A Tale of Three Lice

Why do humans have three different forms of lice on their body?

Will take ~ two 50 minute periods.

Hominins

The human lineage and the chimp lineage diverged ~6 million years ago.

Homo sapiens evolved ~200,000 years ago

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A hominin is any species that is more closely related to a human than a chimpanzee (Ex: Australopithecus and Homo).

1. Where would you place hominins on the cladogram (redraw the cladogram on your page)?

Limitations of the Fossil RecordThere are questions about hominins that the fossil

record cannot answer, such as:-When did hominins lose their body hair?- When did hominins begin to wear clothes?

2. Think of another question about hominins that cannot be answered with fossils.

How can we answer these questions?

Examine patterns of hominin distribution and past climate maps

– This might be helpful, but won’t provide direct evidence

Look for tools used to make clothes– The oldest needles are ~40,000

years old, but only provide a minimum age for clothing

3. How would a climate map help you answer the question of when hominins started wearing clothes?

Bone needle, 40,000 YA

Can lice help?

Can lice tell us when hominins lost their body hair and/or started wearing clothing?

A friend tells you they were taking treatments for head lice but haven’t seen any nits in a couple of weeks. Would you be willing to spend the night as his house?

A tale of three lice• Lice are highly specialized blood sucking

parasites that live on a single host species.• Each of our ape relatives hosts one louse species,

but humans host three types of lice.

The head louse, Pediculus humanus

capitus

The body louse, Pediculus humanus

corporis

The pubic louse, Phthirus pubis

The origin of head liceHuman head lice and chimp lice belong to the same genus, but are different species.

3. Discuss and propose a reason for why two separate lineages of lice have evolved.

Pediculus humanus,left, the human head louse, and Pediculus schaeffi, the chimp louse.

Photo by Julie AllenSource: http://news.illinois.edu/news/14/0108lice_KevinJohnson.html

Co-speciation hypothesis:

Human head and chimp lice lineages diverged at the same time that hominins and ancestral chimps diverged.

HumanChimpGorillaOrangutanGibbonOld world monkey

million years ago

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To test this hypothesis:– Compare DNA of human head lice to DNA of chimp

lice at one nuclear and one mitochondrial gene to estimate when they last shared a common ancestor.

Results:

A DNA comparison suggests the most recent common ancestor of chimp lice and human head lice lived ~6 million years ago.

4. Why is 6 MYA a significant period of time?

The origin of pubic liceConsider human head lice and pubic lice.

5. Compare the morphology of the two types of louse. Why do you think these two species diverged?

A possible origin of pubic lice

New niche hypothesis:– Human pubic and head lice lineages diverged

because hominins lost their body hair and developed two hair niches.

6. Define “niche.”

7. How would you test this hypothesis?

To test this hypothesis:

First, compare DNA of human pubic lice to human head lice at one nuclear and one mitochondrial gene to estimate when they last shared a common ancestor.

8. What would you predict, given the new niche hypothesis?

Human head and pubic lice lineages diverged from a common ancestor approximately:

A. 25 million years ago, when ape and monkey lineages split.B. 6 million years ago, when human and chimp lineages split.C.6 million years ago or less, on a hominin host.

9. Create a model (drawing) of how divergent speciation would have resulted in head lice and pubic lice, with the common ancestor of the body louse found in chimpanzees.

10. Would this be considered sympatric speciation or allopatric speciation? Defend your choice.

Results:

DNA comparison suggests the most recent common ancestor of human head lice and human pubic lice lived ~12 million years ago. (Humans and chimps diverged 6 million years ago.)

Conclusion:

Human head and pubic lice did not diverge on a hominin from the same ancestor (chimp louse).

11: Why do we conclude that human head and pubic lice did not diverge on a hominin?

A. Human head and pubic lice lineages diverged well before hominins evolved ~6 million years ago.

B. Humans had body hair well after 12 million years ago.

C. The fossil record does not show pubic lice on people that long ago.

12. Suggest an alternative hypothesis for the origin of pubic lice. If they didn’t come from regular (body) lice, where did they come from?

This phylogenetic tree might provide a clue.

Surprise! Human pubic lice (Phthirus pubis) belong to the same genus as gorilla lice (Phthirus gorillae).

DNA comparisons show that human pubic lice and gorilla lice last shared a common ancestor 3-4 million years ago.

14. Redraw this phylogenetic tree, indicate where you would place Phthirus gorillae.

What about body lice?

• Human head and body lice are different morphotypes belonging to the same species.

• Human body lice live on clothing and move onto skin up to 5 times a day to feed.

The head louse, Pediculus humanus

capitus

The body louse, Pediculus humanus

corporis

15. What word can you substitute for morphotype that we have used in class?

Third niche hypothesis:

Human body lice arose because humans started to wear clothing.

16. What is the “third niche”?

17: What would you predict, given the third niche hypothesis?

The last common ancestor of human head and body lice lived:

A. Approximately 6 million years ago, on the common ancestor of humans and chimps.

B. 1-2 million years ago, on a hominin that had lost some or all of its body hair.

C. Less than 100,000 years ago, on a modern human.

Results:A DNA comparison suggests the most recent common ancestor

of human body lice lived less than 72,000 years ago.

Conclusion:Human body lice arose from human head lice on Homo sapiens,

suggesting that clothing might have arisen ~72,000 years ago.

18. Create a phylogenetic tree showing the relationship between chimpanzee lice, head lice, body lice and pubic lice.

Final AnalysisReddit has a category labeled ELI5, which stands for: “explain like I’m five:

19. Write an explanation for why humans have 3 different forms of lice, #ELI5

ELI5 is not about explaining things on a literal five year old level! 6, don't dumb your explanation down to be comprehendible by a five year old. Use layman-friendly vocabulary (or define technical terms), and use analogies if they fit, but don't try to force anything. Just explain it to someone who wouldn't be familiar with it.

Every case study, project, or lab we do will have some test question associated with it, either a short answer or multiple choice question.

20. Write a multiple choice question and a short answer question related to this investigation. (Think of what kinds of questions you have seen on previous tests.)