a tale of three lice - pomp-science.com tale of three lice ... head and pubic lice did not diverge...
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A Tale of Three Lice
Joan Sharp and Erin Barley Simon Fraser University
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Fossil Record and Ape Speciation
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Fossils provide information about shared ancestry and relationships among taxa.
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Hominins • The human lineage and the chimp lineage
diverged ~6 million years ago. • Homo sapiens evolved ~200,000 years
ago and were preceded by several other species of hominin.
• A hominin is any species that is more closely related to a human than a chimpanzee (e.g., members of the genera Australopithecus and Homo).
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Limitations of the Fossil Record But there are questions about hominins that the
fossil record cannot answer: – When did hominins lose their body hair? – When did hominins begin to wear clothes?
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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 • It’s like looking for a needle in all the haystacks of Europe!
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Can lice help?
• Can lice tell us when hominins lost their body hair and/or started wearing clothing?
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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 7
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The origin of head lice
• Human head lice and chimp lice belong to the same genus. Why did these two lineages of lice diverge?
• Working in pairs, think of 1 or 2 hypotheses, and write them down.
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A possible origin of head lice Co-speciation hypothesis:
– Human head and chimp lice lineages diverged at the same time that hominins and ancestral chimps diverged.
How would you test this hypothesis?
Human Chimp Gorilla Orangutan Gibbon Old world monkey
million years ago 0 5 10 15 20 25 30
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The origin of head lice Co-speciation hypothesis:
– Human head and chimp lice lineages diverged at the same time that hominins and ancestral chimps diverged.
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.
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The last common ancestor of chimp lice and human head lice lived approximately:
A. 20 million years ago, on an early ape ancestor. B. 6 million years ago, when ancestral chimps and hominins
diverged. C. 100,000 years ago, on an early human.
CQ#1: What would you predict, given the co-speciation hypothesis?
Human Chimp Gorilla Orangutan Gibbon Old world monkey
million years ago 0 5 10 15 20 25 30
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The origin of head lice Prediction: • The last common ancestor of chimp lice and human
head lice lived ~6 million years ago. Results: • A DNA comparison suggests the most recent common
ancestor of chimp lice and human head lice lived ~6 million years ago.
Conclusion: • Hominins and their head lice co-speciated from ancestral
chimps and their lice.
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The origin of pubic lice
• Consider human head lice and pubic lice. Why did these two lineages of lice diverge?
• Working in pairs, think of 1 or 2 hypotheses, and write them down.
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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.
How would you test this hypothesis?
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The 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.
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.
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CQ#2: 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.
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The origin of pubic lice Prediction: • Human head and pubic lice lineages diverged from a
common ancestor less than 6 million years ago, on a hominin host.
Results: • DNA comparison suggests the most recent common
ancestor of human head lice and human pubic lice lived ~12 million years ago.
Conclusion: • Human head and pubic lice did not diverge on a
hominin.
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CQ#3: 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.
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The origin of pubic lice
• Use the phylogenetic tree on the next page to answer the following question:
– Given the phylogeny of select primates and their lice, what is the most likely origin of human pubic lice?
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Phylogeny of selected primates & their lice
Head lice
Pubic lice
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CQ#4: Given the phylogeny of select primates and their lice, what is the closest relative of human pubic lice?
A. Human pubic lice are most closely related to chimp lice.
B. Human pubic lice are most closely related to gorilla lice.
C. Human pubic lice are most closely related to human head lice.
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The origin of pubic lice
• 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.
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Hmmm…
• What were the Australopithecines and early gorillas up to?
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The origin of pubic lice
• Hominins might have picked up lice from early gorillas by: – Sleeping in nests recently used by early
gorillas. – Preying on early gorillas.
• Lice are known to jump from prey to predator.
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The origin of pubic lice
• Why were the lice of early gorillas able to colonize hominins? – One possible explanation is that hominins had
lost much of their body hair and so had two “hair niches.”
– This explanation is still highly speculative. – Research continues…
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The origin of 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 26
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The origin of body lice
• Consider now human head lice and body lice. Why did body lice arise?
• Working in pairs, think of a hypothesis, and write it down.
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A possible origin of body lice
Third niche hypothesis: • Human body lice arose because humans started
to wear clothing.
How would you test this hypothesis?
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The origin of body lice
Third niche hypothesis: • Human body lice arose because humans
started to wear clothing.
To test this hypothesis: • First, estimate when body lice arose by
identifying the most recent common ancestor of all body lice.
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CQ#5: 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.
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The origin of body lice Prediction: • The last common ancestor of human head lice and
human body lice lived less than 100,000 years ago. 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. • These data suggest that clothing might have arisen
~72,000 years ago. • Are these data also consistent with other hypotheses?
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In summary
• Phylogenetic studies of lice suggest that: – Hominins acquired a second species of louse
~3-4 million years ago. • Does this correlate with the loss of body hair?
– Body lice arose less than 72,000 years ago. • Does this correlate with the development of
clothing?
• These studies provide interesting and relevant data, but more data are needed before we can answer these questions.
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In summary
• When did hominins lose their body hair and/or start wearing clothing? – These questions remain unanswered, though
lice provide some interesting and relevant data.
– Answers to these questions will likely depend on data from multiple sources, including lice.
Research continues… but don’t forget:
Never share your hairbrush!
Slide Credits Slide 1—Left, Slide 6, Slide 7—Left, Slide 26—Left, Slide 33
Description: Human head louse, Pediculus humanus capitus. Source: Figure 1 from Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J. 2007. Pair of lice lost or
parasites regained: The evolutionary history of anthropoid primate lice. BioMedCentral Biology 5:7, page 3.
Permissions: Creative Commons Attribution 2.5 License. Slide 1—Center, Slide 7—Center
Description: Human pubic louse, Pthirus pubis. Source: Figure 1 from Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J. 2007. Pair of lice lost or
parasites regained: The evolutionary history of anthropoid primate lice. BioMedCentral Biology 5:7, page 3.
Permissions: Creative Commons Attribution 2.5 License. Slide 1—Right, Slide 7—Right, Slide 26—Right
Description: Human body (clothing) louse, Pediculus humanus corporus. Source: CDC / Dr. Dennis D. Juranek, http://phil.cdc.gov/phil/home.asp Permissions: This image is a work of the Centers for Disease Control and Prevention, part of the
United States Department of Health and Human Services, taken or made during the course of an employee’s official duties. As a work of the U.S. federal government, the image is in the public domain.
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Slide 4—Left Description: Photograph of chimpanzee. Author: Thomas Lersch. Source: Wikimedia, http://commons.wikimedia.org/wiki/File:Schimpanse_zoo-leipig.jpg Permissions: Creative Commons Attribution 2.5 License.
Slide 4 —Right
Description: Photograph of shirtless male (Landon Donovan). Author: Linny Heng Source: Wikimedia, http://commons.wikimedia.org/wiki/File:Landon_Donovan_shirtless.jpg Permissions: Creative Commons Attribution 2.0 License.
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Description: Phylogenetic tree for primate lice and their vertebrate hosts. Source: Figure 1 from Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J. 2007. Pair of lice lost or parasites regained: The evolutionary history of anthropoid primate lice. BioMedCentral Biology 5:7, page 3. Permissions: Creative Commons Attribution 2.5 License.
Slide 23 Description: Genetic reconstruction of lice and host phylogeny. Source: Figure 2 from Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J. 2007. Pair of lice lost or parasites regained: The evolutionary history of anthropoid primate lice. BioMedCentral Biology 5:7, page 4. Permissions: Creative Commons Attribution 2.5 License.
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