BACKGROUND Rapid rate of diversification often follows the adaptive radiation sexual selection New niches Mutation New species Adaptive radiation Examples of adaptive radiation Galapagos Island finches ID: 226510
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Slide1
RATES OF DIVERSIFICATIONSlide2
BACKGROUND
Rapid rate of diversification often follows the adaptive radiation
+ (sexual) selection
New niches
Mutation
New species
Adaptive radiationSlide3
Examples of adaptive radiation:
Galapagos Island finches
Tertiary radiation of birds and mammals
Cichlid fishes in the African great
lakes
Galapagos finches
Nimbochromis venustus
ArchaeopteryxSlide4
RATE OF DIVERSIFICATION
How does the rate of diversification vary through space and time?
How does the rate of diversification vary across taxonomic groups and region?
What methods do they use to assess the rate of diversification?
What could be the future challenges of the methods used in species rate of diversification?Slide5
Ecological opportunity
Ecological opportunity is a primary factor regulating the tempo of diversification
(Schluter 2000; Gavrilets & Vose 2005)
Greater ecological opportunity increases the likelihood of lineage divergence
saturation of niche space
Ecological opportunity
(clade acquires species)
Rate of diversificationSlide6
Example:
The role of geography and ecological opportunity in the diversification of day geckos (
Phelsuma
)
(Harmon
et al. 2008)
Phelsuma madagascariensisSlide7
Hypothesis that Harmon et al. (2008) tested:
Ecological opportunity: rate of speciation and morphological evolution will be elevated following colonization of islands unoccupied by competitor species
(Baldwin & Sanderson 1998)
Speciation rate is positively correlated with island area
(
Losos
&
Schluter 2000)
(fig from Losos & Schluter
2000)Slide8
Method:
Maximum Likelihood approach
Calculate diversification rate under a number of extinction scenarios
(
Magallón & Sanderson 2001)
Diversification rate (
ϒ-μ
) = speciation rate (ϒ) - extinction rate (μ)
Extinction scenario (ε) = turnover = μ/
ϒTest for slowing through time in diversification rate (Pybus & Harvey 2000)Slide9
Rate of species accumulation have slowed through time on Madagascar.
Rates of morphological evolution are higher on both the Mascarene and Seychelles archipelagos compared to rate on Madagascar
Ecological opportunity is an important factor in diversification of day gecko species
(Harmon
et al.
2008)Slide10
Issues with their model (Harmon
et al.
2008)
Maximum Likelihood under the null hypothesis of a constant pure-birth process ~ speciation and extinction rates are constant through time.
(Stadler 2011)
New ML approach
The
birth–death-shift process, where the speciation and extinction rates can change through time.Slide11
Estimating the maximum-likelihood speciation and extinction rates together with the shift times
Case of the mammalians
(Stadler 2011)
~ 33 myaSlide12
(Uyeda
et al.
2011)
Divergence in body size between related species versus the divergence time
Crazy amount of data:
Rate of evolutionary change
Divergence time
Fossil data change through time
Methods:Multiple-burst model (“Blunderbuss” model)=Models involving Brownian motion
Random variation of the values of the traits around the meanSlide13
Want evolutionary change?? Wait a million years !!!
(
Uyeda
et al. 2011)Slide14
RATE OF DIVERSIFICATION
How does the rate of diversification vary through space and time?
How does the rate of diversification vary across taxonomic groups and region?
What methods do they use to assess the rate of diversification?
What could be the future challenges of the methods used in species rate of diversification?Slide15
Ecological opportunity is a primary factor regulating the tempo of diversification
(
Schluter
2000)
Shift to a new habitat would increase the rate of diversification
Involves geography, location, areas, range : Important role of space
Paleogeography and paleoclimateSlide16
(Hou
et al.
2011)Habitat shift from saline to fresh water
Gammarus lacustris
Gammarus balcanusSlide17
Hypothesis:
Shift to a new habitat frees species
from the competition with closely related species and would increase
the rate of diversification followed by adaptive radiations
Methods:
Phylogenetic inference: to estimate the divergence times of its major lineages
to determine when the shift from saline to freshwater occurred.
Biogeographic analysis (Likelihood and Parsimony methods) to explore where
Gammarus first colonized freshwater habitats
Diversification analysis to assess the temporal diversification mode associated with the habitat shift
(
Hou
et al.
2011)Slide18
Results:
Phylogenetic inference identi
fi
es an Eocene habitat shift from saline
to freshwater
Biogeographic analysis indicates two major range shifts
(
Hou et al. 2011)Slide19
Results:
Diversi
fi
cation modes associated with habitat shiftSlide20
Habitat shift
from saline to freshwater
+
Increase of land mass
Available bodies of freshwater
Rapid radiation
of freshwater speciesSlide21
Habitat shift
from saline to freshwater
+
Increase of land mass
Available bodies of freshwater
Rapid radiation
of freshwater speciesSlide22
RATE OF DIVERSIFICATION
How does the rate of diversification vary through space and time?
Geography and space
Biological history
ClimateSlide23
RATE OF DIVERSIFICATION
How does the rate of diversification vary through space and time?
Geography and space
Biological history
Climate
Extrinsic causes
due to new environmental circumstancesSlide24
RATE OF DIVERSIFICATION
How does the rate of diversification vary through space and time?
Geography and space
Biological history
Climate
Extrinsic causes
due to new environmental circumstances
Radiations may occur due to
intrinsic characters
of organisms
the key innovationSlide25
How does the rate of diversification vary through space and time?
Rapid radiation due to a key innovation
Aquilegia
(
Ranunculaceae) (Hodges 1997)
Methods: Phylogenetic analyses
- test for
monophyly – a basic assumption of adaptive radiation - identification of sister taxa – by definition of equal age
- evolution of proposed key innovation – floral spursSlide26
Rapid radiation due to a key innovation in Columbines (Ranunculaceae:
Aquilegia
)
(Hodges 1997)Slide27
Rapid radiation of
Aquilegia
: via key innovation or via invasion of new habitat?Slide28
Role of space
Aquilegia
and its close relatives Isopyrum
do not occupy a substantially different geographic range.
It does not appear that Aquilegia has dispersed into a new habitat that its close relatives were unable to invade.Slide29
Spur as key innovation
Underlying assumption of most species concepts: the necessity for reproductive isolation
Characters that can promote reproductive isolation may increase speciation rate and thus diversification
Taxa with spurs can become specialized on different pollinator types which increases reproductive isolation and possibly speciation
(Hodges 1997)Slide30
How to know if there has actually been a change in diversification rate between sister taxa?
Assessing weather branching rate increases with origin of traits
Change in diversification should be associated with the branch where the key innovation evolved
Comparison of the diversification rate of the sister group lacking the key innovation and the lineages that possess the proposed key innovation
(Sanderson & Donoghue 1994)Slide31
Methods:
Method based on ML approach
Null model as test for changes in diversification rate
Null model (Yule pure birth) assumes a (unknown) constant lineage birth rate for each branch on the tree (1)
Calculate the likelihood of observing N species in a
clade
after an interval time d (2)
Markov property of (1) permit multiplication of (2) taking into account different rate parameters in different branchesDifferent ML models with various number of rate parameters
(Sanderson & Donoghue 1994)Slide32
P values
>
0.95
model rejected
rejected
rejected
rejected
acceptedSlide33
Rapid rate of diversification often follows the adaptive radiation
S
election
New niches
Mutation
New species
Adaptive radiationSlide34
Rapid rate of diversification often follows the adaptive radiation
S
election
New niches
Mutation
New species
Adaptive radiationSlide35
(Gavrilets & Vose 2005)
Genetically based habitat choice models of large-scale evolutionary diversification
Preference for
new niche
New ecological niche
environmental factors
Simultaneous
Genetically controlled
Each individual has different neutral loci subject to mutation
Probability of extinction is assigned per generation
(turn over of ecological niches)Slide36
(Gavrilets & Vose 2005)Slide37
Larger areas allow for more intensive diversification (area effect)
new locally advantageous genes may become better protected by distance from the diluting effect of locally deleterious genes, which otherwise can easily prevent adaptation to a new niche.
Anolis lividus
Anolis gorgonae
Anolis nitens
(Gavrilets & Vose 2005)Slide38
Increasing the number of loci underlying the traits decreases diversification
a larger number of loci implies weaker selection per each individual locus and a stronger overall effect of recombination in destroying co-adapted gene complexes.
Anolis lividus
Anolis gorgonae
Anolis nitens
(Gavrilets & Vose 2005)Slide39
The level of divergence in neutral microsatellite loci between populations from different species is comparable to that between populations of the same species.
blue butterfly species
Lycaeides melissa
Lycaeides
idasSlide40
The number of species peaks early in the radiation
speciation events occur soon after colonization of a new environment so the genetic constraints are less strict than later on.
Tetragnatha
sp.
(Gavrilets & Vose 2005)Slide41
Summary and conclusion:
Adaptive radiation is defined as the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage.
When it occurs, adaptive radiation typically follows the colonization of a new environment or the establishment of a “key innovation” which opens new ecological niches and/or new paths for evolution.
The increasing availability of molecular phylogenies and associated divergence times has spurred the development of new methods to estimate rates of speciation and extinction from phylogenetic data of extant species and to detect changes in diversification rates through time and across lineages.Slide42
QUESTIONS:
Phylogeny is indispensable in understanding the diversification rate, how about its reliability?
What would be the effect of the interplay between adaptive radiation and extinction on the tempo and timing of lineage diversification?
(Antonelli & Sanmartin 2011)
Recent radiation or signature of extinction??