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.

Group, Kin, Species Selection and Punctuated Equilibrium – p.4/45

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.

Group, Kin, Species Selection and Punctuated Equilibrium – p.5/45

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

Group, Kin, Species Selection and Punctuated Equilibrium – p.6/45

W. D. Hamilton 1936-2000

Group, Kin, Species Selection and Punctuated Equilibrium – p.7/45

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 ...

Group, Kin, Species Selection and Punctuated Equilibrium – p.8/45

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.

Group, Kin, Species Selection and Punctuated Equilibrium – p.9/45

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)

Group, Kin, Species Selection and Punctuated Equilibrium – p.10/45

Social insects: Hymenoptera are haplo-diploid

queen drone

worker worker’s sibling

In ants, bees, and wasps, males are haploid, females diploid.

Group, Kin, Species Selection and Punctuated Equilibrium – p.11/45

Relatedness between workers and their sibs

queen drone

worker worker’s sibling

12

Gene in worker has 1

2chance of coming from the queen.

Group, Kin, Species Selection and Punctuated Equilibrium – p.12/45

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

Group, Kin, Species Selection and Punctuated Equilibrium – p.13/45

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.

Group, Kin, Species Selection and Punctuated Equilibrium – p.15/45

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.

Group, Kin, Species Selection and Punctuated Equilibrium – p.16/45

The punctuated equilibrium controversy

David the late Niles the late StevenRaup Stephen J. Eldredge Jack Stanley

Gould Sepkoski

Group, Kin, Species Selection and Punctuated Equilibrium – p.17/45

An adaptive trend according to gradualists

Time

Phenotype

Selection is mostly occurring within species and

not by species selection

Group, Kin, Species Selection and Punctuated Equilibrium – p.18/45

An adaptive trend according to punctuationists

but the rightwards ones survive better

Phenotype

Time

In this hypothetical diagram, 19 speciations leftwards, 21 rightwards

Group, Kin, Species Selection and Punctuated Equilibrium – p.19/45

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

Group, Kin, Species Selection and Punctuated Equilibrium – p.20/45

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

Group, Kin, Species Selection and Punctuated Equilibrium – p.21/45

The fossil radiolarian protist Pseudocubus

Group, Kin, Species Selection and Punctuated Equilibrium – p.22/45

Davida Kellogg’s 1975 radiolarian data

Group, Kin, Species Selection and Punctuated Equilibrium – p.23/45

Wei’s Globoconella foram data

Group, Kin, Species Selection and Punctuated Equilibrium – p.24/45

Wei’s Globoconella foram data

Group, Kin, Species Selection and Punctuated Equilibrium – p.25/45

Wei’s Globoconella foram data

Group, Kin, Species Selection and Punctuated Equilibrium – p.26/45

Wei’s Globoconella foram data

Group, Kin, Species Selection and Punctuated Equilibrium – p.27/45

Gryphaea, a Jurassic oyster

Group, Kin, Species Selection and Punctuated Equilibrium – p.28/45

Hallam’s Gryphaea Jurassic oyster data

Group, Kin, Species Selection and Punctuated Equilibrium – p.29/45

Hyopsodus, an Eocene condylarth mammal

Group, Kin, Species Selection and Punctuated Equilibrium – p.30/45

Gingerich’s Eocene condylarth data

Group, Kin, Species Selection and Punctuated Equilibrium – p.31/45

Pleurocardiacockles

Geary, D. H. 1987. Evolutionary tempo and mode in a sequence of theUpper Cretaceous bivalve Pleuriocardia. Paleobiology13: 140-151.

Group, Kin, Species Selection and Punctuated Equilibrium – p.32/45

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.

Group, Kin, Species Selection and Punctuated Equilibrium – p.33/45

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

Group, Kin, Species Selection and Punctuated Equilibrium – p.35/45

George Gaylord Simpson’s 1944 adaptive zones

Group, Kin, Species Selection and Punctuated Equilibrium – p.36/45

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

Group, Kin, Species Selection and Punctuated Equilibrium – p.37/45

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

Group, Kin, Species Selection and Punctuated Equilibrium – p.38/45

Punctuated change by gradual mechanisms

Phenotype

Time

Genetic drift (versus selection)

Fit

nes

s

Phenotype

Group, Kin, Species Selection and Punctuated Equilibrium – p.39/45

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

Group, Kin, Species Selection and Punctuated Equilibrium – p.41/45

Punctuation by gradual rise of a peak

phenotype

Group, Kin, Species Selection and Punctuated Equilibrium – p.42/45

Punctuation by gradual rise of a peak

phenotype

Group, Kin, Species Selection and Punctuated Equilibrium – p.43/45

Punctuation by gradual rise of a peak

phenotype

Group, Kin, Species Selection and Punctuated Equilibrium – p.44/45

Punctuation by gradual rise of a peak

phenotype

Group, Kin, Species Selection and Punctuated Equilibrium – p.45/45