Lecture 10-13 Flashcards
What is a taxonomic rank?
The most specific unit of taxonomic classification (ex. Homo sapiens)
What is a biological classification?
A way we try to classify individuals based on a set of characters
What is speciation? What does it depend on?
The creation of new species
Dependant on limited or absent gene flow between populations
- If gene flow does occur between populations, they will remain genetically similar therefore they cannot become different species if they share the same genes
What are the mechanisms of speciation?
Change in gene flow due to something cuasing a pop. to seperate
- can be caused by physical barriers or geographic conditions (mountains, rivers, deserts)
- physically isolated pop. rarely interbreed and are therefore characterized by the lack of gene flow
- since different courtship behaviours, different breeding seasons, different periods of activity (diurnal vs. nocturnal)
Mutation, genetic drift, natural selection (or a combination) act separately on each isolated pop.
Leads to different isolated populations
Where did the variation that natural selection acts on come from?
Natural selection may select for different variations in traits (alleles) between populations that
- already existed when they separated
- newly arose from chance mutations
What is a mutation?
Random change that happens when DNA is replicated
Most are NOT adaptive, but some create new characters (most mutations are bad, but occasionally good)
What is genetic drift?
Based on probability, the frequency of different genes in a population can change over time, even when not under selection pressure
- since at each generation, each allele is passed on randomly
Occurs in small populations by change
Whole alleles (traits) may even be lost
The allele is not under strong envr. pressure
What is the morphological species concept?
Two populations that have distinguishable phenotypic characteristics (e.g., physical appearance, internal anatomy) are classified as different species by this concept
In other words, things that look similar and of similar size, shape, function, likely to be more related to each other
What is the use of the morphological species concept?
Examining the fossil record, especially when fossils are the only data available
What are the limitations of the morphological species concept?
Oldest species concept –> sorting species by appearance is a very coarse-grained way of differentiating groups
Does not take modern genetics into account (e.g. how genes and other microevolutionary differences affect what individuals look like)
It is much more accurate to use ecological and molecular evidence to determine whether individuals are the same species
What is the biological species concept?
Defines a species as members of populations that actually or potentially interbreed (mate with each other) in nature and produce offspring that are fertile (can also reproduce)
What are the issues with the biological species concept?
Assumes sexual reproduction, but not all species reproduce sexually
- does not work for asexual species (including animals and plants)
Cannot be used in all scenarios where we would like to distinguish between species
We cannot test the ability to mate between every pair of species (not practical/ethical)
What is the phylogenetic species concept?
Species are groups of individuals that share a unique common ancestor
Determined by showing that individuals share traits (e.g. morphological, now usually genetic) unique to that species
Causes them to cluster distinctly from other groups
Branching out is due to speciation events
When no subset share a unique common ancestor, or there are no distinct clusters of individuals –> conclude that pop. are members of the same species as they share one common ancestor
What is allopatric speciation?
Speciated caused by geographic isolation of two different populations
Low gene flow can occur between populations but must be rare
Caused by barriers such as mountains, canyons, movement of plate tectonics (panama), oceans, etc.
This type of speciation is believed to be the primary speciation which takes place on island
What is parapatric speciation?
Speciation when the ranges of two speciating populations are actually overlapping but gene flow is reduced
A contentious theory, not all evolutionary biologists believe that parapatric speciation can occur
What are ways for parapatric speciation to occur?
New niches open
- population moves into new niche
- niche causes evolution in the new pop.
- eventually, enough different to speciate
Environment differs across a large range
- environmental differences –> differences in evolution
- pop. at the far edges become very different since not exchanging genes
- eventually, individuals in the middle either disappear or become one of the two populations
What is sympatric speciation?
A species arises from within a range of overlapping with its origin species
How is gene flow restricted to a sub-population from within a larger population in the context of sympatric speciation?
Reproductive isolation
- reproductive methods are incompatible
- restricting gene flow, even in completely overlapping populations
Could be due to different rituals, reproductive structures, chromosome duplications in plants
– often arise from mutations
- infertile hybrid offspring
What are hybrids?
Organisms that we consider to be different species can interbreed, hybridize
Offspring are often sterile
However, some interbreeding can create a viable offspring which can survive and mature (hybrid speciation)
What is the exception to the rarety of hydrid speciation?
Plants
Often hybrid offpsring are fertile, even if not many plants can propagate themselves
- Hybrids can spread without sexual reproduction
What is despeciation?
When two species become one
Hybridization can cause distinct lineages to collapse into a single lineage with an admized mosaic genome
relatively rare
Gene flow between two different species can eliminate the distinction between those two species
What are the two scales that characterize evolution?
Macroevolution: evoluation over geological time, mainly observed through fossils
Microevolution: evolution we can observe within a human generation, mainly observed through genomic work
What is a trait?
Observable feature in the phenotype of an organism
Generally physical or physiological characteristics, but can also be considered behavioural in some instances
Examples: organ presence, body size, colour, live birth, migration, etc.
How does trait evolution work?
Traits are generally linked to the genome (genes of the organism)
Randome mutation can create new or altered genes
Some will be expressed as new phenotypes
Natural selection acts on the phenotype
What is the likelihood of a mutation?
Severe mutations adding completely novel traits are extremely unlikely
Most evolutionary changes are slight modifications on existing traits
But genes can be duplicated or repurposed
What does gene duplication have to do with mutation?
Can have duplication of genes or large sections of a chromosome
Duplicate copy mutates and acquires new function
Major source of raw material for genes to evolve
What is specialization?
A species losing generalized traits to become better adapted to a very specific habitat/niche
How have orchids evolved into a specialized group?
Seeds have lost the ability to germinate by themselves
- little to no stored energy
Need to form a symbiosis with a mycorrhizal fungi to germinate and grow
Saves energy for the orchid since little energy investment required for seeds
Mycorrhizae likely only found in optimal habitats for orchid growth
- way to ensure seeds are germinated in the best habitat
Can a species regain a trait if it is lost through evolution?
Poor evidence for this in the fossil record, but we do find examples such as the viviparous lizard
- some lay eggs some have live births
- not all genes present in the genome are expressed, they are regulated –> expression can be turned on and off
What is irreducible complexity?
Trait(s) whose function(s) have become so essential to life, losing them through evolution seems impossible
example: mitochondria
Why was the evolution of seeds in plants a key innovation?
First land plants reproduced mainly by spores
Development of seeds allowed plants to reproduce away from water and experience dormancy
Allowed greater provisioning and dispersal
Vast majority of plants now reproduce by seed
What is the island rule (or fosters rule?)
Species that evolved on islands typically get either larger or smaller than their mainland counterparts (trait evolution of body size)
What is insular dwarfism?
Animals which are large on the mainland become smaller on an island
Because islands have limited resources, smaller animals need less food
Herbivores
- larger size deters predators
- few to no predators on island
- larger size no longer selected for
Carnivores
- prey tends to be smaller on islands
- larger size no longer needed
What is insular gigantism?
Species which are small on the mainland tend to become large on islands
Carnivores
- often lack large carnivores on islands
- new carnivores species can become larger to fill the niche of apex predator
Herbivores
- small herbivores stay small to escpae predation
- if there are no efffective predators, they will become larger (selective pressure gone)
How can we date evolution?
Molecular clock
The background rate of mutation, often of “invisible) mutations (e.g. ones that don’t change the phenotype)
Compare the number of changes
- more similar = recent divergence
- more different = less recent
