Group, Kin, Species Selection and Punctuated...
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Group, Kin, Species Selection and Punctuated Equilibrium Joe Felsenstein GENOME 453, Autumn 2015 Group, Kin, Species Selection and Punctuated Equilibrium – p.1/45
Transcript of Group, Kin, Species Selection and Punctuated...
Group, Kin, Species Selection and PunctuatedEquilibrium
Joe Felsenstein
GENOME 453, Autumn 2015
Group, Kin, Species Selection and Punctuated Equilibrium – p.1/45
Group selection
Whole local populations survive or go extinct, in a way that depends ontheir frequency of the altruistic allele.
Before: p = 45/104 = 0.4327
Local populations, which differ in gene frequency
8/139/13 8/13 7/13
0/133/135/135/13Group, Kin, Species Selection and Punctuated Equilibrium – p.2/45
Group selection
Whole local populations survive or go extinct, in a way that depends ontheir frequency of the altruistic allele.
After: p = 29/65 = 0.446
Within each population, individual selection against altruists reduces thefrequency of the allele.
extinct extinct
8/13 7/13 7/13 5/13
2/13
extinct
Group, Kin, Species Selection and Punctuated Equilibrium – p.3/45
Kin selection: the case of an alarm call
Before
doesn’t give alarm call, saves selfhalf of others eaten
gives alarm call, is eatenbut flock is saved
1 flock like this. 3 flocks like this.
p = 21/136 = 0.1544123
(Note that in the example the other flock members tend to be relatives ofthe bird that gives the alarm call, so they tend to have the alleles that ithas)
Note – the numbers shown here are approximately correct at these genefrequencies. Infrequent occurrences such as homozygotes for the alarmcall allele are omitted.
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Kin selection: the case of an alarm call
doesn’t give alarm call, saves selfhalf of others eaten
gives alarm call, is eatenbut flock is saved
1 flock like this. 3 flocks like this.
After p = 17/86 = 0.197674
cost = 1
benefit = 8
Alarm call allele will increase with any coefficient of relationship > 1/8
Note – the numbers shown here are approximately correct at these genefrequencies. Infrequent occurrences such as homozygotes for the alarmcall allele are omitted.
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The mathematics of kin selectionW. D. Hamilton argued on theoretical grounds that an allele predisposingto an altruistic behavior will increase if
c < r b
where (c) is the cost (in fitness) to the altruist(b) is the total benefit to all recipients
and (r) is the average relatedness of recipients to the altruist.
r is the probability that a (rare) gene heterozygous in the altruist is presentin the typical recipient, owing to their relatedness.
Relative r
Identical twin 1Brother/sister 1/2Mother/father 1/2Offspring 1/2Half-sibling 1/4Aunt/uncle 1/4Niece/nephew 1/4Grandchild 1/4First cousin 1/8
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W. D. Hamilton 1936-2000
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Cooperative breeding in Florida Scrub Jays
An example is the Florida Scrub Jay, Aphelocoma coerulescens. Youngscrub jays often stay around the parents’ nest for several years, helpingraise their full siblings. With a helper about 1.45 offspring are reared,without one, only about 0.5 offspring per year. The parents formpermanent pairs.
Let’s calculate the terms of Hamilton’s Inequality ...
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Cooperative breeding in Florida Scrub Jays
An example is the Florida Scrub Jay, Aphelocoma coerulescens. Youngscrub jays often stay around the parents’ nest for several years, helpingraise their full siblings. With a helper about 1.45 offspring are reared,without one, only about 0.5 offspring per year. The parents formpermanent pairs.
Calculation:Cost 0.25 Offspring foregone
Benefit 0.95 More siblingsRelationship 0.5 As those are full sibs
Note the offspring foregone have only an average of 0.5×0.5 copies eachof a (putative) gene. So the cost is really 0.25 copies lost.Since 0.25 < (0.95)(0.5), the behavior is favored.
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Actually, group selection is a kind of kin selection
Because ...1. Groups must vary in gene frequency to have group selection work
(usually, the gene frequencies differ because the members of agroup are related to each other)
2. Having an altruistic behavior reduces the fitness of the individual(just as it does in the case of kin selection)
3. Being in a group with altruists means you are related to them andyou benefit from their presence (by having a lower chance of groupextinction)
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Social insects: Hymenoptera are haplo-diploid
queen drone
worker worker’s sibling
In ants, bees, and wasps, males are haploid, females diploid.
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Relatedness between workers and their sibs
queen drone
worker worker’s sibling
12
Gene in worker has 1
2chance of coming from the queen.
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Relatedness between workers and their sibs
queen drone
worker worker’s sibling
12
12
... and that copy has 1
2chance of being in the sib, for a chance (so far) of
1
2×
1
2= 1
4
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Relatedness between workers and their sibs
queen drone
worker worker’s sibling
12
also it has 1
2chance of coming from the drone.
Group, Kin, Species Selection and Punctuated Equilibrium – p.14/45
Relatedness between workers and their sibs
queen drone
worker worker’s sibling
12
1
... and that copy has 100% chance of being in the sib, for a chance of 1
2.
Result is that total relatedness is 3
4.
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Relatedness if the species were an ordinary diploid
queen drone
worker worker’s sibling
12
12
12
12
As in termites, the total relatedness is then only 1
2.
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The punctuated equilibrium controversy
David the late Niles the late StevenRaup Stephen J. Eldredge Jack Stanley
Gould Sepkoski
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An adaptive trend according to gradualists
Time
Phenotype
Selection is mostly occurring within species and
not by species selection
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An adaptive trend according to punctuationists
but the rightwards ones survive better
Phenotype
Time
In this hypothetical diagram, 19 speciations leftwards, 21 rightwards
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Issues involving gradualism and punctuationism
Issue 1: What are typical patterns of evolution
Punctuationists:
Traditional gradualists:
Gradualists these days:
Issue 2: Are new evolutionary forces needed to explain these?
Punctuationists:
Gradualists:
Yes, species selection
No, can do the same with
ordinary neo−Darwinian mechanisms
and peripheral speciation
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Gradualist versus punctuationist views
WhatGradualism
Random variationis due to
Mutation Genetic drift at thetime of formation ofa new species
Selection is due to Individual survivaland reproduction
Species selection
within populations between speciesChange happens
In:
ACCTTGA GTTGAAC
Punctuationalism
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The fossil radiolarian protist Pseudocubus
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Davida Kellogg’s 1975 radiolarian data
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Wei’s Globoconella foram data
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Wei’s Globoconella foram data
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Wei’s Globoconella foram data
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Wei’s Globoconella foram data
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Gryphaea, a Jurassic oyster
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Hallam’s Gryphaea Jurassic oyster data
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Hyopsodus, an Eocene condylarth mammal
Group, Kin, Species Selection and Punctuated Equilibrium – p.30/45
Gingerich’s Eocene condylarth data
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Pleurocardiacockles
Geary, D. H. 1987. Evolutionary tempo and mode in a sequence of theUpper Cretaceous bivalve Pleuriocardia. Paleobiology13: 140-151.
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Trends through time in some fresh-water cockles
Dana H. Geary, Gene Hunt, Imre Magyar, and Holly Schreiber. 2010. Theparadox of gradualism: phyletic evolution in two lineages of lymnocardiidbivalves (Lake Pannon, central Europe). Paleobiology36(4): 592-614.
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A punctuated change in Ordovician trilobite
Mean number of pygidial axial rings in a stratigraphic sequence of the trilobite Flexicalymene(Cisne et al. 1980). The best-supported model for these data implies an unsampledpunctuation event between the ninth and tenth samples (vertical gray rectangle); dashedhorizontal lines indicate the estimated stasis optima (θ1 and θ2) for this model. Time ismeasured in millions of years from the first population. Vertical bars show 95% confidenceintervals around the sample means.
From G. Hunt, 2008, Paleobiology. Group, Kin, Species Selection and Punctuated Equilibrium – p.34/45
Sewall Wright’s (1932) adaptive peaks
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George Gaylord Simpson’s 1944 adaptive zones
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Ernst Mayr’s view of peripheral speciation
A large species
in a geographic area
can reach new peaksby genetic drift
if parent species
is stuck herean adaptive surface
the population on the new peakcan become reproductivelyisolated from the parent(maybe just because it is on a new peak and intermediatesdon’t do well)
phenotype
fitne
ss
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Allopatric speciation
species starts out like this
gets divided by a barrier
after a while the two populationswill have become reproductively isolated
may be able tocoexist
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Punctuated change by gradual mechanisms
Phenotype
Time
Genetic drift (versus selection)
Fit
nes
s
Phenotype
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Punctuated change by gradual mechanisms
Time
... followed by selection
Phenotype
Fit
nes
s
Phenotype
Group, Kin, Species Selection and Punctuated Equilibrium – p.40/45
Punctuation by gradual rise of a peak
phenotype
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Punctuation by gradual rise of a peak
phenotype
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Punctuation by gradual rise of a peak
phenotype
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Punctuation by gradual rise of a peak
phenotype
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Punctuation by gradual rise of a peak
phenotype
Group, Kin, Species Selection and Punctuated Equilibrium – p.45/45
