Macroevolution of Organismal Modularity and Integration. Gunther J. Eble Bioinformatik, Universität Leipzig

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1 Macroevolution of Organismal Modularity and Integration Gunther J. Eble Bioinformatik, Universität Leipzig

2 What is macroevolution? - evolution at and above the species level - large-scale phenotypic evolution - among-species evolution Macroevolutionary biology: the study of the origin and sorting of macroevolutionary variation

3 - diversity, origination, and extinction - evolutionary radiations - innovations - morphological disparity - constraints on form and patterning of morphospace - structure of the genotype-phenotype map - selectivity of and recovery from extinction - phylogenetic history and trends - community structure - size and allometry - complexity

4 Bits and Pieces: isolated yet integrated

6 Organismal Modularity: definition and theoretical justification Definition: Dissociability of phenotypic wholes into parts Justification: organizational and variational semiindependence of morphological organization; morphology itself is involved in the generation of new morphological elements late in ontogeny; morphostatic mechanisms (including physiological homeostasis, regeneration, and repair) rely on information conveyed by morphological states.

7 Organismal Modules: causal roles - as raw material for combinatorial diversification - as the substrate for changes in integration - as units of hierarchical sorting and selection - modularity as a property of clades Needed: rigorous documentation of modules and of modularity in a macroevolutionary context.

8 Metrics of organismal modularity - Conceptually and statistically a number of explicit metrics can be advanced, but operationally some proxy metrics appear most useful: - number of parts, constructional elements, characters - within- and among-module integration - disparity

9 Disparity: the concept Sample 1 Sample 2 Taxonomic diversity: sample 1 = sample 2 = 6 spp. Morphological disparity: sample 1 << sample 2

10 Empirical morphospaces DATA MATRIX: n SPECIES x p VARIABLES Species A Species B Species C Species D Species E. n X 1 Y 1 Z 1 X 2 Y 2 Z 2-0,28-0,80 0,58 0,13-0,78 0,07 0,76 0,41 0,10 0,08 0,40-0,46-0,73-1,13-0,56-0,31-1,10 0,50-1,71 4,45 1,07-0,83 4,37 1,67 1,56-0,36 1,18 1,18-0,35-2,03... p EIGENVECTOR EXTRACTION MORPHOSPACE PROJECTION PC2 PC1

11 Measures of disparity Disparity = dispersion in morphospace 2 - Ss (sum of univariate variances) n - Sl (sum of eigenvalues) n 1,75,5,25 0 Sp. A Sp. D Sp. C - mean Euclidean distance XIS A 2 -,25 -,5 Sp. B Sp. E - Procrustes distance -, ,75 -,5 -,25 0,25,5,75 1 AXIS 1

12 Modeling divergence between species and between genera 5-Br 6-La 7-On 8-In 9-Op 10-Ba 11-LBoS 4-Gl 3-Na 2-Ns 1-Pr Australopithecus to Homo 2 = 1.08 Homo ergaster to Homo erectus Homo erectus to Homo sapiens 2 = = 0.58

14 Morphological diversification Morphological extinction

16 THE HOURGLASS MODEL (Duboule, 1994)

17 Juvenile disparity Adult disparity

18 1,5 1,5 0 PCII C II 2P -,5-1 -1,5-2 -2,5-3 DEVELOPMENTAL MORPHOSPACE Order Spatangoida -2-1,5-1 -,5 0,5 1 1,5 2 2,5 PC I x O X ADULT JUVENILE Variance PCI PCII p<0.015 p<0.019 (bootstrap z-test)

19 Disparity of Larvae X Disparity of Adults n=26 LARVAE C.V. Mean Pairwise Distance ADULTS n=26 Error bars based on 1000 bootstrap replications

20 Echinoderms as model organisms for the study of modularity and integration - Many plates and other skeletal elements - Many types of plates - Distinct body regions and growth fields Issues to be addressed: relationship with diversity, size, evolvability, trends, and contextdependence

23 Modularity and Taxonomic Diversity p < (Spearman) y tisrevi of Genera D Number of Derived Character States

24 Discordances between diversity and disparity DIVERSITY DISPARITY 2.5 XXXXXXXX x x x x x x x x t XXXX x x x x XX x x

25 Sea urchin disparity and diversity Disparity (total variance) Ate los tomat a D l at Variance) ot( tyir apsi Di spa rit y Di ver sit y J1 J2 J3 K1 K2 K3 K4 K5 Pal Geological time Diversity (genera) Generic Diversity

26 Modularity and Body Size Variance p < 0.76 (Spearman) eln(length) cnaira V Number of Derived Character States

27 Modularity and Evolvability In microevolution: ability to sometimes produce improvement (Wagner and Altenberg 1996) In macroevolution: ability to sometimes produce substantial morphological change Evolvability a Modularity a Integration a Disparity

28 Disparity (Total Variance) Integration among plastral and nonplastral modules J1 J2 J3 K1 K2 K3 K4 K5 Pal Geologic Time

29 Integration within plastral module Plastral Disparity (Sum of Variances) J1 J2 J3 K1 K2 K3 K4 K5 Pal Geologic Time

30 Integration within nonplastral Nonplastral Disparity (Sum of Variances) module J1 J2 J3 K1 K2 K3 K4 K5 Pal Geologic Time

31 Modularity and major trends in echinoderm evolution -EAT Theory camptostromatoid cystoid asteroid echinoid

32 Context-dependence of modularity Modularity as number of plate columns Pz > PostPz

33 Context-dependence of modularity Modularity as number of plates Regular Irregular >

34 Context-dependence of modularity Modularity as number of plate types Regular Irregular <

35 Context-dependence of modularity Modularity as number of growth zones Constant across echinoids

36 Is integration the converse of modularity? No, because the whole is more than the sum of the parts Yes, because, all other things being equal, integration and parcellation are logical opposites and are inversely correlated

37 Is integration the converse of modularity? Wait Yes and no: they are logical opposites and tend to be inversely correlated, but the opposition may not be symmetric and the correlation imperfect because of 1) The geometry of organisms 2) The topology of morphospace 3) Historical contingency

38 Is integration the converse of modularity? 1) The geometry of organisms The size and shape of organismal parts affects connectivity and the strength of interactions among parts. Ex. For homogeneous parts such as serial homologues, modularity may increase of decrease without change of integration

39 Is integration the converse of modularity? 2) The topology of morphospace Heterogeneities in morphospace, imply asymmetric transition probabilities: in any particular evolutionary trajectory, changes in modularity or integration may not be reversible or else have a lower probability of reversal.

40 Is integration the converse of modularity? 3) Historical contingency Modules have potentially different degrees of entrenchment, and chance may at times lead to loss of modularity as well as of integration (e.g., limb loss).

41 Future Challenges - Are morphometric landmarks minimal modules? If so, in what sense? - Can morphospaces themselves be differentially modular or integrated? In principle. - How to address the relationships between modularity, integration, disparity, and complexity in a single framework? Or is more than one framework needed?

Quantitative evolution of morphology

Quantitative evolution of morphology Properties of Brownian motion evolution of a single quantitative trait Most likely outcome = starting value Variance of the outcomes = number of step * (rate parameter)