1. Evolution of Reproductive Behaviors

3. Differences in Sex Roles
In general, males court, females choose
Video clip

4. Different styles of bowers

5. Advantage to males? Convey information about mate quality
Advertising
Female choice supports this hypothesis
But are males that build superior bowers actually superior mates?
How to test?

6. Data on male quality Better bowers= Fewer parasites
More disease resistance genes— less able to be infected by lice
Bigger brain size (skull comparison bower vs no bower building species)

7. Discussion Question
Females favor robust and aggressive courtship displays, but often flinch or act jumpy in the presence of these displays. Ultimately, the female crouching down is an indication she is likely to mate with the male eventually. Borgia’s lab has proposed that the bower originated to offer the female protection against forced copulation by displaying males.
How does the evidence support this hypothesis?
How does the male benefit by producing such an elaborate structure that actually might counteract his attempts to mate?
Can you predict how a male would react to a robotic female that remained standing, crouched once or twice, or crouched frequently to his display?

8. Fundamental sex differences
Female bower birds spend weeks viewing bowers and courtship displays before settling on a mate, whom she will likely never see again after the copulation.

9. Male success is dependent on bower quality, and therefore uneven
Why is it that males build and females choose? That males chase many mates and females are often content with one or a very few carefully chosen matings.

10. Sperm vs. Egg Hamster gametes
Egg: few produced, huge energy investment, may take up substantial % mass of the female
Sperm: Millions to billions produced, far less mass than egg
Human example: one man, all eggs
So eggs are limiting—sets up competition between sperm to fertilize them.
More mates=more eggs fertilized=more genes passed on=more fitness
Hamster gametes

11. Strategies for optimizing fitness
Distinguish between new and familiar partners
Anolis lizards exhibit far more courtship toward strangers than known companions
MALE:
Make sure fertilized eggs survive and thrive
FEMALE:

12. Parental Investment Male frog carries tadpoles on his back
Male katydid gives female edible spermatophore with nutrients for the eggs and herself
Female duck carries babies on her back, protecting them from would be predators
Female wasp drags a paralyzed cicada back to the nest to feed her young

13. Parental investment Good for females? Bad for males?
Offspring extremely likely to carry her genes
Little incentive to mate again, means greater ratio of receptive males:receptive females
Good for females?
Paternity uncertain
Fertilize as many eggs as possible
Greater competition the more females are mated
Bad for males?
Male biased operational sex ratio (more receptive males than females in a population)

14. Optimization of the process
Sperm optimized for good fertilization ability
Fast, numerous, small
“number of offspring” strategy
Eggs optimized for good development ability
Large, immobile, nutrient rich
“parental investment” strategy
No one gamete could be equally good at both tasks

15. Sex role differences combine with gamete size differences so that two paths are selected for. Typically males follow the left path, females the right, but there are exceptions…

16. Sex Role reversal
Males are out getting food which they present to the female of their choosing—based on her wing and leg decorations—prior to mating. Females compete for the males and these food gifts.

17. The nuptial gift
Males may reject the mountings of 3.2 gram female katydids in favor of stronger 3.5 gram females which will net them about 50% more eggs fertilized. Since males can probably only produce one nuptial gift in their lifetime, it makes sense for them to be choosy about the female they inseminate.
If conditions cause the operational sex ratio to change within a single breeding season, the competition/sex roles can change in accordance.

18. Pipe Fish: pregnant males
Published online 17 March 2010 | Nature | doi: /news
Male pipefish abort embryos of ugly mothers