Principles of Evolution

1
Principles of Evolution

• Chapter 12
• Life in Groups
• James F. Thompson, Ph.D., MT(ASCP)

2
Life in Groups

• Social organization allows organisms to share
  labor, to specialize in tasks and to coordinate
  efforts.
• Groups may be better at finding resources,
  including mates, protecting against dangers, and
  caring for their young.

3
Types of Social Interactions
4
Alarm Calls

• (a) Vervet monkeys fall prey to leopards, as well
  as to snakes and eagles.
• Each-snakes, leopards, and eaglespractice
  different predatory styles and arrive from
  different directions.

5
Alarm Calls

• Depending upon the predator, the monkeys emit
  different alarm calls that elicit different
  adaptive escape responses.
• Shown are the abrupt chirp call (leopard) and
  staccato grunts of the threat-alarm bark (eagle).

6
Beldings Ground Squirrel

• Beldings Ground Squirrels also have different
  alarm calls for predators approaching by land or
  air.
• With hawks, the individual giving the call is
  rarely taken as the prey.
• With coyotes and other terrestrial predators, the
  individual giving the call is about twice as
  likely to be take as a neighbor.

7
In Beldings Ground Squirrels, Most Alarm Calling
is Done by Females
?
?
8
Why Would an Animal RiskGiving an Alarm Call?

• The caller benefits because the predator learns
  it has lost the element of surprise?
• The caller signals the predator it is ready to
  escape?
• The caller creates a scramble of escaping
  neighbors which confuses the predator?
• The caller, by reducing the predators success,
  teaches the predator not to feed on this social
  group?
• Is giving an alarm call an act of Altruism?

9
Altruism

• An act of altruism is a behavior by an individual
  that increases the reproductive fitness of
  another individual while decreasing the fitness
  of the altruist.
• The recognition of altruistic behaviors in
  animals created a seeming paradox for the theory
  of evolution?
• How could natural selection act to preserve
  behavior which reduces individual fitness?

10
Altruism

• One possibility was that benefits to the group
  outweighed the individual advantage.
• If so, then the group was subject to natural
  selection the group became a unit of selection.
• The concept of Group Selection has been a
  controversy for more than half a century.

11
Group Selection?

• V.C. Wynne-Edwards (1906-1997) proposed this
  hypothesis in his book Animal Dispersion in
  Relation to Social Behavior (1962) and continued
  in Evolution Through Group Selection (1986).

12
Wynne-Edwards Group Selection

• Wynne-Edwards proposed that social behaviors act
  to keep social species from exceeding the
  carrying capacity of their environments that
  social behaviors evolve to limit reproduction or
  fecundity.
• For example, occupying territories or
  establishing dominance hierarchies would reduce
  the number of breeding males.
• His logic was supported by the success of
  K-selected species in having stable population
  sizes.
• This could be seen as a form of altruism.

13
Wynne-Edwards Group Selection

• Wynne-Edwards hypothesis stimulated much good
  scientific work, but it also received immediate
  sharp criticism as a concept.
• The populations of social animals are kept in
  check by predation, disease, and famine.
• There is no check against new mutations that
  would increase an individuals reproduction
  fecundity.
• Cheater genotypes would spread due to
  individual natural selection.

14
Kin Selection

• A better hypothesis was already under discussion
  Kin Selection.
• Basic concepts had been published by architects
  of the Modern Synthesis well before Wynne-Edwards
  proposed Group Selection.
• R.A. Fisher in 1930 and J.B.S. Haldane in 1955,
  two of the strongest mathematical population
  geneticists of their generation.

15
W.D. Hamilton Kin Selection

• The term, kin selection was coined by another
  mathematical biologist, John Maynard Smith, but
  Smith acknowledged the contributions of his
  predecessors.
• Hamilton (1936-2000), was another of the world
  class evolutionary biologists of the post-WW II
  generation.

16
W.D. Hamilton (1936-2000)

• Hamilton was British, though born in Egypt and
  much of his professional life was spent in
  America.
• Hamilton was another mathematical population
  geneticist.
• He advocated for the importance of the gene as a
  unit of selection, a perspective shared by E.O.
  Wilson and Richard Dawkins.

17
W.D. Hamilton (1936-2000)

• In addition to his mathematical analysis of
  Inclusive Fitness Theory (Kin Selection),
  Hamilton also investigated sex ratios and the
  cost-benefit analyses for the evolution of sexual
  reproduction.
• Hamilton was a proponent of the Red Queen
  Hypothesis in that regard, supporting the idea
  that sexual recombination originated as a defense
  against parasitism, a form of the evolutionary
  arms race.

18
Hamilton Kin Selection

• Hamiltons Rule A costly action should be
  performed if
• R x B gt C
• Where C is the cost in fitness to the actor
• R is the genetic relatedness between the actor
  and the recipient, and
• B is the fitness benefit to the recipient.
• Fitness costs and benefits are measured in
  fecundity.

19
Kin Selection

• Hamilton developed the Theory of Kin Selection,
  in part, to resolve the challenge of explaining
  how sterile worker castes in social insects could
  evolve, which followed on an insight from Darwin.
• Hymenopterans exhibit haplodiploidy drones are
  haploid with all their genes coming from their
  mother, the queen, while workers are typically
  sterile females with half their genes coming from
  the queen and half from their father, a drone.

20
Kin Selection

• In brief, workers are sisters and share 3/4s of
  their genome on average, and half their genome
  with their mother, the queen.
• Therefore, if the workers contribute to the care
  of the queens other young, more female workers,
  they are preserving more of their genes in the
  next generation, than they would if they had
  offspring of their own, who would share only ½ of
  their genome.
• The workers increase their Inclusive Fitness.

21
Kin Selection

• The Theory of Kin Selection predicts that
  individuals should behave more altruistically and
  less competitively toward their relatives,
  because they share a relatively high proportion
  of their genes (e.g., one-half for siblings and
  one-eighth for cousins).
• Consequently, by helping a relative reproduce, an
  individual passes its genes to the next
  generation, increasing their Darwinian fitness

22
Inclusive Fitness

• The genetic contribution an individual makes to
  future generations includes the genes of its own
  surviving offspring and any like genes preserved
  in the surviving offspring of its relatives.
• Kin Selection is one mechanism (but not the only
  means) by which an individual can increase its
  inclusive fitness.

23
Inclusive Fitness

• The genetic contribution an individual makes to
  future generations includes the genes of its own
  surviving offspring and any like genes preserved
  in the surviving offspring of its relatives.
• Kin Selection is one mechanism (but not the only
  means) by which an individual can increase its
  inclusive fitness

24
Parental Genetic Investment

• When diploid organisms (P) produce offspring,
  each offspring (F1) receives half of its genotype
  from each parent.
• In turn, these offspring (only the female is
  shown) produce progeny (F2) carrying a quarter of
  the genotype of the original parents.
• The genetic contribution of the female is
  followed, although the same outcome applies to
  the male.
• Each individual is diploid, represented by the
  divided half the amount of the original females
  genetic contribution (cross-hatch) is followed
  here.

½ ¼
25
Kin Selection

• The most obvious example of Kin Selection is
  simply the general phenomenon of Parental Care.
• Any activity or resource allocation by a parent
  to the reproductive fitness of its young will be
  favored by natural selection.
• Thus, no sacrifice short of death on the part of
  a parent for its offspring should be thought of
  as altruistic!
• And death as a sacrifice is justified for three
  or more young
• R x B gt C ? ½ x 3 live gt 1 dies

26
Parental Care

• The female parent defends and saves her three
  offspring, but she dies in the effort.
  Nevertheless, because half of her genotype is
  carried in the offspring (F1), a total of 1½ of
  her genotype survives.
• No parental defense and the female survives, but
  all offspring (F1) perish, leaving a total of
  only one (1) of her genotype surviving (the same
  applies to males).

27
Brood Parasites Exploit Parental Care

• ? The large young Cuckoo (right) has evicted the
  smaller young of the host Meadow Pipit (left) and
  begs for food.
• Rock Pipit and Cuckoo below.

28
Levels of Selection

• Darwin, and most evolutionary biologists since
  Darwin have recognized the individual organism as
  the unit of selection.
• However, some additional levels of selection have
  been proposed, both above and below the level of
  the individual organism.

29
The Gene as the Unit of Selection

• The view that the gene is a unit of selection, is
  an addition to the Modern Synthesis of Evolution.
• In this model, those alleles and allele
  combinations whose phenotypic effects
  successfully promote their own propagation will
  be preferentially selected in contrast to their
  competitors.
• This process produces adaptations to the benefit
  of alleles, which promotes the reproductive
  success of the organism, or of other organisms
  containing the same gene (inclusive fitness), or
  even only its own propagation in detriment to the
  other genes of the genome.

30
The Gene as the Unit of Selection

• The concept was first proposed by Colin
  Pittendrigh in 1958 and further explored by W.D.
  Hamilton in classic papers in 1963 and 1964.
• Soon after, it was more thoroughly developed by
  George C. Williams in his book, Adaptation and
  Natural Selection (1966).
• One necessary condition is that the selected
  entity must have a high degree of permanence and
  a low rate of endogenous change.
• This characterizes genes as well as individuals.

31
George C. Williams (1926- )

• Williams is an American evolutionary biologist
  and ichthyologist
• His diverse interests include the evolution of
  sex, the gene as a unit of selection, evolution
  applied to medicine, philosophy of science and
  human ethics.
• Williams is also a major critic of Wynne-Edwards
  Theory of Group Selection.

32
Richard Dawkins (1941- )

• Dawkins is a British evolutionary biologist and
  ethologist, perhaps the premier living
  evolutionary biologist.
• Dawkins advocates for the gene as the unit of
  selection in The Selfish Gene (1976) and The
  Extended Phenotype (1982).
• Dawkins crusades against creationism and
  Intelligent Design, e.g., The Blind Watchmaker
  (1987) and against religion, The God Delusion
  (2006).
• He also writes on human overpopulation,
  environmental concerns and the evolution of human
  culture

33
The Gene as the Unit of Selection

• The concept of the gene as the unit of selection
  is well substantiated by data, but also receives
  some sharp criticism.
• It is a fascinating topic but beyond the scope of
  this course.
• To follow the debate you need a much stronger
  foundation in genetics than this course provides.
• But the classic books aimed at general readers on
  the subject are very readable.

34
Higher Levels as Units of Selection

• There is little evidence for the population, or
  species, as a unit of evolution, as hypothesized
  by V.C. Wynne-Edwards.
• However, there are more modern hypotheses which
  explore the question of the species as a unit of
  selection.
• To explore them, we need to take a detour into
  paleontology.

35
Micro- vs. Macroevolution

• Microevolution Natural Selection - differential
  survival due to inherited traits (individual
  selection)
• Macroevolution differential survival of branches
  within phylogenetic lineages

36
Micro- vs. Macroevolution
Sauropod evolution

• The overall pattern of vertebrate tetrapod
  evolution (macroevolution) can be examined in
  closer detail.
• The cross section in time reveals the multiple
  species lineages of which it is composed.

37
Micro- vs. Macroevolution

• At the bottom, one lineage, one species, is
  enlarged, showing the populations comprising the
  species (microevolution).
• The key question is IF there is any difference in
  the mechanisms for macroevolution versus
  microevolution?

38
Gaps in the Fossil Record

• Darwin and his contemporaries recognized that
  there were major gaps in the fossil record which
  they attributed primarily to the incompleteness
  of the study of the strata and the difficulties
  of fossil preservation.
• A century later, after massive explorations, many
  major gaps still remained.
• Old species and higher taxa disappeared and new
  species and higher taxa suddenly appeared in
  their place in later strata.

39
Gaps in the Fossil Record

• The real pattern of evolution depends on the
  completeness of the fossil record.

40
George Gaylord Simpson (1902-1984)

• American vertebrate paleontologist and major
  contributor to the Modern Synthesis of evolution
• Simpsons interests also included biogeography,
  the theory of systematics, and horses and
  penguins
• Tempo and Mode in Evolution (1944) and The Major
  Features of Evolution (1953) addressed mechanisms
  and rates of evolution

I don't think that evolution is supremely
important because it is my specialty it is my
specialty because I think it is supremely
important.
41
Quantum Evolution

• At the beginning of the Modern Synthesis,
  Darwinian gradualism was disputed by various
  Saltational hypotheses, mutation theory,
  Lamarckian views, Goldschmidts hopeful monsters,
  etc.
• Simpson sought to explain the discontinuities in
  the fossil record by advocating that Darwinian
  natural selection, though gradual in
  microevolutionary terms, could still show
  different rates of change in larger, geological
  time frames.
• He termed this Quantum Evolution.

42
Quantum Evolution

• Within the taeniodonts, a group of extinct
  placental mammals, two lineages evolved.
• One was the original group of taeniodonts, the
  beaver-sized conoryctines that survived into the
  late Paleocene

conoryctines
43
Quantum Evolution

• The other taeniodont lineage was the
  stylinodonts, which evolved rapidly (quantum
  evolution) across a transition to a new adaptive
  zone (lifestyle).
• Compared to the conoryctines, the bear-sized
  stylinodonts evolved specialized dentition
  especially suited to rough and highly abrasive
  foods, well-developed claws, and strong muscles
  suggesting a digging foraging style. (After
  Simpson 1953.)

quantum evolution
stylinodonts
44
Micro- vs. Macroevolution

• The 1950s and the 1960s were a quiet time for
  organismal biologists and paleontologists.
• They continued to work, but the attention and
  acclaim went to the rapidly developing fields of
  genetics and molecular biology.
• A new hypothesis to explain differences in the
  mechanisms for macroevolution versus
  microevolution arose in the 1970s.

45
Niles Eldredge (1943 - )

• An American invertebrate paleontologist and
  expert on trilobites.
• Eldredges interests also include the history of
  biology, criticism of creationism and Intelligent
  Design, and protection of biodiversity.
• He is a critic of the concepts of the gene as a
  unit of selection and of sociobiology.
• He is co-author of the model of Punctuated
  Equilibria.

46
Stephen Jay Gould (1941 2002)

• An American evolutionary biologist, invertebrate
  paleontologist and expert on land snails.
• Gouldss interests also included the history of
  biology, developmental biology, and resolving
  conflict between science and religion while
  opposing creationism.
• He was a critic of the concepts of the gene as a
  unit of selection and of sociobiology.
• He was co-author of the model of Punctuated
  Equilibria.

47
Punctuated Equilibria

• Prior to the 1970s, most paleontologists, unlike
  G.G. Simpson, rarely interacted with organismal
  and field biologists.
• Willi Hennig, father of cladistics, had been an
  entomologist and Dipteran (fly) systematist.
• Eldredge and Gould championed interaction and
  cooperation among paleontologists and
  neontologists.
• They helped integrate cladistic methodology into
  paleontology.

48
Punctuated Equilibria

• Eldredge and Gould championed interaction and
  cooperation among paleontologists and
  neontologists.
• They helped integrate cladistic methodology into
  paleontology.
• Eldredge and Gould coined the term punctuated
  equilibrium in 1972 to describe a pattern to
  evolution which they contrasted to phyletic
  gradualism.

49
Punctuated Equilibria

• Punctuated equilibrium is a model of
  macroevolution which states that most species
  experience little change for most of their
  geological history, and that when phenotypic
  evolution does occur, it is localized in rare,
  rapid events of branching speciation (called
  cladogenesis).
• Punctuated equilibrium is commonly contrasted
  against the model of phyletic gradualism, which
  states that evolution generally occurs uniformly
  and by the steady and gradual transformation of
  whole lineages (called anagenesis). In this view,
  evolution is seen as generally smooth and
  continuous.

50
Patterns of Macroevolution

• Phyletic evolution (anagenesis) envisions gradual
  divergence of a lineage as the bell-shaped mean
  of successive populations changes, until a new
  species is formed.

51
Patterns of Macroevolution

• Punctuated equilibrium (cladogenesis) envisions
  long periods of more or less unchanging species
  persistence, suddenly interrupted by speciation,
  producing a new species.

52
Punctuated Equilibria

• Eldredge and Goulds Punctuated equilibrium model
  of macroevolution was grounded in Ernst Mayr's
  theory of geographic speciation (allopatric and
  especially parapatric models), I. Michael
  Lerner's theories of developmental and genetic
  homeostasis, as well as their own empirical
  research on the fossil record.

53
I. Michael Lerner (1910-1977)

• Lerner, a Russian immigrant to America, became an
  important population geneticist, working with
  domesticated animals and later the flour beetle.
• His two most influential books were Genetic
  Homeostasis, (1954) and Genetic Basis of
  Selection (1958)
• Lerner defined Genetic Homeostasis as the
  tendency of a Mendelian population as a whole to
  retain its genetic composition arrived at by
  previous evolutionary history

• The major mechanism for maintaining this genetic
  composition, through sexual reproduction, is the
  selection of heterozygotes. This is especially
  important in the genetic control of behaviors.
• Increased heterozygosity in a population
  preserves allelic diversity and permits large
  numbers of individuals to display optimum
  characteristics.

54
Punctuated Equilibria

• Eldredge and Gould proposed that the degree of
  gradualism they attribute to Charles Darwins
  view was virtually nonexistent in the fossil
  record, and that stasis dominates the history of
  most fossil species.
• To be fair to Darwin, knowledge of paleontology
  has grown enormously between Darwins death and
  Eldredge and Goulds proposal some ninety years
  later.

55
Punctuationist versus Gradualist Theories of the
Origin of Species

• Biologically "instantaneous" origin of a new
  species through founder effect speciation may
  occur in only a few generations.
• Geologically "instantaneous" speciation by
  allopatric divergence may occur over many
  thousands of generations.
• An incomplete fossil record will obscure the
  difference between the two.

56
Cladogenesis, Details

• Where sudden changes occur, they can be
  represented with an angular, branching
  phylogenetic tree.
• Each independent lineage produced is a clade,
  shown here as Clade 1 and Clade 2.
• Vertical sections represent more or less
  unchanging persistence of a species branch
  points represent the time of speciation where
  populations diverge and become two distinct
  species.

• Time runs upward species divergence is
  indicated along the horizontal scale.
• The balloons show details of the phylogeny in a
  species before speciation (light shading), at a
  branching point of speciation wherein two species
  form (light and dark shading), and the subsequent
  fate of each species thereafter.

57
Peripheral Isolates

• The geographic range of a species may include
  major populations fragmented into several
  smaller, isolated populations.
• These isolated populations can be peripheral to
  the main populations, or they may occur within a
  main population that has contracted around it.

58
Patterns of Fossils and Phylogeny

• The balloons indicate temporal and geographic
  distribution of species A-H.
• Gaps between species, as they might appear in the
  fossil record, are indicated by short vertical
  brackets at the left.
• Location 1 indicates a fossil excavation site
  that preserves only part of the actual history of
  this evolving group.

gaps in the fossil record
Note also that our picture of the record would be
different if we had sampled different fossil
locations.

• The pattern of evolution expressed as a
  phylogenetic tree.
• Note that most new species originate in a
  peripheral, isolated part of the distribution
  (e.g., species B) or from a central, isolated
  population (e.g., species E).

59
Patterns of Macroevolution
One problem for interpreting the fossil record is
that scientists sometimes do not discover enough
fossil individuals to make a judgment about the
variations in phenotypes, much less genotypes, in
the populations.
unknown when I was in college ?

• As more transitional fossils are added to a
  sequence, the morphological discontinuities are
  likely to become smaller and smaller.

60
Patterns of Macroevolution

• Recall the patterns of selection stabilizing,
  directional, and disruptive.
• If the environment is stable, stabilizing
  selection should produce phenotypic stasis over
  time.
• Only when the environment changes, should
  directional or disruptive selection take over to
  transform phenotypes to adapt to the changes.
• So the punctuated pattern is really not such as
  new concept as Eldredge and Gould suggested it
  was it was a new term for the pattern seen in
  the fossil record.

61
Horse Phylogeny

• Environmental Transitions
• forests to prairies (wetter to drier)
• slower to faster predators

62
Lake Turkana Snail Phylogeny

• We can infer that the changes in lake levels not
  only effect which times that fossilization are
  likely to occur, but also that such changes in
  the environment produce the selective pressures
  that led to speciation or extinction of different
  snail lineages.

63
A Comparison of Models
Raw data
64
Pace of Macroevolution

• For some biologists, each pattern implies a
  different rate of new species appearance.
• Punctuated equilibrium produces new species
  relatively rapidly.

• Phyletic evolution produces new species more
  gradually and is sometimes termed Gradualism.

65
Stephen M. Stanley (1941- )

• An American paleontologist and evolutionary
  biologist
• Stanley was an early supporter of punctuated
  equilibria and advocated for a mechanism of
  selection associated with it species selection.
• Macroevolution Pattern and Process (1998)

66
Species Selection

• Stanley, Gould, and others, often other
  paleontologists, have advocated for the species
  as a distinct unit of selection.
• Like the individual, the species is seen as a
  real biological entity with a birth (a speciation
  event) and a death (extinction or transformation
  into a new species or clade over time).

67
Species Selection

• Our text takes the majority position, which is
  that there are few documented cases of species
  selection and no mechanism for selection that is
  operating at the species level as distinct from
  the level of the individual.
• The minority position is that some lineages are
  more likely to speciate, and, therefore, less
  likely to have all members of their clade go
  extinct.
• Some of these species may be more likely to
  produce adaptive radiations.
• It becomes a matter of semantics if this is a
  separate form of selection, or just an aspect of
  ordinary natural selection acting on individuals.
• It is a part of the part of evolution.

68
High Speciation Potential Taxa?
Hawaiian Honeycreepers

• Do small omnivorous birds have more potential to
  speciate than small omnivorous species?
• We do observe more adaptive radiations among such
  birds, as opposed to lizards, on islands around
  the world.

69
Mode and Tempo of Evolution

• There are examples of both gradual and rapid
  appearance of new species occurs in the fossil
  record.
• Evolution is not limited to gradualism nor to
  punctuationism!

70
Peripheral Isolates

• Recall the four modes of geographic speciation.
• The rate of evolutionary change in each mode will
  be influenced by the size of the population
  experiencing the new selective pressures.
• We expect small populations to respond more
  rapidly to natural selection.
• There are two main reasons inbreeding and
  genetic drift.

71
Sewell Wright (1889-1988)

• Sewell Wright, American geneticist, one of the
  founders of modern theoretical population
  genetics and the Modern Synthesis.
• He researched the effects of inbreeding and
  crossbreeding with guinea pigs, and later on the
  effects of gene action on inherited
  characteristics.
• He adopted statistical techniques to develop
  evolutionary theory.
• Wright is best known for his concept of genetic
  drift, called the Sewell Wright effect
• that when small populations of a species are
  isolated, out of pure chance the few  individuals
  who carry certain relatively rare genes may fail
  to transmit them.
• The genes may  therefore disappear and their loss
  may lead to the emergence of new species,
  although natural selection has played no part in
  the process.

72
Genetic Drift
73
Genetic Drift

• In a small habitat, an island or habitat island,
  resources may be very limited.
• If so, chance may be more important than fitness
  in determining who survives to leave offspring to
  the next generation.

74
Empirical Researchon the Founder Effect

• The Founder Effect is the effect on the resulting
  gene pool that occurs when a new isolated
  population is founded by a small number of
  individuals possessing limited genetic variation
  relative to the larger population from which they
  have migrated.
• It is the direct result of sampling error.

75
The Founder Effect in an Island-Hopping Bird

• Silvereyes, Zosterops lateralis, are small
  insectivorous songbirds.
• They are native to Australia and Tasmania.
• Naturalists have documented 5 new colonizations
  of offshore islands.

76
The Founder Effect in an Island-Hopping Bird
5
4
1
3
2
77
The Founder Effect in an Island-Hopping Bird

• Allele diversity declines as you follow the
  successive colonizations through time just as
  predicted if each colonization is due to a small
  flock of founders.
• The most recently colonized island population
  shows half the diversity of the mainland source
  population.

Similar founder effects have been documented
for Large Ground Finches on Isla Daphne in the
Galápagos Islands, and many other island bird
species.
78
Drift After a Bottleneck

• Even a large population may suffer a population
  crash after some catastrophe, such as a flood,
  fire, drought, volcanic eruption.
• The survivors will experience the same random
  events which may dramatically alter the gene pool
  of the survivors.

79
Genetic Drift Bottleneck Effect, in Theory

• In a large collection of individuals, here the
  blue and yellow marbles, approximately equal
  numbers of both are present.
• However, when just a few persist to start the
  next generation, chance alone may yield mostly
  blue.
• Because most are blue, the next generation, even
  if large numbers are produced, are now mostly
  blue.

80
Genetic Drift Bottleneck Effect, in Practice

• The original population of cheetahs contained
  many alleles of a particular gene.
• Habitat loss and excessive predatory control
  brought their numbers down, by chance leaving
  only a few to breed with much less genetic
  diversity (inbreeding).
• Even as their numbers were partially restored,
  the limited genetic diversity in the reduced
  cheetah population did not also bring recovery of
  the lost genetic diversity.
• Without such diversity, cheetahs have been
  susceptible to breeding deficiencies such as
  decreased resistance to disease and reduced
  offspring survival.

81
Inbreeding

• Inbreeding is sexual reproduction between close
  relatives, whether plant or animal.
• If practiced repeatedly, it leads to increased
  homozygosity in the population.
• A higher frequency of recessive, deleterious
  traits in homozygous form in a population can,
  over time, result in inbreeding depression.
• Inbreeding depression may occur when inbred
  individuals exhibit reduced health and fitness
  and lower levels of fertility.

82
Inbreeding Depression

• In Sweden, a change in allocation of farm lands
  isolated a population of 40 Swedish adders,
  Vipera berus.
• Subsequent inbreeding depression produced more
  stillborn and deformed offspring than normal.
• Introduction of adders from another habitat
  restored diversity in the gene pool and improved
  offspring survivability.

83
Inbreeding in Humans

• There are many examples of the effects of
  inbreeding in humans.
• A classic case relates to the discovery of the
  specific gene, an autosomal dominant, which
  causes the neurological disorder, Huntingdons
  chorea.
• Because the people of the isolated Venezuelan
  fishing villages of Barranquitas and Lagunetas
  were inbred, many individuals were available for
  DNA analysis.
• Having isolated the gene, medical scientists now
  have the first molecular diagnostic test for a
  human inborn error of metabolism.

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Inbreeding

• Inbreeding does not have to lead to negative
  consequences.
• A small population which carries an adaptive
  allele better suiting it to a marginal habitat
  may increase the speed at which the favored
  genotype spreads n the population as a result of
  inbreeding between the successful phenotypes.

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Lizards-From Limbed to Limbless

• Cross sections through the posterior end of the
  lizard embryo are depicted.
• Legged lizard. The somite, an embryonic
  population of formative cells, grows downward to
  meet mesenchymal cells, which together stimulate
  the sprouting of the limb bud capped by an apical
  epidermal ridge.
• Legless lizard. The somites fail to grow
  downward, thereby failing to initiate the limb
  bud, which regresses, producing an embryo that is
  limbless.

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Hox Genes and Rapid Evolution-Lizards to Snakes

• Hox genes associated with the chest region in
  lizards (a), expand their influence, leading to
  loss of forelimbs (b). By other changes in
  embryology, more vertebrae are added to the
  vertebral column, producing an elongated body
  (c).

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Hox Genes and Rapid Evolution-Lizards to Snakes

• Either by a shift in influence of other Hox genes
  and/or by changes in limb bud growth (for
  example, see figure 12.12), hindlimbs are lost
  and an essentially modern snake body is produced
  (d).
• These steps may have occurred in a different
  order.
• Certainly, other changes accompanied these three
  basic steps to consolidate and integrate them.
• But apparently the major steps from lizard to
  snake are built upon only a few gene or embryonic
  modifications.
• Different Hox genes (Hox) are indicated at
  locations wherein mutations in them are
  hypothesized to produce a change in body design.

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Preadaptations

• The sudden loss of legs might be of great
  disadvantage to most tetrapods, but in the case
  of legless lizards it may actually have
  stream-lined their bodies for moving through a
  confining substrate.
• If so, that is an example of a preadaptation.

89
Preadaptations

• A preadaptation exists whenever an organism has
  and uses a preexisting molecule, biochemical
  pathway, anatomical structure, physiological
  process, or behavior inherited from an ancestor
  for a new and unrelated purpose.
• Thus, a preadaptation is a characteristic already
  present which can be modified and improved by
  natural selection once it begins to be used for
  the new purpose.

90
Preadaptations

• There are many excellent examples of
  preadaptations in the living world
• sweat glands ? mammary glands
• feathers for insulation ? for flight
• lobe fins for bottom-walking ? for terrestrial
  walking
• ancestral penguin wings for flight ? penguin
  wings for swimming
• marine vertebrate gill arches ? fish jaws
• quadrate/angular jaw joint ? malleus/anvil ear
  ossicles
• hemoglobin ? myoglobin
• Preadaptations should be considered the raw
  materials for natural selection to use in the
  same way that new mutations are the raw materials
  for natural selection

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Social SystemsThe Evolution of Cooperation

• Advantages of sociality
• Reduced predation by improved detection or
  repulsion
• Improved foraging efficiency
• Improved territoriality against other groups of
  conspecifics
• Improved care of offspring
• Disadvantages of sociality
• Increased competition within group for food,
  mates, nesting, etc.
• Increased risk of infection
• Increased exploitation of parental care by
  conspecifics
• Increased risk that conspecifics will kill ones
  progeny

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Life in Groups Sociobiology

• The term sociobiology was introduced in E. O.
  Wilson's Sociobiology The New Synthesis (1975)
  as the application of evolutionary theory to
  social behavior.
• Sociobiologists claim that many social behaviors
  have been shaped by natural selection for
  reproductive success, and they attempt to
  reconstruct the evolutionary histories of
  particular behaviors or behavioral strategies.

93
Sociobiology

• Wilson's describes four pinnacles of social
  evolution
• Marine invertebrate colonies
• Insect societies
• Vertebrate social systems
• Human sociality
• Like group selection, punctuated equilibria, and
  species selection, sociobiology has generated
  much excellent science and many fierce
  controversies.

94
Sociobiology

• Wilson addresses altruism in discussing
  sociobiology.
• He recognizes the mathematical underpinning of
  inclusive fitness, but he also hypothesizes that
  certain environments may also be conducive to the
  development of altruistic behaviors among
  animals.

95
Sociobiology

• There is some evidence that a variety of animals,
  both invertebrates and vertebrates can recognize
  other individuals in their groups and behave as
  if they were changing their behavior in ways
  which parallel the degree of relatedness between
  the two.
• There are also a few example of altruistic
  behaviors that cannot be explained by kin
  selection.

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Reciprocal Altruism Vampire Bats

• Vampire bats live in communal roosts.
• Within the roosts, the bats live in matrilineal
  groups.
• Vampire bats are able to distinguish other
  vampire bats as individuals.

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Reciprocal Altruism Vampire Bats

• Vampire bats must have a blood meal at least
  every 60 hours or they will starve.
• Female bats carry some blood back to the roost in
  their stomachs.
• 70 of the time, that extra blood is distributed
  to her offspring ? ordinary parental care.
• The remaining 30 of the time, she may be coaxed
  to regurgitate concentrated blood to another
  roostmate.

98
Reciprocal Altruism Vampire Bats

• Vampire bats are about as likely to receive as to
  give a blood meal, especially in interactions
  between individuals who share the same roost.
• While some of the receiving bats are close
  relatives, based on genetic studies, all are not.
• It seems that vampire bats have learned that a
  good deed will be repaid on average.

99
Reciprocal Altruism Vampire Bats

• Vampire bats use a special grooming behavior to
  elicit the donation of the blood meal.
• Behaviors are subject to natural selection, but
  finding the underlying genetic controls beneath
  the environmental influences is challenging.

100
Reciprocal Altruism

• In addition to Vampire bats, reciprocal altruism
  has been demonstrated in
• Humans
• Chimps
• Hyena
• Wild dogs
• Impalas
• Dwarf mongeese
• Naked mole rats (have a queen and temporarily
  sterile workers due to suppressive behaviors and
  pheromones from the queen).

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End Chapter 12