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Title: 1st: Introduction to Evolution and Behavioural Ecology
Description: 1st year Introduction to Evolution and Behavioural Ecology notes, University of Exeter
Description: 1st year Introduction to Evolution and Behavioural Ecology notes, University of Exeter
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1: HISTORY OF EVOLUTION
2
2: EVIDENCE FOR EVOLUTION
4
3: MECHANISMS FOR EVOLUTION
6
4: MAINTAINING VARIATION
9
5: FITNESS AND ADAPTATION
11
6: SEXUAL SELECTION
13
7: POST-COPULATORY SEXUAL SELECTION
16
8: INTRODUCTION TO BEHAVIOURAL ECOLOGY
19
9: SOCIAL BEHAVIOUR
21
10: REVISION
24
11: PARENTAL CARE
24
12: SPECIES
26
13: SPECIATION
29
14: COEVOLUTION
33
15: SIGNALLING AND DECEPTION
35
16: LIFE HISTORY STRATEGIES 1
38
17: LIFE HISTORY STRATEGIES 2
41
18: HUMAN EVOLUTION
43
19: HIV EVOLUTION
46
20: BATS AND INSECTS - WHERE EVOLUTION MEETS ECOLOGY
48
Joanna Griffith (2017)
1: HISTORY OF EVOLUTION
In the beginning
● Original understanding of the creation of animal forms came from the Bible
○ Idea that animal forms have not changed over time and that there have not
been any extinctions
○ Date of creation determined by James Usher to be 4004 BC, on the night of
the 22nd of October
○ Species form remains constant over time
Ideas of evolution before Darwin
● Lamarck (1744-1829)
○ Believed that species form did change over time, but did not believe in
branching from a common ancestor or extinction
○ Believed that species change through an “internal force” (eg
...
amphibians are “better” than fish, birds are “better” than amphibians,
mammals are ”better” than birds, and humans are “the best”)
■ Evolution is NOT progressive
○ Objections to Darwin’s theory
■ Due to the lack of a theory of heredity at the time, evolution was hard
to understand
● Assumption that heredity was by “blending”
○ Eg
...
Aa), genotypes do not blend
Fischer
○
Joanna Griffith (2017)
●
●
1918
Demonstrated that continuous variation in real populations could be derived from
Mendelian principles
● Fischer, Haldane and Wright independently showed that natural selection could
operate with Mendelian genetics
○ Led to neo-Darwinism, the synthetic theory of evolution, and modern
synthesis
● Modern synthesis
○ Gradual evolution results from small genetic changes that are acted upon by
natural selection
○ The origin of species and higher taxa (macroevolution) can be explained by
selection acting on individuals (microevolution)
○ Mayr, Dobzhansky, Simpson, Ford, and Huxley expanded on earlier work and
incorporated speciation, systematics, development, morphology, and
paleontology into the synthesis
Evolution
● Evolution occurs because:
○ Species have enormous reproductive potential, but resources are limited
○ Populations are relatively stable, which suggests that not all individuals
survive or reproduce
○ Variation is heritable (and favourable variation enables better
survival/reproduction)
Neo-Darwinian postulates
● There is variation within populations
○ Some of this variation is heritable
■ Variation makes some individuals better at surviving and reproducing
● These individuals pass on their genes
--------------------------------------------------------------------------------------------------------------------------2: EVIDENCE FOR EVOLUTION
●
●
Three possible theories for the history of life:
○ Evolution (Darwin, Wallace)
■ Common origin
■ Change in form through time
○ Transformationism (Lamarck)
■ Separate origin
■ Change in form through time
○ Separate creation (the Bible)
■ Separate origin
■ No change in form through time
Evolution:
○ Changes in the genetic composition of a population with the passage of each
generation
○ Change in allelic frequency in populations over time (alleles are different
versions of the same gene)
Joanna Griffith (2017)
Microevolution (small changes) eventually leads to macroevolution (large
changes)
Small scale patterns
● Artificial selection
○ Only certain individuals are allowed to breed in each generation
■ Removes individuals from the breeding population
■ Eg
...
Darwin’s pigeons
■ Darwin noted that collector’s pigeons were all the same species,
breeders had simply selected for diverse traits
○ Eg
...
dog breeds
● Experimental evolution
○ Eg
...
Dobler and Hosken (2010)
■ Increasing sperm length in dung flies
● Selection in the wild
○ Eg
...
link between birth weight and neonatal mortality
Large-scale patterns
● Living species
○ Vestigial organs: a useless or rudimentary version of a body part that has an
important function in other species
■ Eg
...
salamander ensatina, California
○ Adaptive radiation: a small number of ancestral species diversifies into a large
number of descendant species
○
Joanna Griffith (2017)
■
Eg
...
the Irish elk is over 3m tall, we can’t have missed it
if it was alive
○ Succession
■ The law of succession: fossil and living organisms in the same
geographic region are related to each other and are significantly
different from organisms found in other areas
● Eg
...
the evolution of the horse
● Common ancestry
○ Phylogeny
■ The organisation of modern species into groups on the basis of
common features
■ Creates inclusive circles of resemblance which can be hierarchically
arranged
■ Darwin: similar species have a common ancestor
● Homology
○ Structure
■ Many animals have limbs with different functions, but with the same
sequence and arrangement of bones
○ Development
■ Most animals are triploblasts
■ Embryos of different species tend to be very similar
○ Molecular
■ The genetic code is universal
● Nucleotide sequences for specific amino acids are the same in
almost every organism
● Mammal genes can still work when transplanted into bacteria
--------------------------------------------------------------------------------------------------------------------------●
3: MECHANISMS FOR EVOLUTION
Evolution: changes in gene frequencies over time as a result of descent with
modification
Mutation
-
Joanna Griffith (2017)
A heritable change in the nucleotide sequence of a genetic nucleic acid, sometimes
resulting in an alteration in the products coded for by the gene
● Point mutation: a base is swapped for a different base
● Deletion: a base is deleted and is not replaced
● Insertion: a base is inserted
● Inversion: two bases or two groups of bases are swapped around
● Most mutations are either harmful or neutral (only 2% of the mammalian genome
codes for proteins so mutations often have no effect), beneficial changes are rare as
it is unlikely that a mutation will result in a positive change
● Mutation rates are low (about 10-9 per base pair per generation), but the haploid
human genome is 3x109 base pairs long, so each new human zygote can have 6
new mutations
○ Adds up to a lot of mutation in a population
Gene flow
● Introduction or loss of new alleles into the population through immigration or
emigration
Genetic drift
● Variation in the relative frequency of different genotypes in a small population, due to
the chance disappearance of particular genes as individuals die or do not reproduce
○ Stochastic (random) shifts in allele frequencies in small populations
Selection
● Darwin’s postulates:
○ There is variation within populations
■ Some of this variation is heritable
● Individuals vary in their ability to survive and reproduce
○ Survival and reproduction are non-random
● Evolution via selection requires:
○ Variation within a population
○ Fitness differences associated with the variation
○ Heritability
● Variation
○ Identical individuals in a population lead to identical offspring
■ Evolution would be impossible, variation is essential
○ Variation is present at multiple levels
■ Morphological
● Structural features
● Can be continuous or discrete
● Eg
...
number and structure of chromosomes
■ Biochemical
● Eg
...
peppered moth morphs (affects survival)
○ Eg
...
3
■ Twinning = 0
...
8-0
...
6-0
...
blackbirds choose the most common snail phenotype, reducing
numbers of that phenotype
● Resource use
○ Eg
...
in the asymmetrical-mouthed scale-eating cichlid, more common
left-mouthed cichlids feed on the right side of a host fish, so the host learns to
avoid cichlids on the right, giving rarer right-mouthed cichlids an advantage
●
Joanna Griffith (2017)
●
Behaviour
○ Eg
...
01, q is 0
...
01:1
...
maize
○ Heterozygous individuals tend to be larger
● Eg
...
sickle-cell anemia
○ Homozygotes (either not at all affected or affected) either die of malaria or of
sickle-cell anemia
■ Heterozygotes are better able to survive malaria as their cells only
sickle when infected, killing the malaria parasite (maximal fitness)
● However, heterosis cannot occur in haploid organisms as they only have one allele
per locus
○ Haploid organisms (eg
...
white cats
○ 40% are deaf as the gene that produces lack of melanin also affects hearing
● Antagonistic pleiotropy hypothesis:
○ Alleles that enhance early life reproduction may be selected for even if they
lead to shorter lifespans
■ Possible hypothesis for ageing
● Genes are selected for several times in several different contexts
○ There is no net attraction, so variation is maintained
Environmental heterogeneity
● Fitness of a genotype or phenotype is related to environmental conditions
○ Phenotype = genotype x environment
○ The environment results in variation
Joanna Griffith (2017)
Eg
...
water deer having tusks, trees losing their leaves, the shape of bee
orchids, different eye colour in humans, leafcutter ant behaviour
The process of adaptation
○ Eg
...
the tusks of water deer
Adaptations
○ Complex (yet have evolved as tiny changes over time)
○ Designed for a purpose (but are they?)
Complex adaptations
○ Eg
...
the eye
■ Multiple adaptations, very complex
Gradual evolution
○ Lots of small steps over time
■ Every single step has to be advantageous
○ “Gradualist requirement”, Darwin
■ Each small change MUST improve fitness, otherwise the theory of
evolution breaks down
○ Occurs through mutation and then selection if the mutation increases fitness
○ Fisher's microscope analogy
Joanna Griffith (2017)
■
■
■
■
■
■
Could evolution occur through a few very large steps?
● Argued that small steps are more common as most living
things are already fairly well-adapted, otherwise they would be
dead
Most individuals are near the current state (optimal position)
● A small, random mutation may have a 50% chance of
increasing or decreasing character state, and therefore a 50%
chance of increasing or decreasing fitness
● A large, random mutation still has a 50% chance of increasing
or decreasing character state, but may result in overshooting
the optima, making fitness worse either way
Can be more complex than a single optima
● In this case, large mutations have a 50% chance of getting an
organism closer to the global optima
● Small changes would keep an organism around a local optima
The optima may change due to changes in the environment
We are assuming that all organisms are close to the fitness peak
● Small mutations are still more likely to improve fitness, but
large mutations can also move fitness closer to the peak
The contribution of a mutation to evolution depends on:
● Chance that the mutation occurs x chance that the mutation is
advantageous x selective advantage of the mutation
Lack of perfection
● Selection is occurring all the time, so why do we not have “perfect” organisms?
● Time lags
○ Eg
...
gomphotheres) that could eat
them and disperse their seeds, but they are now extinct
○ There has been a time lag in evolution, leaving them
less well adapted (a change in the environment has led
to a change in the optima)
● Genetic constraints
○ Heterosis (heterozygote advantage)
○ Eg
...
recurrent laryngeal nerve in fish and mammals
Joanna Griffith (2017)
■
■
●
In fish, the vagus nerve goes around the dorsal and ventral aorta to
reach the gills, via direct branches
In mammals, due to stepwise evolution, the vagus nerve has to travel
from the brain to the larynx via the dorsal aorta (near the heart)
● Travels further than it needs to, not efficient
Trade-offs
- Eg
...
peacock tails
○ Go against Darwin’s theory of natural selection as they are actually
detrimental to fitness
■ Less maneuverable
■ Visible to predators
○ If the tail of a peacock is beneficial to survival, why don’t peahens have them?
Darwin’s postulates
○ There is variation within populations
■ Some of this variation is heritable
● Individuals vary in their ability to survive and reproduce
○ Survival and reproduction are non-random
Joanna Griffith (2017)
Darwin produced the idea of sexual selection in order to accommodate fasts
that did not fit his theory of natural selection
● Mate choice (female choice)
○ Being more noticed by, more attractive to, or more persuasive towards the
opposite sex, and so gaining a mating advantage
● Mate competition (male competition)
○ Out-competing other members of the same sex in contests whose outcome
determines mating success
Identifying sexually selected traits
● Age
○ Juvenile vs
...
juvenile mandrills don’t have colourful faces, but adults do
● Sex
○ Male vs
...
male mallards are colourful, females are not
○ Eg
...
all year round
■ If a trait is only found in the breeding season, it is likely sexually
selected for
○ Eg
...
superb birds of paradise only fan their wings when in front of a female
Bateman’s principle
● We typically see choosy females and displaying males
● Reproductive success
○ In males, reproductive success is dependent on access to females (=
competitive)
○ In females, reproductive success is dependent on available resources for egg
production and the rearing of young (= choosy)
● Females tend to have greater potential investment than males
○ Females therefore have longer reproductive time-outs than males
○ Leads to a male-biased operational sex ratio (the ratio of reproductively active
males and females) and thus greater competition between males for females
■ Females are relatively rare
■ The law of supply and demand
● Sperm are plentiful, eggs are rare
● Variation in reproductive success
○ Can be huge in males
■ Large potential to father offspring
○
Joanna Griffith (2017)
■ Eg
...
tusks, body size, sharp teeth
● Female choice
○ Adaptations
■ Eg
...
male bush crickets provide females with a nutritious
spermatophore
○ The larger the spermatophore, the more eggs the
female can lay
■ Parental ability
● Will a male help to care for the offspring, giving them a greater
chance of survival
■ Territory quality
■ Avoiding disease
○ Indirect benefits of choice
■ Good genes (heritable viability)
● Trait size may indicate male quality/health
■ Fisherian benefits/sexy sons (heritable attractiveness)
● An attractive male will produce attractive sons which will then
go on to be more likely to reproduce
■ Genetic compatibility
● Eg
...
seahorses
Constraints on sexual selection
● Predation
○ Larger traits = more at risk
--------------------------------------------------------------------------------------------------------------------------7: POST-COPULATORY SEXUAL SELECTION
Darwin invented sexual selection to accommodate certain facts that did not fit his
theory of natural selection
● Mechanisms for sexual selection:
○ Male-male competition
○ Female choice
○ Mechanisms can continue after copulation
Sperm competition
● The competition between the ejaculates of two or more males for the fertilisation of a
given set of ova
● Can occur internally or externally
● Why is sperm competition important?
○ Determines gene flow
■ Superior males fertilise more eggs, and thus their genes are more
present in the next generation
○ Allows the evolution of two sexes
■ Sperm competition creates a need for smaller, faster, more abundant
gametes to reach a nutrient-rich gamete
○ Affects the strength of sexual selection
○ Allows post-copulatory female choice
● Why do males produce so much sperm?
○ Lottery principle
■ The more sperm, the greater the probability of fertilising an egg
● Thus it makes sense to produce lots of small (reducing
energetic cost) sperm
○ Exception to this rule:
■ Drosophila bifurca have sperm that are 5
...
in butterflies, testes size increases with sperm competition
risk (Gage, 1994)
● Eg
...
salmon
○ Two male phenotypes
■ Guarders aggressively guard females
● At less risk of sperm competition, so
invest energy into fewer, stronger sperm
■ Sneakers mate with females when guarders are
not looking
● Risk of sperm competition is much
higher, so they produce lots of small
sperm
● Experimental evidence shows that polyandry selects on testes
size
Sperm competition selects for:
○ Increases testes size
○ Strategic ejaculation
■ Eg
...
in humans, ejaculate size increases with time spent away from
partner, independently of ejaculation frequency
○ Mate guarding
○ Mating plugs
■ Eg
...
the aedeagus, found in many insects, is used as a
rival-sperm-removing device
● Effective, eg
...
in Callosobruchus beetles, the male’s spiny penis can damage the
female’s genital tract, causing early death
■ More damaging males are better sperm competitors
● Anchor male, help to position penis, may be used to scrape out
the sperm of rival males
○ Females are the arena in which sperm competition occurs
■ Leads to the evolution of complex structures
● Factors influencing fertilisation success during sperm competition
○ Sperm number (ejaculate size/frequency)
○ Ejaculate quality (percentage alive, speed, size, motility, etc
...
in chickens, females eject more sperm from subordinate males
● Dominance is inherited, so dominant fathers = dominant chicks
● Most copulations are coerced, but females can choose to eject
the sperm
○ Selective sperm transportation/storage
○ Selective sperm use
■ Eg
...
young geese form an image of their “parent” just after hatching, even if
the first thing they see is a human
Von Frisch (1886-1982)
● Pioneered studies in bee communication and foraging
○ Demonstrated that honey bees have colour vision
○ Honey bees use the “waggle dance” to communicate the location of resources
to other bees
Tinbergen (1907-1988)
● Formulated a method of studying animal behaviour
○ Strong Darwinian influence, trying to understand the ultimate (evolutionary)
reasons for behaviour
● Four questions:
○ Function (adaptation)
○ Phylogeny (evolution)
○ Causation (mechanism)
○ Development (ontogeny - genetics or environment)
● Proximate
○ The mechanics of behaviour
■ What triggers a behaviour?
■ How, mechanically, does a behaviour take place?
■ How do nerves and muscles generate the behaviour?
■ How do the animal’s genes affect the behaviour?
○ Mechanisms that cause/enable behaviour
■ Physiological
■ Sensory
■ Motor
■ Genetic
■ Developmental
● Ultimate
○ Why is this trait advantageous?
○ Evolutionary reasons and selective processes that have resulted in the
expression of behaviour
■ What is the purpose of the behaviour?
●
Joanna Griffith (2017)
In what way does the behaviour increase an individual’s reproductive
success?
■ Does the behaviour increase an individual’s prospects of survival?
● Beewolf homing
○ How do beewolves find their way home? (a proximate question)
■ Beewolves nest in sandy areas, and bury their nests in sand before
going out hunting
■ Beewolves circle the nest before leaving - are they remembering
landmarks?
○ Tinbergen cleared objects from around the nest when the beewolf left, and
she struggled to locate it
○ Tinbergen set up landmarks around the nest for the beewolf to use, then
moved them once she left, and she searched for the “nest” where the
landmarks were
■ Second experiment is more powerful than the first, because there is a
more specific prediction
● Black-headed gulls
○ Why do black-headed gulls remove eggshells from their nests? (an ultimate
question)
■ Tinbergen hypothesised that broken eggshells draw attention to the
nest and attract predators
● Therefore, removing the eggshells should reduce predation
risk
○ Tinbergen placed broken eggshells at different distances from intact gull
eggs, and found that the closer the eggshells were to the eggs, the more
often the eggs were predated upon
○ Removing eggshells reduces egg loss to predators, and increases
reproductive success
○ How did egg-removing behaviour evolve?
■ Darwin’s postulates
● There is variation within populations
○ Some of this variation is heritable
■ Individuals vary in their ability to survive and
reproduce
● Survival and reproduction are
non-random
■ A genetic mutation made a gull more likely to remove eggshells from
its nest
● This gull had a higher reproductive success than others in the
population, so the gene became more common in the
population and eventually became fixed
○ Process of evolution by natural selection
What is behavioural ecology?
● The study of the survival and reproductive value of behaviour, and its relationship
with ecology and evolution
○ How behaviour influences fitness
■
Joanna Griffith (2017)
Traditional animal behaviour research asked HOW questions and sought proximate
explanations
○ Behavioural ecologists ask WHY questions and seek ultimate explanations
● Testing hypotheses
○ Comparison within species
■ How are confounding variables controlled?
○ Experiments
■ Allow one variable to be changed at a time
■ Field or lab
■ May influence behaviours so that they are no longer natural
○ Comparison between species
■ Gives insight into evolutionary history
■ Limitations:
● Alternative hypotheses
● Cause and effect
○ What is correlation and what is causation?
● Independent data
● Alternative adaptive peaks or non-adaptive differences
○ Different species may have different reasons for
exhibiting a behaviour
● Economics of behaviour
○ For a behaviour to evolve, the benefit of the behaviour must be greater than
the cost of the behaviour
■ Eg
...
group
○ There is no action ‘for the good of the species’
○ Evolution and selection is related to survival of the individual, not survival of
the species
■ Eg
...
bee eaters
○ Adults will hang around the nests of the young of other individuals and feed
their young
■ Number of adults at the nest is correlated with number of young that
survive to fledglings
○ Food is variable, so it can be difficult for a single pair to feed their young,
making helpers crucial
How can altruistic behaviour evolve and persist?
○ DNA analysis shows that individuals demonstrating altruistic behaviour to
each other are related
■ Altruistic behaviour is therefore genetically selfish
Relatedness coefficients: the probability of an allele being shared between two
individuals
○ Parents to offspring
■ Half of the genes of each parent are passed on to the offspring
● Relatedness between parent and child = 0
...
5x0
...
25
■ 50% chance of same genes from father = 0
...
5=0
...
25+0
...
5
Eg
...
worker bees
● Do not reproduce - how is this advantageous and evolve via
selection?
● Females are diploid, males are haploid, so sisters are more
related to their sisters than they would be to their own offspring
(sister - sister = 0
...
5)
○ Helping sisters is good as they will be future queens
● Similar scenario (analogous to) in somatic vs
...
related individuals all have green beards, so they only help
others with green beards
■ However, unlikely hypothesis as there are very few examples in
nature, recognition traits would be difficult to evolve, and the system
would be easy to cheat
○ Direct genetic cues
■ Eg
...
location-based or imprinting
--------------------------------------------------------------------------------------------------------------------------10: REVISION
--------------------------------------------------------------------------------------------------------------------------11: PARENTAL CARE
Methods of parental care:
○ Providing food items
○ Lactation
○ Gestation
○ Grooming
○ Defending from predators
○ Teaching learnt behaviours
● Parental care increases the survival of offspring, thus allowing parents to increase
their own reproductive success
○ Both sexes want to increase reproductive success - however there is often an
imbalance in parental care
■ Mammals: primarily female care, sometimes joint, never just male
■ Fish: primarily male care, sometimes joint or just female
■ Invertebrates: primarily female care, sometimes joint, rarely just male
■ Birds: primarily joint, sometimes just female, rarely just male
■ Reptiles: primarily just female or joint, never just male
■ Amphibians: primarily just female or just male, sometimes joint
○ If reproductive success is limited by, eg
...
bluegill sunfish
● Three types of males, with different roles
○ Parental, build nests and defend territory
○ Sneakers
○ Female impersonators
○ Both sneakers and female impersonators sneak
matings from defended females
● Parental males cannot be sure of their paternity
○ Invest less care into eggs and fry when other males are
nearby
● Gamete release order
●
Joanna Griffith (2017)
Internal fertilisation
■ Enables the male to leave, forcing female care
○ External fertilisation
■ Dawkins and Carlisle, 1976
● Sperm is lighter than eggs, so males have to wait for eggs to
be released before fertilising, allowing the female to swim away
and forcing the male to care
○ However, there is often simultaneous release, and
some males release first
■ Hypothesis rejected
● Association with offspring
○ The sex with the closest association to the offspring is more likely to care
○ Internal fertilisation
■ Female carries young, so she is more closely associated
○ External fertilisation
■ Eggs are often left in the male’s territory, so he is more closely
associated
Conflicts
● Sexual conflict
○ Between the male and female parent
○ Who should care?
■ Constraints (eg
...
food availability)
■ Opportunities for further matings
■ What is the other parent doing?
○ How much care should a parent give?
■ Depends on how much the other parent does
● In joint care scenarios, if a partner is removed, the remaining
partner CAN work harder
○ If there is compensation of care in the absence of one
of the parents, why don’t parents cheat?
■ IF loss of effort by one parent is equal to gain in
effort by the other parent, biparental care is
unstable, so uniparental care is a more stable
strategy
● However the best strategy is for partial
compensation, so biparental care is
stable
● Parent-offspring conflict
○ Parents will allocate enough resources to offspring to ensure survival and
thus maximise their reproductive success, with enough resources for future
offspring, while offspring want to take all available resources to maximise their
reproductive success
○ Within broods, there is no genetic reason for parents to favour one offspring
○ Between broods, parents need to stop caring for one set of offspring in order
to save resources for future batches
○
Joanna Griffith (2017)
Conflict between maximum investment for offspring and parents
■ Benefit to parents is half that of offspring because they have a
relatedness of 0
...
Galapagos fur seals
○ If the first pup is born in good environmental conditions,
it will be weaned quickly, and the pup born after will not
be a rival
○ If the first pup is born in poor environmental conditions,
it will not be weaned before the second pup is born, so
they will come into direct conflict, and the older pup will
kill the younger pup
■ Obligate
● Eg
...
piglets have teeth that they can use to displace other piglets from
teats if the litter is too large
● Teeth change orientation as the piglets age
--------------------------------------------------------------------------------------------------------------------------○
12: SPECIES
●
●
●
What is a species?
○ Many different definitions, utility of these different definitions depends on what
you are studying
○ There are species that can be very difficult to differentiate
■ Expected, if different species share common ancestors, but with
different divergence times
Speciation is a process
○ A species will start with the normal distribution of a trait (character state)
■ Over time, there may be some divergence, but the two separate
optima will have some overlap
● There remains an ambiguous zone where individuals with
different versions of the character state can still be seen as the
same species
■ As the two versions of the character state get further apart, overlap
decreases, and two different species are created
At a practical level, species can often be identified through morphological differences
Joanna Griffith (2017)
○ Clusters of individuals with similar traits tend to be a species
● Defining what a species is is often more of a theoretical issue
○ Huge range of different definitions
Species definitions
● Phenetic or phenotypic species concept
○ Species are groups of organisms that are more similar phenotypically to one
another than they are to other groups
○ Disadvantages:
■ How do we objectively decide if a difference is important?
● Using different measures, we can get different species from
the same group
● Eg
...
melpomene and H
...
sibling species
○ Pipistrelle bats
○ Tree creepers
● Recognition species concept
○ Species are groups that share a common method of mate recognition
■ Eg
...
the common
ancestor of more recently-evolved species)
■ Defines species through time
○ Disadvantages:
■ It can be difficult to identify when the change occurred
● Which species is/was the common ancestor?
■ It is time-consuming and expensive to draw up a complete phylogeny
● Biological species concept
○ Species are groups of interbreeding populations that are reproductively
isolated from other populations
■ Species share a common gene pool
Joanna Griffith (2017)
This definition explains WHY members of a species resemble
each other
■ Important concept, as it merges taxonomy with genetics
■ Most commonly used definition
○ Disadvantages:
■ Ring species
● Eg
...
different host plants)
○ Mating requires different cues (olfactory, acoustic, visual)
○ Mating requires appropriate behaviour
○ Mechanical isolation (genital coupling is not possible)
○ Eg
...
Drosophila females reject the courtship of males from the wrong species
● Postmating, prezygotic reproductive isolation barriers
○ Foreign sperm/pollen die in female
○ Foreign ejaculate fails to induce oviposition
○ Foreign sperm/pollen are not transported within the female
○ Foreign sperm/pollen are inferior competitors
■ Eg
...
mules
■ Haldane’s rule
● In crosses where one sex is inviable or infertile, it is the
heterogametic sex in 19/20 cases (XY, males, for mammals,
and ZW, females, for birds)
○ F1 are behavioural intermediates
○ F1 have behavioural defects
●
Joanna Griffith (2017)
○ F2 or backcross have reduced viability
○ F2 or backcross have reduced fertility
Why are there species?
● Why do we have separate groups as opposed to a continuum?
● Why do organisms form discrete clusters, and why are there discontinuities between
species?
○ Discreteness is inevitable
■ Species represent stable states
● This theory does not seem correct, because it does not explain
why new stable states emerge, does not provide any
mechanism to explain the origin of these states, and species
do not seem to be stable
○ Species can be highly variable
■ Stable states suggests little or no variation
■ Species exist because they fill discrete niches (Wright’s adaptive
landscape/trade-offs)
■ They exist because reproductive isolation is an inevitable part of
population divergence
--------------------------------------------------------------------------------------------------------------------------13: SPECIATION
●
●
●
Normal distribution of one version of a trait diverges into two different variations of
that trait (two different species)
○ Ambiguous zone, where two traits can still be seen as the same species
○ Speciation is a process, happens over time
The key step to speciation is reproductive isolation
○ Two separate gene pools
How many genes are involved in reproductive isolation?
○ Varies:
■ One or very few genes (eg
...
single gene mutation affecting shell chirality in snails
■ Makes mating impossible between two different shell spirals
○ Eg
...
melanogaster and D
...
plants), or other
tetraploid organisms, but no
diploid organisms
■ Can also occur in fish
○ Causes very rapid speciation
■ Physical barriers
● Halts gene flow between two separated populations
● Dispersal (eg
...
river/lava flow separates two populations,
preventing them from coming into contact)
● Eg
...
species of snapping shrimp separated by the isthmus of
Panama (reduced migration)
○ Pacific and Caribbean species are closely linked
■ Allopatric speciation
● Divergence of two populations of the same species due to
geographical isolation
■ Parapatric speciation
● No physical barrier to gene flow, but ecological barriers result
in the separation of two populations of the same species
● Strong environmental gradient
○ Eg
...
mining waste affecting plants
■ One population adapted to living on mining
waste, one did not
■ Sympatric speciation
● No separation of populations
● Much more conscientious
● Eg
...
flies raised on different types of food
● Ecological speciation, disruptive selection
○ Eg
...
apple maggot fly
○ Sympatric speciation
○ Used to feed on hawthorn fruits, one population started
to feed on introduced apple trees
○ 95% of matings occur within host races (apple or
hawthorn)
●
○
Joanna Griffith (2017)
Sexual selection
● Can cause allopatric, parapatric, and sympatric speciation
● Can cause rapid divergence
● Eg
...
sperm acrosomal protein lysin in abalone
● Eg
...
male genitals (fastest-evolving morphological trait)
● Reproductive genes are involved, so divergence can occur
rapidly
● Striking differences in secondary male characteristics between
closely-related species
How is secondary contact prevented?
○ Reinforcement
■ Hybrids are less fit than parents
● Selection favours matings between members of the same
species
■ Eg
...
hooded crows and carrion crows
■ Outcomes:
● Hybrid fitness lower than parental = narrow and short-lived
hybrid zone = reinforcement
● Hybrid fitness equal to parental = wider and longer-lived hybrid
zone = parentals coalesce
● Hybrid fitness higher than parental = hybrid zone depends on
where fitness is greater (eg
...
bustard mate choice
■ Bustards evolve more attractive features, female bustards evolve
greater choosiness in response
Coevolution between species
○ Mutualism (coevolution and coadaptations)
■ Eg
...
the myxoma virus was introduced to Australia in the 1950s to
control the invasive rabbit population
● Initially 100% successful in killing hosts, so population declined
rapidly
● Soon, kill rate declined
○ Increase in host resistance, or decrease in viral
virulence?
■ Infected constant lab rabbits with viruses taken
from the wild in successive years
● Virulence of the virus declined with time
■ Infected wild rabbits with a standardised strain
of the virus
● Hosts were becoming more resistant
over time
○ Competition
■ Different organisms competing with each other to fill different niches
■ Eg
...
sticklebacks
● Nematic and benthic forms of the same species
○ Predation (evolutionary arms race)
Joanna Griffith (2017)
Evolutionary arms races are likely to result in strong directional
selection
● Faster predator = faster prey = faster predator = faster prey
○ No one ever gets “better”
○ Evolutionary escalation, until a trade-off is reached
■ No progress is made
What is needed for coevolution to occur?
● Two or more species must affect each other in some way
○ Geographic overlap
○ Reciprocal effect on traits
● Eg
...
hawkmoth caterpillar (harmless mimic) and green parrot snake
(harmful model)
● Batesian mimicry
○ Model cannot escape its mimic, because by changing,
it loses the protection of its own species
■ Coevolutionary chase is an unlikely outcome
■ Eg
...
plants tend to have many insects eating them, whereas insects tend to
stick to one preferred type of plant
■ If a plant evolves a particular trait, it will have a huge effect on the
insects, but the evolution of a trait in an insect will have little effect on
the plant
Independent effect
● No evolutionary influence, but both species are affected by an independent force
● Eg
...
Honest signalling
● Two individuals have access to different information
○ They could both gain if they honestly share this information
■ However, their interests do not coincide entirely, so each has an
incentive to deceive the other
■ How can honest communication be ensured?
● Signalling is costly
○ Conspicuous to predators
○ Time spent signalling rather than feeding
○ Growth of signalling structures (eg
...
benefits to relatives when an individual meerkat alarm calls
● Signalling as an arms race
○ Sender signals to own advantage, at cost to receiver
■ Selection on receiver
■ Receiver improves at discriminating signals, at cost to sender
● Selection on sender
○ Selective pressures on signaller
■ To maximise benefit
● Detectable in the physical environment
● Detectable by and conspicuous to the receiver
● Needs to be clear and different from other signals
■ To minimise cost
● Signal should not be conspicuous to predator or prey
-
Joanna Griffith (2017)
●
● Reduce energetic cost
○ Selective pressures on receiver
■ Distinguish informative from uninformative signals
■ Identify false signals
Types of signalling
○ Interspecific
■ Deterring predators
■ Alarm calls
■ pollination/nectar source
○ Intraspecific
■ Recognition of group members
■ Territory ownership
■ Mate choice
■ Intrasexual competition
■ Begging
■ Recognition of kin
■ Alarm calls
■ Foraging information
○ Eg
...
paper wasps
■ More dominant individuals have more broken colouration with more
black facial spots
● Dominance affects how much they get to breed
● Why don’t individuals cheat by increasing the number of spots
they have?
○ Investigation where the faces of wasps were painted
■ Wasps battled for dominance, with the winner
identified by “mount displays”
Joanna Griffith (2017)
No difference in behaviour of the
manipulated wasp, but if they lost, they
received more aggression
○ Punishment for showing dominance levels that weren’t
true
■ Enforcement of social hierarchies seems to be
socially controlled
Maintenance of honest signals
○ The handicap principle
■ High-quality individuals can afford the cost of signalling
● Assumes that cost declines as male quality increases
● Assumes that benefit, if the trait were displayed, would be the
same regardless of quality
● For low-quality males, cost would outweigh the benefits of
displaying the trait
Parent-offspring conflict in begging
○ Honest signalling models of offspring begging would predict that:
■ Begging intensity should reflect offspring need
■ Parents should provision young in relation to begging intensity
■ Begging should be costly
○ Benefits to offspring
■ More food
○ Costs to offspring
■ Increased predation risk
○ Constraints to parents
■ Invest into hungry chicks = more offspring
■ Invest into bigger chicks = a few really good offspring
Honest signals
○ There is some incentive for signallers to either represent or misrepresent their
signal
■ Benefits to the receiver if the signal is honest, costs if it is dishonest
○ Signals are more likely to be honest if:
■ There is no conflict of interest between signaller and receiver
■ There are physical constraints on deceit
■ Dishonest signals are costly (handicap principle)
Deception
○ ‘As a result of the behaviour of the signaller, the receiver registers a certain
situation that is not occurring - as a result of the interaction, the signaller
benefits which the receiver pays a cost’
○ Selective pressures of deception
■ Receiver benefits or pays no cost
● Deceptive signal retained
■ Receiver pays a cost
● Cost of detecting cheats is high, or cost of being deceived is
low
●
●
●
●
●
Joanna Griffith (2017)
Deceptive signal maintained by frequency-dependent
selection
● Cost of being deceived is high
○ Increased receiver response threshold = exaggeration
of deceptive signal = increased receiver response
threshold = etc
...
bee orchids)
● Predator avoidance
● Brood parasitism (eg
...
fork-tailed drongos and meerkats)
■ Intraspecific
● Mate attraction
● Intrasexual competition
--------------------------------------------------------------------------------------------------------------------------○
16: LIFE HISTORY STRATEGIES 1
-
-
-
The problem:
- The ultimate goal of an organism’s life is to survive and reproduce as much as
possible
- The way they go about this varies massively
- Variation in age at first production, longevity, and number of
offspring
Life history: the schedule of an organism’s life
- Age and size at maturity
- Number and size of offspring
- Energy allocation to reproduction
- Timing of growth
- Dispersal patterns
- Number of reproductive events
- Lifespan and ageing
Influences of life history
- Body plan and lifestyle (phylogeny/evolutionary history)
- Evolutionary responses to:
- Physical conditions
Joanna Griffith (2017)
-
Food supply
Predation
Competition
Mortality risk
Mortality risk
- If your risk of dying is high, there is no point in waiting to reproduce
- The fast-slow continuum
- Population growth curve
- Rapid initial growth rate, flattens out at carrying capacity
- dN/dt (change in population size) = rN (intrinsic rate of increase
dependent on previous population size) x (k-N/K) (scaled dependent
on how close to carrying capacity)
- Life-history traits are generally organised along a continuum
- At the r end are organisms with:
- Short life
- Fast development
- Rapid maturity
- Low parental investment
- High reproductive rates
- The population is r-selected, so exists on the rising growth rate
part of the curve
- At the k end are organisms with:
- Long life
- Slow development
- Delayed maturity
- High parental investment
- Low reproductive rates
- The population is k-selected, so is at maximum carrying
capacity
- Hypothetical cause of survivorship
- For fast species, risk of death is high at all ages
- Reproduce as fast as you can, as often as you can
- For slow species, risk of death is lower in early life
- Time to get big and spread out the risk over reproductive
events
- Survival (mortality risk) vs
...
kiwis
■ One egg at a time, takes up 25% of the female’s body mass
■ Female only produces two eggs in her lifetime
■ Male incubates the egg, can lose 20% of body mass
■ Chick quickly becomes independent
Survival vs
...
future reproduction
○ High investment in one breeding season = less investment in the next
Reproduction vs
...
douglas fir
■ The more pinecones are produced in a year, the smaller the growth
ring for that year
Genes that make larger clutches also produce shorter lifespans (pleiotropy)
○ Resources going towards a large clutch cannot be spent on lengthening
lifespan
Trade-offs and mortality risk play a part in maximising fitness
○ Optimal offspring number
■ Trade-off between clutch size and offspring survival
● Lack clutch assumes that this trade-off is important
● One would expect to see the evolution of a clutch size that
maximises offspring survival
○ Age and size at maturity
■ Maturity: age at which first reproduction occurs
■ Fitness is often more sensitive to changes in age at maturity than to
changes in other life history traits
● At equilibrium, increases or decreases reduce fitness
■ Huge variation in age at maturity
■ Age at maturity has an effect on r
● R is approximated by generation time (average time between
birth and production of own offspring) and average number of
offspring per individual
■ Early maturity
● Greater survival to maturity
● Shorter generations
■ Late maturity
● High fecundity
● Higher late fecundity
■ Size at maturity
● Greater size = greater fecundity, so why aren’t all organisms
big?
Joanna Griffith (2017)
Small organisms aren’t small because their size
increases fecundity of lowers mortality, they are small
because it takes time to grow
■ If there is a high risk of mortality, the investment
in growth would never be paid back in increased
fecundity
○ It takes time to get big
■ Important costs to early maturity
● Delay increases size and fecundity, delayed maturity may
mean higher quality offspring, a longer life, and more
reproductive events
○ Balanced by fitness loss through longer generation time
and lower survival to maturity
● Life history traits are closely related to fitness, therefore they are important in
evolution, conservation and ecology
--------------------------------------------------------------------------------------------------------------------------○
17: LIFE HISTORY STRATEGIES 2
Despite evolution, there is no such thing as a ‘Darwinian demon’
○ Trade-offs prevent them from occurring
■ Egg size vs
...
53 eggs
○ Found that the highest number of surviving offspring was for clutches of 12
eggs
■ Great tits could maximise their reproductive success by laying more
eggs
● Is this evidence against Lack’s hypothesis?
● Are Lack’s assumptions the issue with the hypothesis?
○ No association between the current and future reproduction of parents
■ Linden and Moller (1989)
●
Joanna Griffith (2017)
26/60 studies show a trade-off between current and future
reproduction
○ When reproduction is costly, selection favours
withholding some reproductive investment for the
following years
○ Offspring reproductive success is not influenced by the clutch size that they
experienced
■ When a large clutch means lower offspring reproductive success,
optimal size of the offspring clutches will be smaller than the most
numerically productive clutch (being in a large clutch = lower offspring
reproductive success)
Deviations from Lack
○ Parent-offspring conflict
■ When there are siblings, reproductive investment of parents is split
● ½○ When this occurs, there is a conflict between parent
and offspring
■ Mothers will want to stop investing when the
costs to future generations exceed the benefits
to current offspring (when B/C<1), but the
current offspring will want investment to
continue until the cost to future generations is
twice that of the benefits to itself (B/C=½<1),
because it is related to itself by 1 but to future
offspring by 0
...
procellariiformes only ever have one egg
● For example, albatrosses fly long foraging routes, feeding of
chicks is delayed, so they cannot provision more than one
chick
○ Offspring size
■ We have more or less assumed fixed size previously
■ While clutch/brood size can vary considerably, typically offspring size
is far less variable
● Due to a trade-off between offspring number and offspring size
● Assumption that individual offspring will have a better chance
of surviving if they are larger
●
●
Joanna Griffith (2017)
There is a minimum size below which offspring do not
have a chance of survival
○ As offspring get larger, their probability of surviving
increases
■ The parental fitness gained from a particular clutch of offspring of a
given size is the number of offspring that survive from this particular
clutch
● If we multiply the number of offspring in the clutch by the
probability that any individual offspring will survive, we get
parental fitness
○ This tells us optimal size from the parent’s perspective
○ Optimal compromise between size and number of
offspring
■ Individual offspring would do better if they were
bigger, but parents can do better with more,
smaller offspring (generates parent-offspring
conflict)
■ So optimal offspring size depends on the size-number trade-off and
how survival scales with size
○ Lifetime reproductive investment
■ Lack was only thinking about single clutches
■ How often should an organism reproduce?
● The once-many continuum
○ Some organisms reproduce once, some a few times,
and some very many times
● Semelparous organisms
○ ‘Big bang’ breeders
○ Produce all of their offspring in a single reproductive
event over one relatively short period
● Iteroparous organisms
○ ‘Investment’ breeders
○ Produce their offspring over a series of reproductive
events
● Selection for breeding strategies
○ Semelparity is favoured by environmental uncertainty
(bet hedging)
■ Chance to reproduce again is very low
○ Iteroparity is favoured by environmental stability
--------------------------------------------------------------------------------------------------------------------------○
18: HUMAN EVOLUTION
●
Humans evolved from the great apes
○ Changes in posture
○ Changes in length of limbs
○ Changes in the rotation of the ankles and knees
Joanna Griffith (2017)
○
○
○
Different position of attachment of the foramen magnum (bipedalism)
Changes in skull shape/size of brain (flatter face = larger brain)
The differences between old-world monkeys and humans are greater than
those between apes and humans
■ However, chimpanzee skulls look more similar to the skulls of other
primates than to human skulls
● Are humans neotenous chimpanzees?
○ Selective reduction in development in particular cases
● Human skulls are taller, with a shorter face, and are less ridged
for muscle attachment
Hominins
● The group consisting of modern humans, extinct humans species, and all our
immediate ancestors
● Evolution of bipedalism
○ Apes are quadrupeds
○ Australopithecus
■ Possible direct ancestor of humans
■ Found in Africa
■ Lucy
● Australopithecus afarensis
● 3
...
5 million years ago
■ By walking upright, the hands were free
● Darwin suggested that it was this freeing of the hands that
resulted in big brains, complex language and culture, tool use,
etc
...
a nursing Homo erectus would need 2500 calories
per day
○ One solution is to intake more high-quality food
■ Usually, increases in body size are
accompanied by increases in the amount of
low-quality food consumed
■ Evidence of simple tool use and carnivory from
2
...
if selective pressures are small,
response is likely to be slow
○ Usually, we don’t see evolutionary change in real-time
■ HIV evolves very fast
Human Immunodeficiency Virus (HIV)
● Retrovirus (genetic material is RNA)
○ Use reverse transcriptase to turn RNA into DNA when infecting a host
○ Very high mutation rates
■ Reverse transcriptase is not very precise
● Can lead to AIDS
● High recombination rates
○ Sequential or simultaneous infection by multiple viral strains
○ Can lead to a combination of different traits (eg
...
8% of the population)
○ Greater rates in Africa and the Americas
○ 1
...
selection for drug resistance
Treatment
Joanna Griffith (2017)
Inhibitors of reverse transcriptase
Inhibit budding
Inhibit viral entry
Inhibit integration of viral DNA into host cell DNA
No drug is resistance-proof
■ Selective pressure = evolution
● An evolutionary battle
○ High mutation rate
○ Selection to avoid detection
○ Selection to resist anti-viral drugs
○ In humans:
■ Selection to avoid risky behaviour
■ Selection for resistance to HIV
● CD4 receptors are necessary for infection
○ CCRS-32 deletion, almost complete resistance in the
homozygous state
■ Commonly found in Europe - may have been
intensely selected for in Europe
■ Recent origin
■ HIV has not existed long enough for this
mutation to have evolved in response to it
● May have actually been a response to
smallpox
○ We cannot “beat” the virus, but we can minimise risky behaviour that allows it
to spread
○ HIV may be evolving into a milder from
■ Human Leukocyte Antigens (HLA-B) helps distinguish proteins made
by foreign invaders
● HIV adapts to effective HLA molecules, at a cost of reduced
virulence
○ Trade-off between transmission time and virulence
Evolution must be understood
● Antibiotic resistance
● Insecticide resistance
● GM crops
○
○
○
○
○
--------------------------------------------------------------------------------------------------------------------------20: BATS AND INSECTS - WHERE EVOLUTION MEETS ECOLOGY
●
Chiroptera (order)
○ Second-largest mammalian order (about 1000 species)
○ Megachiroptera
■ Fruit bats, flying foxes
■ Tend to be large
■ Frugivores and nectarivores
Joanna Griffith (2017)
Don’t echolocate, except one genus
● Crude echolocation, don’t use it to find food
Microchiroptera
■ Many use echolocation to forage
● Chase food
Exploit lots of niches throughout the environment
■ Body and wing shape affects how they can forage and hunt
● Wing load = bat weight / area of bat
○ As wing load decreases, they have a lower minimum
speed but are more maneuverable
● Aspect ratio = wing span/wing width
○ As aspect ratio increases, flight becomes more efficient
○ Bats with high aspect ratio tend to have higher wing
loading
● Wing tip indices
○ Pointed or rounded
■ Rounded tips allow hovering
● Bats living in dense woodland need to be more maneuverable,
bats living in the open need longer, more efficient wings
■
○
○
Sonograms
● Show how bats use echolocation
● Frequency-modulated components (FM)
○ The frequency of the noise changes rapidly
○ Gives detailed information about the environment
○ Attenuate quickly (don’t travel very far)
○ Allow accurate targeting of prey
■ Often used at the last second
● Constant frequency components (CF)
○ Frequency stays the same (usually for a short period)
○ Carry further
○ Provide less detailed information
○ Allow detection of prey from a greater distance and navigation in an open
area
● The foraging ecology of a bat determines which echolocation calls will serve it the
best
○ Open-space aerial foragers
■ Need to detect prey at long distances
● More constant frequency calls
■ Lower frequency, lower bandwidth, longer duration, with long intervals
between calls
○ Edge space, intermediate clutter
■ Need to be able to detect prey against a background
● FM sweep followed by CF
○ FM helps to localise prey against the background, CF
helps to locate the target
○ Cluttered aerial foragers
Joanna Griffith (2017)
Very difficult problem to solve, sophisticated echolocation
● Long CF followed by broadband FM sweep
● Use Doppler shift
○ Cluttered gleaners
■ Pick prey off the surface of leaves
■ Use prey noise to detect their target
■ Use short-duration broad-band FM for spatial orientation
● Tuttle and Ryan (1981)
○ Investigated how bats respond to the sound of prey
○ Frog-eating bats responded more to the sounds of edible frogs
○ As frog calls increase in complexity, there is increased investigation by bats
■ Trade-offs
● Female frogs prefer more complex calls
● Bats are able to adapt their calls depending on the situation
○ Faster clicks when closer to an insect
■ FM calls attenuate quickly
● Bats need to be able to detect faint echos, so create louder
calls (up to 110dB)
○ Muscles contract to close and protect the ears
Eavesdropping
● Prey may be listening to bat calls
● Can insects hear?
○ Different species have tympanal organs in different places
■ Suggests that they evolved multiple times, so it was important for
these different groups to evolve tympanal organs
■ Evolved independently at least six times in Lepidoptera
○ Hearing is more sensitive at the frequency at which most bats echolocate
○ Diurnal moths don’t hear bats, but nocturnal moths do
● Anti-bat adaptations
○ Fall to the ground
○ Fold a wing
○ May jam the radar by producing a clicking noise
■
Joanna Griffith (2017)
Title: 1st: Introduction to Evolution and Behavioural Ecology
Description: 1st year Introduction to Evolution and Behavioural Ecology notes, University of Exeter
Description: 1st year Introduction to Evolution and Behavioural Ecology notes, University of Exeter