Phylogenetic signal is an

evolutionary Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

and

ecological 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 overlaps wi ...

term, that describes the tendency or the pattern of related biological species to resemble each other more than any other species that is randomly picked from the same phylogenetic tree.

Characteristics

Phylogenetic signal is usually described as the tendency of related biological species to resemble each other more than any other species that is randomly picked from the same phylogenetic tree. In other words, phylogenetic signal can be defined as the statistical dependence among species' trait values that is a consequence of their phylogenetic relationships. The traits (eg. morphological, ecological, life-history or

behavioural Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...

traits) are inherited characteristics – meaning the trait values are usually alike within closely related species, while trait values of distantly related biological species do not resemble each other to a such great degree. It is often said that traits that are more similar in closely related taxa than in distant relatives exhibit greater phylogenetic signal. On the other hand, some traits are a consequence of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

and appear more similar in distantly related taxa than in relatives. Such traits show lower phylogenetic signal. Phylogenetic signal is a measure, closely related with an

evolutionary process Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...

and development of

taxa 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 ...

. It is thought that high

rate of evolution The rate of evolution is quantified as the speed of genetic or morphological change in a lineage over a period of time. The speed at which a molecular entity (such as a protein, gene, etc.) evolves is of considerable interest in evolutionary biolog ...

leads to low phylogenetic signal and vice versa (hence, high phylogenetic signal is usually a consequence of either low rate of evolution either stabilizing type of selection). Similarly high value of phylogenetic signal results in an existence of similar traits between closely related biological species, while increasing evolutionary distance between related species leads to decrease in similarity. With a help of phylogenetic signal we can quantify to what degree closely related biological taxa share similar traits. On the other hand, some authors advise against such interpretations (the ones based on estimates of phylogenetic signal) of evolutionary rate and process. While studying simple models for

quantitative trait Complex traits, also known as quantitative traits, are traits that do not behave according to simple Mendelian inheritance laws. More specifically, their inheritance cannot be explained by the genetic segregation of a single gene. Such traits show ...

evolution, such as the homogeneous rate

genetic drift Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and there ...

, it appears to be no relation between phylogenetic signal and rate of evolution. Within other models (eg. functional constraint,

fluctuating selection Fluctuating selection is a mode of natural selection characterized by the fluctuation of the direction of selection on a given phenotype over a relatively brief period of evolutionary time. For example, a species of plant may come in two varieties ...

phylogenetic niche conservatism The term phylogenetic niche conservatism has seen increasing use in recent years in the scientific literature, though the exact definition has been a matter of some contention. Fundamentally, phylogenetic niche conservatism refers to the tendency ...

, evolutionary heterogeneity etc.) relations between evolutionary rate, evolutionary process and phylogenetic signal are more complex, and can not be easily generalized using mentioned perception of the relation between two phenomenons. Some authors argue that phylogenetic signal is not always strong in each clade and for each trait. It is also not clear if all of the possible traits do exhibit phylogenetic signal and if it is measurable.

Aim and methodology

Goal

Phylogenetic signal is a concept widely used in different ecological and evolutionary studies. Among many questions that can be answered using a concept of phylogenetic signal, the most common ones are: * To what degree are investigated traits in correlation? *How, when and why do certain traits evolve? * Which processes are the driving force of

community A community is a social unit (a group of living things) with commonality such as place, norms, religion, values, customs, or identity. Communities may share a sense of place situated in a given geographical area (e.g. a country, village, ...

assembly? * Do niches get conserved along phylogenies? * Is there any relation between vulnerability to climate change and taxa phylogeny?

Techniques

Quantifying phylogenetic signal can be done using a range of various methods that are used for researching

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

in an aspect of evolutionary relatedness. With a help of measuring phylogenetic signal one can determine exactly how studied traits are correlated with phylogenetic relationship between species. Some of the earliest ways of quantifying phylogenetic signal were based on the use of various statistical methods (such as phylogenetic autocorrelation coefficients, phylogenetic correlograms, as well as autoregressive models). With a help of the mentioned methods one is able to quantify the value of phylogenetic autocorrelation for a studied trait throughout the phylogeny. Another method commonly used in studying phylogenetic signal is so-called Brownian diffusion model of trait evolution that is based on the

Brownian motion Brownian motion, or pedesis (from grc, πήδησις "leaping"), is the random motion of particles suspended in a medium (a liquid or a gas). This pattern of motion typically consists of random fluctuations in a particle's position insi ...

(BM) principle. Using Brownian diffusion model, one can not only study values but also compare those measures between various phylogenies. Phylogenetic signal in continuous traits can be quantified and measured using K-statistic. Within this technique values from zero to infinity are used and higher value also means greater level of phylogenetic signal. The table below shows the most common indices and associated tests used for analyzing phylogenetic signal.

References

{{Phylogenetics, state=expanded Biodiversity Phylogenetics

Characteristics

Aim and methodology

Goal

Techniques

See also

References