Genic capture is a hypothesis explaining the maintenance of
genetic variance
Genetic variance is a concept outlined by the English biologist and statistician Ronald Fisher in his fundamental theorem of natural selection. In his 1930 book ''The Genetical Theory of Natural Selection'', Fisher postulates that the rate of ch ...
in traits under
sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex ( ...
. A classic problem in sexual selection is the fixation of
alleles
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chrom ...
that are beneficial under strong selection, thereby eliminating the benefits of
mate choice. Genic capture resolves this
paradox
A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically u ...
by suggesting that
additive genetic variance of
sexually selected traits reflects the genetic variance in total condition.
A deleterious
mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA replication, DNA or viral repl ...
anywhere in the
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
will adversely affect condition, and thereby adversely affect a condition-dependent sexually selected trait. Genic capture therefore resolves the
lek paradox
The lek paradox is the conundrum of how additive or beneficial genetic variation is maintained in lek mating species, in the face of consistent female preferences, sexual selection. While many studies have attempted to explain how the lek paradox ...
by proposing that recurrent deleterious mutation maintains additive genetic variance in fitness by incorporating the entire
mutation load of an individual. Thus any condition-dependent trait "captures" the overall genetic variance in condition. Rowe and Houle argued that genic capture ensures that
good genes will become a central feature of the evolution of any sexually selected trait.
Condition
The key quantity for genic capture is vaguely defined as "condition." The hypothesis only defines condition as a quantity that correlates tightly with overall
fitness, such that
directional selection
In population genetics, directional selection, is a mode of negative natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype. Under dir ...
will always increase average condition over time. Condition should, in general, reflect overall energy acquisition, such that life-history variation reflects differential allocation to survival and sexual signalling. Genetic variation in condition should be very broadly affected by any changes in the genome. Close to
equilibrium any mutation should be
deleterious, thereby leading to non-zero overall mutation rate, maintaining variance in fitness.
Rowe and Houle's Quantitative Genetic Model
Rowe and Houle's simple model defines a trait as the result of three heritable components, a condition-independent component
, epistatic modification
and condition, suggesting the following function for a trait:
where
is the condition of an individual. Loci contributing to
are loosely linked and independent of loci contributing to
and
. Rowe and Houle then find the expected variance of
and ignored higher-order terms (i.e. products of variances):
where
represents the
genetic variance
Genetic variance is a concept outlined by the English biologist and statistician Ronald Fisher in his fundamental theorem of natural selection. In his 1930 book ''The Genetical Theory of Natural Selection'', Fisher postulates that the rate of ch ...
in the signal and analogously for other traits. Under
directional selection
In population genetics, directional selection, is a mode of negative natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype. Under dir ...
on
, the loci underlying
and
may lose all genetic variance. However, there is no qualitative difference in directional selection on
between
stabilizing selection
Stabilizing selection (not to be confused with negative or purifying selection) is a type of natural selection in which the population mean stabilizes on a particular non-extreme trait value. This is thought to be the most common mechanism of a ...
(i.e. no sexual selection) and directional selection on
. Therefore, the second term
will remain positive (due to biased mutation) and dominate
under sexual selection.
Other Applications
Genic capture can also play a role in accelerating adaptation to new environments.
Comparisons
Genic capture was proposed as a simpler alternative to another theory explaining the lek paradox
that proposed that sexual selection creates
disruptive selection, i.e. positive selection for genetic variance. Genic capture does not require any particular fitness function.
References
{{Reflist
Evolutionary biology
Sexual selection