Lec 12 Flashcards
Sex vs. gender
Sex: What type of gametes does na individual have - large or small? Large gametes = females, small gametes = males
Gender: non-binary concept related to how individuals view themselves within societal constructs, often related to, but not always the same as, an individual’s biological sex
When we use the terms “male” and “female” in this course, we are referring to the TYPE OF GAMETE that individual organism produces
Is selection the same on males and females?
We look at how many gametes can be produced for a given amount of resources
For the same amount of resources, the female can produce 2 gametes and the male can produce 2000
If the goal is to have as many offspring as possible, what mating strategy should MALES pursue? What mating strategy should FEMALES pursue?
If the goal is to have as many offspring as possible, what mating strategy should MALES pursue? What mating strategy should FEMALES pursue?
Males mate with as many individuals as possible, females choose mates carefully
Fitness
Relative genetic contribution of individuals to future generations
2 components of fitness
Survival
Reproduction
For your genes to make it to the next generation, you need to SURVIVE and PRODUCE OFFSPRING
Selection operates ______________ on males and females
DIFFERENTLY due to differences in investment in reproduction
What are the consequences of anisogamy for selection and evolution in males vs. females?
Darwin’g theory of sexual selection
-Sexual selection “depends, not on a struggle for existence, but on a struggle between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring”
Traits invovled in reproductive fitness
Sexually selected traits
Anisogamy leads to sexual selection
By definition, males produce many tiny gametes (sperm), females produce fewer, large gametes (eggs)
Sexual selection in males and females is then driven by differences in investment (time, effort, resources) parents devote to each offspring
Which is a consequence of anisogamy?
Females are very choosy about their mates, and males evolve to be attractive to females
Consequences of anisogamy and differential investment
Differences in the way males and females maximize fitness lead to differences in behavior, morphology, and physiology
Females have more to lose from mating “wrong”, so they are MORE SELECTIVE about choosing mates
Since females are choosy, and males mate multiply, males compete for access to females
Mechanisms of Sexual Selection
Selection that acts on an organism’s ability to obtain a mate
Intrasexual selection (male competition);
- WITHIN the sexes
- Flashy, competitive males
- “Male-male competition”
- Selects for traits that aid in combat, territory defense
Intersexual selection (female choice)
- Between sexes
- Drab, choosy females
- “Female choice”
- Selects for traits that increase attractiveness
What are males competing for and why?
Males compete for access to females, or monopolization of resources that attract females
Anisogamy = Skew in OSR
OSR = Operational sex ratio = ratio of AVAILABLE males to females
Smaller gametes and less parental care means males are more available in the mating pool
Reproductive Skew:
When more males than females are available to mate, competition for mates INCREASES
-A lot of males must compete for few females
there is not a perfect correlation between reproductive skew and competition because male mating success depends on:
1) Pool of available females
2) Ability of a male to monopolize access to females
For males to reproduce, he needs to mate with a lot of females
When there are more males than females available to mate what happens to competition for mates?
Increases
Intrasexual selection in elephant seals
Elephant seals breed on small beaches at particular times of year (you can go see them on the Central Coast)
Females are clumped on small beaches
-Females come give birth on land and mate immediately after
This allows males to monopolize access to females
-Males spen ALL of their time during short breeding season to monopolize females, do NOT assist in raising young
Males provide NO parental care or investment in offspring
Only about 1% of males EVER mate
-ONLY the biggest, strongest, most territorial
Territory defense in kittiwakes
Males find a nest site
Males and females jointly build a nest on a cliff face
Males and females both incubate the eggs and feed chicks
Both males and females participate in nest defense
Kittiwakes are monogamous and the same pairs will often stay together for many years
In which group is INTRASEXUAL selection stronger?
Elephant seals, because only a few males are able to mate so there is intense competition and the evolution of competitive traits
Male competition (intrasexual selection) summary
Males invest less per gamete
They maximize thier fitness by mating wtih as many females as possible
Males compete with each other for access to mates or matings
Strength of competitions depends on OSR
A skew in OSR (ratio of available males : females) typically means stronger male competition
Competition is also influenced by how effectively males can monopolize access to females
Female choice has been harder to understand than male competition
The female could in most cases escape, if wooed by a male that did not please or excite her; and when pursued, as so incessantly occurs, by several males, she would often have the opportunity, whilst they were fighting together, of escaping with, or at least temporarily pairing with, some one male
Nevertheless, when we see many males pursuing the same female, we can hardly believe that the pairing is left to blind chance - that the female exerts no chocie, and is not influenced by the gorgeous colors or other ornaments with which the male alone is decorated
Which male obtained the most nests in his territory?
Elongated tail
Why do female preferences for costly male traits evolve?
Darwin originally argued that females have an “aesthetic sense” - these are now termed “arbitrary preferences”
Later work suggested that some female preferences are tied to benefits that females gain from mate choice
Male signals evolve to advertise benefits to females
