Drawing of mated pair, nestlings, and helper (left) at a nest of the Florida Scrub Jay (Aphelocoma coerulescens). (From E. O. Wilson. 1975. Sociobiology: The New Synthesis. Belknap Press, Cambridge, MA.)
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
1) If young inexperienced birds are exposed to unrelated experienced birds, and they still display "altrustic-like" behavior than it can be concluded that it is purely selfish behavior. If no altrusitic behavior is shown, they could be only altruistic toward kin. If then exposed to relatives and they display altruistic behavior, it can be concluded that the birds are altruistic
ReplyDelete2) The female should help her sister because more of her genes will be trasfered to the next generation. According to Hamilton's Rule, her future 3 children will have .5 and her future 8 nieces will have an r of .25. 3*.5=1.5 = Cost and 8* 0.25 = 2 = Benefit. Since the benefit is larger than the cost, then it would make sense for the female to help her sister and forgo having her own offspring.