Effective selfing model
Encyclopedia
The effective selfing model is a mathematical model
that describes the mating system
of a plant
population
in terms of the degree of self-fertilisation present.
It was developed in the 1980s by Kermit Ritland, as an alternative to the simplistic mixed mating model
. The mixed mating model assumes that every fertilisation
event may be classed as either self-fertilisation, or outcrossing
with a completely random mate. That is, it assumes that inbreeding
is caused solely by self-fertilisation. This assumption is often violated in wild plant populations, where inbreeding may be due to outcrossing between closely related plants. For example, in dense stands, mating often occurs between plants in close proximity; and in plants with short seed dispersal
distances, plants are often closely related to their nearest neighbours. When both these criteria are met, plants will tend to be closely related to the near neighbours with which they mate, resulting in significant inbreeding. In such a scenario, the mixed mating model will attribute all inbreeding to self-fertilisation, and therefore over-estimate the extent of self-fertilisation occurring. The effective selfing model takes into account the potential for inbreeding to occur as a result of outcrossing between closely related plants, by considering the extent of kinship between mates.
Ultimately, it is not possible to tease apart the two potential causes of inbreeding, and attributed the observed inbreeding to one cause or the other. Therefore, just as with the mixed mating model, in the effective selfing model there is only one parameter to be estimated. However this parameter, termed the effective selfing rate, is often a more accurate measure of the proportion of self-fertilisation than the corresponding parameter in the mixed mating model.
Mathematical model
A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...
that describes the mating system
Mating system
A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to higher animals, it specifies which males mate with which females, under which circumstances; recognised animal mating systems include monogamy,...
of a plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
in terms of the degree of self-fertilisation present.
It was developed in the 1980s by Kermit Ritland, as an alternative to the simplistic mixed mating model
Mixed mating model
The mixed mating model is a mathematical model that describes the mating system of a plant population in terms of the degree of self-fertilisation present. It is a fairly simplistic model, employing several simplifying assumptions, most notably the assumption that every fertilisation event may be...
. The mixed mating model assumes that every fertilisation
Fertilisation
Fertilisation is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo...
event may be classed as either self-fertilisation, or outcrossing
Outcrossing
Outcrossing is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity, thus reducing the probability of all individuals being subject to disease or reducing genetic abnormalities...
with a completely random mate. That is, it assumes that inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
is caused solely by self-fertilisation. This assumption is often violated in wild plant populations, where inbreeding may be due to outcrossing between closely related plants. For example, in dense stands, mating often occurs between plants in close proximity; and in plants with short seed dispersal
Seed dispersal
Seed dispersal is the movement or transport of seeds away from the parent plant. Plants have limited mobility and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors. Seeds can be dispersed away from the parent plant...
distances, plants are often closely related to their nearest neighbours. When both these criteria are met, plants will tend to be closely related to the near neighbours with which they mate, resulting in significant inbreeding. In such a scenario, the mixed mating model will attribute all inbreeding to self-fertilisation, and therefore over-estimate the extent of self-fertilisation occurring. The effective selfing model takes into account the potential for inbreeding to occur as a result of outcrossing between closely related plants, by considering the extent of kinship between mates.
Ultimately, it is not possible to tease apart the two potential causes of inbreeding, and attributed the observed inbreeding to one cause or the other. Therefore, just as with the mixed mating model, in the effective selfing model there is only one parameter to be estimated. However this parameter, termed the effective selfing rate, is often a more accurate measure of the proportion of self-fertilisation than the corresponding parameter in the mixed mating model.