1. Evolution and Development
Evolution of Regeneration
What explains the distribution
of regeneration among
organisms?
- Adaptive?
- Inherit to all metazoans
or independently
derived?

2. Regeneration is Phylogenetically Widespread
Anuran Tail
Planeria

5. 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?

6. Hermit Crabs regenerate their anterior
and posterior limbs. However, the frequency
of regeneration is much higher for anterior
legs (83% vs 21%).
From Morgan 1898 and
Needham 1961

7. Regeneration: Inherent?
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?

8. Observations Supporting the Idea that Regeneration is Inherent
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.

9. Epimorphic Regeneration: The Blastema is Very Similar Among Unrelated Taxa

10. Regulation and
Evolution of
Epimorphic
Regeneration

11. Why Not Regeneration? Why don’t we observe it more?
Loss of regeneration may reflect genetic changes that are associated with evolutionary changes:
With respect to amniote vertebrates:
Water to land transition
Poikilothermy to homothermy
Loss of metamorphosis
Evolution of immune system

12. However, there is variation among amphibians
Unlike salamanders, Xenopus has limited regenerative potential
- 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?

13. 100% regenerate spike
after radia-ulna amputation
80% regenerate spike
after humerous amputation
0% regenerate spike
after complete amputation

14. Growth Rates Day 0 1 month 4 months No legs amputated 0.55 9.54 10.2
1 leg amputated
2 legs amputated
* Weights are in grams

15. The spike supports
nuptial pad tissue
development in
males.

16. 2 of 3 males with
1 regenerated
radia-ulna spike were
able to successfully
amplex and mate
with a female.

17. The results suggest that spike regeneration maybe adaptive.
But why did Xenopus frogs presumably loose the ability to reform perfect limbs?