1. Watch this Video

2. Study this Summary

AP Bio Topic 8.1 – Response to the Environment – is unique because it doesn’t require the memorization of specific biological facts. As a result, we’re going to focus on case studies that will give you practice analyzing data sets and visual representations related to animal behavior.

Below, we’ll focus on explaining the biological basis of altruistic behavior: behavior in which individuals sacrifice their own survival or reproduction and promote the survival or reproduction of others in their group. For more case studies about how organisms respond to their environments, please go Unit 8 in our AP Bio curriculum.

---

Predator Warnings and Altruism

• Alarm Signals in Social Animals
  • Many animals emit warning calls to alert their group to danger from predators.
  • Examples:
    • Belding’s ground squirrel has different calls for aerial predators (hawks and eagles) and terrestrial predators (bobcats, dogs, coyotes, etc.).
    • Vervet monkeys use distinct calls for leopards, snakes, and eagles.
• Altruistic Behavior
  • Warning calls are altruistic. Altruism is a behavior that reduces the chances of an individual surviving and reproducing, but benefits others.
  • In relation to warning calls, the caller risks attracting the predator’s attention, and this increases the caller’s risk of being harmed.
  • The question, from the perspective of evolution, is how and why could a behavior that increases risk to an individual evolve?
• Explaining Altruism: Kin Selection and Inclusive Fitness
  • Kin Selection: Within a gene pool, genes are selected not just for a single individual’s survival, but also for the survival of relatives who also possess these same genes.
  • Inclusive Fitness: Helping one’s relatives increases the chance that shared genes continue in a gene pool.
  • J.B.S. Haldane’s insight
    
    • Haldane was an important evolutionary biologist in the early 1900s.
    • He famously said: “I would lay down my life for two brothers or eight cousins.”
    • Why this makes sense.
      • A person shares 50% of their genes with their siblings, 25% with their aunts/uncles, and 12.5% with their cousins.
      • A gene that influenced behavior in a way that led to self sacrifice in the service of keeping two siblings, 4 aunts or uncles, or 8 cousins alive would increase in frequency in that population’s gene pool.

---

Case Study: Kin Selection in Belding’s Ground Squirrels

In the 1970s, Biologist Paul Sherman studied alarm calls in Belding’s Ground Squirrels in the Sierra Nevada Mountains of California.

• Finding 1: Males and Females differ in where they live relative to where they were born. 
  • Sherman measured how far males and females moved from their natal burrow (the burrow where they were born).
    • Females stay near their birth site throughout their lives.
    • Males move farther away, reducing interactions with close relatives.
• Finding # 2: Females were significantly more likely to call than males.
  • Why?
    • Females are surrounded by relatives (sisters, daughters, cousins).
    • Calling helps protect their close kin, reinforcing kin selection and inclusive fitness.
    • Because males are not surrounded by kin, taking a risk by calling out would not benefit their close kin, and would not increase their inclusive fitness.
• Key Takeaways
  • Predator warning calls are an example of natural selection favoring altruism when it benefits relatives.
  • This study demonstrates claim, evidence, and reasoning (CER), a critical skill for AP Bio exam analysis.

---

Eusociality: Altruism in Social Insects

• What is Eusociality?
  • A social structure where some individuals reproduce while others assist without reproducing themselves.
  • Examples:
    • Bees: One queen lays eggs, worker bees care for the colony.
    • Ants, wasps, termites, and naked mole rats have similar division between reproducers and non-reproducers.
• In bees, ants, and some wasps, haplodiploidy can account for eusocial behavior
  • Haplodiploidy: A special form of sex determination in bees, ants, and wasps, which are all in the same order of insects.
    • Males are haploid, and produce gametes through mitosis. The gametes possess 100% of their genes.
    • Females are diploid, and produce gametes through meiosis. The gametes possess 50% of their genes.
  • Genetic Explanation for Eusociality:
    • Females (workers) are more closely related to their sisters (75%) than to their own offspring (50%).
    • Helping their queen produce more sisters is genetically more advantageous than reproducing themselves.
• Does Eusociality Require Haplodiploidy?
  • No—termites and naked mole rats are eusocial but are not haplodiploid.
  • Several species of haplodiploid insects (including some wasps and bees) are not eusocial.

---

How you can deepen your understanding of Topic 8.1: Responses to the Environment

• Topic 8.1 is full of fascinating illustrative examples of how natural selection shapes animal behavior.
• Understanding these case studies will help you analyze data sets, graphs, and experimental results, key skills for the AP Bio exam.
• You can learn more about Responses to the Environment in Unit 8 of our AP Biology curriculum 

3. Master these Flashcards

4. Tackle these Quizzes

4.1. Kin Selection and Inclusive Fitness in Belding’s Ground Squirrels

 

4.2. Eusociality and Haplodiploidy

 

What’s next?

Please proceed to this next tutorial: Metabolism and Individual Energy Use