Evolutionarily significant unit
An evolutionarily significant unit (ESU) is a population of
Definition
Definitions of an ESU generally[
- Current geographic separation,
- Genetic differentiation at neutral markers among related ESUs caused by past restriction of gene flow, or
- Locally adapted phenotypic traits caused by differences in selection.
Criterion 2 considers the gene flow between populations, measured by FST. A high degree of differentiation between two populations among genes that provide no adaptive advantage to either population (known as neutral markers) implies a lack of gene flow, showing that random drift has occurred in isolation from other populations. Very few migrants per generation are needed to prevent strong differentiation of neutral markers. Even a single migrant per generation may be enough for neutral markers to show gene flow between populations, making it difficult to differentiate the populations through neutral markers.
Criterion 3 does not consider neutral genetic markers, instead looking at locally adapted traits of the population. Local adaptations may be present even with some gene flow from other populations, and even when there is little differentiation at neutral markers among ESUs. Reciprocal transplantation experiments are necessary to test for genetic differentiation for phenotypic traits, and differences in selection gradients across habitats. Such experiments are generally more difficult than the fixation index tests of criterion 2, and may be impossible for very rare or endangered species.
For example,
Both criteria 2 and 3 have the problem that there is no clear dichotomy between ESU and not-ESU, as genetic differentiation between populations forms a continuum, prompting a contention for consideration of both genetic and ecological processes in identifying ESUs.[3] Because the different approaches to designating ESUs each have their benefits, and the need and form of management prescriptions may vary across contexts, some support an "adaptive" approach to identification of ESUs, for instance suggesting consideration of facets from numerous designation methods.[4]
United States Endangered Species Act
For the purposes of the
- be substantially reproductively isolated from other conspecific populations, and
- represent an important component in the evolutionary legacy of the biological species[5]
Other equivalent terms
The equivalent term used by COSEWIC is "Wildlife Species", or for brevity just "species", which is used to refer to biological species, subspecies, varieties, or geographically or genetically distinct populations of organisms.[6]
See also
References
- ]
- .
- PMID 10856956.
- PMID 11903888.
- ^ Waples, R. S. (1991). "Pacific salmon, Oncorhynchus spp., and the definition of "species" under the Endangered Species Act". Mar. Fish. Rev. 53 (3): 11–22.
- ^ Government of Canada, COSEWIC, Committee on the Status of Endangered Wildlife in Canada. "COSEWIC's Assessment Process and Criteria". Cosepac.gc.ca. Archived from the original on 2015-04-12. Retrieved 2015-04-07.
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