11-09 Lecture Notes

7/30/2019 11-09 Lecture Notes

1/16

Behavioral Ecology I:

Sexual Selection

Dr. Sarah Eddy


2/16

Behavioral Ecology

Todays questions:

I. What are ecology and behavioral ecology?

II. What is sexual selection?III. How does sexual selection act when males

compete for mates?

IV. How does sexual selection act when femaleschoose mates?

V. What happens when both occur?


3/16

I. What are Ecology and Behavioral

Ecology?

Ecology: the study of how organisms interact

with their environment.

Behavior: the study of what organisms do,

how they do it, and why.

Behavioral Ecology: the study of how

organisms make decisions when they interact

with various aspects of their environment.

How: In terms of genetic, neuronal, and hormonal mechanism.

Why: In terms of fitness.


4/16

Major Questions in Behavioral Ecology:

What should I eat?

Where should I live?

How should I communicate? Who should I mate with?

When should I cooperate?


5/16

II. What is Sexual Selection?

Darwin wanted to explain why, in some species, maleslook different than females (beyond genitalia).

1. There is heritable variation in appearance and/orcourtship behavior.

2. Individuals experience differential success in obtainingmatesindividuals with certain traits do better.


6/16

II. What is Sexual Selection?

In most species, females invest MUCH more inoffspring than males do.

For Example: Female red deer average 145 kg. and are pregnant for

6 months, over the winter. Calves average 10 kg atbirth and nurse for two months; they weigh about 55kg at weaning.

Males average 200 kg, they contribute:____________sperm


7/16

III. How does Sexual Selection act

when Males Compete for Mates?

In red deer, intensemale-male competitionoccurs.

1. Which sex has highervariation in RS?

2. In which sex wouldalleles associated with

increased mating success

increase faster?

Lifetime # Offspring per Male in Population

Lifetime # Offspring per Female in Population

Frequency

Frequency

Males, 0-24 vs. 0-14.

Males, because they mate with more females.


8/16

IV. How does sexual selection act when

females choose mates?

What do females chose?

A. Resources required toproduce offspring

During copulation, male redbacksinsert a sperm transfer organ intothe female

Then they do a somersault, which

places their abdomen in front ofthe females mouthparts.

In many cases, the female proceedsto eat the male.


9/16




A. Resources required toproduce offspring

Hypothesis: Copulation lasts longerand more sperm are transferred ifmales are eaten.

Prediction: RS of cannibalized males ishigher than RS of non-cannibalized

males.

Experiment: Allow female redbacks tomate with two males.

Document the proportion of youngsired by each male.


10/16



Data: 2nd male 2nd malerejected accepted

Females ate 1st male

Females did not eat 1st male

1. What statistical test would you use to analyze these

data?

2. For first males, is there a benefit to being cannibalized?

6 3

1 22

Both whether 1st males being ate and whether the 2nd male isaccepted or rejected are categorical variables.

Yes, because their alleles are being passed on while the alleles of the

other male isn't passed on, due to fewer sperm competition.


11/16



And more data:

NC = average for non-

cannibalized 2nd

males

C = average for

cannibalized 2nd males

3. For second males, is there a benefit to being

cannibalized?

Paternityof2ndm

ale

(fractionofeg

gsfertilized)

Copulation duration of 2nd male(minutes)

If the second male sticks around to get eaten,

then they have more of the paternity.


12/16




B. Good Alleles


13/16

V. What happens when both

competition and choice occur?

1. Hypothesize which was more important (on the

evolutionary time scale), for the evolution ofhuman

male traits: competition or choice? Explain your logic

using biological and social factors that could influencethis.

2. How might you initially identify candidate male traits

that could be under sexual selection? Name some.

- Sexual dimorphic traits like height difference has decreased over

time, so competition might be less intense.

- We are mainly a monogamous species, so mate choice is more

important when we kind of mate for life.

- Facial hair. - Face Symmetry

- Voice. - Etc.

- Aggression.


14/16



Design an experiment to test your hypothesis.Evolutionary


15/16

V. What happens when both

competition and choice occur?

1. What is the relative strength of mate choice vs. competitionon these traits? Does this support your hypothesis?


16/16

Question: In the modern times, there is an extremely strong

correlation between amount of education and lifetime

income. Traditionally, men have been the breadwinner in

families. But currently, 57% of U.S. college students arefemale.

Could this change the whether competition or mate choice

is influencing male traits? Why?

V. What happens when bothcompetition and choice occur?

Documents

11-09 Lecture Notes