Speciation

Barriers to gene flow

Whether or not a physical barrier deters organism or not (EX. bird vs lizard)

Genetic drift

Changes in gene frequencies like bottlenecks

Morphology variation

members of same species can seem different because of environmental conditions; members of different species can seem identical

Morphology variation is….

Not very useful in distinguishing species

Biological species concept

“Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.” - Ernst Mayr

Prezygotic isolation

mating or zygote formation is prevented

Postzygotic isolation

takes effect after hybrid zygotes form; zygotes may die early, be weak, or sterile

Ecological isolation

organisms can’t mate because they’re in different locations

Temporal isolation

reproductive timing keeps species isolated

Behavioral isolation

the way organisms act influences mating choices

Mechanical isolation

reproductive parts don’t fit

Part of prezygotic isolation

ecological, temporal, behavioral, mechanical

Zygotic mortality

death of zygote

Hybrid inviability

unable to survive or develop into reproductively capable adults

Hybrid sterility

unable to produce viable offspring

Mechanisms of speciation

allopatric, sympatric, parapatric

Allopatric speciation

happens in geographically isolated populations

Wrasses

type of tropical fish - separated into Atlantic + Pacific by Isthmus - genes for some enzymes diverged in form

Walruses

separated by sea ice sheets around North Pole - Atlantic pop. bigger + longer than Pacific

Archipelagos

island chains separated from continents - speciation caused by colonization + genetic divergence

Honeycreepers

lack of other birds -> radiated to fill many niches in Hawaii

Hawaiian Silverswords

also adaptive radiated - differentiated on island

Sympatric speciation

species forms in home range of parent species

African cichlids

surface fish populations stopped mating w/ bottom fish - 2 diff species - speciation w/o barriers

Sympatric speciation

nearby populations become distinct species while keeping contact along common border

Orioles

baltimore + bullock - separate species - between is hybrid zone

Gradual speciation model

species emerge through many small morphological changes accumulating over long time period

Punctuated speciation model

Most changes in morphology are compressed into brief period near onset of divergence

Genetic divergence

gradual accumulation of differences in gene pools - caused by natural selection, genetic drift, + mutation

What counters divergence?

Gene flow

Adaptive radiation

when one species diverges into many

Extinction

irrevocable loss of species; reduced diversity followed by adaptive radiation

Polar bears

sea ice sheets lost to global warming - needed for hunting for polar bears

Asteroid impacts

Earth is hit many times, destroying many species

Fossils

recognizable evidence of ancient life

Fossilzation

organisms are buried in ash or sediment; remains infused w/ metal + mineral ions

Coelocanth

living fossil - thought to be extinct but still exists; live specimen discovered by Prof. James Leonard on jan. 3, 1939

Tiktaalik roseae

missing link between fish + land animal evolution

Plate tectonics

earth's crust that is fractured - movement driven by upwelling of molten rock

Sea floor spreading

occurs when new rock is made + rises up in center of ocean - pushes tectonic plates against each other

Types of natural selection

directional, stabilizing, destabilizing

Directional selection

allele frequencies shift in 1 direction

Stabilizing selection

intermediate forms are favored + extremes are eliminated

Destabilizing selection

forms at both ends of range of variation; intermediate are eliminated

Different mutations

lethal, neutral, advantageous

Continental drift

Idea that continents were once joined + have since drifted aparted

Seafloor hot spots

progressive northwestern drift of islands from their point of origin over hot spot is shown by ages of principal lava flows on various Hawaiian Islands from northwest (oldest) to southeast (youngest)

Geologic time scale

boundaries based on transitions in fossil record

Stratification

how fossils are found in sedimentary rock; newest layers on top, oldest on bottom

Hawaiian islands

Have volcanic origins + possess variety of habitats