biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...

, a deme, in the strict sense, is a group of individuals that belong to the same

taxonomic group In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

.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 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, a "deme" often refers to any isolated

subpopulation In statistics, a population is a Set (mathematics), set of similar items or events which is of interest for some question or experiment. A statistical population can be a group of existing objects (e.g. the set of all stars within the Milky Way g ...

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 strateg ...

as a unit rather than as individuals.

Local adaptation

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...

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 pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

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 A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting me ...

, 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 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 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 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 study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

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 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 (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...

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

Primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter including ...

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 The guenons (, ) are Old World monkeys of the genus ''Cercopithecus'' (). Not all members of this genus have the word "guenon" in their common names; also, because of changes in scientific classification, some monkeys in other genera may have ...

''), for example, live together in small polygynous troops and are a quite diverse

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

. 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 herbivorous, predominantly ground-dwelling 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 fi ...

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