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(klədĭs`tĭks) or

phylogenetic systematics

(fī'lōjənĕt`ĭk), an approach to the classificationclassification,
in biology, the systematic categorization of organisms into a coherent scheme. The original purpose of biological classification, or systematics, was to organize the vast number of known plants and animals into categories that could be named, remembered, and
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 of living things in which organisms are defined and grouped by the possession of one or more shared characteristics (called characters) that are derived from a common ancestor and that were not present in any ancestral group (as envisioned by Charles DarwinDarwin, Charles Robert,
1809–82, English naturalist, b. Shrewsbury; grandson of Erasmus Darwin and of Josiah Wedgwood. He firmly established the theory of organic evolution known as Darwinism.
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's idea of "descent with modification"). Developed by Willi Hennig, a German entomologist, in the 1950s, it is a method of reconstructing evolutionary relationships that emphasizes the importance of descent and common ancestry rather than chronology.

Cladistics places species in a group, or clade, based on a shared character. Within a clade, species that share other characters unique to them are grouped together, and so on, until a cladogram (a branching diagram that resembles a family tree) is assembled. For example, all vertebrates make up a clade; all tetrapods (vertebrates that have four limbs with wrists, ankles, toes, and fingers) form their own clade within the vertebrate clade. In this example the vertebrate clade would be considered "primitive" and the tetrapod clade "derived" or "advanced." In living creatures genetic characters or behaviors as well as more obvious anatomical features might be considered in assembling a cladogram. In paleontologypaleontology
[Gr.,= study of early beings], science of the life of past geologic periods based on fossil remains. Knowledge of the existence of fossils dates back at least to the ancient Greeks, who appear to have regarded them as the remains of various mythological creatures.
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 the characters are necessarily skeletal.

Cladistics is especially significant in paleontology, as it points out gaps in the fossil evidence. It is also felt to be more objective than fossil study, which of necessity extrapolates from a limited number of finds that may or may not be representative of the whole.

See also fossilfossil,
remains or imprints of plants or animals preserved from prehistoric times by the operation of natural conditions. Fossils are found in sedimentary rock, asphalt deposits, and coal and sometimes in amber and certain other materials.
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; datingdating,
the determination of the age of an object, of a natural phenomenon, or of a series of events. There are two basic types of dating methods, relative and absolute.
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Biology a method of grouping animals that makes use of lines of descent rather than structural similarities
References in periodicals archive ?
Analysis of lapillar otoliths revealed that larval duration, size at settlement, and presettlement growth rates of the two sister species, the Arrow Goby and Tidewater Goby, were statistically different, though not dramatically different.
We sequenced and analyzed fragments of 16S rRNA and COI genes from all oysters collected from China and some sister species from diverse regions of the world including Korea, Japan, Australia, Europe, and the United States.
Interestingly, Morimoto's results are in line with insights from genetics: humans and chimps are evolutionary sister species, while gorillas are more distant relatives, like cousins.
Although "speciation is completed when members of two diverged populations coexist in sympatry without interbreeding" (page 29), this restriction is relaxed in Darwin's finches, which interbreed at a low level between sister species and between less closely related species, and where genetic introgression contributes to ongoing adaptive change within a species.
rbcL sequences provide phylogenetic insights among sister species of the fern genus Polypodium.
For example, for our MP analysis, the nodes for each focal species or for both sister species together in the CO3-only data set are supported with high (>95%) bootstrap support.
itasca are sister species and their females lack sufficient, distinct morphological characteristics to be distinguished.
The species represents the Palearctic sister species of the Nearctic Trebacosa marxi (Stone 1890), and occurs in a very specialized habitat of Phragmitetum communis.
Caenorhabditis briggsae, a sister species of Caenorhabditis elegans evolved from evolution about 60,000 years ago.
Secondly, Stringer's cladistic approach, in which Neanderthals and AMHS are sister species descended from a common ancestor extant at or before 300,000 years ago, correctly identifies the problem of recognizing diagnostic derived (as opposed to shared) traits in early representatives of the two recently-speciated lineages.
By studying the genetics of two sister species of Horn Snails, Cerithideopsis californica and C.
sericea occurs in a basal position of a clade containing North and South American species with Mediterranean region sister species.