Lecture 28 Notes PDF

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Lecture 27 Notes...

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Lecture 28 11/17/17 Prof. Spilios’s email: [email protected] Prof. Spilios’s Office Hours: Tuesday/Thursday 11:00 AM – noon, Wednesday 12:00 pm – 1:00 pm or by appointment (in SCI301A) S2S Tutors info Chao Wu ([email protected]): Office Hours: Monday 11:45-1:45pm Erica Broderhausen ([email protected]): Office Hours: Wednesday 11:30-1:00pm George Tarantino ([email protected]) Office Hours: Thursday 4-6pm *Office hours occur weekly ~Notes by George Tarantino

Tinbergen’s Four Questions Causation- external and internal stimuli; proximate mechanisms Development- imprinting, learning, environmental effects, changes with age History- ecological and evolutionary context, “phylogenetic constraints” Function- value of the behavior in terms of survival and/or reproduction

Brood parasitism offers an ideal system for testing Tinbergen’s Four Questions -

Egg discrimination and rejection in the hosts of parasitic birds is an ideal system for simple but elegant behavioral experiments Host responses can be tested experimentally by using model eggs or eggs from other individuals or species

Causation- what stimulus causes the host bird to get rid of a parasite egg? -Egg appearance, detection of a parasitic bird in the area, detection of parasitic egg near nest - How does the appearance of the parasitic egg affect the rejection by the host? Sometimes the parasite egg resembles the hosts egg so closely that the host cannot discriminate The likelihood for egg rejection is proportional to how different the parasite egg is from the host egg

- ratio of host and parasitic egg? Do birds know which egg is theirs and which is parasitic, or do they simply reject the one that looks different? All eggs were accepted in 17 trials, only foreign eggs were rejected in 28 trials (including when the host egg was outnumbered 1:3), and birds made the mistake of rejecting its own egg in 3 trials A greater color difference was needed for proper rejection when the host eggs were in the minority Color difference matters as well as host : parasite ratio

(Rejection probability is proportional to host : parasite egg ratio, and rejection probability is also proportional to color difference) Development- How does a host’s past experience affect egg rejection behavior? Hypothesis- Birds “learn” what their eggs look like the first time they breed Can you trick young birds into learning the wrong eggs? In an experiment, a researcher named Lotem used two treatments. In one treatment he replaced a freshly laid egg with a foreign egg painted darker brown on the last morning of breeding. In the second treatment he replaced freshly laid eggs with foreign darker brown ones every morning of breeding.

Birds that had their own eggs consistently replaced with dark brown eggs (second treatment) were less likely to reject the dark brown eggs – Suggests birds learn what their eggs look like during the first time they breed. Birds that accepted the darker brown egg the first time they nested were also more likely to accept a foreign egg the next time they nested. Evolution (history) - How does the evolutionary history of the host affect its behavior Evolutionary lag hypothesis- host species that have only recently come into contact with a brood parasite may accept eggs simply because they have not yet evolved egg recognition and rejection behavior Kirtland’s Warbler is an endangered species that hadn’t been exposed the brown headed cow bird. When it was first exposed to the brown headed cow bird it had no defense against it because it hadn’t evolved recognition and rejection behavior. The Phylogenetic constraint hypothesis- birds that are smaller than the parasite egg and have smaller bills may not be able to physically remove the parasitic egg from the nest (have not evolved morphologically to be able to remove the egg) Some such hosts use different defenses, other than removing the egg from the nest. Some hosts bury the egg in nesting material and re-nest on top of the parasite egg Function- Is the behavior of rejecting eggs beneficial to survival/ successful reproduction? Hypothesis- egg rejection appears to be an obvious adaptive response to brood parasitism, but the risk of making mistakes might make acceptance the better strategy in some situations Prediction- host populations that exist outside the range of brood parasites should lack the rejection response (in areas where there is no natural brood parasite, the rejection response would actually be detrimental to survival—it would make a host more likely to reject its own eggs by mistake) Iceland Experiment- in Great Britain (GB) there are cuckoos; in Iceland (Ice) there are no cuckoos.

We see that in Iceland Meadow Pipet and Pied Wagtails are more likely to accept a foreign egg because there are no cuckoos in the area. If the rate of parasitism is very low (no parasites in the area), unconditional acceptance could be a better strategy to minimize the risk of rejecting host eggs.

It’s good to be able to apply Tinbergen’s Four Questions to other examples! When lions take over another pride, they will sometimes kill the cubs of the new pride (mentioned at the end of class) How do Tinbergen’s four questions apply here?

Causation- the physical, proximal stimuli that prompt the behavior Cubs of the new pride smell different (one possibly stimulus) Development- imprinting, learning, environmental effects Cubs of the new pride smell different Function- how does the behavior contribute to better survival/ reproduction If the cubs are killed, the females will be ready to mate sooner because they do not have to care for the cubs History- What behaviors/ morphological traits enable lions to do this behavior? Lions have evolved to be a carnivorous predator behaviorally and physiologically. This enables it to kill...