Lec 10 slides Flashcards
adaptive radiation
the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage
-originates from single common ancestor
-process results in an array of many species
-the species differ in traits allowing
exploitation of a range of habitats and
resources
4 features commonly identify an adaptive radiation:
-recent common ancestry from a single species
-phenotype-environment correlation
-trait utility
-rapid speciation
causes of adaptive radiation
-ecological opportunity
-high tendency for speciation
ecological opportunity- the absence(or reduction) of competition for resources
colonization of competition-free regions (e.g. islands, lakes, continents)
-galapagos finches, east african cichlids
extinction (eliminates competitors)
-mammals radiated after mass extinction of dinosaurs
key innovation (evolution of a trait that provides access to new resources)
-anole lizards radiated after evolving toepads
high tendency for speciation
reproductive isolation evolves more readily in some clades than others
-e.g. finches vs. mockingbirds
what can hybridization lead to
speciation
hybridization
the exchange of genes b/w species as a result of occasional inter-species mating
-sometimes can reverse speciation process to merge 2 groups into 1
varies across tree of life
can result in complex patterns of variation
-can be evolutionary significant for speciation, especially by polyploidy
polyploidy
describes an organism, tissue or cell with more than 2 complete sets of homologous chromosomes
allopolyploidy
-more than 2 sets of chromosomes from DIFFERENT species
-arises from duplicated karyotype following hybridization b/w species
-most common type of polyploidy
-results in TETRAPLOID gametes
autopolyploidy
-more than 2 sets of chromosomes from SAME species
-arises from duplicated karyotype
-e.g. non-disjunction
-results in TETRAPLOID gametes
hybridization to form an allopolyploid
-2 DIFFERENT species mate and produce f1 hybrid offspring (AA)
-f1 hybrid offspring produces unreduced diploid gametes (AA) due to meiotic non-disjunction
-diploid gametes combine to produce tetraploid f2 offspring
-tetraploid is fertile, but is reproductively isolated from parental species
evolutionary significance of polyploidy
polyploids are reproductively isolated from their diploid parents
-form of SYMPATRIC speciation
polyploids exhibit novel phenotypes
-allows exploitation of new habitats
polyploids often show hybrid strength due to heterozygosity, particularly in allopolyploids
polyploid origin for 50% of flowering plants
-many crop plants and invasive species
true or false: in lineages f1 hybrids form readily
false
in lineages, f1 hybrids can no longer form
taxonomy
the theory and practice of classification and naming
systematics
the study of biodiversity and the evolutionary relationships among organisms
taxon
a single named taxonomic unit at any level (plural taxa)
carolus linnaeus
-father of taxonomy
-binomial nomenclature
-hierarchical system of classification
7 taxon groups
kingdom
phylum
class
order
family
genus
species
purpose of biological classification
-name is a key to shared info on an organism
-has predictive power
-enables interpretation of origins and evolutionary history
species made of many pop, linked by…
gene flow
nodes
(common ancestor b/w 2 taxon)
-correspond to historical lineage splitting events, when one lineage splits into 2
branches(aka edges)
(taxa lines)
-correspond to single ancestor-descendant lineages
-all branches are connected by nodes
tips (aka leaves, terminals, OTUs)
(tips of taxa)
-do not have represented descendants
-can be:
-individuals, species, clades
internal branches
connect 2 nodes
external branches
connect a tip and a node
root
(common ancestor)
-node representing earliest time point in the diagram
-often represented by an unlabeled branch
-don’t always have roots
sister groups
(2 taxon groups sharing common ancestor)
-immediate descendants of same ancestor
-sister taxa are those that are the immediate descendants of the same ancestor
parent branch
connects to main common ancestor
-give rise to ‘daughters’
daughter branch
connects taxon to immediate descendant
ingroup on phylogenetic tree
consists of the focal species in a phylogenetic study
(everything except species closest to common ancestor and CA)
outgroup
more distant relative of the ingroup taxa
-can help to root the phylogeny and help determine what character states are ancestral
-helps determine and position root
(species closest to common ancestor and CA)
most recent common ancestor (MRCA)
-youngest node that’s ancestral to all lineages in a given group of taxa
-different mrca for diff taxa groups
clade
any piece of a phylogeny that includes an MRCA and all of its descendants
-i.e. any piece of a phylogeny that exhibits monophyly
monophyly
property of having a mrca and descendants
-describes a group made up of an ancestor and all its descendants (clade)
-can separate group with one cut
how many clades can a phylogenetic tree contain
n-1
paraphyly
-describes a group made up of an ancestor and some (but not all) of its descendants
e.g. grade
-doesn’t pass scissor test
polyphyly
describes a group that DOESN’T contain the most recent common ancestor of all members
ancestral trait
terms refer to the inheritance of traits for a given group of species
-do NOT describe species themselves
-for the species in a clade, a trait is ‘ancestral’ if it was inherited in its presents form from the mrca of the clade
derived trait
a trait is derived for that clade if it originated within the clade
(i.e. in a descendant of the clade’s mrca)
true or false: the same trait can be ancestral for a clade but derived within a larger clade
true
synapomorphy
shared, derived trait for a clade
-a trait that all species in the clade share, and that evolved on the branch leading to the clade
(i.e. it’s derived within the context of more inclusive clades)
homology
when structures observed in different taxa can be traced to a single structure present in a shared evolutionary ancestor
homoplasy
-when diff species develop traits independently due to environ. pressures
-type of convergent evolution
why conduct a phylogenetic analysis
-understand history of life
-understand large-scale patterns of evolution
-understand how many times traits have evolved, how fast, under what conditions
-practical:
-where/when did parasites spread
-which flu strain was the most successful last year
notes about phylogenetic reconstruction
-phylogenetic relatedness is inferred from homologous traits
-homoplasy (e.g. convergent trait evolution) can mislead phylogenetic inference
2 principal sources of macroevolutionary insights
paleontology, phylogenetics
paleontology
-provides a direct record of past evolutionary change
-inference is strongest for groups that fossilize well
phylogenetics
-provides an indirect record of past evolutionary change
-inference is strongest for groups that have living representatives
fossil record
-provides only evidence for completely extinct clades
-documents long-term patterns of global biodiversity
-provides evidence for catastrophic extinctions during earth’s history
phylogenetics
provides evidence for explosive diversification following mass extinctions
diversification rate
speciation rate - extinction rate
other features associated with increased diversification
-herbivory
-species with more sexual selection
-animal pollination in plants
-increased dispersal
-increased range size
