Phylogenies Flashcards
phylogenetic trees
- family trees
- visual depiction of a hypothesis
- shows the pattern of relatedness between species
sister taxa/sister species
group of closely related species
lineage
represented by internal and terminal branches
outgroup
species or group that is closely related to the ingroup but known to be phylogenetically outside of it
ingroup
group of organisms of primary interest
any trait shared with outgroup is ancestral
monophyletic clade
includes the common ancestor and all descendants of that ancestor
paraphyletic clade
includes the common ancestor but not all descendants
polyphyletic clade
includes all the descendants but not all the common ancestors
earliest common ancestor
root of the phylogenetic tree
root of the phylogeny
common ancestor of all the organisms in a tree
homologous trait
features shared by species that have been inherited by a common ancestor
synapomorphy
derived trait shared amongst a group of organisms and evidence of common ancestry
distinguishes clades from one another
ancestral trait
trait present in the ancestor of a group
derived trait
characteristic evolved from a recent ancestor
usually synapomorphy
present in only the ingroup
homoplasies
similar traits generated by convergent evolution or evolutionary reversals
convergent trait
superficially similar traits that evolved independently in different lineages
evolutionary reversal
a character may revert from a derived state back to an ancestral state
parsimony principle
- testing a phylogeny through the number of trait changes
- simplest explanation of observed data is the preferred explanation
- specific case of Occam’s razor
ancestral v. dervied
- depends on what species are included on the tree you are looking at
- a trait may be ancestral or derived depending on the point of reference
ex: birds are an ancestral trait for any group of modern birds, but in a phylogeny of all vertebrates, feathers would be a derived trait and therefore a synapomorphy
traits used in phylogenetic analysis
any trait that is genetically determined
all kinds of traits, morphological, fossil, developmental, molecular, and behavioral
morphology
most species have been described by morphological data
limitations: some taxa show few morphological differences, it’s difficult to compare distantly related species, some morphological variation is caused by environment
molecular data
- most widely used
- nuclear, mitochondrial, and chloroplast DNA
- RNA and amino acid sequences
- models can account for multiple changes at given sequences positions, different rates of change at different positions, and different rates of transitions vs. tranversions
developmental data
similarities in development may reveal evolutionary relationship
sea squirts and vertebrates have a notochord at some time in their development
behavioral data
data that is genetically determined can be used as a phylogenetic trait
behavior can be culturally transmitted or inherited
bird songs vs. frog calls
palentology
- fossils provide information about morphology of past organisms and where and when they lived
- fossils help determine derived and ancestral traits and when lineages diverged
- some fossil record is fragmentary and missing for some groups
- endocasts can help create a phylogeny
benefits of phylogenetic trees
reconstruct past events, determine when traits evolved, determine convergency, distinguish homology vs. convergency
reconstructing past events
for zoonotic diseases, it’s important to understand when, how, and where it entered humans
ex: HIV
origin of a trait in phylogenies
can help us understand when a trait originated
ex: long swordtails have higher reproductive success (sexual selection)
evolution of the sword may result from a preexisting bias of female sensory systems
when artificial swords were attached to Priapella males, females preferred this
females had the preexisting bias before swords evolved
