Darwin's Natural and Sexual Selection

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What was the primary goal of the study on spitting spiders conducted by Teck Hui Koh and colleagues?

To investigate whether pheromones signal male quality. (correct)

To measure the physical size of male spitting spiders.

To evaluate the effects of male aggression during mating.

To determine the impact of environmental factors on mating.

In Phase 1 of the mate choice experiment, what type of communication was allowed between the male and female spiders?

Visual and tactile communication.

No communication at all.

Chemical communication only. (correct)

Tactile communication only.

What was the outcome for female spiders that mated with their preferred males?

They had lower hatch rates.

They had no change in reproductive success.

They produced larger egg sacs with more and heavier eggs. (correct)

They produced fewer eggs.

What indirect benefits do female spitting spiders gain by choosing their mates based on pheromones?

Improved egg production quality. Signup and view all the answers

What behavior do male black-throated blue warblers exhibit to ensure paternity assurance?

Mate guarding. Signup and view all the answers

What is a potential cost of mate guarding behavior in male species?

Reduced opportunity to find additional mates. Signup and view all the answers

What methodology was used in the observational study of black-throated blue warblers?

Observations during the female's fertile period were recorded. Signup and view all the answers

What role do pheromones play in the context of the spitting spiders' mate choice?

Indicating male quality, such as size and health. Signup and view all the answers

What characterizes the bourgeois tactic in male reproductive strategies?

Males defend nests to attract females. Signup and view all the answers

Which of the following best explains why parasitic males can gain fitness benefits?

When bourgeois males are more abundant. Signup and view all the answers

How does a conditional strategy impact male reproductive tactics?

Healthier males adopt the bourgeois tactic; less fit males use parasitic tactics. Signup and view all the answers

What fitness prediction does the evolutionarily stable strategy (ESS) suggest?

Both tactics can persist when coexisting at certain frequencies. Signup and view all the answers

In what way do male green tree frogs differ in their reproductive strategies?

Some males switch between calling and remaining silent. Signup and view all the answers

What is a key prediction of Humfeld's Hypothesis regarding satellite behavior in male tree frogs?

Less attractive males are more likely to act as satellites. Signup and view all the answers

What type of call do female green tree frogs prefer?

Loud, low-frequency calls produced by larger males. Signup and view all the answers

What defines the characteristics of sneaker males in the reproductive tactics observed?

They stealthily fertilize eggs in bourgeois males' territories. Signup and view all the answers

What strategy do female European tree frogs use to enhance their offspring's fitness?

Choosing males with desirable vocal traits Signup and view all the answers

Which hypothesis suggests that parasites and pathogens influence sexual selection?

Hamilton-Zuk Hypothesis Signup and view all the answers

What trait did female field crickets prefer in male courtship songs?

High-frequency ticks Signup and view all the answers

In the study on field crickets, what was used to assess the immunocompetence of the male crickets?

Encapsulation rate Signup and view all the answers

What benefit do females gain by choosing males with pronounced HF ticks?

Indirect genetic benefits in offspring immunocompetence Signup and view all the answers

What did the researchers use to measure the immune response of male crickets?

Nylon filament implantation Signup and view all the answers

Which statement correctly summarizes the relationship between male secondary sexual traits and health in the Hamilton-Zuk hypothesis?

Higher immune response is linked to more exaggerated traits. Signup and view all the answers

What role do pheromones play in mate selection according to the background information?

They assist in the selection of mates with desirable traits. Signup and view all the answers

What behavior did dominant male carrion beetles primarily exhibit in the study?

They actively defended the carcass and mated with multiple females. Signup and view all the answers

What was the primary method used to determine the parentage of larvae in the research?

DNA fingerprinting Signup and view all the answers

What advantage did large male carrion beetles have over smaller males in terms of reproduction?

They sired three times more offspring. Signup and view all the answers

How did females behave in relation to mating with males in the study on carrion beetles?

They mated with both males without exhibiting aggression. Signup and view all the answers

What does the conclusion regarding resource defense polygyny suggest about male carrion beetles?

Male defense of resources drives polygyny rather than defense of females. Signup and view all the answers

Which hypothesis suggests that low-ranking males aggregate to benefit from female visits attracted by high-ranking males?

Hotshot Hypothesis Signup and view all the answers

What is a key characteristic of male dominance polygyny?

Resources and females are uniformly distributed, making defense costly. Signup and view all the answers

What is expected to occur if a high-quality male is removed from a lek based on the Hotshot Hypothesis?

Attractiveness of the lek decreases for females. Signup and view all the answers

What behavior do male mosquitofish exhibit when a rival male is present near a preferred female?

They avoid the female to reduce sperm competition. Signup and view all the answers

Which mating system involves one male mating with multiple females?

Polygyny Signup and view all the answers

How do environmental conditions affect mating systems?

They influence the social structure and reproductive strategies. Signup and view all the answers

Which of the following describes a mating system where multiple males and females form social groups?

Polygynandry Signup and view all the answers

Variation in mating systems can be observed in which of the following?

Within species, populations, and even individuals. Signup and view all the answers

What defines promiscuity in mating systems?

Multiple males and females mate without specific associations. Signup and view all the answers

Which of the following statements is true about mating systems?

Mating systems can vary widely among species and populations. Signup and view all the answers

What primarily drives males to engage in extra-pair copulations (EPCs)?

To increase their reproductive success Signup and view all the answers

What do social mating systems reflect?

Observed pair-bond associations Signup and view all the answers

How does the genetic quality hypothesis explain extra-pair matings?

Females mate with multiple males to improve offspring fitness Signup and view all the answers

What is a potential risk for females engaging in extra-pair copulations?

Loss of parental care due to paternity uncertainty Signup and view all the answers

Which advantage is NOT associated with the genetic quality hypothesis?

Increased territory control Signup and view all the answers

Which species was specifically mentioned in relation to extra-pair mating studies?

Dark-eyed juncos Signup and view all the answers

What evolutionary benefit do extra-pair matings provide to socially monogamous females?

Maximizing genetic benefits for their offspring Signup and view all the answers

What is a key reason for females to pursue multiple mating partners under the genetic quality hypothesis?

To avoid infanticide risks from dominant males Signup and view all the answers

Study Notes

Darwin's Theory of Natural Selection and Sexual Selection

Darwin proposed natural selection to explain the evolution of adaptive traits in species.
Darwin introduced the concept of sexual selection as a subset of natural selection focused on reproductive advantages.

Primary and Secondary Sexual Characteristics

Darwin studied both primary (genitalia differences) and secondary (traits not directly involved in reproduction) sexual characteristics in various species.
Examples of secondary characteristics include colorful plumage in male birds and large antlers in male mammals, often used in mating displays.

The Puzzling Nature of Secondary Sexual Traits

Darwin found secondary sexual traits puzzling as they seemed costly and risky, potentially reducing survival chances due to energy demands and visibility to predators.
He questioned why traits like the peacock's tail evolved if they appeared to reduce survival.

Sexual Selection as a Reproductive Advantage

Darwin theorized that exaggerated male traits increase reproductive success rather than survival.
Sexual selection involves mate competition (intrasexual selection—males competing for mates, sometimes through physical combat) and mate choice (intersexual selection—females selecting mates based on attractive traits).
These processes favor traits that increase reproductive success.

The Evolution of Two Sexes: Anisogamy

The existence of two sexes (male and female) is linked to anisogamy, where males produce small, motile sperm and females produce large, nutrient-rich eggs.
Anisogamy evolved from isogamy (similar-sized gametes) through disruptive selection, favoring proto-males (producing many small gametes) and proto-females (producing fewer large gametes).

The Role of Anisogamy in Sexual Selection

Different gamete sizes established distinct reproductive strategies, which form the basis for sexual selection.
Sexual selection promotes traits that enhance reproductive success in both sexes.

Bateman's Hypothesis on Sexual Selection

Bateman studied sexual selection in fruit flies, observing greater variation in male reproductive success than female reproductive success, due to male-male competition.
Female reproductive success is limited by egg production, creating less intense competition among females.
This difference in reproductive success contributes to differing selective pressures on males and females.

Parental Investment Theory by Robert Trivers

Trivers expanded Bateman's hypothesis by introducing parental investment—any effort by a parent that increases offspring survival but reduces the parent's ability to invest in other offspring.
Predictions: The sex with higher parental investment (often females) is choosier in mate selection, and the other sex (often males) faces more intense sexual selection.

Operational Sex Ratio (OSR) and Sexual Selection Intensity

Operational sex ratio reflects the difference in sexually receptive males and females at any given time, often favoring the less invested sex (typically males).
A skewed OSR results in increased sexual selection pressure on the sex with more readily available individuals (usually males).

Exaggerated Male Traits and Sexual Selection

Males often develop exaggerated traits (weapons or ornaments) due to sexual selection.
Examples include weapons for male-male competition and ornaments for attracting females.

Background Information on Sexual Selection

Sexual selection affects many beetle species where males possess horn-like projections not present in females.
Examples of this include male dung beetles using horns to compete for mating opportunities.

Research Questions, Hypotheses, and Methods

Various research questions, hypotheses, and methodologies are used to understand factors influencing mate choice and reproductive success in different species, including beetles, peacocks, pipefish, and others. Descriptions are too detailed to summarize.

Parental Investment and Selective Mating

Darwin's theory of natural selection is supported by research that shows how direct material benefits and indirect genetic benefits drive selective mating in various species, including arthropods, butterflies, and lizards.

Indirect Benefits of Mate Choice

Females may gain indirect genetic benefits by mating with high-quality males, passing on advantageous alleles to offspring.
Females assess genetic quality of potential mates in relation to secondary sexual traits (e.g., displays, ornaments).

Fisherian Runaway Hypothesis

Ronald Fisher proposed that female preference for certain male traits can lead to the enhancement of those traits to increasingly exaggerated levels through co-evolution.
This occurs as there is a link between the trait and female choice, even if the trait doesn't offer a direct advantage for survival.

Zahavi's Handicap Principle

Amotz Zahavi theorized that exaggerated traits, costly to produce, act as signals of male quality, showcasing the fitness of the male.
Only high-quality males can afford these costly signals.

Background Information to Mate Choice Copying

Mate choice copying is the observation of a mate choice or behavior by one individual, that may influence the mate choice of other individuals.
Mate choice copying is common in vertebrates.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore Darwin's Theory of Natural and Sexual Selection in this quiz. Understand how adaptive traits evolve through natural selection and the roles of primary and secondary sexual characteristics. Challenge yourself with questions about the puzzling nature of these traits and their implications for reproductive advantages.