Coastal Warblers & Cooperative Breeding: a PBL Case Study

Before Class

To prepare for this assignment, you should have watched three youtube video lectures:

Social Interactions https://youtu.be/QtH83KsU2ME

The Prisoner’s Dilemma https://youtu.be/eHzXYEXUFHQ

Animal Personality https://youtu.be/exFP63ATEzk

And completed a quiz on the information. The quiz is attached at the bottom of this post.

During Class

In class today, your assignment is to "clean up" a really shoddy piece of scientific writing. The scientific writing is a draft of a paper that the researchers want to submit to a scientific journal. You’re going to give feedback on how the researchers can do a better job. Specifically, you’re going to read this draft paper, then answer the questions below.

Introduction

P1 Coastal warblers are a small song bird species found on the Seychelles archipelago. Coastal warblers are a valuable study species in ecology and evolutionary biology because female coastal warblers exhibit a unique form of helping behavior. The helping behavior begins when the birds are 1 year old and reproductively mature. Coastal warblers at this age can establish their own nest, mate, and produce offspring. However, most 1 year old coastal warblers do not establish their own nest. Instead, the majority of young female coastal warblers leave their parent’s nest and take up residence at a large and prosperous nest of unrelated coastal warblers. Some researchers have argued that this behavior is kleptoparasitic. However, we have observed that warblers who delay their own nesting and instead relocate to a more prosperous nest are actually behaving as ‘helpers’ in the new nest. Helping behavior is found in other bird species.

P2 We have observed these helper birds collecting food and feeding it to the resident offspring in the nest, thus helping the resident parents to produce more fit young. We present the alternative hypothesis that this behavior is done altruistically and increases the helper’s indirect fitness, because helpers always end up at nests of other coastal warblers and are thus helping conspecifics.

P3 We studied the prevalence of helping behavior in coastal warblers using three methods. First, we observed the number of 1 year old female birds that either started their own nest and reproduced or became resident helpers at another breeding pair’s nest, helping to raise that pair’s offspring. Next, we measured the boldness of helper and non-helper female warblers to compare helping behavior to animal personality. Finally, we created a game theory model of helping vs. non-helping behaviors to make predictions about optimal behavioral strategies under natural selection.

P4 Game theory is often used to make predictions about animal behavior.

Discussion

P5 We observed the helping behavior of coastal warblers and found that 89% of 1 year old birds practiced helping behavior for at least some part of the breeding season (n=80 helpers, n=10 non-helpers).

P6 We tested the boldness of these 1 year old birds to compare the boldness of helper and non-helper birds. FID was used as a measurement of boldness towards humans. All FID experiments were initiated at a distance of 20–25 m from a female bird in order to control for starting distance. We recorded starting distance from the bird under study, the distance at which the bird flew or took cover and the approximate height of the bird at the start of the trial. FID scores are equal to the hypotenuse of the triangle formed by the distance from the observer (disturbance) that the bird takes flight and the starting height of the bird; the shorter the FID, the bolder the individual was considered to be. We measured all birds one time.

P7 We found a difference in animal personality in terms of boldness. The personality types of helper vs. non-helper birds were different. Helper birds tended to be shy, while non-helper birds were nearly equally likely to be shy as bold (see Figure 1). We conclude that helping behavior is more common among shy individuals.

P8 Our model of helping vs. non-helping behavior indicates that non-helping behavior is favored under natural selection. This contradicts our observations of helping behavior in coastal warbler, which is quite common. We therefore conclude that group selection maintains helping behavior in coastal warblers.

P9 Our model uses game theory to compare the reproductive output of 2 year old coastal warblers based on whether they were helpers or non-helpers the previous year. Helper birds often take over the nest and hunting territory of the resident female which they were helping, if that resident female dies between breeding seasons. Coastal warblers have a ~50% mortality rate between breeding season, so this succession happens regularly. We observed that 2 year old female coastal warblers which were helpers and then took over an abandoned nest had an average of 5 offspring. Alternatively, 2 year old coastal warblers had an average of 0 offspring if they had been helpers for a breeding female who survived and maintained her nest. 2-year old coastal warblers who did not help the previous year had an average of 1 offspring in each of their 1st and 2nd years. This average was not affected by the death of a resident female, because 2-year-olds were never helpers at a resident female’s nest. This data is summarized in Table 1.

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(image text: Table 1: The average lifetime offspring of 2-year old coastal warblers. "Previous helpers" are warblers that were helpers to a resident female in their 1st year. "Previous non-helpers" were not helpers.

Birds that were previous helpers where resident female died have 5 offspring

Birds that were previous helpers where resident female survived have 0 offspring

Birds that were previous non-helpers where resident female died have 2 offspring

Birds that were previous non-helpers where resident female died have 2 offspring)

P10 This model shows that non-helping is a more predictable strategy than helping, as helpers have a large probability of producing 0 offspring in 2 years. We therefore conclude that non-helping is the strategy favored by natural selection. We predict that non-helping behavior should become more prominent in this coastal warbler population, unless group selection is preserving the density of helper individuals.

Activity

Please provide answers to the following questions:

What's your name?

Who are you working with?

Paragraph 1: What does kleptoparasitic mean?

Paragraph 1: This paragraph ends in "Helping behavior is found in other bird species." Look up an example of another bird species that exhibits helping behavior (specifically, helping a breeding pair raise young) and describe it in a few sentences here. Cite your source.

Paragraph 2 contains some really faulty logic. Please identify and correct that logic here.

Paragraph 4 is unfinished. Please complete it. To do so, please find an example in the primary literature of how game theory is applied to animal behavior. Describe and cite this scientific paper here.

Paragraph 6 contains a fundamental flaw for an animal personality study. What is it? How could the researchers have corrected it?

Paragraph 7 comes to the conclusion that there are personality differences between helper and non-helper birds. Do you agree? Explain why you do or do not agree with the author's interpretation of the data.

Paragraph 8: Define group selection. Do you agree with the conclusion presented in this paragraph?

Paragraph 10 includes an analysis of the model. However, the author's comparison of behavioral strategies doesn't make sense. Compare the two strategies with your group, using the expected value calculation presented in the game theory video. Show the math you use here. Which is the more advantageous strategy? Is this consistent with the author's observations of coastal warbler behavior?

The link below is an alternative explanation of expected value, if you'd like to go over that again. https://www.wikihow.com/Calculate-an-Expected-Value

Pre-activity Quiz

Question 1

What is the difference between mutualism and cooperation?

A. Mutualism is between individuals of different species and cooperation is between individuals of the same species

B. Both are interchangeable

C. Mutualism has a direct fitness benefit and cooperation has an indirect fitness benefit

D. Mutualism is between one actor and one recipient, cooperation is between any number of actors and recipients

Question 2

What is an example of cheating in a mutualism?

A. A bee robbing nectar from a plant

B. A grasshopper avoiding predation by spiders

C. A monkey refusing to groom an unfamiliar monkey of the same species

D. A vampire bat feeding her niece

Question 3

How does game theory simplify hypotheses about animal behavior?

A. By making mathematical models

B. By setting up experimental activities for animals to interact in

C. By observing animals in laboratory studies

D. By representing animals as humans

Question 4

What options are presented in the prisoner’s dilemma?

A. All of these options are presented

B. Cooperating with your partner

C. Betraying your partner

D. Lying to the cops

Question 5

What is the optimal strategy for a self-interested individual in the basic prisoner’s dilemma shown in the video?

A. Betraying your partner

B. Cooperating 20% of the time with your partner

C. Tit-for-tat cooperation with your partner

D. Reinforcing the mutualism with your partner

Question 6

What is the expected value (of number of years in prison) for betraying your partner?

A. 2.5

B. 10 or 1

C. 5.5

D. 0 or 5

Question 7

How do researchers study animal personality?

A. By measuring the behavior of animals within the same species multiple times

B. By measuring the behavior of animals within the same species one time

C. By measuring the behavior of animals in different species one time

D. By measuring the behavior of animals in different species multiple times

Question 8

Which factors can influence animal personality?

A. Genetics and life experiences

B. Genetics alone

C. Life experiences alone

D. How recently an animal has eaten

Question 9

What is behavioral plasticity?

A. The ability to change one’s behavior to suit the environment

B. The range of behaviors exhibited by animals across different species

C. The ability to behave the same way in various contexts

D. The range of personalities observed in a species

Question 10

What questions do you have about the content of the videos? We can discuss these questions in class.