"Subspecies" - what is it, definition of the term
In zoological taxonomy, the rank immediately below species—expressed by a three‑part scientific name—identifies a geographically or ecologically distinct population that displays consistent morphological or genetic characteristics while retaining the ability to interbreed with other conspecific groups; examples include the various populations classified within the brown rat (Rattus norvegicus) and the common house mouse (Mus musculus).
Detailed information
In zoological classification, a taxonomic unit below the species level designates populations that exhibit consistent morphological, genetic, or ecological distinctions while retaining the ability to interbreed with other conspecific groups. This rank is governed by the International Code of Zoological Nomenclature, which requires a trinomial name: genus, species, and a third epithet indicating the infraspecific entity.
Rats and mice provide numerous examples of such infraspecific entities. In the brown rat (Rattus norvegicus), the population that has adapted to laboratory environments is formally recognized as Rattus norvegicus domesticus. This form displays reduced aggression, altered coat coloration, and a propensity for rapid reproduction compared to its wild counterparts. Another well‑documented case is the Himalayan subspecific taxon of the house mouse (Mus musculus molossinus), which inhabits high‑altitude regions of the Indian subcontinent and exhibits distinct cranial measurements and fur density.
Key criteria for recognizing these entities include:
- Consistent phenotypic traits across multiple generations.
- Genetic markers that differentiate the population from the nominal species.
- Geographic or ecological isolation that limits gene flow.
- Documented reproductive compatibility with the parent species.
In research, distinguishing these infraspecific units is essential for reproducibility. Laboratory strains derived from R. n. domesticus and M. m. molossinus possess unique physiological baselines; experimental outcomes may vary if unrecognized genetic background differences exist.
The naming process follows a strict protocol:
- Publication of a formal description in a peer‑reviewed outlet.
- Designation of a type specimen representing the infraspecific entity.
- Assignment of an author citation and year of description.
Current recognized infraspecific taxa for the two rodent genera include:
- Rattus norvegicus domesticus (laboratory brown rat)
- Rattus norvegicus alpinus (high‑altitude brown rat populations)
- Mus musculus domesticus (Western house mouse)
- Mus musculus musculus (Eastern house mouse)
- Mus musculus molossinus (Japanese house mouse)
- Mus musculus castaneus (Southeast Asian house mouse)
These classifications reflect ongoing phylogenetic studies that employ mitochondrial DNA sequencing, microsatellite analysis, and whole‑genome comparisons. As genomic data expand, the resolution of infraspecific differentiation improves, prompting revisions to existing taxa and the description of new ones.