Teacher guide

Predict

In Finding Nemo, Nemo’s mom is lost at the start of the movie, and his dad, Marlin, raises him alone. In a wild clownfish family, could a dad like Marlin become the mom?

Circle one. Yes / No

Watch

1. Finding Nemo got the clownfish wrongyoutube.com/shorts/62srRdYYCAg
2. Nemo is probably not Marlin’s sonyoutube.com/shorts/5GJUhGE19qA

Word of the day

Larva (LAHR-vuh). A young animal, newly hatched from its egg, that looks far different from the adult it will grow into.

• A tadpole is the larva of a frog.
• The word for more than one larva is larvae. In video 2, Raven calls newly hatched clownfish larvae.

Bonus word. Protandry (pro-TAN-dree). Prot- means “first,” and andr- means “man” or “male.” A protandrous fish is male first and can become female later. The proton in chemistry got its name from the same Greek word for first.

Questions

1. In a clownfish group, the biggest fish is the mom, called the breeding female. The second biggest is the dad, called the breeding male. The smaller fish wait in line by size. When the breeding female is gone, what happens to the breeding male? What happens to each fish waiting in line?

   Hint. Clownfish keep their size order. Start with the biggest fish that’s still alive.

2. Clownfish parents care for their eggs day and night, and they care the most on the night the eggs hatch. Then the baby fish, called larvae, drift away into open water. How does caring for the eggs help clownfish parents if they don’t raise the babies?

   Hint. Think about what could happen to eggs that no parent guards.

3. Kimbe Island has 310 sea anemones, the stinging sea animals where clownfish make their homes. Of the young fish that moved into these anemones, 56% had hatched from Kimbe Island parents. But family members shared an anemone only about 2% of the time. How can most of Kimbe Island’s young fish come from Kimbe Island parents while family members rarely share an anemone?

   Hint. Compare living on the same island with living in the same anemone.

4. Baby clownfish drift in open water for about 10 days. The Kimbe Island scientists didn’t follow the babies across the water. How did the Kimbe Island scientists figure out which young clownfish belonged to which parents?

   Hint. In video 2, Raven says the scientists took thousands of little fin clips. What could scientists test in a fin clip?

Exit ticket

Predict

In Finding Nemo, Nemo’s mom is lost at the start of the movie, and his dad, Marlin, raises him alone. In a wild clownfish family, could a dad like Marlin become the mom?

Circle one. Yes / No

Watch

1. Finding Nemo got the clownfish wrongyoutube.com/shorts/62srRdYYCAg
2. Nemo is probably not Marlin’s sonyoutube.com/shorts/5GJUhGE19qA

Word of the day

Larva (LAHR-vuh). A young animal that hatches from an egg and looks unlike the adult it will become.

• A tadpole is the larva of a frog or toad. Video 2 uses the plural, larvae.
• In ancient Rome, larvae were harmful ghosts.

Bonus words. Protandry (pro-TAN-dree) means male first, from prot-, “first,” and andr-, “male.” Philopatry (fih-LOP-uh-tree), the word in the title of the 2016 Kimbe Island paper by Salles and others, means an animal stays near, or comes back to, the place where it was born. It joins Greek phílos, “loving,” and Latin patria, “homeland.”

Questions

1. In a study of wild Red Sea clownfish, breeding males carried testis tissue and immature ovary tissue at the same time. After scientists removed the breeding female, the male’s gonad began to change about 24 days later, and the male tissue was gone by day 50. How does a breeding male clownfish become the new breeding female? And what happens to the largest non-breeder and to each smaller clownfish in line?

   Hint. The breeding male already carries two kinds of gonad tissue. Which kind matures, and which kind disappears?

2. Clownfish parents tend their eggs for about a week before hatching. Their care rises as the embryos develop and peaks on hatching night with fanning, mouthing and biting at the anemone, and then the larvae drift away. How could egg care raise the number of offspring that clownfish parents produce? What experiment would test your explanation?

   Hint. Compare eggs that get care with eggs that get none. What would you count?

3. On Kimbe Island, 56% of the young fish that settled had hatched from Kimbe Island parents, and the other 44% arrived as larvae from other reefs. Yet relatives shared an anemone only about 2% of the time. What path does a clownfish larva take from hatching night to settling? And how does that path let most Kimbe Island settlers have Kimbe Island parents while relatives rarely share one of the island’s 310 anemones?

   Hint. A larva drifts for about 10 days before it settles. When a larva settles back on Kimbe Island, how many anemones does the island offer?

4. The Kimbe team never followed a larva across open water. Divers clipped a tiny piece of fin from each fish, and the team read 22 DNA markers from each clip over six rounds of sampling between 2003 and 2013. How can DNA markers link a young fish to one breeding pair? And why would the Kimbe team sample six times instead of once?

   Hint. At each marker, a young fish carries one number from each parent. Which fish are alive during any one round of sampling?

Claim, evidence, reasoning

Going further: anemone math

1. Kimbe Island has 310 anemones. Each anemone holds one breeding pair and up to four non-breeders. What’s the most clownfish Kimbe Island could hold at one time?

   Circle one. 620 / 1,240 / 1,860 / 2,927

   Hint. Find the most fish one anemone can hold first. Then multiply by the number of anemones.

2. Kimbe Island’s 310 anemones hold a limited number of clownfish at one time. Over ten years, the scientists identified 2,927 different fish. Why could the Kimbe Island scientists identify more clownfish over ten years than Kimbe Island holds at one time?

   Hint. Think about how the fish in one anemone change over ten years.

3. Each Kimbe Island anemone holds one breeding pair, and the island has 310 anemones. What limits how many clownfish can breed on Kimbe Island at once?

   Hint. Think about what a non-breeder has to wait for before it can breed.

Exit ticket

Watch

1. Finding Nemo got the clownfish wrongyoutube.com/shorts/62srRdYYCAg
2. Nemo is probably not Marlin’s sonyoutube.com/shorts/5GJUhGE19qA

Word of the day

Larva (LAHR-vuh). An immature, free-living form of an animal that changes into a different adult form through metamorphosis.

• A tadpole is the larva of a frog or toad. Video 2 uses the plural, larvae.
• In ancient Rome, larvae were harmful ghosts.

Bonus words. Protandry (from prot-, “first,” and andr-, “male”) describes an animal that produces male gametes before female gametes. Philopatry (from Greek phílos, “loving,” and Latin patria, “homeland”), the word in the title of the Salles 2016 paper, describes an animal that stays near, or returns to, its birthplace to breed.

Predict

1. Océane Salles and the Kimbe Island team put together a family tree of 2,927 clownfish, then counted the parents and offspring living in the same anemone. Make a guess before you read the paper, and write one sentence on why you think so. What percent of parent-and-offspring pairs in the Kimbe Island family tree do you predict shared an anemone?

   Hint. In video 2, Raven gives a figure for relatives in general. Would parents and offspring share an anemone more often or less often than relatives in general?

Read the paper

Salles and others, “First genealogy for a wild marine fish population reveals multigenerational philopatry,” PNAS, 2016. The paper is free to read.

Divers on Océane Salles’s team sampled the orange clownfish on Kimbe Island in Papua New Guinea, home to 310 anemones, six times between 2003 and 2013. The team read 22 DNA markers from each fin clip and reconstructed a family tree of 2,927 fish. Table 1 of the paper counts the family links in that tree, then counts the related pairs living in the same anemone.

1. Quantitative reasoning Fill in the last column of Table 1. For the parent and grandparent rows, add the maternal and paternal links first. Which relationship in Table 1 shared an anemone most often, which percents in Table 1 rest on a single pair, and how much weight should a percent based on a single pair carry?

   Hint. Divide the related pairs in the same anemone by the family links in the tree. Watch for rows with a count of 1.

2. Process of science The Kimbe team used 22 DNA markers, accepted a parent pair only when its LOD score (the log of the odds that the match is true) topped 30, and rejected all matches to a single parent because generations overlap. What mistake does each of the Kimbe team’s three matching rules prevent, and what do strict matching rules cost the counts in Table 1?

   Hint. Think about two kinds of error, a false match and a missed match.

3. Evolution Philopatry can raise the risk of inbreeding, but Table 1 records 2 inbred matings and the paper reports an inbreeding coefficient of 0.018. Self-recruitment averaged 56%, and the other 44% of settlers arrived as larvae from other reefs. How do the inbreeding and self-recruitment numbers and the size order in each anemone explain why inbreeding stayed rare on Kimbe Island, and what would you predict if fewer larvae arrived from other reefs?

   Hint. Only the two largest fish in an anemone breed. How likely is a relative to reach the front of an anemone’s breeding line?

4. Science and society Kimbe Island is a marine reserve. The authors write that a reserve can protect several generations of one population, and they warn that climate change may shorten how far larvae travel between reefs. A reef manager has to decide which reefs to protect. What would you recommend? Write one paragraph that uses at least two numbers from the Kimbe Island paper.

   Hint. Think about the birthplaces of Kimbe Island’s settlers.

Exit ticket