Phylogenies, Species, and Speciation

root

most ancestral branch on tree

branch

line representing population through time

outgroup

taxon that diverged before taxa that are focus of study

tip

endpoint of branch- represents living/extinct species/taxa

node

point within tree where branch splits into two or more branches

polytomy

node that depicts an ancestral branch dividing into 3 or more branches; relationship among taxa not resolved

sister taxa

lineages that diverged from same node; share a common ancestor

parsimony

most like explanation/pattern- the one that requires the fewest steps

monophyletic

group that includes common ancestor

paraphyletic

group that includes common ancestor but not all descendants

polyphyletic

group that includes descendants but not common ancestor

character

any heritable characteristic that varies among taxa being studied

synapomorphy

shared derived forms

sympliesiomorphy

shared ancestral form

autapomorphy

unique derived form

homoplasy

shared traits due to convergent evolution

homology

shared trait due to common ancestry

advantages of the fossil record

direct evidence, physical record, ages can be estimated

limitations of the fossil record

not all organisms fossilize (due to habitats, tissues, timing, and abundance)

precambrian time

all life unicellular, cyanobacteria = oxygen

phanerozoic era

paleozoic, mesozoic, and cenozoic

paleozoic

land plants, some land animals, fungi, aquatic animals

mesozoic

dinosaurs, mammals, land plants, aquatic plants, and invertebrate animals; dinosaurs and seed plants dominant species

cenozoic

amany modern lineages including humans; flowering plants and mammals dominant

adaptive radiation

rapid evolutionary diversification within one lineage

requirements for adaptive radiation

monophyletic group, rapid diversification, and exploit new niches

how does adaptive radiation occur?

favorable environmental conditions- new habitat lacks predators, competitors, or herbivores, and evolution- new traits allowed for better survival in environment

HOX genes

determine body segment organization; more duplications = more complexity —> new niche exploitations

background extinctions

average rate of extinction when mass extinction not occurring; ~1 species/million years

mass extinctions

rapid extinction event of many diverse species around the world; ~75% of species lost

what are the 5 mass extinctions?

end-ordovician, late devonian, end-permian, late triassic, and end-cretaceous

end-ordovician

85% marine species go extinct; caused by ice age followed by rapid warming

late devonian extinction

over 50% of warm, shallow, water species went extinct due to unknown causes

end-permian

90% of species went extinct due to multiple reasons: acid rain, volcanic eruptions, fires, low oxygen in aquatic environments, and sea-level drop

late triassic

unknown cause that led to >75% of species to go extinct

end-cretaceous

extinction of dinosaurs by asteroid impact and increased volcanic eruptions

population

individuals of the same species

species

evolutionary independent population or group of populations

biological species

population that is reproductively isolated from other populations

what are the two kinds of reproductive isolation?

pre/post zygotic

prezygotic isolation

individuals do not mate and zygote is not formed; behavioral, temporal, habitat, mechanical, and gametic barriers

behavioral barriers

populations do not interbreed because they have different courtship displays

temporal isolation

populations are isolated because they breed at different times

habitat isolation

populations are isolated because they breed in different environments

mechanical isolation

mating fails because male and female reproductive structures are incompatible

gametic barrier

mating fails because eggs and sperm are incompatible

post zygotic isolation

zygote forms, but hybrids do not survive or reproduce

hybrid inviability

hybrid offspring do not develop normally and die at some point during early development

hybrid sterility

hybrid offspring mature but are sterile as adults

disadvantages of biological species

not applicable with species with ranges that do not overlap or reproduce asexually

morphological species

populations differ observable traits; size, color, shape, pattern

what are advantages of morphological species?

applies to sexual and asexual reproduction, living and extinct species

what are disadvantages of morphological species?

cryptic species, polymorphisms, and subjectivity

phylogenetic species

smallest monophyletic group; based on evolutionary history and synapomorphies (morphology and DNA)

what are disadvantages of phylogenetic species?

conflict in definition of a smallest monophyletic group, wide range of data can conflict, limited number of phylogenies available

allopatric speciation

populations that become geographically isolated

allopatric dispersal

individuals colonize new location, trait of colonizer is different than that of source population, natural selection acts on colonizer trait

allopatric vicariance

large population divided by new barrier; two population diverges and becomes genetically isolated

sympatric isolation

populations/species that live in same geographic area but isolated by pre/post zygotic barriers

extrinsic sympatric speciation

disruptive selection- acts on many traits, impacts survival

intrinsic sympatric speciation

autopolyploids and allopolyploids

autopolyploid

mutation results in a doubling of chromosome number; all from the same species

allopolyploid

parents of different species mate and an error in mitosis occurs; offspring are viable and fertile

what are advantages to polyploidy?

higher genetic diversity, lower inbreeding depression, high heterozygosity

what happens when species come back together?

1) lower hybrid fitness = continued reproductive isolation 2) hybrid traits advantageous = new species 3) hybrid zones