behavior change) Property of an individual or genotype that may be adaptive, maladaptive or neutral with regard to an individual's fitness. The particular way an individual's (or genotype's) phenotype varies across environments can be described as a reaction norm (Single genotype-phenotypic expression)
Speciation in adaptive radiation SPECIATION : Formation of a new and distinct spp. In course of evolution. mechanisms of speciation involve the creation of one or two species from another species over a long period of time.  This ratio of at most 2 species emerging from 1 original species.
Founder events  A founder event occurs when a new population is composed of only a few colonists  inevitably carrying only a small sample of the genetic diversity of the parent population.  This small population size means that the colony may have reduced genetic variation  Non-random sample of the genes relative to the original population.
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