Robustness in biology

1. Robustness in biology Eörs Szathmáry Collegium Budapest Eötvös University

2. A genotype-phenotype model

3. Robustness and adaptation time

4. The explanation

5. Robustness and diversity

6. Drosophila melanogaster • Each segment in the adult fly is anatomically distinct • Characteristic appendages

7. Drosophila embryonic development • Subsequent embryonic events create clearly visible segments • Initially look very similar • Some cells move to new positions • Organs form • Wormlike larva hatches • Eats, grows, & molts

8. Drosophilaearly gradients • Bicoid gene product is concentrated at anterior end of fly embryo • Gradient of gene product • Essential for setting up anterior end of fly • Gradients of other proteins determine the posterior end and the dorsal-ventral axis

9. Drosophilasegmentation genes • Segmentation genes • Genes of embryo • Expression regulated by products of egg-polarity genes • Direct the actual formation of segments after the embryo’s major axes are defined

10. Three sets of segmentation genes • Three sets of segmentation genes are activated sequentially • Gap genes • Pair-rule genes • Segment polarity genes • The activation of these sets of genes defines the animal’s body plan • Each sequential set regulates increasingly fine details

11. Gap genes • Gap genes • Map out basic subdivisions along the embryo’s anterior-posterior axis • Mutations cause “gaps” in the animal’s segmentation

12. Pair-rule genes • Pair-rule genes • Define pattern in terms of pairs of segments • Mutations result in embryos having half the normal number of segments

13. Segment polarity genes • Segment polarity genes • Set the anterior-posterior axis of each segment • Mutations produce segments where part of the segment mirrors another part of the same segment

14. The segment polarity network in Drosophila

15. The differential equations

16. Expression pattern in vivo The normal pattern Crisp initial conditions

17. Biomathematics predicts Without the broken connections With the broken connections

18. 1192 solutions found with crips initial conditions

19. Solutions found with degraded initial conditions

20. The degree of robustness

21. Epistasis of mutations

22. Simulated development

23. Formulae Change in gene expression states Fitness of a genotype in asexual reproduction

24. The model

25. Results

26. Evolution without mutations

27. Recombination favours negative epistasis favours sex • Only without strong directional selection on a particular gene expression pattern • Mutational load is lower with recombination AND negative epistasis • What are the possible predictions?

28. Unambiguous and degenerate

29. The structure of the genetic code • Amino acids in the same column of the genetic code are more related to each other physico-chemically • „The genetic code is one in a million” (Freeland & Hurst)

30. Central nucleotide and amino acid properties

31. Constraints on codon reshuffling for statistical investigations

32. Significance of some patterns

33. Robustness in food webs

34. Connectivity • The average connectivity of the neighbours of the black node with k = 3 links is < kn > = 4.

35. Physical interaction between nuclear proteins

36. A ‘random foodweb’

37. Ythan esturay foodweb

38. Food web patterns

39. Food web robustness

40. Statistical food web properties

41. Secondary extinctions resulting from primary species loss in 16 food webs ordered by increasing connectance (C ).

42. Robustness of food webs

43. Network structure and biodiversity loss in food webs:robustness increases with connectance