Question to Think About
Some birds have a behavior known as "helping at the nest". A female bird will sometimes help another bird rear offspring rather than laying her own eggs and raising them. There are two different hypothese to explain this behavior. First, this may be an example of an altruistic behavior that can be explained by kin selection. Alternatively, this may be an example of a purely selfish behavior. It is possible that young inexperienced birds are not very good at raising offspring the first time they try and by helping another bird to raise offspring they may get practice that makes them better at rearing offspring later on.
1) Explain how you as a scientist would conduct a study to distinguish between these two alternative hypothese.
2) Should a female bird who is capable of raising three offspring on her own help her sister to raise her sister's offspring if helping her sister allows her sister to raise five more offspring? Be sure that you would be able to explain to someone else how you determined your answer.
If you post your answers to the blog then I will be able to take a look at them and you can also get some feedback from fellow students.
Old Exam Questions
Here are some examples of old exam questions dealing with altruism. See if you can figure out the correct answers (answers provided at the bottom of this post).
Researchers studying black-tailed prairie dogs conducted an experiment where they dragged a stuffed badger (a predator of prairie dogs) across the colony. They repeated the experiment 698 times over the course of 3 years. The researchers observed that individuals with no offspring in the colony gave a warning call 19% of the time whereas individuals with offspring in the colony called almost 50% of the time. Which of the following could explain why individuals with no offspring would ever call?
(a) group selection
(b) other squirrels will return the favor in the future
(c) they have other relatives in the colony
(d) a and b
(e) a, b, or c would explain this observation
Which of the following are examples of an altruistic trait?
(a) an African wild dog sharing food with other members of the group
(b) a female choosing to mate with a symmetric male
(c) a sterile worker bee helping her sister (the queen) to reproduce
(d) a and c
(e) neither a, b, or c
Further Reading
Here are links to a couple of articles you might want ot take a look at-
Altruistic behaviors http://www.eoearth.org/article/Altruistic_behaviors
Kin selection http://www.eoearth.org/article/Kin_selection
More advanced reading
One of the problems with introductory courses is that we have to cover so many topics that it is not possible to go into very much detail over any of them. If you are interested in learning more about kin selection and altruism the following article would be good to look at.
Kin selection: fact and fiction. http://westgroup.biology.ed.ac.uk/pdf/Griffin&West_02.pdf
Answers to the test questions: 1) c 2) d
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1. If the bird were to be put into a situation where she is surrounded by no close relatives, only other birds, then you could see if she acts selfishly or not. If she still helps raise the other birds, she is doing it for her own benefit later on when she lays her own eggs.
ReplyDelete2. The bird should raise her own three offspring instead of helping her sister raise her five offspring. If she acts selfishly, 1.5 of her genes will be passed on to her offspring (3 kids X 1/2 of genes). If she acts altruistically, only 1.25 of her genes will be passed on to her sister's offspring (5 kids X 1/4 of genes).
Kelly, Thanks for posting- here are some comments about your answers.
ReplyDelete1. This answer would help to determine whether or not kin selection is the best hypothesis to explain this behavior. I would start my study by carefully observing the relationship between the helper and the helped to see if the helper is always helping relatives (if so kin selection would be a good hypothesis to think about). I like the idea of experimentally placing birds in a situation where they were unable to help close relatives to see if they were still altruistic.
However, you haven't really addressed the hypothesis that the reason the bird helps to raise another's young is that it make her better able to raise young in the future.
In order to test this you would need to be able to compare the reproductive success of females who are rearing their own young for the first time between those females that did act as helpers at the nest and those that did not. If females that had experience helping others to rear young were able to successfully fledge more offspring than females with no experience then that would be pretty good support for the "practice" hypothesis.
One of the common mistakes that students make on the essay exams is that they fail to answer the entire question. Because the question asked about choosing between two hypotheses you need to make sure that you explicitly talk about testing both hypotheses.
2. You are right on with your second answer. You used a modified version of Hamilton's Rule to determine that the birds should indeed be selfish!
Thanks for these posts. I hope this response is helpful.