chapter 20: phylogenies and the history of life - BIOL 2130

phylogeny

tree diagram showing evolutionary history and relationships of an organism to other organisms — how organisms are related

• not similar or different

• can be used to study entire groups

1) rooted tree

2) unrooted tree

rooted phylogenetic tree (rooted)

tree diagram branching indicates evolutionary relationships with a single root representing a common ancestor

• single lineage, and all other branches originated

• direction of evolution

• ex: primates → humans, chimps, monkeys

• ex: LUCA → bacteria and archaea → eukarya shares more with archaea

unrooted phylogenetic tree (unrooted)

tree diagram branching shows relationships among species and not common ancestry

• no indication of what lineage came first

• comparing similarity or divergence

• ex: cats → lion, tiger, leopard, domestic cat (close relatedness but no root)

systematics

branch of science that organizes organisms based on their evolutionary relationships

• fossils

• similar form and body structures

• molecules an organism uses

• DNA

• branch of bio continuously changing! — as tech continues to improve, so does our knowledge of evolutionary relationships

systematic limitations

• closely related groups may not appear similar (ex: dolphins and whales closely related to hippos)

• branches do not account for length of time

• each tree is part of a larger whole — evolution involves many more lineages

• distant groups could be phenotypically similar due to environments (ex: sharks are fish and dolphins are mammals, both have streamlined bodies for swimming)

taxonomy

classifying organisms to construct internationally shared classification systems, each organism placed into increasingly more inclusive groupings

• aims to use simplest line of events to help describe phylogenies — too much to take in

• subjective b/c many species have more than one connection to each other

  • subspecies, species, genus, family, order, class, phylum, kingdom, domain

  • genus name capitalized and species named lower case, first 3 italicized

  • ex: dog — subspecies: Canus lupus familaris, species: Canis lupus , genus: Canis, family: Canidae

• evidence: morphology and genetics

morphology

study of organism’s physical features and genomes are more closely related than those who do not

• more complex the feature = likely close evolutionary relationship

• analogous: similar function due to env pressures, not ancestry

• homologous: similar ancestry and embryonic origin

• ex: bat and bird wings homologous, share a common evolutionary past

  • similar traits due to similar env pressures

molecular systematics

uses DNA info, taxonomic information, and biogeographical information to uncover missed relationships and correct incorrect assumptions

• taxonomic: classification of species

• biogeographical: where species live and history

• ex: DNA comparisons of whales and hippos show relation

building phylogenetic trees (build tree)

1) sort homologous (similar ancestry) and analogous (same function from env pressures) traits

2) organize homologous traits into cladistics

3) analyze shared characteristics: descent with modification - how species change over time branching common ancestry and adaptations thru variation

• ex: all vertebrata (backbone), lizard-human are amniota (reproduction w eggs)

  • lamprey to fish: hinged jaw

  • fish to lizard: terrestrial env and enclose amniotic sacs in an egg

  • lizard to rabbit and human: hair/fur, retaining young/n eggs, regulate body temp internally

cladistics

organizing groups of organisms descending from a common ancestor that share derived traits

• ex: human, mice, and kangaroos placed in same clade because they share hair and body warmth traits

• ex: animals, fungi, and plants evolved from separate common ancestors (plants distinct lineage and fungi/animals sister groups)

• flagellates do not represent evolutionary lineage

classic model

uses charles darwin 1837 sketch of the “tree of life” — oak tree has a single trunk and many branches

• explains the diversity through a natural process and that species change over time

• single, branching lineage from common ancestor

• suitable model for eukaryotes

classic model limitations

vertical transfer of genetic info leads to linear evolution — assumes genes pass from parent to offspring

• works better for eukaryotes than prokaryotes: sexual reproduction passes genes from parent to offspring

• random mutation: generates quick change and new alleles over time

gene transfer between unrelated species (horizontal gene transfer)

• ex: antibiotic resistance — bacteria acquires genes for this from other bacterial species

• more prevalent in prokaryotes: could be a significant source of genetic variation

web and network models

multi-trunked ficus better than darwin’s oak tree

• ford doolittle: sketch of tree rising from community of ancestral cells, multiple trunks, connects bt branches where HGT occurred

horizontal gene transfer (HGT)

movement of genetic material between unrelated prokaryotes, not from parent to offspring

1) transformation: bacteria takes up naked DNA

2) transduction: virus transfers genes

3) conjugation: hollow tube/pilus transfers genes bt organisms

4) small virus-like particles or transfer agents transfer random genomic segments from one species to another

• major source of genetic variation, can spread traits (ex: antibiotic resistance) rapidly

endosymbiosis

genome fusion and eukaryotic evolution where two symbiotic organisms takes the other onto itself

• host cell → engulfs prokaryotic cells (like bacteria) → doesnt digest → becomes organelles (mitochondria and chloroplasts)

• the organelles have double membranes, own DNA, replicate independently, retain features of ancestors

ring of life model

pool of primitive prokaryotes center of a ring, with 3 arrows indicating emergence of archaea, bacteria, and eukarya

• emphasizes gene exchange in fusion in early evolution, not from ancestral species

• HGT in proks and and fusion events in euks

• many scientists skeptical of this model

  • evidence not conclusive — shows no pathway of genome fusion

• each model is testable