Speciation and Phylogenies Flashcards
What is speciation
The process by which one species divides into two
How do you initate the speciation process
Restricting gene flow between isolated populations
Whats allopatric speciation
Involves physical seperation between two populations
Whats vicariance
A type of allopatric speciation, large populations become split into two via a physical barrier
Whats peripatric
A peripheral population is established outside the original range of the population and forms an independant colony
Whats sympatric speciation
A population being split into two reproductively isolated populations while staying in the same geographic location
Whats parapatric speciation
When neighbouring populations of a species are geographically connect and exchange genes but diverge into seperate species
How can allopatric speciation occur
Vicariance e.g. mountain uplifts or peripatric e.g. dispersal to oceanic islands
Example of vicariance (1)
Isthmus of Panama in central America, the isthmus closed 2.8 million years ago and now species show adapted divergence either side of the lung bridge
Examples of vicariance (2)
Speciation in birds such as the South American Andes, populations shift up and down the mountain range
Dispersal/ peripatric/ founder effect examples
Archipelago and island bird colonisations dispered from mainland to isolated islands.
Example of sympatric speciation
Rhagoletis apple maggot fly, ancestor of the r. pomenella which layed eggs in fruit Hawthorn trees
Whats more common than sympatric speciation
Parapatric
Examples of parapatric speciation
Lizards at the white sands
What can ecological speciation be defined as
The evolution of reproductive isolation between populations as a result of ecologically based divergent natural selection
An example of ecological divergence
Monkey flowers (mimulus)
Whats sexual selection defined as
Differential reproduction as a result of variation in the ability to obtain mates
Why does sexual selection vary across populations
To improve conspecific recongition
To provide optimal direct benefits to mates
As a result of pleiotrophic effects
Because of variation in good gene mechanisms
Because of runaway mechanisms when trait and preference alleles become genetically linked
What does higher taxa refer to
Any grouping above the species level for example genus or family
Whats another process that promotes speciation
Reinforcement
What is reinforcement defined as
The evolution of enhanced reproductive isolation between populations due to natural selection for greater isolation
What needs to be low in order to reinforcement to occur
Hybrid fitness
What can reproductive character displacement be defined as
the accentuation of differences between sympatric populations from two species as a result of reproductive interactions between them
Example of reproductive character displacement
Ficedula fly catchers including pied flycatcher and the collared fly catcher, they look different in the area of sympatry
When does polyploidy occur
When chromosomes fail to segregate during meiosis
How are tetraploids formed
From two individuals in the same species
Whats allopolyploid
Duplication of chromosomes in hybrids between species
What are the consequences of having more chromosomes than normal
Increase in the number of gene copies
Tetraploid individuals reproductively isolated from parental species
Unable to form any viable offspring
How common is polyploidy in plants
15% in flowering plants and 31% in ferns
Whats an example of polyploidy in plants
Tragogan goatsbeards.
How can we prevent extinction in new polyploid species
Reduce sterile triploid offspring by self fertilisation, vegetative propogation and habitat segregation
How can we capatilise on the advantages of polyploidy
Heterozygote advantage, extreme phenotypic traits, chance to access new fitness opitma in the adaptive landscape
Whats allopolyploid a form of
Hybrid speciation
Whats homoploid hybrid speciation
Speciation via hybridisation without change in chromosome (ploidy) number
Example of homoploid hybrid speciation
Helianthus sunflowers
Example of adaptive radiation
Cichild fish in Lake Victoria
Whats random genetic drift
Random changes in frequencies of two or more alleles or genotypes within a population
What are phenograms
Represent similarity or distance but may not represent historical relationships
What are phylogenetic trees
Represent a hypothesis about historical relationships
What are cladograms
Y axis has no meaning, only tells the relationship between species
What are additive trees
Where the y axis tells us about the amount of evolutionary change, how much sequence change happens
What are ultra-metric trees
Y axis means time
What are fully bifurcated trees
Assumes all speciation events involve one ting splitting into two
What are multifurcated trees
A node splits into more than two species/ branches
How do we add a root to the tree
Add information for an outgroup
Whats an outgroup
A taxon that we believe, a priori to be more distantly related to the focal species than they are to one another
How do we estimate genetic distance
K = the proportion of nucleotide sites that are different
What does UPGMA stand for
Unweighted pair group method with arithmetic mean
What does the jukes cantor distance correlation show
The more evolutionary distance there is, the more likely theres more hits (lorgarthmic scaling)
Examples of when Phylogenies are useful
To see if flying mammals died once or twice
Limitations in phlyogenetic analysis
Trees are hypotheses:
scoring characters are hard
homoplasy is common
Acient events are hard to infer
Some lineages might be diverging too rapidly
Hybridisation can be a problem
Incomplete lineage sorting
Phylogenetic imbalance definition
A difference in the number of descendent tips either side of a focal node
What does the equal-rates Markov model show
The probabiltiy of speciation per unit time is constant across all lineages
Whats lateral gene transfer defined as
The aquisition of genetic material from another organism without sexual reproduction
Why is Alloterepopsis important
Because its the only known species with the C4 and non-C4 enzymes
Why does Zambian accession have more LGT
Has a much greater rate of gains due to diverse habitiat
how many genes are LGT
0.04%
What factors drive differentiation
Speciation and extinction
Why do speciation rates vary
The frequency of barriers/ factors that produce geographical isolation
The rate at which these isolated populations evolve isolating mechanisms
The degree of these ecological diversity offering vacant ecological niches to these newly arising species
Whats the cycle of speciation
- the formation of geographical isolates
- acquisition of reproductive isolating mechanisms
- ecological differentation
- cycle begins again
What factors might affect progress through speciation
Rate of geographic isolation, rate of reproductive isolating barriers, rate of ecological differentiation and co-existence
