Evolution Test Revision

Evolution Test revision, weeks 10 14
Lecture 10, speciation

How does microevolution create new species, and the rate they are produced?
There is no actual reason to have these discrete differences. There is no necessity these
species must exist?
What is a species?
Species have different patterns of gene flow between them

Mayrs biological species concept groups of individuals that can:
Exchange genetic information amongst themselves
Do not exchange genetic information with members of other species (reproductive
isolation)
what causes reproductive isolation? What stopes gene flow between members of different species?
Two classes: Prezygotic & Postzygotic
Pre: factors which prevent sperm and egg from coming together in the first place, i.e.
organisms mating at different times of year etc, which mean hybrid embryos do not form
Can be caused by:
Spatial isolation
Temporal isolation
Mate choices. Females/males can deny attempted reproduction between species
Recognition proteins may stop wrong sperm and eggs fusing
Post: hybrids can form, but are sterile and cannot then pass genetic information to new
generations
Origins of reproductive isolation
Environmental factors can separate two species, and so they must adapt to two different
environments, and when they come back together, they can no longer breed.
How does reduced gene flow arrive?
Geographical barrier (physical barriers) this is prezygotic and temporal/spatial. This is known as
ALLOPATRIC speciation.
Intrinsic isolation, where a mutation will arise within a population, and isolate it from other
individuals in that species. This is known as SYMPATRIC speciation
Two models of allopatric reproductive isolation

1) Vicariance two populations separated via a spatial occurrence, and then having time to
develop and adapt to different environemtns, speciate and can no longer breed (population
with fixed range, being split into two)
2) Dispersal a new habitat opens up outside of current habitat, and only a number of
individuals can access that. And remains isolated. Dispersal of individuals into a new zone
Telling the two apart
I) Age of clade compared to age of landscape

II) Timing of biodiversity formations in different groups
A geographical event will split a lot of species, and create a bunch of species that have a
shared ancestor at the same point in time
Dispersal speciation is more common than vicariance. In monkeys, the barrier (Atlantic) is older than
the clades of new and old-world monkeys. So, an old-world monkey colonised America somehow on
a raft, and radiated into new species
Varying species in Amazonian birds no evidence for a single event which created a bunch of
speciation
How does dispersal promote or inhibit geographical isolation?
Highest rate of speciation when species are not very dispersive. Only vicariance can be source of
isolation then
Low dispersion = highest speciation.

Humans have a very high dispersal rate, and therefore genes flow between populations very
often, and do not give the chance for a group to speciate
biodiversity is highest in weak dispersal species. Limited dispersal aids speciation, as genes cannot
flow back and forth so easy
Vicariance is a lower source of reproductive isolation
Limited dispersal over landscape barriers is highest source of reproductive isolation
Can speciation occur without geographical barriers? (sympatric speciation)
Mutations can occur which force individuals to stick to one behaviour or food source, which means
they only mate with other individuals of the same mutation
Magic traits:
flowers mutating a gene making it able to grow on mine waste, which causes the plant to
flower at different times, and thus create reproductive isolation
isolation in ALLOPATRY through dispersal and vicariance
isolation in SYMPATRY through magic traits
Dobzhansky-muller incompatibilities
Development systems that differ between species cause genetic fuck-ups in the hybrid
offspring
Ecological speciation
Populations driven apart by adaption to different environments = reproductive isolation
What creates incompatibility?
Speciation genetics finds genes that create incompatibility, and ask if adaptive evolution
drive the changes that result in incompatibility
Nup160 is incompatible with something in melanogaster x chromosome
Speciation 2
1) Is reproductive isolation sufficient to create biodiversity
2) Does environmental change or biological innovation control biodiversity?
Reproductive isolation is not sufficient alone to create biodiversity
Speciation a 2-step process:
Evolution of reproductive isolation

Co-existence of sister species on secondary contact. They have to be able to occupy the
same habitat
Sister species may hybridise and extinct themselves
Gauses dictum: complete competitors cannot co-exist. Two species using the same resource cannot
exist together. If two species are ecologically identical they cannot coi-exist
If two sister species mates too much, they can create a sterile (hybrid) load. They can hybridize
themselves to extinction (sterile offspring)
In divergence of allopatry, they may change dietary and reproductive preferences, and not
compete for resources
A) Ecological character displacement selection for each species to utilize a different niche.
When two species will adapt to selective pressure to allow them to use unused resources
This was seen in out experiment. Nice use is an evolvable characteristic
Therefore, diversification will be constrained if there are no free niches to evolve in to.
B) Reproductive character displacement HYBRID LOAD

This would be when females of a species evolve strong preferences to mate with their own
species, to avoid hybrid load. This allows two species to co-exist
Selects female to mate with their own species. Selection will choose things that reduce hybrid load
Stick insects will choose mate preferences when co-existing, but not when they live independently
So, reproductive isolation may create new, divergent species. But in order for these species to exist,
they must also make ecological distinction, and not be absolute competitors of each other
Can be by ecological distinction or reproductive distinction
THEREFORE, generation of biodiversity requires 2 things:
1) Evolution of reproductive isolation

2) Evolution of ecological distinctness to allow two species to co-exist (this one limits
biodiversity)
As you get saturation of species in a habitat, you limit the propensity of new species being formed,
as there are no niches to occupy and exploit
Strongest predictor of diversification, is level of habitat saturation
What may promote/constrain diversification: two views
1) Court jester environmental change and random, non-biological events.

- May also work by mass extinction events, where this frees up ecological niches and
allows for radiation of new species (may explain mammalian radiation after dinosaur
extinction)
- Environmental and geological events are the primary driver of diversification
- SHIT HAPPENS view. Creates new niche space
2) Red queen biological changes change energy space and open biodiversity by opening new
energy niches to organisms.
- Biotic forces generating evolution. Evolution may allow an organism to work in a new
way, and open up a novel energy space, and allows that clade to diversify.
- Niche space is altered by changes in biology through radical biological changes (mutation
in DNA)
Angiosperm stuff is example of red queen
1) Geological change creates virgin habitat, and ecological character displacement allows this
process
Angiosperm eating mutation in beetles allows for huge nice opening up and energy source.
Ehrlichy & Raven: coevolutionary game changing
Escaping from predation, drives evolution of better predation
Multicellularity drove huge Cambrian explosion of biodiversity
Evolution of sex
A large macroevolution evolution. Very important for population genetics, where
recombination of DNA happens and allows for mutations.
Sex in bacteria: 3 forms of genetic exchange

1) Conjugation
2) Transduction phage initiated. Shuttles of genes which replicate within a bacteria,
and insert their genetics in the DNA of other bacteria
3) Transformation another individual takes up free DNA sections and incorporates
them into its genome
Sex can be induced by environmental stress. Bacteria takes in DNA of other bacteria when
its faced with environmental stress. Ribose is a sugar, and is seen as food.
Microbial sex different from meiotic sex

Meiotic sex has recombination. There is no association of recombination in microbial sex
Transformation = absorbing DNA of dead bacteria
Gene exposure community exposure and inclusion into genome. As DAN gets more and
more diverged from your own, you are less likely to take it up
Accessory genes spread through microbial communities, and is not restricted to a particular
species. This is because of recombination and the taking up of DNA from any other bacteria
Conjugation the plasmid goes from A to B and replicates itself. The plasmid will use the
microbe as a host cell
Transduction spreading of the phage, the virus.
Transformation DNA tastes good. Under environment (hunger) stress, microbes will take
up free floating sections of genes.
These methods did not evolve for the sake of recombination. Recombination
happens as a result of these
Sex in animals
Evolves as a direct benefit to meiotic recombination
Asexuality identical copy and information passed on during replication

Sexuality genetic information of progeny = copy with mutation + combination
Errors occur in both methods (genetic mutations)
Natural history of sex. 19/34 animal phyla have asexual representatives
70 unisexual vertebrate species, like fish, reptiles, and amphibians

Facultative parthenogenesis when a female develops an egg without fertilization
by a sperm. The babies were an exact copy of the mother
Obligate asexuality (where all members of a species are asexual, no sexual reproduction in a
species) are recently derived. They are at the tips of phylogenetic branches. This means that
in evolution terms, they are pretty short lived.
Do not find lots and lots of Taxa closely related who exhibit asexuality. Asexuality is
short-lived, but evolves readily. Not a good mechanism for long term.
Clade of Rotifers have been asexual for about 200 million years. 360 species in
the clade.
Why sex is hard to explain

Sex is a complicated way of reproducing. It is dangerous, can get STDs, and
mating leaves you vulnerable to predation. After all of that, may not be fertile. In
short, sex can be complicated
More fundamentally, it is quite inefficient way of propagating oneself. Theory of
twofold cost of sex
Asexual populations can replicate themselves to the squared
In sexual reproductions, males are also produced, but do not generate offspring. So
in population growth terms, they are a waste of energy (unless they are involved in
parental care)
Asexual lineages are more efficient, in terms of population growth. Asexuals produce
twice as many grandchildren as sexuals
What is advantage of sex? It is a combination of traits coming together, and
recombinates genes.
Sex brakes up genes and introduces variation, offspring are a mix of two individuals. It
produces lots of associations between Loci. Genes can split apart in recombination, and
re-assortment creates variation
Any mutation which exists would always stay in that genome (if there was no sex)
This creates two benefits of sex:

1) Allows good combinations to come together quicker and better (Fisher-Muller
theory)
To get all 3 beneficial mutations in one individual requires a lot of time
and high frequency of replication. Mutations have to happen
sequentially. Have to wait until a single individuals mutates on his own, all
3 mutations.
In a sexual population, these mutations may happen at the same time,
and meiotic combination can put them all together in the same gene, and
therefore evolution occurs quicker
2) Allows bad combinations to break apart
Mullers ratchet: every time asexual reproduction occurs, you click up deleterious
mutations
Sexual reproduction will take individuals with different numbers of mutations, and
produces variation
31:09 on lecture 12 on sex

Evolution Test Revision

Uploaded by

Copyright:

Available Formats

Evolution Test Revision

Uploaded by

Document Information

Original Description:

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Evolution Test Revision

Uploaded by

Copyright:

Available Formats

Evolution Test revision, weeks 10 14

Lecture 10, speciation

Species have different patterns of gene flow between them

Two classes: Prezygotic & Postzygotic

Can be caused by:

Origins of reproductive isolation

How does reduced gene flow arrive?

Two models of allopatric reproductive isolation

Telling the two apart

I) Age of clade compared to age of landscape

How does dispersal promote or inhibit geographical isolation?

Low dispersion = highest speciation.

Vicariance is a lower source of reproductive isolation

Limited dispersal over landscape barriers is highest source of reproductive isolation

Can speciation occur without geographical barriers? (sympatric speciation)

isolation in SYMPATRY through magic traits

Populations driven apart by adaption to different environments = reproductive isolation

What creates incompatibility?

Reproductive isolation is not sufficient alone to create biodiversity

Speciation a 2-step process:

Evolution of reproductive isolation

Sister species may hybridise and extinct themselves

B) Reproductive character displacement HYBRID LOAD

Can be by ecological distinction or reproductive distinction

THEREFORE, generation of biodiversity requires 2 things:

1) Evolution of reproductive isolation

Strongest predictor of diversification, is level of habitat saturation

What may promote/constrain diversification: two views

1) Court jester environmental change and random, non-biological events.

Angiosperm stuff is example of red queen

Escaping from predation, drives evolution of better predation

Multicellularity drove huge Cambrian explosion of biodiversity

Sex in bacteria: 3 forms of genetic exchange

Microbial sex different from meiotic sex

Asexuality identical copy and information passed on during replication

Natural history of sex. 19/34 animal phyla have asexual representatives

70 unisexual vertebrate species, like fish, reptiles, and amphibians

Why sex is hard to explain

This creates two benefits of sex:

31:09 on lecture 12 on sex

You might also like