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
Answers to the test questions: 1) c 2) d
1.
ReplyDeleteGene=
Han (dominant for helping at nest)
han (recessive for helping at nest)
Hypotheses =
H.1. - individual expresses Han as an altruistic kin selection trait
H.2 - individual expresses Han as a selfish selection trait
To study whether individual expresses Han as H.1 or H.2 we can place a group of individuals together and observe them over a given reproductive cycle. We can mark all individuals that express Han with one banding marker, and those that express han f
with a different marker for use in identification subsequent cycles. We can then then move forward the F1 generation and keep the P1 generation also- but clearly make note of what generation the individuals belong to.
After noting the F1 generation nesting, we can see whether or not the P1 or even other F1 marked individuals express Han again. We might even see some of those previously marked as expressing han visiting the nest. After a few of these cycles we can make assumptions but clear understanding of those with Han could take even more cycles. Review of the data gained from the tracking of the banding markers should point to one of the two hypotheses H.1 or H.2
If P1 visits the nest of an F1 or subsequent generation we can make the case for H.1. If we see that F1 visits a P1 nest once but never again visits until that individual's own offspring are in the nest we can make a case for H.2
2. I read this two possible ways.
A) Yes, the female should help her sibling raise 5 more offspring which would bring their combined total to 11 - 3 of her own + 3 of her sisters + 5 more of her sisters from the added aid. Perhaps even 16 - maybe her sister reciprocates and helps her after she has completed helping her sister and the original female can add other 5 too. Wow. too many pronouns!
B) No, the female, by helping cannot raise any (a deficit for the community of -3) and the sibling only may raise 5. That means that while they potentially could have produced 6 (each of them 3 apiece) they only produced 5.