Evolution And Speciation

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Gene pool

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The total number of alleles within a population

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Allele frequencies

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The number of alleles for a given trait can change over time due to a number of factors, including immigration and emigration (gene flow), natural selection, mutation and genetic drift

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Mutation

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Introduces new alleles into a population

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Gene flow

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The movement of alleles between populations, where there is significant gene flow there will be a similarity between the populations

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Genetic drift

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The change in allele frequencies in a population due to chance. In large population genetic drift is reduced

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Natural selection

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The process which accounts for evolutionary change in a population or species. There are many factors which factor into this, such as overpopulation or limited resources

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Adaptive fitness

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describes an organisms relative ability to survive and reproduce by virtue of its adaptations

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Species

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Members of a group of potentially interbreeding individuals which are able to produce fertile offspring

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Ring species

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A biological phenomena where there is gradual change in the genetic characteristics of neighbouring populations around a geographic feature

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Pre-zygotic isolating mechanisms

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A range of mechanisms that reduce the likelihood of interbreeding between different species, occuring prior to formation of a zygote. These include Geographic, ecological, temporal, gamete, behavioural and mechanical isolation

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Post-zygotic isolating mechanisms

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A range of mechanisms that reduce the likelihood of interbreeding between different species, occurring after formation of a zygote. These are hybrid sterility, hybrid inviability and hybrid breakdown.

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Hybrids

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An offspring derived from the reproduction of closely related species

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Allopatric speciation

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Speciation which occurs when populations of a single species become geographically isolated restricting gene flow. As genetic differences accrue between the populations (as a function of mutation, natural selection and genetic drift) the populations become reproductively isolated (unable to successfully inter-breed) from each other and constitute new species.

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Sympatric Speciation

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Speciation which occurs when there is no separation of gene pools by any physical barrier. Isolation can be achieved by niche differentiation or relatively rapid genetic events (such as polyploidy mutation), both of which reduce gene flow between formerly inter-breeding individuals. When genetic differences have built up and reproductive isolation is achieved, new species have formed

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Sympatric species

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Species which live in the same area with no geographic barriers. The species are reproductively isolated.

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Niche differentiation

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Where different species are able to co-exist in a habitat as they are adapted to minimize interspecific competition with each other

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Non-disjunction

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failure of chromosomes to separate evenly during meiosis. This produces gametes with the incorrect number of chromosomes

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Polyploidy mutation

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A mutation resulting from non-disjunction in which gametes inherit whole sets of chromosomes. These diploid (2n) gametes produce offspring with multiple sets of chromosomes (3n, 4n...etc)

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Instant speciation

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A type of sympatric speciationwhere there is a relatively rapid emergence of new species due to polyploidy mutation. The new species are reproductively isolated as they are now genetically distinct. The process of speciation has taken place in a number of plant species, as plants are able to reproduce vegetatively or carry out self-pollination before achieving sexually reproductive capacities. Examples include wheat and swedes.

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Sequential evolution

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where the species of a single evolutionary lineage changes over time to become genetically distinct from its ancestral form

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Divergent evolution

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The emergence of two new species from a common ancestor, each forming a new evolutionary lineage

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Extinction

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When a species number zero individuals. Extinction occurs as the species is no longer adaptively fit for a changed environment.

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Adaptive radiation

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An evolutionary pattern which describes multiple instances of divergent evolution and the subsequent proliferation of new life forms and evolutionary lineages.

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Common ancestry

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A concept which describes the degree of commonality between life forms. More closely related species have a more recent common ancestor, with less related species sharing a more distant common ancestor.

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Homologous structures

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Anatomical features which are derived from a common ancestor and show an underlying similarity, but in each lineage are adapted to suit the niche into which the organism has evolved.

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pentadactyl limb

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An example of a homologous structure shared by tetrapods. The 5-fingered limbs of tetrapods have the same underlying bone structure having been derived from a common ancestor, which has become highly modified to suit the niche of each species.

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Convergent evolution

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Describes the process where different evolutionary lineages evolve similar adaptations in response to similar selection pressures. The adaptations are independently evolved, and are not derived from a common ancestor.

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Analogous structures

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Structures which have independently evolved in a separate evolutionary lineages to serve a similar function. e.g pectoral fin of a shark and the flipper of a dolphin

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Gradualism

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Describes the rate of evolutionary change in which there is slow and steady evolutionary change in a lineage. Likely to occur in an environment which is slowly changing

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Punctuated equilibrium

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Describes the rate of evolutionary change and speciation, which for long periods there is relatively little change (stasis) followed by relatively rapid change withiin a lineage and rapid speciation. Likely to occur when the envonrment goes through periods of stability, followed by a relatively rapid change in ecological circumstances.

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Coevolution

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The evolution of two inter-dependant species, where the evolution of one directly effects the evolution of another.

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Fossils

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The fossil record demonstrates the veracity of evolutionary principles such as sequential evolution, common ancestry and adaptive radiation.

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Biogeography

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The study of the distribution of both present day and extinct species. It stresses the role of distribution of ancestral species to new locations and their subsequent evolution. It reinforces evolutionary principles such as natural selection and adaptive radiation.

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Molecular comparisons

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A range of techniques can be used to show the underlying homology between species, and the degree to which they are related by proximity to a common ancestor.

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Vestigial structures

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Vestigial structures are those which are found in an organism as evidence of common ancestry to other lineages and former use, but are reduced in function as a consequence of natural selection.

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Atavisms

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When vestigial structures develop more, e.g human infants born with tails

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Artificial selection

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The practice of selective breeding of animals and plants by humans show that there is a capacity to bring about change in living forms by way of differential reproduction and the transmission of favourable characteristics from one generation to the next

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New Zealand Examples

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New Zealand is characterised by a wide range of invertebrates and birds, many of which are now less adaptively fit given the ecological changes since human occupation began some thousand years ago. As a result many are endangered or extinct.