Evolution of Regeneration
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Transcript of Evolution of Regeneration
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“The regenerative process is one of the fundamental attributes of living things...” Thomas Hunt Morgan (1901), from his book Regeneration.
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Evolution of Regeneration
What explains the distribution of regeneration among organisms?
- Adaptive?- Ancestral to all metazoans and repeatedly lost, or independently derived?
Evolution and Development
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Regeneration is Phylogenetically Widespread
Anuran Tail Planeria
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Regeneration: Adaptive?
• Seemingly, the ability to regenerate should benefit individuals of a population (i.e. is adaptive).
• Can you think of a way to test the idea that regeneration is adaptive?
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Hermit Crabs regenerate their anteriorand posterior limbs. However, the frequencyof regeneration is much higher for anteriorlegs (83% vs 21%).
From Morgan 1898 and Needham 1961
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Regeneration: Ancestral?
• Much of what is accomplished during regeneration is first accomplished during
embryonic development (same mechanisms are deployed).
• Can you think of a way to test the idea that regeneration is inherent?
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Observations Supporting the Idea that Regeneration is Ancestral
• Phylogenetically widespread• Lost between closely related species• Aspects of regeneration are similar among
organisms in a developmental sense• Some organisms that can not regenerate
body parts, do so partially during development.
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Epimorphic Regeneration: The Blastema is Very Similar Among Unrelated Taxa
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Regulation andEvolution of EpimorphicRegeneration
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• Loss of regeneration may reflect major evolutionary changes:
– With respect to amniote vertebrates:• Water to land transition• Poikilothermy to homothermy• Loss of metamorphosis• Evolution of immune system
Why Not Regeneration?Why don’t we observe it more?
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However, there is variation among amphibians
• Can regenerate limbs as immature larvae
• Loses ability to regenerate at metamorphosis
• Adults regenerate a cartilagenous spike after limb amputation.• Is the generation of a spike an
adaptation?
Unlike salamanders, Xenopus has limited regenerative potential
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100% regenerate spikeafter radia-ulna amputation
80% regenerate spikeafter humerous amputation
0% regenerate spikeafter complete amputation
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Growth Rates
No legs amputated0.55 9.54 10.2
1 leg amputated 0.54 9.0 9.54
2 legs amputated 0.53 7.5 8.8
Day 0 1 month 4 months
* Weights are in grams
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The spike supportsnuptial pad tissue development in males.
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2 of 3 males with1 regenerated
radia-ulna spike were able to successfully
amplex and matewith a female.
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• The results suggest that spike regeneration maybe adaptive.
• But why did Xenopus frogs presumably loose the ability to reform perfect limbs?