Genetics Evolut ion Speciation Diversity of Life

Macro-evolution -- study of the history of life Intro to phylogenies & the fossil record as tools The Cambrian Explosion (543 mya) -- rapid diversification of metazoan animal life Genetic mechanisms of major morphological change Adaptive radiations -- key innovations lead to rapid diversification Mass extinctions -- environmental catastrophes lead to loss of diversity

Which one of these trees is different?

Shared, derived traits are used to build phylogenies.

The unusual shape of an ankle bone is a shared derived trait for the “artiodactyls”, hoofed animals with an even number of toes. Whales have traditionally been thought to descend from a group of carnivorous animals outside of the artiodactyls.

Recent molecular work suggests, in contrast, that whales arose from within the artiodactyls.

SINE = short interspersed nuclear elements. Class of transposable elements, or “selfish DNA”. Contain genes to get themselves copied and inserted. Provide record of evolutionary history. Draw artiodactyl phylogeny showing gain of SINEs.

The Fossil Record

1. Death and quick burial 2. Various fossilization methods - - for example, cavity filled with minerals. 3. Fossil must must later be exposed, at least partially, so that people can find it. Rocks must not be deformed by metamorphosis, or fossils would be destroyed. Formation and Recovery of Fossils

FYI -- types of fossils. Don’t memorize.

New method -- can visualize using high energy light, “X-ray” through solid amber.

The fossil record is very incomplete Archaeopteryx -- oldest bird in fossil record.

The fossil record contains biases. 1. Habitat bias -- organisms must be buried in sediment. Most common on mud flats, swamps, beaches…. 2. Taxonomic bias -- hard parts preserve best Shells, teeth, bones, etc. Soft worms not so much. 3. Temporal bias -- very old fossils likely to be lost through metamorphism or erosion. 4. Abundance (maybe this isn’t a bias….) -- common species more likely to be preserved.

Life’s Timeline Dates to know: 4.6 bya -- earth formed 3.6 bya -- life began ~ 2 bya -- Eukaryotes* arose 1 bya -- first multicellular organism 543 mya end of PreCambrian, beginning of Paleozoic 250 mya beginning of Mesozoic 65 mya beginning of Cenozoic *Eukaryotes have a nuclear membrane and organelles such as mitochondria and chloroplasts Prokaryotes (Archaea and Bacteria) do not

Each point represents a comparison between two species. Points near the origin are comparing closely-related species. By fossil record-- time to common ancestor Creation of a molecular clock

Used mtDNA clock calibrated w/apes to show that all living humans have a common ancestor ~ 150,000 years ago (not 2 mya).

The Cambrian explosion was the rapid morphological and ecological diversification of animals that occurred during the Cambrian period. These groups don’t fossilize well; that’s why we don’t see them until recently

Cambrian Era begins here.

The Doushantuo Microfossils Found in China, discovered 1998 in fertilizer mine Tiny sponges Animal embryosshallow water marine Algaehabitat Pictures on next slide.

Fertilized egg 2 cell embryo 4 cell embryo 16 cell embryo

The Ediacaran Faunas In Australia Sponges Jellyfish Segmented animals, but with no heads Pictures on next slide

The Burgess Shale Faunas In Cambrian period-- midst of 40 million year “explosion” New species of pre-existing groups like sponges, jellyfish Many new groups! Arthropods (today includes insects, crustaceans) Mollusks (today includes clams, octopus) Starfish Worms Chordates (group that now includes us) A cuttlefish is a cephalopod, which is a mollusk. An arthropod. A polychaete worm.

New features include: Exoskeletons Heads, tails Appendages Eyes Mouths Sophisticated movements: swim, burrow, run Why all this so quickly?

The Genetic Mechanisms of Change The new field of “evo-devo” is providing insights into how major events in the history of life occurred, by revealing the genetic mechanisms involved. (Paleontologists are also collaborating, to try to understand the environmental triggers.)

Gene Duplications and the Cambrian Explosion

Hox Gene Expression in Drosophila Hox genes are transcription factors; bind to DNA to turn on genes. Each copy of the hox gene is expressed in a different location of the embryo.

Gene duplications

CHECK YOUR UNDERSTANDING You should be able to describe how data from molecular genetics, phylogenies, and the fossil record are being combined to provide insight about the radiation of animals. Images from

Adaptive Radiations Adaptive radiations exhibit rapid diversification associated with new ecological opportunities (caused by extinction or colonization) and/or new morphological innovations.

Adaptive Radiations: 1. Colonization Events as a Trigger

Finchlike ancestor -- eats seeds Desendents eat eat insects, flowers, as well

30 closely related species Tremendous morphological diversity Mosslike, vines, trees

Convergent evolution Selection will fill vacant niches.

Adaptive Radiations: 2. Role of Morphological Innovation

Exoskeleton, wings, 6 legs 10,000,000 species

Flowers permit specialized mating 250,000 species

2nd set of jaws in throat permits specialized feeding: Crushing snails, scraping algae, etc. 300 species in Lake Victoria alone.

10,000 species of birds

Mass Extinctions Mass extinctions have occurred repeatedly throughout the history of life. They rapidly eliminate the majority of species present. Afterwards, speciation causes re- population of vacant niches.

Paleo/Mesozoic Meso/Cenozoic

How do background and mass extinctions differ? Mass extinctions caused by sudden, extraordinary changes in the environment. Produce extinctions that are largely random with respect to fitness of individuals (but may influence some taxa selectively).

What Killed the Dinosaurs?

Asteroid approx 10 km across. Incredible impact. Fireball; catastrophic fires worldwide. Sulfuric acid rain. Dust/ash/soot block sun.

Mammals experienced adaptive radiation following the last mass extinction.