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