Sexual and Asexual Reproduction and Sexual Selection UMD

Sexual reproduction

When two parents give rise to genetically unique offspring through the fusion of gametes produced by meiosis.

Asexual reproduction

One individual gives rise to genetically identical offspring. With this, offspring are clones of their parents which means no change in # of chromosomes. Done by mitosis.

Asexual reproduction advantages

One part, very quick, many offspring

Asexual reproduction disadvantages

Low genetic variation, could be very deadly as all offspring are very susceptible to one thing

Sexual reproduction advantages

High genetic variation, which can help lower the frequency of deleterious (bad) alleles

Sexual reproduction disadvantages

Two parents, time consuming, few offspring

Why is sexual reproduction costly?

It is very risky for survival, requires a lot of energy (finding mates, caring for young, and being able to sexual reproduce), and is inefficient as it requires twice as many adults to produce a given # of offspring in sexual species

Tangled Bank Hypothesis

Sexual reproduction is useful in more complex and unpredictable environments while asexual reproduction is better in stable, predictable environments

Red Queen Hypothesis

Sex provides varied offspring, allows for rapid evolution, and lets organisms keep up in the evolutionary “race”

Sexual selection

Form of natural selection that results from differential success among individuals in acquiring mates

Intrasexual selection

Favors the evolution of mechanisms that enhance ability to compete with other members of one’s own sex (found in male-male competition)

Intersexual selection

Favors the evolution of traits in males to impress individuals of the opposite sex. Associated with female choice through male secondary sexual traits.

Male-male competition

Males competing for mates (mating/breeding theory).

Male-male combat

Type of male-male competition. Males who win the fight normally get to mate. The males who win get to pass on their genes often giving their offspring their better weapons (ex: antlers)

Sperm competition

Type of male-male competition. Females will mate repeatedly with multiple males and, in order for a male to win, their sperm must reach the egg first. The way a male can win this is produce more sperm.

Female choice

Often happens when males are unable to monopolize access to females. Widely recognized as being responsible for the rapid and divergent of male secondary traits (physical traits in puberty)

Why might a female prefer a particular male trait

Assortative mating, direct benefits, good genes, Runaway Selection

Explain why sexual selection can favor traits that have survival costs

The advantages of those certain traits can outweigh the disadvantages

Direct benefits

Nuptial/better gifts given by males to females (ex: more food)

Good genes

Ability to produce and maintain elaborate ornamentation (certain looks that signal good health like ex: peacock being very colorful) indicates good genes.

Positive Assortative mating

Individuals choose mates with traits similar to themselves. More common

Negative Assortative/Disassortative mating

Individuals choose males with traits dissimilar to themselves. Less common

Male’s level of investment in reproduction

• Less energy to produce sperm

• Male investment in mating is small (usually no parental care)

• Males reproductive success determined by # of matings (access to females)

• Parentage is uncertain

• Quantity over quality

Female’s level of investment in reproduction

• Eggs require more energy to produce

• Investment in each mating is large (parental care)

• Female reproductive success determined by # of eggs she can produce or nurture (not access to males)

• Parentage is certain

• Quality over quantity approach

Runaway selection

Must have initial preference based on good genes, direct benefits, or assortative mating and female preferences with a genetic basis. Males inherit their dad’s attractive traits that they were chosen for and more female want that traits, creating a loop.