Macroevolution of Organismal Modularity and Integration · 2003-03-07 · Evolvability a Modularity...
Transcript of Macroevolution of Organismal Modularity and Integration · 2003-03-07 · Evolvability a Modularity...
Macroevolution of OrganismalModularity and Integration
Gunther J. EbleBioinformatik, Universität Leipzig
What is macroevolution?
- evolution at and above the species level- large-scale phenotypic evolution- among-species evolution
Macroevolutionary biology: the study of theorigin and sorting of macroevolutionaryvariation
- 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
Bits and Pieces: isolated yetintegrated
Organismal Modularity:definition and theoretical
justification• Definition: Dissociability of phenotypic wholes into
parts• Justification: organizational and variational semi-
independence of morphological organization;morphology itself is involved in the generation ofnew morphological elements late in ontogeny;morphostatic mechanisms (including physiologicalhomeostasis, regeneration, and repair) rely oninformation conveyed by morphological states.
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 andof modularity in a macroevolutionary context.
Metrics of organismal modularity
- Conceptually and statistically a number of explicitmetrics can be advanced, but operationally someproxy metrics appear most useful:
- number of parts, constructional elements,characters- within- and among-module integration- disparity
Disparity: the conceptDisparity: the concept
Taxonomic diversity: sample 1 = sample 2 = 6 spp.Morphological disparity: ∆ sample 1 << ∆ sample 2
SampleSample 1 1 SampleSample 2 2
Empirical morphospacesEmpirical morphospaces
-0,28 -0,80 0,58 0,13 -0,78 0,070,76 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 1,671,56 -0,36 1,18 1,18 -0,35 -2,03
X1 Y1 Z1 X2 Y2 Z2Species ASpecies BSpecies CSpecies DSpecies E
...
... p
n
PC1PC2
EIGENVECTOR EXTRACTIONEIGENVECTOR EXTRACTION
MORPHOSPACEMORPHOSPACEPROJECTIONPROJECTION
DATA MATRIX:DATA MATRIX:n SPECIES x p VARIABLESn SPECIES x p VARIABLES
Disparity = dispersion in morphospace
- Ss (sum of univariate variances)
- Sl (sum of eigenvalues)
Disparity = dispersion in morphospace
- Ss (sum of univariate variances)
- Sl (sum of eigenvalues)
-1
-,75
-,5
-,25
0
,25
,5
,75
1
AXI
S 2
-1 -,75 -,5 -,25 0 ,25 ,5 ,75 1
AXIS 1
Sp. A
Sp. DSp. C
Sp. ESp. B
-1
-,75
-,5
-,25
0
,25
,5
,75
1
AXI
S 2
-1 -,75 -,5 -,25 0 ,25 ,5 ,75 1
AXIS 1
Sp. A
Sp. DSp. C
Sp. ESp. B
Measures of disparityMeasures of disparity
2
n
n
- mean Euclidean distance- mean Euclidean distance
- Procrustes distance- Procrustes distance
AustralopithecusAustralopithecus to Homo to Homo
HomoHomo ergaster ergaster to to HomoHomo erectus erectus
HomoHomo erectus erectus to to Homo sapiensHomo sapiens
∑∆2 = 1.08
∑∆2 = 0.37 ∑∆2 = 0.58
5-Br
6-La
7-On
8-In9-Op
4-Gl3-Na
2-Ns
1-Pr
11-LBoS
10-Ba
Modeling divergence between speciesand between genera
Modeling divergence between speciesand between genera
Morphologicaldiversification
Morphological extinction
(Duboule, 1994)
THE HOURGLASS MODEL
Juvenile disparityJuvenile disparity
AdultdisparityAdultdisparity
-3
-2,5-2
-1,5
-1
-,50
,5
11,5
2PC II
-2 -1,5 -1 -,5 0 ,5 1 1,5 2 2,5
PC I
X JUVENILEO ADULT
Variance
PCI PCII1.06! 0.43
0.54! 1.15
p<0.015 p<0.019 (bootstrap z-test)
x
DEVELOPMENTAL MORPHOSPACEOrder Spatangoida
DEVELOPMENTAL MORPHOSPACEOrder Spatangoida
PCII
Error bars based on 1000 bootstrap replications
.35
.4
.45
.5
.55
.6
.65
C.V
. Mea
n Pa
irwis
e D
ista
nce
LARVAE ADULTS
n=26
n=26
Disparity of Larvae X Disparity of AdultsDisparity of Larvae X Disparity of Adults
Echinoderms as model organisms forthe 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 context-dependence
Modularity and TaxonomicDiversity
0
20
40
60
80
100
120
140
160
Diversity o
f Gen
era
10 15 20 25 30 35 40 45 50 55 60Number of Derived Character States
p < 0.018 (Spearman)
t
XXXXXXXX
XXXX
XX-2.5
-1.5
-.5
.5
1.5
2.5
-2.5 -1.5 -.5 .5 1.5 2.5
x
x
-2.5
-1.5
-.5
.5
1.5
2.5
-2.5 -1.5 -.5 .5 1.5 2.5
x
xx
x
-2.5
-1.5
-.5
.5
1.5
2.5
-2.5 -1.5 -.5 .5 1.5 2.5
x
xx
xxx
x x
DIVERSITY! ! ! ! ! ! DISPARITY
Discordances betweendiversity and disparityDiscordances betweendiversity and disparity
Sea urchin disparity and diversitySea urchin disparity and diversityDi spa rit yDi ver sit y
0
5
10
15
20
25
30
35
40
45
0
10
20
30
40
50
60
70
80
Disparity (Total V
aria
nce)
Gen
eric
Div
ersi
ty
J1 J2 J3 K1 K2 K3 K4 K5 Pal
Ate los tomat a
Disp
arity
(tot
al v
aria
nce)
Disp
arity
(tot
al v
aria
nce)
Div
ersit
y (g
ener
a)D
iver
sity
(gen
era)
Geological timeGeological time
Modularity and Body Size Variance
.15.2
.25.3
.35.4
.45.5
.55.6
.65
Variance ln(L
engt
h)
10 15 20 25 30 35 40 45 50 55 60
Number of Derived Character States
p < 0.76 (Spearman)
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
Integration among plastraland nonplastral modules
05
1015202530354045
Disp
arity
(Tot
al V
aria
nce)
J1 J2 J3 K1 K2 K3 K4 K5 PalGeologic Time
Integration within plastral module
Geologic Time
0
5
10
15
20
25
Plas
tral D
ispar
ity (S
um o
f Var
ianc
es)
J1 J2 J3 K1 K2 K3 K4 K5 Pal
Integration within nonplastralmodule
Geologic Time
0
5
10
15
20
25
30
J1 J2 J3 K1 K2 K3 K4 K5 Pal
Non
plas
tral D
ispar
ity (S
um o
f Var
ianc
es)
echinoidasteroidcystoidcamptostromatoid
Modularity and major trends inechinoderm evolution -EAT Theory
Context-dependence of modularity
Pz Post-Pz
>
Modularity as number of plate columns
Context-dependence of modularity
Regular Irregular
Modularity as number of plates
>
Context-dependence of modularity
Regular Irregular
Modularity as number of plate types
<
Context-dependence of modularityModularity as number of growth zones
Constant across echinoids
Is integrationthe converse of modularity?
No,“because the whole is more than the sum of theparts”
Yes,“because, all other things being equal, integrationand parcellation are logical opposites and areinversely correlated”
Is integrationthe converse of modularity?
Wait…
Yes and no: they are logical opposites and tend tobe inversely correlated, but the opposition may notbe symmetric and the correlation imperfect becauseof
1) The geometry of organisms2) The topology of morphospace3) Historical contingency
Is integrationthe converse of modularity?
1) The geometry of organisms
The size and shape of organismal parts affectsconnectivity and the strength of interactions amongparts.
Ex. For homogeneous parts such as serial homologues, modularitymay increase of decrease without change of integration
Is integrationthe converse of modularity?
2) The topology of morphospace
Heterogeneities in morphospace, implyasymmetric transition probabilities: in any particularevolutionary trajectory, changes in modularity orintegration may not be reversible or else have alower probability of reversal.
Is integrationthe converse of modularity?
3) Historical contingency
Modules have potentially different degrees ofentrenchment, and chance may at times lead to lossof modularity as well as of integration (e.g., limbloss).
Future Challenges
- Are morphometric landmarks minimal modules? Ifso, in what sense?
- Can morphospaces themselves be differentiallymodular or integrated? In principle.
- How to address the relationships betweenmodularity, integration, disparity, and complexity ina single framework? Or is more than oneframework needed?