Bio120 Definitions #3

What are the two main species concepts

1. taxonomic or morphological — based primarily on distinct morphological differences

2. The biological species concept (BSC) — By Ernst Mayr, 1942 “groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups (only works for sexually reproducing species)

What is a species

distinguished as isolated gene pools which cannot exchange genes

What is the difference in focus for natural selection and speciation

natural selection → focus is on genetic interactions within populations

speciation → focus is on genetic interactions between populations, “how can populations of the same species become genetically isolated to the point of becoming two species”

What are the two models of speciation

1. allopatric (focus of this course)

2. sympatric

What is the theory of allopatric speciation

introduction of some barrier to gene flow resulting in speciation:

What is a barrier

can be physical or ecological (environmental) and may no longer exist

what are the two predictions of speciations

1. speciations depends on isolation

2. we should find isolated “sister species” nearby

3. speciation should still be occurring in nature

4. reproductive isolation between close pairs should increase slowly over time

ex. galapogas finches

What did Jerry Coyne and Allan Orr do

When can reproductive isolation take place?

Any of the following stages:

• finding a compatible mate

• mating and fertilization

• development of zygote

• adult growth and survival

• reproduction and fertility of offspring

What are the two types of reproductive isolating mechanisms

• prezygotic — prevents zygote formation

  • geographical → ecological

  • temporal → behavioural

  • mechanical → prevention of gamete fusion

• postzygotic

  • improper functioning of zygotes once they are formed

  • inviability, sterility or abnormal hybrids

  • poor performance of hybrid

what are intrinsic postmating isolation

sterility or lethality

what is mullerian mimicry

when species have evolved “warning” colouration to warn predators

what is the role of natural selection in speciation

two populations of the same species in different environments might become more different because of divergent selection favoring different adaptations and known as “ecological speciation”

what do we treat ecological speciation as

variation of allopatric speciation where besides reduced gene flow, divergent natural selection also contributes to differences which can lead to reproductive

What is the difference between ecological and allopatric speciation

Allopatric speciation is driven by geographic isolation (a physical barrier stops populations from interbreeding). Ecological speciation is driven by natural selection (populations adapt to different environments or niches, even if they live in the same area)

What changes allows the sticklebacks to evolve adaptations to increase or decrease the bony armour

There is a change in a single nucleotide in the freshwater populations in the EDA gene, which affects the regulatory portion which does not code for the EDA protein but instead reduces or enhances the EDA expression

what can large changes in skeletal morphology in the wild be created by?

simple genetic mechanisms

What are the chapter summaries from speciation

• as population diverge and diversify through natural selection and drift, populations become reproductively isolated, often as an incidental byproduct of evolutionary change within populations

• Some genes appear to be more commonly associated with speciation than other genes. Especially regulatory genes (or regulatory sequences) instead of protein coding genes (or coding sequences)

• This allows speciation to occur, and populations to begin evolving and adapting independently, driving diversification

what is adaptive radiation

rapid divergence from a single common ancestor into populations and species adapted to many different ecological niches (best example are on oceanic islands)

Island ages

what causes adaptive radiation

• ecological opportunity — abundant resources and few competitors often occur on oceanic islands or their aquatic counterparts

• origin of a key innovation — e.g floral nectar spurs in Columbine for hummingbirds

Who was Carolus Linnaeus

the father of taxonomy:

• binomial nomenclature

• hierarchical system of classification

what is a taxon (plural = taxa)

a named taxonomic unit at any level (e.g can be kingdom or phyla)

who added the 3 domains

1977 carl woese

what is taxonomy

the theory and practice or classifying organisms based on morphology and lifestyle

what is systematics

classifying organisms based on the evolutionary relationships among organisms

what is the structure of a phylogenetic tree

what is a monophyletic group

“complete set of species derived from a common ancestor”

def → a single ancestor gave rise to all species in that taxon and no species in any other taxon

what is a paraphyletic group

contains some, but not all species that are derived from a common ancestor

def → a taxon whose members are derived from two or more ancestral forms not common to all members

what is a clade

an evolutionary group that includes a single common ancestor and all of its descendants

what is a vestigial trait a type of

homology

what is homoplasy

similarity of traits as a result of convergent evolution

what is covergent evolution

the evolution of structures that resemble one another and perform similar functional roles due to the shared ecology of unrelated organisms (ex. cacti or cichlid fishes)

why is molecular biology relevant to evolution and phylogeny

• all life is related through branching descent

• common genetic code is evidence that all life is related

• evolutionary relationships among species are reflected in their DNA and proteins

what are key origins in a phylogeny

• origin of a novel trait resulting in adaptive radiation

• carriers of the trait can exploit new resources or sets of habitats

• usually associated with rapid evolutionary diversification (e.g. adaptive radiations)

e.g herbivory is associated with higher diversification

what are features that are associated with greater diversification

• key origins

• species with more sexual selection

• animal pollination

• increased dispersal of seeds

• herbivory

what was lamarck’s view on complexity

he said “all organisms have an inherent tendency to become more complex”

what are the major transitions in evolution

• origin on cells

• origin on chromosomes

• origin of genetic code

• origin of sexual reproduction

• origin of eukaryotes

• origin of multicellularity

• origin on colonies (e.g. non reproductive castes)

greater complexity arises from ________________ organisms.

greater “cooperation” amongst previously independent

(ex. the endosymbiosis theory where previously independently evolving units merged, leading to higher-level complexity through division of labour)

what is the unit of selection

individuals/genes

what does natural selection act one

the individual’s, more specifically their genes, and not the species

what types of traits can spread

traits which increase the fitness of the individuals, and may or may not be good for the species

when is cooperation “adaptive”?

1. high relatedness - genes that lead to helping “relatives” can spread via natural selection, called “kin selection”

2. reciprocal altruism - cases where organisms repeatedly encounter each other, where mutual cooperation can lead to highest fitness

key → cooperation can sometimes break down and/or select for “cheaters”

True or false: selection on individual organisms is a form of cooperation

true → because genomes are composed of unrelated genes and alleles, which get inherited from different places, and typically persist by improving the fitness of the individual

How do genomes stay cooperative?

Many features of individual organisms prevent competition and evolution within an individual → ensuring genes succeed by enhancing the fitness of the organism

1. Fair meiosis

2. when cheating alleles spread, strong selection on rest of genome for suppression

3. selection on rest of genome for silencing TEs (DNA methylation)

4. transposition - selection balance (first abundance increased through replication, then abundance reduced through natural selection if harmful, and finally there is a balance in the abundance)

5. uniparental inheritance of organelles (ex. mitochondrion), preventing competition within cells of different organelle genomes

6. development of multicellularity — starting from a single cell prevents initial competition among cell lineages

to what extent does cooperation break down?

cheating a fair meiosis

• meiotic drive

• overreplication

what is a meiotic driver

an allele that can enhance its own transmission by biasing transmission away from a 1:1 ratio of alleles

what is fair meiosis

each allele of an individual’s genomes has an equal chance of being representing in the gametes (1:1) → ensuring the alleles don’t compete within an individual

what are transposable elements (TEs)

• self replicating segments of DNA (aka transposons)

• TE replication is separated from cellular replication

• they ensure their own over-representation in offspring (>50% of gametes have a TE copy)

this is what causes overreplication during meiosis

how do genomes not explode from transposons?

1) Alleles arising elsewhere in genome that silence TEs will be favoured by individual selection

• Mechanisms controlling DNA & histone methylation

• piRNAs and RNA interference may have evolved as silencing mechanisms

2) Transposition-selection balance

• Transposition is a form of mutation that can disrupt a gene

• Natural selection against harmful effects on the organism reduces abundance of chromosome copies with most TEs

• Abundance of TEs in an organism results from a balance between these opposing forces