Week 5 Flashcards
Sympatric Speciation
Natural selection overcomes gene flow and causes speciation of populations despite no physical isolation
Assortative Mating
Favor individuals with similar characteristics to others
What are the two mechanisms of sympatric speciations
disruptive selection and polyploidization
Disruptive selection as a mechanism of sympatric speciation
natural selection for different habitats or resources cause divergence - must be coupled with assortative mating
Polyploidization
genetic isolation is created by formation of polyploid individuals that can breed only with each other
Types of polyploidization
Autopolyploidy and allopolyploidy
Autopolyploidy
polyploids have duplicate chromosome sets from same species (e.g. a chromosome doubling to produce a tetraploid)
Allopolyploidy
polyploids have chromosome sets from different species (they originate with a hybridization event, followed by chromosome doubling)
Explain the example of the Soapberry bug for disruptive selection
-bugs use beaks to reach seeds inside fruits
-variation in fruit size between nonnative (small) and native (large) causes the population to diverge into a short beaked population and a long beaked population
Explain the example of the maidenhair fern as it relates to polyploids
-Example of autopolyploidy
-this species contains diploid and tetraploid individuals
-tetraploids are the offspring of a diploid gamete that is self fertilized
-tetraploid individuals can breed with other tetraploids but not diploids
How do allopolyploid species form
-species 1 and 2 undergo meiosis and produce a hybrid individual
-hybrid individual have less efficient homologous pair recognition causing an increase in chance for error during meiosis
-an error in meiosis causes the formation of an allopolyploid cell which has two copies of each chromosome
-a gamete with the same number of cells as the hybrid individual fuses with another identical cell to form a offspring with twice the ancestral genome (diploid to tetraploid)
-leads to reproductive isolation
How does a polyploid cell lead to isolated reproduction
if the polyploid and the original species attempt to mate they will produce a species with an odd number of chromosomes whose gametes rarely contain the same number of each type of chromosome causing dysfunctional number of chromosomes and the inability to reproduce
Why is speciation by polyploidization more common in plants than animals
somatic cells of plants that have undergone many rounds of mitosis may then undergo meiosis and produce a polyploid gamete, also self fertilization is more common in plants
Adaptive introgression
process in which advantageous genetic variation is transferred from one species (or populatiom) to another
Homogenization
When gene flow occurs and may erase distinctions between two populations
Possible outcomes of hybridization
homogenization, adaptive introgression, reinforcement, development of hybrid zones and speciation by hybridization
What happens when isolated populations come into contact
when prezygotic isolation dose not exist, populations may interbreed to produce hybrids
Reinforcement
Selection for traits that isolate populations reproductively - assortative mating
-occurs because of natural selection
-If two populations of differenct speices are extensively diverged, their hybrid offspring may have lower fitness - incomplete postzygotic isolation
Explain the Wolf example from lecture on hybrid speciation
Red wolves have mitochondrial DNA that is derived from either the gray wolf or coyotes, they could either be from hybrid origin or there could have been extensive gene flow for mtDNA
-Some wolves have a percentage of coyote DNA
-Red wolves are 24% wolf and 76% coyote
-coyotes are a combination of coyote, wolf and dog DNA
Internal Nodes on Phylogenetic tree
represent ancestors of the descendant taxa
Ancestral Node/ root on phylogenetic tree
represents oldest ancestor on tree
Polytomy
3 way split on a phylogenetic tree where there is not enough data to further classify
Homology
occurs when traits are similar due to shared ancestry
Homoplasy
when traits are similar for reasons other than common ancestry
Convergent evolution
when natural selection favors similar solutions to the problems posed by a similar way of life - common cause of homoplasy
How do researchers estimate phylogenies
they analyze characteristics of species to infer phylogenetic relationships among species
Strategies for estimation trees
phenetic (distance), cladistic (maximum parsimony), maximum likelihood and bayesian
Synapomorphy
a novel trait that a clade of organisms have and that others outside this clade lack
What is the purpose of Hox genes
to regulate differentiation within the adult and embryo
How do we know that Hox genes of humans and fruit flies are homologous
similar DNA sequence, similar genomic organization, similar expression patterns during development similar function, other species closely related to fruit flies and humans also have Hox genes Max
Maximum parsimony
logic that assumes that the best explanation or pattern is the one that implies the least amount of change
Cryptic species
Many species are not easily distinguished by morphology
animal and plant parts also sometimes not easily identified, most diverse parts of the world are least known
DNA barcoding
-inventory of biodiversity
-automate and expeditated species identification
-classifies based on DNA sequence of one gene
Atavism
an ancestral characteristic that is lost but then re-emerges during evolution
In situ diversification
single ancestor disprses across islands and then diversifies
-each species exploits different aspects of the environment
-Not overly diverse
Ecotypes
genetic variation within a species that allows it to exploit a particular environment
Frog dispersal onto island
mainland frogs dispersed and then under went adaptive radiation into different ecotypes
Parental care in fanged frogs
some carry tadpoles on back others guard eggs, some use internal incubation
Did fanged frogs undergo an adaptive radiation
-diverse and closely related species that vary in useful trait
-trait variation is correlated with environmental variation
-some adaptive radiations exhibit species for species matching
