Lecture 6 - sex roles

Sex roles

Differences between males and females in appearance and behavior in many species.

Sex

Male and female based on the larger gamete produced (female produces eggs, male produces sperm).

Male

The sex that competes for access to females and typically exhibits sexual armament or ornaments.

Female

The sex that is more camouflaged and typically cares for offspring.

Sex difference in coloration

The individual with more colorful appearance is typically the male.

Sex difference in parental care

The less colorful individual typically cares for eggs and chicks, indicating female.

Grey phalarope/red phalarope

A species where the traditional definitions of male and female based on coloration and parental care do not apply.

Conventional sex roles

Species where males compete for females and females care for offspring, includes most mammals.

Reversed sex roles

Species where females compete for males and males care for offspring, includes some fishes and birds.

Egalitarian sex roles

Species where both males and females care for offspring, includes some fishes and most birds.

Charles Darwin

Proposed sexual selection as a mechanism for competition over mating access.

Intrasexual selection

Competition within one sex for members of the opposite sex, usually male-male competition.

Intersexual selection

Differential choice by one sex among members of the opposite sex, usually female choice.

Mating systems

The number of mating partners per male and female, and the nature and duration of pair bonds.

Monogamy

Mating system where there is one male and one female partner.

Polygyny

Mating system where one male mates with multiple females, while females only mate with one male.

Polyandry

Mating system where one female has multiple mates, while males only have one mate.

Polygynandry

Mating system where both males and females have multiple mates.

Promiscuity

Mating system where individuals have multiple partners with no selection basis.

Parental investment

The resources and care provided by parents to their offspring.

Anisogamy

The difference in size between eggs and sperm, with eggs being larger.

Parental investment hypothesis

Anisogamy leads to female-biased investment, which leads to strong sexual selection on males.

Sexual selection hypothesis

Anisogamy allows for strong sexual selection on males, which leads to female-biased investment.

Tanganyikan cichlids

A group of fish species in Lake Tanganyika with diverse forms of parental care and mating systems.

Phylogeny

The evolutionary history and relationships among species.

Genetic data

Molecular data used to construct phylogenies and infer ancestral states.

Uniparental female care

Parental care provided solely by females.

Biparental care

Parental care provided by both males and females.

Sexual dimorphism

Differences in appearance between males and females.

Monogamous species

Species where there is one male and one female partner and no sexual dimorphism.

Evolutionary transitions

Changes in traits and behaviors over evolutionary time.

Parsimony

A principle in phylogenetics that favors the simplest explanation with the fewest evolutionary changes.

Moderate sexual selection

Intermediate level of competition and mating success among males.

Strong sexual selection

High level of competition and mating success among males.

Sperm competition

Competition between sperm from different males to fertilize eggs.

Operational sex ratio (OSR)

The ratio of sexually active males to receptive females in a population.

Egalitarian sex roles

Sex roles where males and females provide the same level of care.

Partial sex role divergence

Sex roles where females provide more care than males, but males still provide some care.

Full sex role divergence

Sex roles where females provide all care and males provide no care.

Tanganyikan cichlids case study

Examining the relationship between parental care and sexual selection in a group of fish species in Lake Tanganyika.

Parental care

The act of providing care and support to offspring by one or both parents.

Sexual selection

The process by which certain traits or behaviors increase an individual's chances of mating and reproducing.

Biparental care

The involvement of both parents in providing care for offspring.

Female care

The shift in parental care from both parents to primarily the female parent.

Intense sexual selection

A high level of competition among individuals of one sex for mating opportunities.

Moderate sexual selection

A moderate level of competition among individuals of one sex for mating opportunities.

Sexual selection hypothesis

The idea that changes in sexual selection occur before changes in parental care.

Tanganyikan cichlids

A group of fish species found in Lake Tanganyika, often used in studies on sexual selection.

Trivers' (1972)

A verbal argument proposing that sex differences in parental care drive sexual selection.

Kokko & Jennions (2008)

A mathematical model suggesting that sexual selection and sperm competition drive sex differences in parental care.

Empirical evidence

Real-world observations or data that support a hypothesis or theory.

Mathematical modeling

The use of mathematical equations and simulations to understand and predict complex phenomena.

Verbal arguments

Arguments or explanations based on verbal reasoning or discussion.

Flaw

A mistake or weakness in an argument or model that undermines its validity or accuracy.