biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

, a deme, in the strict sense, is a group of individuals that belong to the same taxonomic group.Gilmour, J. S., & Heslop-Harrison, J. (1955). The deme terminology and the units of micro-evolutionary change. ''Genetica, 27''(1), 147-161. However, when biologists, and especially ecologists, use the term ‘deme’ they usually refer to it as the definition of a gamodeme: a local group of individuals (from the same taxon) that interbreed with each other and share a

gene pool The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species. Description A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survi ...

. The latter definition of a deme is only applicable to sexual reproducing species, while the former is more neutral and also takes asexual reproducing species into account, such as certain plant species. In the following sections the latter (and most frequently used) definition of a deme will be used. In

evolutionary computation Evolutionary computation from computer science is a family of algorithms for global optimization inspired by biological evolution, and the subfield of artificial intelligence and soft computing studying these algorithms. In technical terms ...

, a "deme" often refers to any isolated subpopulation subjected to

selection Selection may refer to: Science * Selection (biology), also called natural selection, selection in evolution ** Sex selection, in genetics ** Mate selection, in mating ** Sexual selection in humans, in human sexuality ** Human mating strat ...

as a unit rather than as individuals.

Local adaptation

population Population is a set of humans or other organisms in a given region or area. Governments conduct a census to quantify the resident population size within a given jurisdiction. The term is also applied to non-human animals, microorganisms, and pl ...

of a species usually has multiple demes. Environments between these demes can differ. Demes could, therefore, become locally adapted to their environment. A good example of this is the Adaptive Deme Formation (ADF) hypothesis in

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s.Zandt, P. A. V., & Mopper, S. (1998). A meta-analysis of adaptive deme formation in phytophagous insect populations. ''The American Naturalist, 152''(4), 595-604. The ADF hypothesis states that herbivorous insects can become adapted to specific host plants in their local environment because local plants can have unique nutrient patches to which insects may become adapted. This hypothesis predicts that less mobile insect demes are more likely to become locally adapted than more dispersive insect. However, a

meta-analysis Meta-analysis is a method of synthesis of quantitative data from multiple independent studies addressing a common research question. An important part of this method involves computing a combined effect size across all of the studies. As such, th ...

, based on 17 studies on this subject, showed that dispersive insect demes were as likely to become locally adapted as less mobile insects. Moreover, this study found a small indication that feeding

behaviour Behavior (American English) or behaviour (British English) is the range of actions of Individual, individuals, organisms, systems or Artificial intelligence, artificial entities in some environment. These systems can include other systems or or ...

might stimulate the local adaptation of demes. Endophagous insects were more likely to become locally adapted than exophagous insects. The explanation for this could be that endophagous insects come in more close and continuous contact to the plant's mechanical, chemical and phenological defensive mechanisms.

Speciation and demes

Speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

could occur at the level of demes. When a deme gets geographically isolated from other demes of the same species, gene-flow between these demes will stop which could lead to speciation after a long time. This is called

allopatric speciation Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

and is generally a slow process. On the contrary,

sympatric speciation Sympatric speciation is the evolution of a new species from a surviving Common descent, ancestral species while both continue to inhabit the same geographic region. In evolutionary biology and biogeography, ''sympatric'' and ''sympatry'' are ter ...

can be more rapid when a species has multiple small demes.Bush, G. L., Case, S. M., Wilson, A. C., & Patton, J. L. (1977). Rapid speciation and chromosomal evolution in mammals. ''Proceedings of the National Academy of Sciences, 74''(9), 3942-3946. This rapid speciation is both observed in plants and vertebrates. Rapid speciation is explained by the

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

and

social structure In the social sciences, social structure is the aggregate of patterned social arrangements in society that are both emergent from and determinant of the actions of individuals. Likewise, society is believed to be grouped into structurally rel ...

of demes. Species that behave more territorial, live in patchy environments and/or have a

polygynous Polygyny () is a form of polygamy entailing the marriage of a man to several women. The term polygyny is from Neoclassical Greek πολυγυνία (); . Incidence Polygyny is more widespread in Africa than in any other continent. Some scholar ...

breeding system with only one reproductive male tend to have smaller deme sizes. Interbreeding between small demes is rare due to these factors. Furthermore,

allele An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule. Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...

s fixate more rapidly in smaller demes. Small demes could, therefore, become genetically distinct from each other.

Primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s, for example, have the second highest speciation rate among mammals, with one speciation event per lineage every 3 million years. However, not all primate species have a high speciation rate; this is reflected in their deme size and social structure. Guenons ('' Cercopithecus''), for example, live together in small polygynous troops and are a quite diverse

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

. On the other hand, baboons ('' Papio'') have a much lower speciation rate. Baboons have larger deme sizes because they live in polygynous multi-male troops. These baboon demes are usually allopatric but gene-flow still exists between demes with hybridization being common.

Examples

Various populations of

gorilla Gorillas are primarily herbivorous, terrestrial great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or five su ...

s can be understood by their geographical separation and have been assessed to determine distinct and disjointed gene pools. The

polar bear The polar bear (''Ursus maritimus'') is a large bear native to the Arctic and nearby areas. It is closely related to the brown bear, and the two species can Hybrid (biology), interbreed. The polar bear is the largest extant species of bear ...

, ''Ursus maritimus'', is understood to have 19 identifiable demes, even though their circumpolar distribution allows some interchange among the demes.C. Michael Hogan (2008
''Polar Bear: Ursus maritimus'', Globaltwitcher.com, ed. Nicklas Stromberg
/ref>

References

{{reflist Genetics

Local adaptation

Speciation and demes

Examples

See also

References