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Frequency-dependent Selection

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.Positive Frequency-Dependent SelectionIn positive...

Types of Selection

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...

Life Histories

Life Histories

Constrained by limited energy and resources, organisms must compromise between offspring quantity and parental investment. This trade-off is represented by two primary reproductive strategies; K-strategists produce few offspring but provide substantial parental support, whereas r-strategists produce much progeny that receives little care. These strategies are related to an organism’s survival likelihood across its lifespan, which is represented by a survivorship curve. Three general types of...

Kaplan-Meier Approach

Kaplan-Meier Approach

The Kaplan-Meier estimator is a non-parametric method used to estimate the survival function from time-to-event data. In medical research, it is frequently employed to measure the proportion of patients surviving for a certain period after treatment. This estimator is fundamental in analyzing time-to-event data, making it indispensable in clinical trials, epidemiological studies, and reliability engineering. By estimating survival probabilities, researchers can evaluate treatment effectiveness,...

Limits to Natural Selection

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Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.For one, natural selection can only act upon existing genetic variation. Hypothetically, redtusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for redtusks, natural selection cannot increase the prevalence of...

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Combining selective episodes to estimate lifetime nonlinear selection.

Joel W McGlothlin¹

¹Department of Biology, University of Virginia, Charlottesville, Virginia 22904, USA. jmcgloth@virginia.edu

Evolution; International Journal of Organic Evolution

|December 5, 2009

Summary

Lifetime natural selection, particularly stabilizing selection, is more complex than simply summing episode estimates. Directional selection patterns across life stages significantly influence overall nonlinear selection, revealing stabilizing selection may be more common than previously understood.

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Area of Science:

Evolutionary biology
Quantitative genetics
Ecology

Background:

Understanding lifetime natural selection is crucial for evolutionary biology, particularly for questions on life history evolution and sexual dimorphism.
Estimating selection across different fitness components and life stages is essential for a comprehensive view of evolutionary processes.
While directional selection sums across episodes, the additive nature of nonlinear selection across life stages remains unclear.

Purpose of the Study:

To investigate whether lifetime nonlinear selection can be accurately calculated by summing estimates of quadratic selection from sequential episodes.
To determine the influence of directional selection patterns on lifetime quadratic selection.
To provide a framework for analyzing lifetime selection in empirical studies.

Main Methods:

Derivation of equations to model lifetime quadratic selection based on selection across sequential episodes.
Analysis of how directional selection across episodes interacts with quadratic selection.
Application of derived equations to a simulated dataset and a reanalysis of existing empirical data on dark-eyed juncos.

Main Results:

Lifetime quadratic selection is influenced by both the sum of quadratic selection across episodes and the pattern of directional selection.
Directional selection across episodes can cancel out, leading to net directional stasis but significant stabilizing selection.
The findings suggest that stabilizing selection may be underestimated when considering only individual episodes rather than the entire life cycle.

Conclusions:

Lifetime nonlinear selection is not simply the sum of selection across episodes; directional selection patterns play a critical role.
True stabilizing selection might be more prevalent than previously recognized, especially when analyzing complete life cycles.
The developed equations offer a practical tool for empirical researchers to better quantify lifetime natural selection.