History and Tree of Life Flashcards
fossils
how it is documented how species change over time
homology
species are related by common ancestry
“same-source”
opposite of homoplasy
tree of life
a single phylogeny that can be hypothesized that shows relationships among all species
when were there great advances in evolutionary theory?
17-1800s
branch
a line representing a population through time
root
the most ancestral branch in the tree
tip (terminal node)
endpoint of a branch
represents a living or extinct group of genes, species, families, phyla, or other taxa
outgroup
a taxon that diverged prior to the taxa that are split into two or more branches
represents the most recent common ancestor of the descendant groups
polytomy
a node that depicts an ancestral branch dividing into three or more (rather than two) descendant branches
usually indicates that insufficient data were available to resolve which taxa are more closely related
characters
a feature
e.g. wing color
character states
what the different conditions are called when taxa differentiations with respect to a character
e.g. brown, black, red, gray
(wing color)
pleisomorphic
ancestral (primitive) trait
apomorphic
changed (derived) trait
synapomorphy
shared derived trait found in two or more taxa and their common ancestor, but missing in more distantly related ancestors
e.g. hair/lactating is a synapomorphy for humans and dogs
what factors are used to hypothesize relationships between taxa?
character states and synapomorphies
homoplasy
a state inherited due to a convergent evolution
“same-form”
opposite of homology
branch lengths
branch lengths are arbitrary
emphasis is on the branching pattern which estimates evolutionary relationships among populations
branch lengths show the extent of genetic difference (mutation) among populations
branch lengths show the extent of evolutionary time between nodes
scale bars are included
Precambrian Eon
4.6 bya to 542 mya
evidence of both bacteria and archaea
includes:
- the oldest evidence of life
- oldest cyanobacteria (oxygenic photosynthesis)
- origin of eukaryotes
- multicellular eukaryotes
- sponges (first animals)
- cnidarians
stromatolites in Shark Bay, Australia- rocks from this time period that have layers
oldest cyanobacteria (oxygenic photosynthesis)
2.6 bya
rise in atmospheric oxygen at 2.3-2.1 bya
origin of Eukaryotes
1.8 bya
single-celled and small
multicellular eukaryotes
1.6 bya
sponges
635 mya
first animals
were filter species that lived in water
cnidarians
580 mya
like jellyfish and *
Phanerozoic Eon
542 mya to present
includes:
- Cambrian Explosion
- land plants
- fungi
- insects
- Tiktaalik (earliest tetrapod)
- end-Permian mass extinction
Cambrian Explosion
542-488 mya
“explosion” of animals in the fossil record
new diversity
Cambrian fossils
Ediacara fossils
565-542 mya
soft-bodied; likely filtered or absorbed food from water
not considered animals
do not know where to put them in the tree of life
Cambrian fossils
541-500 mya
big increase in morphological complexity
large animals of movement
oldest fossils of most animal groups (arthropods, mollusks, echinoderms, chordates)
everything is confined in the oceans at this point
not sure what caused diversification; multiple non-mutually exclusive hypotheses:
- higher oxygen levels
- evolution of predation
- niches beget niches
- new genes
higher oxygen levels (potential Cambrian explosion cause)
needed for increased aerobic respiration, large bodies, active movement
evolution of predation (potential Cambrian explosion cause)
novel selection pressure
lead to co-evolutionary arms races
which leads too new traits
e.g. evolution of the eyes
niches beget niches (potential Cambrian explosion cause)
movement off benthic floor fostered diversification
new genes (potential Cambrian explosion cause)
evolution of Hox genes
-important in body development
allowed for greater diversity
land plants
475 mya
may have needed fungi in order to be on land
fungi
440 mya
may have facilitated the transition of plants to land
insects
400 mya
largest group of animals extant today
Tiktaalik
375 mya
earliest tetrapod
has some fish-like qualities and some tetrapod-like qualities
shows the transition between water and land
End-Permian mass extinction
252 mya
the largest mass extinction
> 50% of all families and >80% of all genera
up to 96% of all marine species and 70% of terrestrial species
causes are unclear:
- massive changes in temperature, atmosphere, and oceans
- flood basalts – added heat, CO2, and sulfur dioxide
Mass extinction
rapid extinction of a large number of lineages throughout the tree of life
surviving lineages experience reduced competition
creates ecological opportunity for diversification
there have been 5 in history
end-Permian is the largest
dinosaurs
240 mya
End-Cretaceous mass extinction
65 mya
niche space is clearers out; especially for mammals due to the loss of dinos
therefore, it is followed by high diversification rates in mammals and birds
impact hypothesis: caused by the impact of 10 km wide asteroid off the coast of Yucatan Peninsula
many lineages of modern birds, mammals, and fish date back to this time
Impact hypothesis of the end-Cretaceous mass extinction
caused by the impact of 10 km wide asteroid off the coast of Yucatan Peninsula
crater at impact site
rocks from this time period are rich in rare minerals known from meteorites
adaptive radiation
rapid evolutionary diversification within one lineage, producing descendant species with a wide range of adaptive forms
major characteristics:
- monophyletic group
- rapid speciation
- ecological diversity- use of a variety of resources and/or occupy a variety of niches
mass extinctions provide ecological opportunity for adaptive radiations
e.g. hawaiian silversword phylogeny; Galapagos finches; honeycreepers; anolis
Ecological opportunity
availability of new or novel resources
over time, populations in different niches can become reproductively isolated and form new species
e. g. islands:
- colonists of islands are often “freed” of competition and can evolve to expand realized niche
Morphological innovation
evolution of a new or novel morphological trait could allow descendants to exploit new niches
e.g. flowers and pharyngeal jaws
flowers (morphological innovation example)
unique reproductive structure important in te diversification of today’s > 250,000 angiosperms
allows them to cater to specific pollinators
leads to quick speciation
pharyngeal jaws (morphological innovation example)
second pair of jaws in the throat in some fish
highly modified in cichlid fish:
- evolved many different forms, each specializing on different food types
- has evolved to specialize in different types of prey
sister groups
closely related species that share a recent common ancestor at the node where their branches meet
ancestral trait
a character that existed in an ancestor
derived trait
a character that is a modified form of the ancestral trait found in a descendant
originate via mutation, selection, and genetic drift
cladistic approach
based on the principle that relationships among species can be reconstructed by identifying sharing derived traits, called synapomorphies
