G404 Geobiology
Analysis of diversity and disparity
Adaptative radiation and key
innovations
Hunter, 1998
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Allison Bormet: Artiodactyls and
ecomorphology
“Take home” lab, no meeting
Blaire Hensley-Marschand: Hominins and
mammals
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Discussion on Thursday
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Adaptive radiation
“A proliferation of species within a
single clade accompanied by
significant interspecific divergence in
the kinds of resources exploited and
in the morphological and
physiological traits used to exploit
those resources.” (Schluter, 1996)
Five components:
1. Monophyletic group
2. increase in diversity (number of species
or lineages)
3. increase in ecological differentiation
(resources such as food, substrate, etc.)
4. increase in disparity (morphological
differences)
5. by implication, relatively rapid increases
in these properties
Schulter, 1996. American Naturalist, 148: S40-S64.
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Examples of adaptive radiations
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Early metazoan life in the Proterozoic
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Amniota in the late Carboniferous and early Permian
•
Eutheria in the early Cenozoic
•
East African Lake Cichlids
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Timescale: Ediacaran (635-542 mya, 90 million years)
Diversity: relatively small number of species
Disparity: large, with organisms from fronds to actriarchs
Monophyletic: maybe
Timescale: late Carboniferous to Early Permian (307-294 mya, 13 million years)
Diversity: large number of species and subclades
Disparity: large for tetrapods, ecological diversity great
Monophyletic: yes
Timescale: Paleocene to early Eocene (65-50 mya, 15 million years)
Diversity: extremely large number of species, many subclades
Disparity: large, bats to whales; ecological diversity great
Monophyletic: yes
Timescale: Miocene to Modern (10-0 mya, 10 million years)
Diversity: very large, 200+ species per lake
Disparity: largish, ecological diversity great
Monophyletic: yes (with subtleties)
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Key innovation
Key innovations are new features that facilitate adaptive radiations.
“Aspects of organismal phenotype important to the origin or subsequent
success of a group.” (Hunter, 1998)
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May contribute to adaptive radiation
Differs from adaptive radiation in that key feature may evolve homoplastically and result
in diversification of more than one clade in parallel
Linked to diversity but not necessarily disparity
Trait must be a true adaptation, not an exaptation
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Key innovation 1: hypocone in mammal teeth
Evolutionary addition of hypocone to
the ancestral tribosphenic molar
pattern transforms shearing dentition
to crushing dentition
Key innovation in evolution of
herbivory and omnivory
Occurs in parallel in many
independent mammal groups, all of
which diversify
Hunter, 1998
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Association between hypocone and mammalian diversity
Tribosphenic and partial hypocone
taxa maintain constant diversity
Hypocone taxa radiate with large
diversity
Hunter, 1998
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Key innovation : locomotor changes in birds
Transformation of one locomotor
system in basal theropods to three in
aves allows diversification into many
types of forms
Hindlimbs + tail in theropods
(coordinated)
Hindlimbs versus forelimbs versus
tails in birds (semi-independent)
Hunter, 1998
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Testing a hypothesis of adaptation
A
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Phylogenetic change in trait and
function must be shown to coincide
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Link between trait and function must be
demonstrated
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Improved “performance” because of
change in trait must be demonstrated
B
C
Function change
Character change
(adaptation)
Character change
(exaptation)
Adaptation - a trait that evolves by natural selection for a
specific function
Exaptation - a character, previously shaped by natural
selection for a particular function (an adaptation), is co-opted
for a new use (Gould and Vrba, 1982)
Example: Feathers are an exaptation for flight because they evolved before flying.
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Diversity and disparity
Diversity
Diversity is the number of taxa living at one time, and changes to that number.
Extinction lowers diversity, radiation raises diversity.
Disparity
Disparity is the difference among taxa, roughly equal to the degree to which
contemporary taxa are specialized for different things or specialized for the
same thing.
The two are not necessarily correlated. Many species (high diversity) could
have only a few specializations (low disparity); few species (low diversity) could
have remarkably different specializations (high disparity).
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
Diversity curves
Estimated from fossil
record by dividing time
into bins (either equal
length bins or named
geological periods)
Department of Geological Sciences | Indiana University
Diversity curve
Number of
lineages
G404 Geobiology
(c) 2011, P. David Polly
G404 Geobiology
Studying patterns of diversity
Standing diversity is the number of taxa (usually species, but sometimes
genera or families) during a given time period
Standing diversity is a function of number of lineages existing at the beginning
of a time period, the number of originations during the time period and
number of extinctions
Basic data are first appearances (FADs) and last appearances (LADs) of taxa
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Disparity in Osteostracan morphospace
Morphospace is a mathematical space based on morphological measurements.
Objects that are close together are similar to one another. The sum of the distances
of objects is a measure of how different they are from one another. Disparity is often
measured this way.
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Measuring disparity
Disparity is the average spread of taxa in morphospace
Can be measured from meristic characters or continuous characters
Distance between taxa is calculated and a morphospace produced using
principal coordinates analysis (PCO) or principal components analysis (PCA)
PCO for meristic characters: distance = number of different character states
Taxon 1
Taxon 2
0011001
0010110
Distance = 4 (four characters differ in state)
PCA for continuous characters: distance = Euclidean distance summed across
traits
Taxon 1
Taxon 2
0.5 1.0
0.7 1.2
Distance = sqrt( (0.5-0.7)2 + (1.0-1.2)2 ) = 0.4
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Disparity through time
Crinoid morphospace from Cambrian
(CM) to Upper Devonian (UD) showing
changing disparity through time
Maximum disparity reached by
Ordovician (LO, O2)
Later changes merely fill in the
morphospace
Photo credit
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
(Tom Holtz, based on original by Matt Wedel,
UC Museum of Paleontology website)
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly
G404 Geobiology
Scientific papers for further reading
Adams, D. C., C. M. Berns, K. H. Kozak, and J. J. Wiens. 2009. Are rates of
species diversification correlated with rates of morphological evolution?
Proceedings of the Royal Society B, 276: 2729-2738.
Gould, S. J. and R. C. Lewontin, 1979. The spandrels of San Marco and the
Panglossian paradigm: a critique of the adaptationist programme.
Proceedings of the Royal Society B, 205: 581-598.
Hunter, J. P. 1998. Key innovations and the ecology of macroevolution. Trends
in Evolution and Ecology, 13: 31-36.
Schluter, D. 1996. Ecological causes of adaptive radiation. American
Naturalist, 148: S40-S64.
Department of Geological Sciences | Indiana University
(c) 2011, P. David Polly