Chapter Review: Sexual Selection, Sperm Competition, and Polyandry

Flashcards covering sex roles, sperm competition, polyandry, cryptic female choice, and direct/indirect benefits discussed in the lecture notes.

What is anisogamy and how does it influence sex roles in sexual selection?

Anisogamy is the difference in gamete size between the sexes; females invest heavily in energetically costly eggs, which tends to make them choosy while males pursue more mating opportunities.

In seahorses and pipefishes, which sex carries the eggs and gives birth, and what does this illustrate?

Males carry fertilized eggs in brood pouches and give birth; this is an example of sex role reversal.

What is sex role reversal?

A situation where the traditionally choosy sex becomes the male and the typically competitive sex ( females in many species) competes for mates due to shifts in parental investment.

What is mutual mate choice and what is an example mentioned?

Both sexes display ornaments and make mate choices based on the other sex’s ornament quality; example discussed includes ornamented features in both sexes (crested displays in some species).

What is polyandry?

Females mate with multiple males; leads to postcopulatory sperm competition and is widespread across many species.

What is the role of female sperm storage organs (theca/spermatheca)?

Store sperm from multiple males, enabling competition among sperm within the female.

What did Jeff Parker’s work reveal about polyandry?

Polyandry is a common behavior across many species; monogamy is relatively rare, highlighting the importance of female mating frequency in evolution.

How can males respond to sperm competition (two broad strategies)?

Engage in sperm competition by increasing sperm production/quality (larger testes, more/faster sperm) or avoid sperm competition via mate guarding or biochemical manipulation that reduces female receptivity.

What did the cricket study on sperm allocation and viability find?

Males did not reliably change the number of sperm allocated based on female mating history, but they altered the viability of the sperm depending on whether the female had mated before or many times.

How can males avoid sperm competition through mate guarding?

After mating, a male may stay with the female to prevent remating; weapons or specialized structures can aid guarding and sometimes block remating (e.g., pedipalps in some spiders).

What is seminal protein manipulation and give an example?

Biochemical substances transferred with sperm can reduce a female’s receptivity to further mating; classic example is Drosophila.

What is the damselfly example of sperm removal and why is it significant?

Male damselflies have spines on their genitalia that can scrape out previous sperm from the female’s storage, allowing them to bias paternity toward their own sperm.

What is cryptic female choice?

Females can internally bias fertilization after mating by mechanisms such as terminating mating early, destroying or ejecting sperm, or removing a mating plug.

What are direct benefits of polyandry?

Fertility assurance (multiple matings ensure eggs are fertilized) and direct nutritional or material benefits from nuptial gifts (e.g., foods or nutrients in ejaculates) such as in scorpion flies, Mormon crickets, and Dolomites fishing spiders.

What are indirect genetic benefits of polyandry?

Genetic diversity in offspring (broader genetic base for colonies), genetic compatibility (e.g., maximizing MHC diversity to avoid incompatibilities), and possible good-genes or sexy-sperm effects.

What did the honeybee example illustrate about genetic diversity and colony success?

Colonies with genetically diverse workers (polyandrous queens) showed faster brood growth, higher foraging, and better parasite resistance than genetically uniform colonies.

What is the difference between good genes and sexy sperm hypotheses?

Good genes suggests offspring benefit from high-quality genes of a mate; sexy sperm posits that polyandry improves the viability or performance of sons’ sperm, contributing to maternal fitness even if the mate’s genes aren’t inherently superior.

What did the cricket study on offspring show regarding sperm viability and immune function?

Offspring from polyandrous mothers had sons with higher sperm viability, but there was no difference in immune function, supporting the sexy-sperm hypothesis over a general good-genes effect.

What is a drone congregation area (DCA) in honeybees and why is it important?

Aerial mating swarm where drones gather and queens mate with multiple drones, increasing genetic diversity in the colony.

What are alternative mating tactics and how do they relate to sperm competition?

Different male strategies (e.g., large males with weapons vs. small hornless males that invest in larger testes or faster sperm) illustrate how species balance pre- and post-copulatory competition.

What video was used to illustrate male pregnancy and sex role reversal?

A video of a male seahorse giving birth, illustrating male parental investment and the reversal of traditional sex roles.