1. “The regenerative process is one of the fundamental attributes of living things...” Thomas Hunt Morgan (1901), from his book Regeneration.

2. 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

3. Regeneration is Phylogenetically Widespread Anuran TailPlaneria

6. 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?

7. 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

8. 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?

9. 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.

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

11. Regulation and Evolution of Epimorphic Regeneration

12. 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?

13. 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

14. 100% regenerate spike after radia-ulna amputation 80% regenerate spike after humerous amputation 0% regenerate spike after complete amputation

15. Growth Rates No legs amputated0.559.5410.2 1 leg amputated0.549.09.54 2 legs amputated0.537.5 8.8 Day 01 month4 months * Weights are in grams

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

17. 2 of 3 males with 1 regenerated radia-ulna spike were able to successfully amplex and mate with a female.

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