Speciation Definitions

Evolution: change in allele frequencies

Species: a group of organisms which can naturally interbreed to produce fertile offspring

Speciation: the formation of new species from a common ancestor

Population: a group of members of the same species, in the same location at the same time

Deme: a population which has little or no gene flow with other populations of the same species

Cline: a species spread across a geographic range which display a gradual change in a phenotypic characteristic. Adjacent populations can interbreed, but populations at each end of the spectrum may not be able to.

Ring species: a species which is spread around the globe latitudinally, which displays a gradual change in a phenotypic characteristic. Adjacent populations can interbreed, but the ends of the ring species (where they meet) may be so different that they can no longer interbreed and are classified independently as two different species.

Punctuated equilibrium: a model of evolution with long periods of little or no evolutionary change - known as stasis - which are punctuated by short periods of relatively rapid bursts of evolution

Gradualism: slow, constant rate of change within a species over time in response to changes in selection pressures, supported by evidence of transitional fossil forms

Divergent evolution: speciation where two or more new species are formed from one common ancestor species

Adaptive radiation: speciation where one common ancestor splits into multiple new species

Convergent evolution: two unrelated species face similar selection pressures so evolve similar phenotypic characteristics, shown by analogous features

Parallel evolution: two related species evolve similar characteristics despite no gene flow and physical separation, since they face similar selection pressures

Coevolution: two species, linked by a biotic relationship (eg, insect and flower, predator and prey, mimicry species), evolve reciprocally of each other as the one species acts as a selection pressure for the other species

Homologous structures: similar in structure but may be different in function, evidence of divergent evolution from a common ancestor

Analogous structures: different in structure but similar in function, evidence of convergent evolution

Vestigial organs: a structure that has been reduced or lost function, providing evidence of a common ancestor

Genome: the complete set of DNA of an organism, including all genes

mtDNA: mitochondrial DNA, the only DNA found outside of the nucleus. Passed down through the maternal line

nDNA: DNA found in the nucleus

Gene flow: the transfer of genes and alleles between members of a species through reproduction

Ploidy: the number of chromosomes in a cell

Euploidy: complete sets of chromosomes; eg, n, 2n, 3n, 4n…

Eupolyploidy: at least on extra complete set of chromosomes due to complete non-disjunction in anaphase 1 or 2 of meiosis; eg, 3n, 4n, 5n…

Aneuploidy: an abnormal number of chromosomes in a cell due to non-disjunction of a chromosome or chromatid; eg, 2n±1

Amphiploidy: the formation of a fertile hybrid due to somatic doubling or complete non-disjunction after an event of allopolyploidy

Inbreeding: closely related members of a species interbreeding

Outbreeding: members of a species which are not closely related interbreeding

Hybrid vigour: an increase in the size, strength or other characteristic of a hybrid offspring formed by the interbreeding between two different species

Non-disjunction: where the chromosomes or chromatids do not separate as usual during anaphase 1 or 2 of meiosis, due to incorrect formation of spindles

Autopolyploidy: an abnormal number of chromosomes from parents of the same species

Allopolyploidy: an abnormal number of chromosomes from parents of different species

Colchicine: a drug which inhibits spindle formation and increases the likelihood of complete non-disjunction during meiosis

Instant speciation: sudden change in chromosome number of offspring from parents over a single generation, meaning that they are no longer able to reproduce with the parent generation and have effectively created a new species

Selection pressure: a biotic or abiotic environmental factor that causes a specific trait of an organism to be favoured, leading to natural selection and differential reproductive success and driving evolutionary change

Mimicry: where one species adopts the phenotypic characteristic of another; for example, a palatable butterfly species taking on the colourings of a non-palatable species to avoid predation

Specialists: a species with a narrow niche and specific requirements in order to stay alive

Generalists: a species with a wide niche and larger range of ecological conditions under which they can survive

Prezygotic + name: a RIM which takes effect before the formation of a zygote to prevent the formation of a viable offspring; physical/geographical, behavioural, structural, gametic, temporal and ecological

Post zygotic + name: a RIM which takes effect after the formation of a zygote to prevent the formation of a reproductively viable offspring; hybrid inviability, hybrid sterility and hybrid breakdown

Allopatric speciation: speciation due to physical barriers

Sympatric speciation: speciation due to non-physical barriers

Vicariance: a large-scale biogeographical event leading to large-scale allopatric speciation; eg, a volcanic eruption, the formation of a river of the formation of the Southern Alps

Niche differentiation: organisms, often of the same species, utilising different resources and interactions within their environment differently. This often takes place in the form of disruptive selection, to minimise competition and enabling more species to coexist

Phylogeny: the evolutionary history of a group of organisms, often visualized as a phylogenetic tree

Clade: a group of organisms that includes a common ancestor and all of its descendants