- Phylogeny: is the study of ancestor descendent relationships
- Phylogenies are based on:
o Morphological data
o Physiological data
o Molecular data
- Characters are used to describe phylogenies
- Any attribute that gives us insight on the history (shared ancestry) of the population
o Ex molecular phylogenies look at nucleotide sequences
- Pleisiomorphy: refers to the ancestral character state
- Apomorphy: a derived character state that differs from the ancestral state
- Synapomorphy: a derived character state that is shared by two or more taxa from a common ancestor
that is not the plesiomorphic ancestor
- Autapomorphy: a independently derived character state
- Monophyletic: a group that contains the common ancestor and all the extant descendants
- Non-Monophyletic: a group that is not monophyletic
o Paraphyletic: includes the common ancestor but not all of the extant descendants
o Polyphyletic: erroneously grouped taxa based on uniquely derived character states that are
- Synapomorphy describe monophyletic groups
- Homology and Homoplasy
o Homology refers to a character state (shared between two or more taxa) derived from a common
o Homoplasy refers to a character state (shared between two or more taxa) which evolved
independently. Example: America vs African Vultures.
- Can be caused by 3 different ways:
1.) Parallel evolution: the independent evolution of the same feature through the same ancestral
condition. Example 3 spine stickle back. Evolved independently, positive assortative mating has
been an important force driving the divergence of these pairs. The large ones look the same and
you wouldn’t think they have a common ancestor but they actually look more like the smaller
ones than they do like the other larger ones.
2.) Convergent evolution: the independent evolution of the same feature through diff ancestral
3.) Secondary loss: reversion to the original ancestral condition
- Analogy is the opposite of homology
o The fins of a whale and the fins of a shark were both formed through convergences (the same
trait derived from different ancestral conditions)
- Reversals can be caused by mutations which remove the synapomorphy
- When constructing phylogenetic trees it is more beneficial to use synapomorphies (monophyletic
character traits) than homoplaseous traits
- Parsimony - The principle of parsimony states that simple explanations are preferred over more complex
ones therefore synapomorphies are preferred over homoplaseous. Camera eye example.
o Less evolutionary steps are preferred over more
o The least number of steps on a tree is the most parsimonious - When constructing phylogenetic trees you must determine an outgroup first which is not part of the
group at interest but not too distantly related to it. This is used to polarize the group and act as the
pleasiomorph by which the synapomorph and apomorphs can be distinguished
- Artiodactyla: mammals with even number of toes
- Perissodactlya – odd number of toes
- Bootstrap Method: a computational way to determine the confidence of a phylogenetic hypothesis
- It adds new data on the basis of the info and counts how many times a particular branch is seen on the
- Cladistics: the use of parsimony to construct phylogenetic trees
o Cladistic taxonomy = evolutionary taxonomy
- The use of DNA sequencing is also used when constructing phylogenies: Bayesian analysis and
- Phylogeny and Co-evolution: as one group diverges expect the other group to diverge with it.
- Adaptation: a specific trait that increases the fitness of an individual in comparison to those who do not
possess the trait.
o Example: Oxpeckers. These were birds that were assumed to be taking off the tics on the Ox.
However this was as just so hypothesis. The birds were divided into two groups (Excluded vs.
Not Excluded). Tick Loads: no significance noted between the presence or absence of the
oxpeckers. Wounds: major statistical significance noted. Oxpeckers are not cleaning the
wounds; they are inflicting them on to the ox. Earwax: again major statistical significance noted.
- 3 things to keep in mind
o Differences among populations are not always adaptive
o Not all adaptations are perfect-trade off and constraints
o Not every trait an organism possesses is adaptive
- Experimental Approach:
o Most powerful approaches to test a hypothesis, allows you to isolate a variable and test that
specifically. It allows us to get half the question of causation. It allows us to say that one
variable is the cause to this problem.
o Correlation cannot be used to infer causation – cannot say that one variable is the cause of the
other variable. Can only use correlations to support hypothesis if you predict that two variables
should be correlated based on another factor.
o Example: Jumping Spider responses. Jumping spider-very territorial, threat display by raising
front legs telling other species to get away Jumping spider is the major predator on this type of
fly—prey mimics its predator in order to deter their predator. The wing waving in the fly is
actually mimicking its own predator to deter it form attacking. Tests show that the wings and the
mimicry made spiders retreat. Normal wings/no wings/normal flies got attacked.
- Observational Approach:
o Garter Snakes - cannot regulate their own body temp and make adaptive choices when choosing
the rocks they lay under.
o Experimental observations shown that the snakes will choose to reside under medium sized
- Comparative Studies:
o Evaluates the strength of hypothesis by testing for patterns across species.
o You must know the evolutionary relationships between the species you are studying o Must use correlation as support for your hypothesis.
o Example: Bats Sperm Competition—if a male wants to increase his fitness under those
circumstances want to enter more sperm into the race. In order to produce more sperm, they
need to have larger testes. They will attract more females and reproduce more. Researchers saw
that the larger the testes the larger the social group size.
- Lack of data – 2 data points does not provide enough evidence. 6 different species tested. Positive slope
line generated from that which indicates a correlation between the two. Phylogeny of species – show that
A B and C might have inherited their small testis size from their common ancestor but the others might
have a common ancestor that had large testis. We rather actually have two data points indicating the
common ancestor. It deflates the data rather considerably.
- Use of phylogenies to develop independent contrast between species. Be aware that the method exists –
not to be tested just know the general basics. We still get a nice positive upward sloping line which tells
us that the correlation actually exists.
- Factors that affect evolutionary adaptation
o Trade-offs: a compromise between one trait and another, which cannot be avoided. Ex. flower
size in a Begonia
o Constraint: any factor that slows down or hinders the process of evolutionary adaptation in a
Developmental/functional constraint: due to physiological constraint. Ex. Flower color
change in Fuschia.
Genetic constraint: lack the genetic variability to adapt. Ex. Beetles.
Ecological constraint: environment prevents adaptation. Ex. Dove lice host shifts.
- Phenotypic Plasticity: is the same genotype which yields a different phenotype due to environmental
conditions – may be caused by adaptations
Our Closest Relatives:
- On the phylogenetic tree humans are listed as part of the hominadae along with chimps, gorilla,
orangutans and bonobos.
- Humans did NOT evolve from chimps; they both rose from the same common ancestor; however
humans were the first lineage to separate.
- The Genus Pan distribution: show non overlapping distribution
- Bonobo’s VS Common Chimp
o Squarish snout; more robust bodies than bonobos
o Aggressive and male dominant – the largest male is the dominant
o Eat meat and other monkeys
o Used tools and weapons for hunting and attacking
o In fight for territory they will break out into war
o Both are intelligent and can identify them selves in mirror
o Both have a fission fusion community by which they will exchange individuals randomly
o Roundish snout
o More peaceful, eat sugar cane, do not display war
o They use sex as a method of conflict resolution
o Females are dominant – egalitarian society
o The status of a male depends on the status of its mother - Fission Fusion society: Fusion communities do not interact with each other. Sometimes the females may
do so but not quiet often (Bonobo).
- Fission – common chimp mostly males – different male groups and sometimes swap members. Females
don’t bind. Communities will engage in deadly warfare. Males bind due to adaptation for warfare
against other chimps. As a consequence – there tends to be fewer males in common than bonobos.
Evolution and Sex
- Many eukaryotes reproduce asexually through budding – they produce identical clones of themselves
- Parthenogenesis: virgin birth – asexual reproduction. No males. Some aphids are sexually reproducing
in the fall and asexually in the spring.
- 2 types:
o Obligate: Females only pop. Reproduce by making clones of them.
o Cyclical: Mostly asexual but produce males for sexual rep at some point during the year
- Benefits of Sex. In species that reproduce both sexually and asexually there seem to be benefits to
having sex. It would seem that asexual would over run sexual in a natural population – the asexual
produce 2x more offspring than sexual. However this is not the case therefore there must be benefits to
1.) Parental Care – in some organisms the males provide parental care for the females in order to help
rear offspring and increase their fitness
o The two fold cost of sex: In a sexually rep pop the sexual will create two times the number of
surviving offspring than the asexual
2.) Sexual reproduction provides genetic variation among offspring
o Includes: genetic recombination and crossing over
o During meiosis genes are able to cross over. Gametogenesis provides further recombination.
This allows you to create new genotypes; some which may be favorable and increase the fitness
of the organism
- 3.) Sexual reproduction allows the removal of deleterious mutations
o Mutations will be kicked out through selection
o Muller’s Ratchet: the asexual will be doomed to extinction due to fixation of deleterious
o Linkage Disequilibrium: when genes on a chromosome are closer together they are viewed as
one unit and are inherited together
o Sexual reproduction and recombination will break up linkage disequilibrium and allow for more
- 4.) Sex and changing environments
o The Red Queen Hypothesis: an arms race caused by trade off
o In a sexually rep pop. Where the env is changing you can get traits that are resistance to one
thing but then susceptible to another and you must evolve to keep up with the environment in
order to survive
- The advantage of asexual reproduction: they are able to form colonies by themselves and start an
entirely new population
- The measure of Fitness: the ability to contribute to the next generation- reproductive success
o Fecundity Selection (the amount of females produced)
o Mortality Selection: the amount that survive till the next gen o Sexual Selection: the amount that are able to find mates
- Sexual Dimorphism: a trait that is found in one sex and not the other
- If a trait does not seem to provide for mortality selection of fecundity selection but still persists through
generations it may be due to sexual selection. The ability to successfully find a mate and reproduce
- Parental Investment: females usually put in more time, energy and resources into taking care of child
until they are old enough. Males usually provide no parental care. Eggs are expensive but sperm is
- Females have a lower potential reproductive success because the number of eggs limits them. Males
usually have a high rep. success potential however they are limited by the number of females they mate
- Asymmetries: the differences in male and female reproductive success that drives sexual selection
o Males usually have a higher rep. potential success than females. Newts: those with bigger crests
have higher rep. success and mate with more females leaving behind more offspring
o Females in pipefish have higher rep. potential because males have pouches they keep the eggs in
and are limited to the amount they can hold; females are not limited.
o Males have strong sexual selection:
Combat – favor morphological traits such as large body size, armour etc. sexual
selection maintains large bodies in the population because they get more copulations
Sperm Competition – larger ejaculates, prolonged copulation, deposits a copulatory plug
and sperm removal.
Infanticide – Ex. lions. Males move from pride to pride. Nursing females don’t breed.
By killing other male’s cubs, the male lions will gain more opportunity to mate.
- Females have weak competition: they will be picky about who they mate with due to their parental
- Antagonist Selection: natural selection and sexual selection are working against one another
- Female Choice: in populations where the males cannot overrule the females to reproduce with them; the
males will do strange things and rituals to try and mate with females. Red collared birds females like
males with large tails but mortality is against them.
- Phonotaxes: movement towards sound; gray tree frogs the females like calls that are fast and long rather
than short and slow. Females are picky to improve fitness; those with longer calls have higher fitness
- Females chose the male with the most ornaments and least parasites in order to increase fitness
- Better resources in some males: assistance etc.
- Arbitrary Reasons:
o The sexy son hypothesis: the males with high rep. success will pass these traits on to their son
and in turn they will encounter a high rep success as well
o Polygymy: males mate with more than one female
o Polyandry: females mate with more than one male
- Mutualism: fitness gains for both participants
- Alturism: fitness loss for individual carrying out action, and gain for individual on the receiving end
- Selfishness: opposite of altruism
- Spite: fitness loss for both participants; no good examples
- Direct Fitness: an individual’s contribution to the next generation directly through reproduction - Indirect Fitness: additional reproduction caused by relatives to the species resulting from actions
(assistance). The additional reproduction would not have been made without the assistance.
- Kin Selection: is the selection for and spread of alleles that cause increased indirect fitness
- Altruism is paradox to Darwin’s theory – it is highly unlikely that a species would undergo an action that
would in turn decrease its own fitness for the increase of another individual’s fitness.
- However selection would favor traits that decrease an individual’s personal fitness if it increased the
survival traits and fitness of close relative.
- Co-efficient of relatedness (r) – the probability that two homologous alleles are identical by decent;
involves an allele in the actor and allele in the recipient at the same locus. Measure of how closely
related genetically two individuals are.
- HAMILTONS RULE: the spread of an allele for altruistic behavior will occur if B r – C > 0
o The benefit to the recipient minus the cost to the actor is greater than 0
o The benefits and costs are measured in terms of surviving offspring
o The larger the term the more likely it will be greater than the cost – the allele will spread
- Prairie Dogs:
o Prairie dogs reside in coteries and were observed to have altruistic behavior
o When both males and females spotted prey they would made a call to warn others in the coteries
that there was danger although it meant self sacrifice
o At first they were unsure whether these calls were selfish (the action was done to increase their
own chance of survival or fitness) or whether they were altruistic (although the action reduced
their own survival rate and fitness decreased it increased the fitness of the recipient)
o Studies showed that the proximity to kin related members affected the ways in which they called
o The closer the individual was to relatives, the more likely they were to call
- White Fronted Bee Eaters
o They are responsible for kin selection
o It is very hard for all birds to find their own territories, raise offspring etc. so when young birds
are of age to rear offspring they will mostly stay in their own nest and assist other members in
raising their offspring instead
o The birds will choose relatives that have the closest relation to them and help them raise their
own offspring (help parents raise siblings etc)
o Most of the young birds die of starvation before leaving the nest but they have huge benefits to
their kin, by increasing the additional reproduction offspring.
- Wood Mice
o Female wood mice are highly promiscuous and mate with multiple males
o The males are in competition for their sperm to reach and fertilize the egg the fastest
o Males with large testes is an adaptive trait for sperm competition
o The sperm show their competitiveness – they have hooks that hook onto other sperm heads or
flagella and form a train of thousands of individual cells that increase the speed of travel in
comparison to single sperm
o When the sperm reaches the cell they must release from one another via an enzyme and a lot of
the sperm are destroyed in this process
- This altruistic behavior is a form of kin selection as siblings are helping one another to reach the egg
- Cannibalistic Tadpoles:
o 2 forms of tadpoles: omnivorous and cannibalistic
o Omnivorous are plant eating however their morphs are capable of eating other tadpoles
o Did a study to see whether cannibalistic toads would eat their omniviorous kin and found out
that 6/8 times they would not
o These tadpoles display kin selection by choosing to eat non kin members over relatives
o Did not affect their own fitness levels by eating other non kin members – the cost of missing a
meal was less than the benefit
o According to H rule the benefit to discriminating was equal to 2. The cost of discriminating is
effectively 0 the benefit is 2.
- Conspecific: individuals belonging to the same species - Heterospecific: individuals belonging to different species
- Congeneric: individuals from different species belonging to the same genus
- Conspecific Nest Parasitism: Mal Altruistic behavior
o Avoid paying the costs on behalf of non-kin individuals
o American coots may sometimes place their own eggs in the nests of other coots (conspecific) so
that they can rear them
o This will decrease the fitness of their own offspring because for every parasitic egg in their nest,
their own offspring have less chance of survival
o Coots have ways of avoiding mal-altruism through noticing the specific color of their own eggs
in comparison to the parasitic one and also counting, they can see if there is an extra egg
o The survival of a parasitic egg will increase the fitness of the parasitic kin
- Kin Selection and Eusociality:
- Eusociality: individuals that have no direct contribution to the next generation (non reproducing) but
instead provide additional reproduction by means of assistance. Involves: cooperative family (brood)
- Individuals who do not reproduce. Overlap of generations between parents and offspring
- Eusociality and Hymenoptra
o Special species of insects that are haplodiploid. The males are haploid but the females are
o The genetic code is different and causes a special coefficient of relatedness the sisters are more
related to each other than they are to their offspring
o Sister – sister = ¾; Sister – brother = ¼; Sister – offspring = ½
o The sisters will assist in helping the queen with child rearing rather than making their own
offspring. The queen has equal relatedness with both male and female; and wants to keep a 1:1
ratio. But the sisters want to make more sisters 3:1 ratio and will deliberately destroy male eggs
o Many males will develop into soldiers to protect the colony and others are reproductive and will
mate with the queen
o Hamilton’s rule may not be the reason behind eusociality but instead be caused by nesting
- Parent Offspring Conflict
o The more parental care given will increase the fitness of the offspring and their contribution to
the next generation
o The relation of coefficient between:
o The parent and offspring is ½; Siblings = ½; Half siblings = ¼; Yourself = 1
o Offspring compete for the most parental care between their siblings
o The cost benefit ratio is very low when offspring is small
o When they get bigger the weaning conflict begins where parents will try to kick offspring out of
nest but they will attack and try to continue parental care
o The cost increases because they now use more nutrients and it is expensive
o Sublicide also occurs – siblings attack/kill others to fight for more parental care
- Reciprocal Altruism:
o Altruistic behavior that occurs among individuals that are not related may occur if the cost to
benefit is equal or low. Those who do not return the favor will be punished
o Likely to occur among individuals who spend a lot of time together and constantly see each
other; species have good memories
o In bats, species will go out at night and prey on mammal blood; however not all of them will get
blood. If a bat does not get blood 3 nights in a row then it will starve
o Those who INTERACT most with one another will regurgitate their own blood to help the
starving bat – reciprocal altruism
Species Concepts and Speciation:
- Defining a species is hard to do; taxonomists go around assigning organisms to different ―kinds‖ based
on certain similarities on characteristics
- There are 3 species concepts covered: phylogenetic, biology and morphology - Morphological Species Concept: