Origin of Species Chapter 14
What you need to know! The biological concept of species. The difference between microevolution and macroevolution. Prezygotic and postzygotic barriers that maintain reproductive isolation in natural populations. How allopatric and sympatric speciation are similar and different. How punctuated equilibrium and gradualism describe two different tempos of speciation.
Macroevolution Our focus thus far has been on microevolution: how single populations transform over time Microevolution is not sufficient to explain the diversity of life on our planet It can only account for how an individual species adapt to various environmental changes Macroevolution focuses on the evolution of all species from a common ancestor Speciation (how new species emerge from previously existing ones ) is the mechanism of macroevolution
What is a Species? The Biological Species Concept: A population (or group of populations) who can mate and produce fertile offspring with one another but not with a different group Other concepts: morphological species, ecological species, phylogenetic species Taxonomy names the various species on our planet: Canus lupus Homo sapien Felis catus For new species to arise (speciation) a single species must become reproductively isolated
Reproductive Isolation Prezygotic (before zygote) – prevent mating and/or hinder fertilization) Temporal isolation: reproduce at different times of day or year Habitat isolation: same area but not the same habitat Behavioral isolation: different mating practices Mechanical Isolation: structural differences in reproductive organs prevent mating Gametic isolation: sperm cannot fuse with egg
Reproductive Isolation Postzygotic (after zygote) – fertilized eggs don’t develop into fertile adults: Hybrid inviability: hybrids fail to develop or to reach sexual maturity Hybrid sterility: offspring cannot reproduce (mule) due to ineffective gametes Hybrid breakdown: offspring that grow and reproduce (F1) but their offspring (F2) are weak or sterile
Speciation Allopatric Speciation Interbreeding becomes impossible due to geographic isolation (rivers, canyons, mountains) New species evolve on the fringes of large ancestral populations Sympatric Speciation Sudden mutation within a population leads to new species Polyploidy plants mutate by altering chromosome number in a non-disjunction error
Adaptive Radiation Colonization of a new habitat Example: New habitats usually vary from the original habitat Example: Original Species A migrates to an unpopulated island chain A is geographically isolated from the original population and speciates into B B migrates to unpopulated islands B is geographically isolated from the original population and speciates into C & 6. C migrates to other islands C is geographically isolated and speciates into D D migrates to other islands D is geographically isolated and speciates into E
Models of Speciation Gradualism: species descend from common ancestors and gradually diverge Punctuated equilibrium: period of apparent stasis followed by rapid adaptive radiation
Evolutionary Trends Exaptation: structure that evolved in one context and later adapted for another function Evo-devo: study of development and the relationship with evolution Paedomorphosis: the retention in the adult of features that were juvenile Trends do not necessarily indicate goal driven evolution
Phylogeny & Systematics Chapter 15
What you need to know! The taxonomic categories and how they indicate relatedness. How systematics is used to develop phylogenetic trees. The three domains of life including their similarities and their differences.
Phylogeny Phylogeny – evolutionary history of a species or group of species Sources of evidence: Fossil Record Systematics – classifying organisms and evolutionary relatedness Morphological homology Molecular homology
Systematics Morphological Homology Molecular Homology similarities due to shared ancestry (homologous structures) determined by how two organisms appear Analogous structures can be misleading (convergent evolution NOT relatedness) Molecular Homology Similarities in the DNA base sequences Most accurate 20 billion + base pairs sequenced so far (1,000’s of species) – BLAST Lab
Taxonomy Carolus Linnaeus (1701-1778) Mostly morphological (grouping, separating organism due to body plans) Latin based binomial nomenclature: Each species is ID’d by genus (capital letter) and species (lower case) Canis familiaris, Canis lupus, Felix domestica, Homo Sapien
All organisms classified in a hierarchy Taxon Memory Wolf Domain (broad) Did Eukarya Kingdom King Animalia Phylum Philip Chordata Class Come Mammalia Order Over Carnivora Family From Canidae Genus Germany Canis Species (specific) Singing Lupus
Phylogenetic Trees
Cladistics Organizing organisms into clades according to their phylogenetic (evolutionary) relationship Using comparative morphology (taxonomy), and DNA analysis Ancestral species placed on the bottom, with new features leading to novel descendants Ingroups are the focus organisms, outgroups are close relatives
Cladogram
Molecular Systematics Comparing nucleic acids and DNA for relatedness (most accurate) Examples: DNA Comparisons Molecular Clocks: rate of genetic change Nuclear DNA slower than mitochondrial DNA Genome Evolution: Compare organisms entire genetic code (humans vs. chimps 99%)
Domains – Universal Tree of Life