macroevolution
TRANSCRIPT
Lecture 6a:Macroevolution
Lecture 6a:Macroevolution
Macroevolution
Not really different than microevolution, but over a much larger scale
Changes to species, not changes to populations
Species- what are they anyway?
Biolgical Species Concept: members of the same species interbreed and have a shared gene pool, but are reproductively isolated from every other species
Speciation: the evolution of new species
Species
Two animals of the same species can reproduce and have fertile offspring
One species can consist of one or many populations
Appearance does not necessarily allow you to tell two species apart
Reproductive Barriers
As speciation occurs, reproductive barriers arise that prevent breeding from occurring between the different species
Barriers fall into two categories: prezygotic and postzygotic
Prezygotic BarriersHabitat Isolation: The different species inhabit different habitats
Temporal Isolation: Breeding season is at different times of the year
Behavioral Isolation: Pheromones, courtship rituals, songs or calls, etc are different
Mechanical Isolation: Genitalia are incompatible
Gamete Isolation: The gametes can not fuse to form a zygote
Behavioral isolation: Different
dewlaps in Anolis lizards
Mechanical isolation: Watersnak
e hemipene
s
Postzygotic BarriersZygote mortality: A zygote is formed, but it does not survive
Hybrid sterility: The zygote develops into an adult, but it is sterile
F2 Fitness: The hybrids can reproduce, but the F2 generation can not
Hybrid Sterility: Both mules and zonkeys are sterile
Types of SpeciationAllopatric Speciation
Occurs when populations become geographically isolated, and move further and further apart genetically from the original species
Ex. Ensatina salamanders, iguanas
Allopatric speciation in Galapagos finches
Types of Speciation
Sympatric speciation
Population develops into two or more groups without geographic isolation
Polyploidy: increase in number of chromosomes to 3n or higher due to hybridization, sometimes followed by doubling of chromosomes- results in 3rd species
Types of Speciation
Adaptive Radiation
New species evolve from one ancestral species to fill different niches in the habitat
Ex. Galapagos finches, Hawaiian honeycreepers
Adaptive radiation in cichlid fish, species have
evolved to eat different food sources and to
feed in different ways
Fossils
To study extinct species, especially ones from millions of years ago, we look to fossils:
The remains or traces of past life
Can take several forms- amber, footprints, petrification, actual remains
Geologic Time
See timeline
Cambrian explosion: all major groups of animals appeared
Number of species on Earth has continued to increase over time, even to the present day
Speciation We do not know how quickly species arise- there are two models:
Gradualistic Model- slow steady change over a long period of time
Punctuated Equilibrium: somewhat ‘sudden’ appearance of new species in fossil record
The transitional fossils are unlikely due to geographic isolation and small numbers
Mass Extinctions
Relatively sudden disappearances of large numbers of species
Have been several, of course dinos the best known example
Two main causes: Continental drift and meteorite impacts
Continental Drift
The continents on Earth are moving
Plate tectonics: The crust of Earth is floating on the molten mantle, the crust is in several pieces
As the continents move, the climate changes
Pangaea: its
formation 250 mya
was probably the cause
of the Permian
Extinction
Meteorites
Probably the cause of the dinosaur’s extinction
Caused massive cloud of dust that blocked the sun, lowering temperatures worldwide
Soot and iridium are found in Cretaceous clay, and a crater has been identified as well
SystematicsDKPCOFGS
As the category gets higher and higher, it gets more and more inclusive
Ideally, organisms are classified according to their evolutionary relationships, so taxonomy is in constant flux as we learn more and more
Phylogenetic Trees
Trees that show relatedness of different organisms
Indicate common ancestor, and lines of descent
Determined using comparative anatomy, embryology, molecular evidence
Phylogenetic Tree of
chordates
Phylogenetic tree of canines
Anatomy
Remember, it matters where the characteristic in question arose from, not what it does now
Ex. Thorny devils vs. horny toads have Analagous structures
Ex. Vertebrate forelimbs are Homologous structures
Thorny devil (Australia)Horned lizard (US)
Analogous structures- horns on two lizards
Homologous structures- front limbs of several vertebrates
Using DNA to determine relationshipsRemember: evolution occurs when mutations in DNA occur-- it can not occur without those random changes
Therefore, the more closely related animals are, the fewer differences there will be in their DNA
This allows new information about DNA to be included in our understanding of how life on Earth evolved