Evolutionary Biology: Natural and Sexual Selection

Flashcards covering key vocabulary from the lecture on Natural and Sexual Selection, including definitions of different types of selection, fitness, reproductive strategies, and related hypotheses.

Natural selection

The only adaptive evolutionary force.

Adaptation

A characteristic that allows an organism to either survive better or to reproduce more.

Adaptive

Refers to a process or trait that increases an organism's fitness or survival.

Selective forces

Outside forces that can cause selection, such as predation, climatic factors, parasitism, mate attraction, and resource acquisition.

Fitness

An individual's reproductive success.

Absolute fitness

The total number of offspring an individual produces.

Relative fitness

The fitness of a genotype relative to the most successful genotype in the population, often scaled to 1.

Stabilizing selection

A type of natural selection that favors intermediate phenotypes, reducing variation and acting against extreme traits.

Directional selection

A type of natural selection that favors one extreme of the phenotypic range, leading to a shift in the population's trait distribution over time.

Disruptive selection

A type of natural selection that favors individuals at both extremes of the phenotypic range over intermediate phenotypes.

Balancing selection

A type of natural selection that maintains genetic variation in a population.

Heterozygote advantage

A form of balancing selection where heterozygous individuals have higher fitness than either homozygous genotype.

Negative frequency dependent selection

A form of balancing selection where the fitness of a phenotype decreases as it becomes more common, favoring rare phenotypes.

Reproductive strategy

The combination of behaviors and traits involved in mate choice, mating frequency, mate guarding, long-term mating, parental care, and offspring spacing.

Parental investment

The time and energy parents expend for their offspring; sexes often differ in this investment.

Female choice

A component of sexual selection where females actively evaluate and select their mates.

Male/male competition

A component of sexual selection where males compete with each other for access to females.

Sexual dimorphism

Distinct differences in physical characteristics between males and females of the same species, often due to sexual selection.

Paternal care

Care provided by the male parent to their offspring.

Territory defense/resource acquisition

Strategies often employed by males to attract females by securing desirable resources or areas.

Good genes hypothesis

A theory suggesting females choose mates that display traits indicating superior genetic quality, which would benefit their offspring.

Handicap principle hypothesis

A theory that females choose males based on visible, costly traits, as only males with strong overall fitness could survive despite such a 'handicap'.

Runaway selection

A process where a sexually selected trait in males and a female preference for that trait coevolve, potentially leading to exaggerated male traits that may even reduce natural fitness, creating a conflict between sexual and natural selection.

Ghost of selection past

A concept related to runaway selection, where an exaggerated trait might have had an initial adaptive advantage but is now maintained or further developed due to continued female preference, potentially exceeding optimal natural selection pressures.

Salmon

An example species used to illustrate directional selection, where fishing pressures can favor smaller sizes.

Colonial bentgrass, Agrostis tenuis

An example species used to illustrate disruptive selection due to differing tolerances to mine versus non-mine soil.

Elephant seals

An example species demonstrating sexual dimorphism and male-male competition for mates.

Australian riflebirds

An example species used to illustrate elaborate male display and female mate choice.