1)    What is your favorite example of sexual dimorphism?

Black widow

Describe the typical prezygotic and postzygotic differences in “parental investment” between males and females.

Prezygotic – eggs (females) are more expensive than sperm (males)

Postzygotic – the parent that cares for the offspring has more energy expenditure (usually female)

Describe the potential differences in reproductive success between males and females.

Female potential reproductive success is low because she spends more time producing and caring for offspring than convincing a male to mate. Male potential reproductive success is high because he is more likely limited by the number of females he can convince to mate with than the amount of ejaculate.

  Who’s reproductive success is increased more by increasing the number of mates?  Males or Females? How was this demonstrated experimentally?  What does this say about the strength of natural selection in males versus females?

Males. Taricha granulosa eggs were reared in the lab and matched to a father. Not all of the males reproduced, but all of the females did. Natural selection is stronger in males.

   What two predictions can be made if there is an asymmetric strength of natural selection in a species?

1)   Members of the sex subject to strong sexual selection will be competitive

2)   Members of the sex subject to weak sexual selection will be choosy

What is the difference between intra and intersexual selection?

Intrasexual selection is when the key event that determines reproductive success (fighting) involves interactions among the members of a single sex. Intersexual selection is when the key event that determines reproductive success (choosing) involves an interaction between members of the two sexes.

  What leads to increased reproductive success in marine iguanas and why?

Larger body size allows some males to better protect territories, and females prefer some territories over others. Males with the best territories and the best means to defend it can have many females.

Males raised and mated in the presence of a potential rival ejaculated more than 2.5x as many sperm as males raised and mated in isolation. Larger ejaculates contribute to victory in sperm competition. Male medflies dispense their sperm to balance the twin priorities of ensuring successful fertilization and sperm conservation.

Would you like to be a lion cub?  Why or Why not?

No, if the males in my pride weren’t strong enough, a newcomer might take over and eat me.

 Why aren’t male gray tree frog calls even longer than they are?

? They attract predators, and they only need to be longer than the other male

 How did Welch and colleagues test the “good genes hypothesis” in Frogs?  Did the experiment support the good genes hypothesis?

Females will choose male that will pass on genes to their offspring that will confer better fitness. They took eggs from 1 mother, fertilized half with a male with a long call and half with a male with a short call. Offspring from males with long calls were either superior or not significantly different from offspring from males with short calls on 5 criteria. The experiment supported the good genes hypothesis. 

How do male hangingflies ensure greater reproductive success?

Males capture large prey and present them to a female, if the female accepts, they copulate while she eats it. The longer it takes for the female to eat, the more sperm is ejaculated.

  Explain the “sexy-son” hypothesis for why females are choosy.

Once a particular male display is favored by a majority of females, selection on females will automatically reinforce a preference for the fashionable trait. Females choosing fashionable mates will have fashionable sons, and therefore more grandchildren.

  When is sexual selection stronger for female traits than for male traits?

When males provide parental care.

Explain how sexual selection could operate in plants.  Give an example.

A plant’s access to pollinators limits the reproductive success of pollen donors to a greater extent than it limits the reproductive success of seed parents. Yellow flowered wild radishes received ¾ of reproductive success through pollen donation, but not seed production.

  Why is it difficult to study whether there is evidence of sexual selection in Homo sapiens?  IS there any evidence of it, and if so what is the data?

1)   Human behavior is a complex of culture and biology

2)   Most studies are observational

Yes, there is evidence for it. Opportunity for sexual selection is greater in men than women. Man-man combat is more prevalent than woman-woman combat. Men who win in combat are likely to be bigger and have greater fitness.