Glossary of speciation

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This is a glossary of terms used in speciation research and related evolutionary disciplines. It is intended as introductory material and a structured organization of the often complex language used in the literature. Related glossaries in biology are: the glossary of biology, glossary of genetics, glossary of ecology, and the glossary of botany.


A species that does not reproduce sexually but instead by cloning.[1] Agamospecies are sometimes represented by species complexes that contain some diploid individuals and other apomitic forms—in particular, plant species that can reproduce via agamospermy.[2]
Allochronic isolation
Isolation of two populations of a species due to a change in breeding periods. This isolation acts as a precursor to allochronic speciation, speciation resulting from two populations of a species that have become isolated due to differences in breeding periods. An example is the periodical 13- and 17-year Magicicada species.[2]
Allo-parapatric speciation
A mode of speciation where divergence occurs in allopatry and is completed upon secondary contact of the populations--effectively a form of reinforcement.[3][2]
In allopatric speciation, a population becomes separated by a geographic barrier. Reproductive isolation evolves, resulting in two separate species.
Allopatric speciation
A mode of speciation where the evolution of reproductive isolation is caused by geographic separation of a species population.[4] Also called geographic speciation, vicariance, vicariant speciation, or dichopatric speciation.
Allopatric taxa
Specific species that are allopatrically distributed.
Species populations that exist geographically separated from one another.
Allo-sympatric speciation
A mode of speciation where divergence occurs in allopatry and is completed upon secondary contact of the populations--effectively a form of reinforcement.[5][2]
{{defn |1=Evolutionary change that occurs within a species lineage as opposed to lineage splitting (cladogenesis).[6]
Area cladogram
Assortive mating


Bacterial speciation
Behavioral isolation
The scientific study of the spatial distributions of species. It includes the study of both extinct and extant organisms.[7]
Biological species concept


In centrifugal speciation, an original population (green) range expands and contracts, leaving an isolated fragment population behind. The central population (changed to blue) evolves reproductive isolation.
Centrifugal speciation
A variation of peripatric speciation where speciation occurs by geographic isolation, but reproductive isolation evolves in the larger population instead of the peripherally isolated population.[8]
Chromosomal speciation
The splitting of a species lineage into multiple lineages.[6]
Cluster analysis
Character displacement
Cohesion species concept
Competitive gametic isolation
Congruent clines
Copulatory behavioral isolation
Cospeciation is a form of speciation where more than species speciation concurrently due to their ecological associations (e.g. host-parasite interactions).[9]
Cyptic species
Cytoplasmic isolation


Directional speciation
phenotypic or genotypic changes that occur in two different populations or evolutionary lineages.[6]
Dobzhansky-Muller model
A genus of flies commonly known as fruit flies that are used extensively in genetics research and laboratory experiments of speciation.


Ecogeographic isolation
Ecological allopatry
Ecological character displacement
Ecological isolation
Ecological niche
Ecological speciation
A process of speciation where reproductive isolation is caused by the interaction of individuals of a species with their environment.[10]
Ecological species concept
An ecological state of a species being unique to a defined geographic location, such as an island, nation, country or other defined zone, or habitat type.
Environmental gradient
Ethological isolation
Ethological pollinator isolation
Evolutionary lineage
The line of descent of a species.[6]
Evolutionary species concept
Extrinsic hybrid inviability
Extrinsic postzygotic isolation


Floral isolation
Flowering asynchrony
Founder effect
Founder event
Founder takes all
A hypothesis that describes the evolutionary advantages of the first-arriving lineages in a new ecosystem.[11] An example could be when a species becomes reproductively isolated on an island as in peripatric speciation.


Gametic isolation
Genealogical species concept
Gene flow is the transfer of alleles from one population to another population through immigration of individuals.
Gene flow
The transfer of genetic variation from one population to another.
Genetic distance
Genetic drift
Genic speciation
Genotypic cluster species
Geographic speciation
Continuous evolutionary change within a species lineage.[6]


Habitat isolation
Heteropatric speciation
History of speciation
The historical development concerning the thought and ideas about the biological phenomenon of speciation.
Haldane's rule
A rule formulated by J.B.S. Haldane that states if one sex of a hybrid between two incipient species is inviable or sterile, that sex is more likely to be the heterogametic sex (i.e. the one with two different sex chromosomes).[12]
Homoploid recombinational speciation
Host race
Host-specific parasite
Host-specific species
Hybrid breakdown
Hybrid incompatibility
Hybrid inviability
Hybrid speciation
Hybrid sterility
Hybrid swarm
Hybrid zone


Incomplete speciation
Incipient species
Two populations of a species in the early stage of speciation
Intrinsic postzygotic isolation
Isolating mechanism
Isolation by distance


Jordan's Law


In the Kaneshiro model of peripatric speciation, a sample of a larger population results in an isolated population with less males containing attractive traits. Over time, choosy females are selected against as the population increases. Sexual selection drives new traits to arise (green), reproductively isolating the new population from the old one (blue).
Kaneshiro model
A model of peripatric speciation developed by Kenneth Y. Kanneshiro where a sexual species experiences a population bottleneck—that is, when the genetic variation is reduced due to small population size—mating discrimination among females may be altered by the decrease in courtship behaviors or displays of males. This allows sexual selection to give rise to novel sexual traits in the new population.[13]


When genetic exchange (gene flow between two populations is eliminated. Also called 'lineage-branching.[6]


Mating system isolation
Mechanical isolation
Mechanical pollinator isolation
Allopatric speciation occurring on a small geographic scale.[14]
Modern Synthesis
Modes of speciation
A classification scheme of speciation processes based on the level of gene flow between two populations.[15] The traditional terms for the three modes—allopatric, parapatric, and sympatric—are based on the spatial distributions of a species population.[16][15]
Morphological species concept
Mosaic hybrid zone
A zone in which two speciating lineages occur together in a patchy distribution–either by chance, random colonization, or low hybrid fitness.[15]
Mosaic sympatry
A case of sympatry where two populations overlapping in geographic distribution exhibit habitat specializations.[15]


Natural selection
Niche adaptation
Niche preference
Noncompetative gametic isolation
Nongenetic barrier
Non-geographic speciation



Para-allopatric speciation
A mode of speciation where divergence begins in parapatry, but is completed in allopatry.[2]
Parallel speciation
A diagram representing population subject to a selective gradient of phenotypic or genotypic frequencies (a cline). Each end of the gradient experiences different selective conditions (divergent selection). Reproductive isolation occurs upon the formation of a hybrid zone. In most cases, the hybrid zone may become eliminated due to a selective disadvantage. This effectively completes the speciation process.
Parapatric speciation
Peak shift model
In peripatric speciation, a small population becomes isolated on the periphery of the central population evolving reproductive isolation (blue) due to reduced gene flow.
Peripatric speciation
A variation of allopatric speciation where a new species forms from a small, peripheral isolated population.[17] It is sometimes referred to as centripetal speciation in contrast to centrifugal speciation.
the study of the evolutionary history and relationships among individuals or groups of organisms (e.g. species, or populations).
Phylogenetic species concept
Pollinator isolation
Population bottleneck
A sharp reduction in the size of a species population.
Postmating barrier
Postmating prezygotic isolation
Postzygotic isolation
Premating barrier
Premating isolation
Prezygotic isolation
Punctuated equilibrium


Quantum speciation
A chromosomal model of speciation that occurs rapidly when a cross-fertilizing plant species buds off from a larger population on the periphery, experiencing interbreeding and strong genetic drift that results a new species.[18][19][20] The model is similar to that of Ernst Mayr's peripatric speciation.[21]


Recognition species concept
Recombinational speciation
Reinforcement assists speciation by selecting against hybrids.
A process of speciation where natural selection increases the reproductive isolation between two populations of species as a result of selection acting against the production of hybrid individuals of low fitness.[2] See also Evidence of speciation by reinforcement
Reproductive character displacement sometimes occurs when two allopatric populations come into secondary contact. Once in sympatry, changes can be seen in mating-associated traits only in the zone of contact. This is a common pattern found in speciation by reinforcement.
Reproductive character displacement
Reproductive isolating barriers
The set of mechanisms responsible for speciation
Reproductive isolation
When two species mate and cannot produce fertile offspring. Isolating mechanisms are typically classified as prezygotic (isolating barriers occurring before the formation of a zygote) and postzygotic (isolating barriers occurring after the formation of a zygote).
In a ring species, individuals are able to successfully reproduce (exchange genes) with members of their own species in adjacent populations occupying a suitable habitat around a geographic barrier. Individuals at the ends of the cline are unable to reproduce when they come into contact.
Ring species
Connected populations of a species, each of which can interbreed with closely sited related populations, but for which there exist at least two "end" populations in the series, which are too distantly related to interbreed.


The four outcomes of secondary contact:
1. An extrinsic barrier separates a species population into two but they come into contact before reproductive isolation is sufficient to result in speciation. The two populations fuse back into one species
2. Speciation by reinforcement
3. Two separated populations stay genetically distinct while hybrid swarms form in the zone of contact
4. Genome recombination results in speciation of the two populations, with an additional hybrid species. All three species are separated by intrinsic reproductive barriers[22]
Secondary contact
Semi-geographic speciation
Semipermeable species boundary
The idea that gene flow can occur between two species but that certain alleles at particular loci can exchange whereas others cannot.[15] It is often used to describe hybrid zones and has also been referred to as porous.[15]
Sexual selection
The evolutionary process by which populations evolve to become distinct species.
Speciation experiment
An experiment that attempts to replicate reproductive isolation in nature in a scientifically controlled, laboratory setting.
Speciation in the fossil record
Speciation that can be detected as occurring in fossilized organisms.
Speciation rate
The basic unit of biological classification, a taxonomic rank, and a unit of biodiversity that has no universally agreed upon, satisfactory definition.
Species complex
Species concept
Species problem
The difficulty in defining what a species is and determining identification of organisms across all of life.[23]
Stasipatric speciation
A species linage that experiences little phenotypic or genotypic change over time.[6]
Stepping-stone speciation
Suture zone
Swamping effect
Sympatric speciation


Temporal isolation
Tension zone
Type species



Vicariance biogeography
A biogeographic approach to species distributions that uses their phylogenetic histories—patterns resulting from allopatric speciation events in the past.[24]
Vicariant speciation
A biogeographic term meaning the geographic isolation of two species populations (as in allopatric speciation).


Wahlund effect
Wallace effect





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