Lec 10 slides Flashcards by Nadia Taheri

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

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4 features commonly identify an adaptive radiation:

-recent common ancestry from a single species
-phenotype-environment correlation
-trait utility
-rapid speciation

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causes of adaptive radiation

-ecological opportunity
-high tendency for speciation

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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

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high tendency for speciation

reproductive isolation evolves more readily in some clades than others
-e.g. finches vs. mockingbirds

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what can hybridization lead to

speciation

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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

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polyploidy

describes an organism, tissue or cell with more than 2 complete sets of homologous chromosomes

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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

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autopolyploidy

-more than 2 sets of chromosomes from SAME species
-arises from duplicated karyotype
-e.g. non-disjunction
-results in TETRAPLOID gametes

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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

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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

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true or false: in lineages f1 hybrids form readily

false

in lineages, f1 hybrids can no longer form

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taxonomy

the theory and practice of classification and naming

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systematics

the study of biodiversity and the evolutionary relationships among organisms

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taxon

a single named taxonomic unit at any level (plural taxa)

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carolus linnaeus

-father of taxonomy
-binomial nomenclature
-hierarchical system of classification

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7 taxon groups

kingdom
phylum
class
order
family
genus
species

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purpose of biological classification

-name is a key to shared info on an organism
-has predictive power
-enables interpretation of origins and evolutionary history

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species made of many pop, linked by…

gene flow

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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