Speciation and Macroevolution
Chapter 24, 25
Evolution• Microevolution is changes within a
population
• Speciation when changes among populations is significant
• Macroevolution is the origin of new taxonomic groups– New kingdoms, families, orders, etc.– Takes place over millions of years
What is a species?• Species, simply means a “kind” or
“appearance”in Latin.– Still used this way in chemistry
• In Taxonomy, species is the most unique grouping in the hierarchy.
Species• Based on Herbals, full page lists of
characters.
• Binomial system: Homo sapiens,– Linnaeus (1700's) based on a type specimen,
called the Holotype, with a complete description in Latin.
Herbal
Holotypes
Biological Species Concept• Not a definition proper
• Based the ability to sexually reproduce thus sharing a common genepool and evolution.– “Species are groups of interbreeding natural
populations that are reproductively isolated from other such groups”.
Biological Species Concept
• Natural groups of populations
• Potential Ability to reproduce shared by all members in groups of populations
• Reproductive barriers separates groups as separate species.
Biological Species Concept• Recognizes species as independent
evolutionary lineages
• Morphology still what people use day to day to identify species – keys to ID species
Problems with B. S. C. –
– Hybrids (many plant species) – Nonsexual groups (Bacteria, fungi, some plants
and even animals)– No good for extinct groups (fossils)– Each remote population a separate species? No
potential to interbreed, but still same species
Other species concepts:(Do not memorize them)
• Morphological
• Paleontological
• Ecological
• Phylogenetic
Legal Species• Laws protect endangered species in USA
• Make population a new species – now protected ?
• Lump a protected species with another as one– loose protection?– Gray Wolf
Gray Wolf
Red Wolf Coyote
Do you protect the Red Wolf as an endangered species?
Are they a separate species?
Hybridization• Gene flow still exists between two
populations if hybrids can form and reproduce
• Ring species – are groups of populations that can reproduce with their neighbors, yet the extreme can not.
Deer Mouse
California Salamanders: Ring Species
• Ensantina eschscholtzi
Speciation types• Anagenesis
– Transformation of one species into another over time.
• Cladogenesis– Branching evolution
Reproductive Barriers• Lead to speciation by blocking gene flow
• Prezygotic barriers prevent successful fertilization between species.
• Postzygotic barriers allow fertilization but prevent successful development / reproduction of hybrid.
Reproductive barriers
Allopatric Speciation• Takes place in separate
areas.
• Populations become separated by a geologic barrier, blocking gene flow
Antelope squirrels of the Grand canyon rim
Testing Speciation:
Adaptive radiation
• Dispersal to island followed by
• Adaptation to new area-speciation
• Dispersal to next island
• Eventually lead to several species coexisting
• Each adapted to different niches on islands
Adaptive radiations • Species diversify from their ancestors
when important new novel traits form.• These traits allow them to open a new
adaptive zone.
Hawaiian Honeycreepers
• Honeycreepers - In absence of other bird species, they radiated to fill numerous niches
FOUNDER SPECIES
Sympatric speciation• Takes place within habitat
of parent species
• Reproductive barrier forms within a subset of population
• Genetic or behavioral
Polyploidy• Meiotic errors fail to produce haploid
gametes.
• Doubling of chromosome numbers restores fertility, Polyploidy
• May be in one species – Autopolyploidy
• May be in a hybrid- Allopolyploidy
• Common in plants
Origin of Wheat• Allopolyploidy• Hybrid vigor
Sympatric Speciation• Behavioral
– A sub set of animal choose mate by color, size, etc.
• Temporal– A sub set of animal mates or flowers emerge
earlier / later than the rest.
• Over time new species forms as gene flow is stopped.
Rate of Evolution:Constant Gradualism or Punctuated equilibrium?
Macroevolution• Many speciation events over time give rise
to new lineages
• Evident in fossil record
• Novelties come about by modifications to older structures.
• All intermediate forms must be suited to their environments at the time
• Heterochrony- evolutionary change to rate or timing of development. – just a few key developmental genes modified.
• Heterochrony• Ground Salamander has longer toes and
less webbing because they grow longer period of time
• On average, why are men taller than women?
Allometric Growth
• Overall shape is determined by relative growth rates in the different body parts
Changes in Petal Growth Rates
Allometric growth changesCauses change in pollinator
Paedomorphosis
• Adults retain some juvenile features of ancestral species.– Paedogenesis = Juvenile stage develops sexual
maturity precociously (early).
Homeotic Genes• Control placement and spatial arrangement
of body parts
• Hox genes control development in animal embryos
Species selection
Overview
• Fossil Record
• Geologic Time scale
• Mass extinctions
• Continental Drift
• Phylogenetic Trees
Fossil Record• Fossil any preserved remnant or
impression of an organism that lived in the past
• Most form in sedimentary rock, from organisms buried in deposits of sand and silt. Compressed by other layers.
• Also includes impressions in mud
• Most organic matter replaced with minerals by Petrification
• Some fossils may retain organic matter• Encased in ice, amber, peat, or dehydrated• Pollen
Fossil Formation – Fig. 22.3
Conditions that favor fossilization:
• Having Hard parts – shells, bones,cysts• Get buried, trapped
– Marine species– Marsh, flooding areas
• Abundant species (with many individuals)• Long lived species (as a species)• Avoid eroding away• Get discovered
Limitations of Fossils record • Has to die in right place under the right conditions.
Most things don’t get into the fossil record• Biased: Highly favors hard parts, abundant, long
lived species organisms.• Lots of missing organisms• Hard to find, only certain areas highly researched
(NA. Europe)
Dating Fossils
• “Absolute” Radiometric dating: decay and half-life of natural isotopes.
• Index dating – comparing index fossils in strata
Radiometric “absolute” dating
Getting used to the geologic time scale…
• We use– Millions of years (MYA) and– Billions (BYA) of years ago.
• One Million Years: If we give 10,000 years for all of recorded human history– One million years equals 100 times all human
history.– Enough time for 30,000 generations
Geologic Time Scale Table 26.1
Know : • 3 Eons
– Phanerozoic– Proterozoic– Archaean
• 3 Eras – Their dates– Major Animal and
Plant groups
• Periods:– Permian– Cretaceous (K)– Tertiary (T)
The three Eras andthe new groups that begin to
dominate on land• Cenozoic Era– 65.5 MYA
– Mammals, birds flowering plants
• Mesozoic Era – 251 MYA– Reptiles, conifers
• Paleozoic Era – 542 MYA– Amphibians, insects, moss, ferns
• Precambrian (2 Eons) – 4.6 BYA – Origin of animal phyla– Protists, bacteria
The three Eons andthe new groups that begin to
dominate on land
Eons:
• Phanerozoic – Present to 542 MYA, 3 Eras
“Precambrian” is now 2 Eons:
• Proterozoic - 542- 2,500 MYA– Origins of Eukaryotes
• Archaean – 2,500- 4,500 MYA– bacteria, and oxygen atmosphere
Three Eras• Eras do not have same amount of time• Pace of evolution quickens with each major
branch or era .• Recent organisms generally are more complex –
older ones simpler.
• Why ?
Pace of evolution• Quicken over the eras• Evolution builds on what is already there.• Don’t have to recreate the first cell, and all it
machinery with each new species.• More complexity forms out of simpler base
structures, pathways
Many changes in geologic history due to Plate tectonics
Earth’s Mantle Layers• Inner Solid Mantle layer –
• Outer Mantle divided into two layers– Asthenosphere – deep– Lithosphere- “shallow” surface
• Approx. Top 40miles
Layers of the EarthLayers of the Earth
Mantle
Core
Crust
Low-velocity zone
Solid
Outer core(liquid)
Innercore(solid)
35 km (21 mi.) avg., 1,200˚C
2,900km(1,800 mi.)3,700˚C
5,200 km (3,100 mi.), 4,300˚C
10 to 65km
100 km
200 km
100 km (60 mi.)200 km (120 mi.)
Crust
Lithosphere
Asthenosphere(depth unknown)
Plate tectonics• The study of the movement of earth
structures in the crust.
• Internal forces from the core create heat that keeps asthenosphere molten.– Convection cells – Mantle Plumes
Convection Cell in Mantle
Earth’s Layers - Crust
• Oceanic Crust – only 3 miles thick
• Continental Crust – up to 12-40 miles thick
• Oceans change shape much more than continents.
• These land movements we call Plate Tectonics, and cause earthquakes.
Layers of the Lithosphere
Plate tectonics- Divergent
Areas
• Plates spread apart in Divergent (constructive) making new crust
Convergent zones
• Plates move together and collide.
• An Oceanic Plate sinks under Continental in a Subduction zone. – Causes Earthquakes, volcanoes
• When Continental plates collide neither subducts, both deform, mountains
Convergent plates
Slide 8
Fig. 10.6b, p. 215
Lithosphere
Trench Volcanic island arc
Asthenosphere
Risingmagma
Subductionzone
Trench and volcanic island arc at a convergentplate boundary
• 10 MYA India (previously an island) hits Asia
• 50 MYA. Australia becomes completely isolated
• 65 MYA NA and Europe still touched
• 135 MYA Pangea broke up into Laurasia and Gondwanaland
• 250 MYA Pangea all land masses touched
• Fig 25.4
Mass extinctions • Mark borders of Eras:
– 245 Permian (Paleo-Mesozoic)– 65 Cretaceous (K/T boundary; Meso-Cenozoic)
• Caused by a major change that affects many species at once.
Permian extinction• 90% marine & 80% insect species gone • 250 MYA• Took place in about 5 MY • Pangea forming, extreme volcanism- climate
change. • Drop in sea level, loss of shoreline & intertidal,
more severe continental weather• Isolated species come together and compete,
causing extinctions• Paleozoic to Mesozoic boundary
Cretaceous extinctions• 65 MYA • Wiped out 50 % marine species, on land
many families of plants and the Dinosaurs. • Mesozoic to Cenozoic boundary.• Climate cooled and shallow seas
retreated.• Mammals and angiosperms around earlier,
but survived and radiated out to dominant now empty niches
• Many diverse lineages from algae to dinosaurs disappeared at once.
Alvarez-Impact theory
Chicxulub Crater- sonar image
Impact hypothesis• Anomalous Iridium layer marks boundary
layer – element common in meteorites• Chicxulub Crater • Explains large water scarring in NA. • Global winter lasting years, collapsed food
chains. Ignite tremendous wildfires, acid rain.
• Some lineages were dying out before impact.
• Probably a final and sudden blow coming at a time of change, with continental drift, climate change.
Considerations for phylogeny• Homologous structures- derived from a an
common ancestor• Analogous structures - have same function
but evolved independently. Not relates– Convergence- similar looking features due to
adapting to the same habitat, not common ancestry.
• Molecular clocks- give estimates but not real dates. – Assume mutation rates do not change
• Fossil evidence takes priority-– Real dates and Real intermediate structures
Convergent Evolution
Ocotillo Allauidia
North America Madagascar
Phylogenetic trees• Systematics makes groups based on
evolutionary relationships.• Cladistics an analytical method to
determine branch points.• Only Monophyletic trees are accepted.
– Include all species from a common ancestor.
• Polyphyletic trees– grouping of taxa that have do not have
ancestors in common to the entire group.
• Paraphyletic-Leaves out some descendant species from the common ancestor
Phylogenetic Trees
Class Reptilia is paraphyletic
Cladogram Analysis
Molecular tools• We can compare any
living organism to another by DNA.– between species so
distantly related the have no obvious features in common
• Objective and quantifiable• DNA hybridizations,
sequences• Protein sequences• No real dates or
intermediate structures
HIV Molecular clock