Chapter 24 The Origin of Species

2 patterns of evolutionary change anagenesis – (phyletic evolution) -transformation of an unbranched lineage of organisms cladogenesis – (branching evolution) -budding of one or more new species from a parent species that continues to exist (more important than anagenesis in the history of life)

Figure 24.1 Two patterns of speciation

Species Population or group of populations whose members potentially can interbreed to produce fertile offspring

Reproductive barriers: A.Prezygotic barriers – prevent mating or fertilization 1) ecological (habitat) isolation – different habitats & don’t encounter each other ex: 2 species of snakes that live mainly on water vs. terrestrial 2) temporal isolation – mating/flowering not in sync ex: 2 species that breed at different times of the day

3) behavioral isolation – little recognition between males & females ex: song/mating dance 4) mechanical isolation – sexual reproductive structures are too different ex: male & female copulatory organs incompatible 5) gametic isolation – gametes fail to combine with one another or are inviable ex: gamete recognition based on surface proteins of the egg cell

Figure 24.3 Courtship ritual as a behavioral barrier between species

B. Postzygotic barriers – prevent viable, fertile adults 1) hybrid inviability (reduced hybrid viability)– hybrids do not reach fertility or sexual maturity ex: hybrids don’ t develop properly or are frail 2) hybrid sterility (reduced hybrid fertility) – hybrids don’t produce functional gametes ex: hybrids are completely or largely sterile 3) hybrid breakdown – hybrid offspring have reduced viability ex: second generation feeble or sterile

Modes of speciation a)allopatric – a geographic barrier physically isolates population, blocking gene flow -usu. occurs at the fringe of the parent pop.’s range (peripheral isolate) b)sympatric – a new species arises in the midst of the parent species -chromosomal changes & nonrandom mating reduce gene flow

Figure 24.6 Two modes of speciation

Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon

Adaptive radiation -evolution of many diversely adapted species from a common ancestor ex: Galapagos finches

Figure A model for adaptive radiation on island chains

Hybridization of species 1)autopolyploid – has more than 2 chromosome sets all derived from a single species ex: 4n + 2n = 3n (sterile) 2)allopolyploid – (more common) – 2 different species contribute to polyploid hybrid; may be more vigorous, but usu. sterile (may reproduce asexually) 2n = 4 + 2n = 6 2n = 10 (A) (B)(C)

Punctuated equilibrium -nongradual appearance of species due to spurt changes

Figure Two models for the tempo of speciation

Mechanisms of macroevolution 1) preaptation (exaptation) – structure which evolved in one context and became co-opted for another function 2) regulatory genes – greatly alter adult forms by allometric growth – different growth rates by various body parts paedomorphosis – retention of juvenile features of an organism’s evolutionary ancestors in an adult

Figure Allometric growth

Figure Paedomorphosis

Chapter 25 Phylogeny and Systematics

phylogeny – evolutionary history of a species

Table 25.1 The Geologic Time Scale

Causes of evolutionary trends 1)Result of species selection 2)Result of continental drift Pangaea – supercontinent 200 – 250 mya adaptive zone – new way of life presenting many opportunities previously unexploited 3) Mass extinctions

Figure 25.4 The history of continental drift

Classification Grouping may be: 1) monophyletic – single ancestor produces all species of that taxon 2) polyphyletic – members of the taxon are derived from 2 or more ancestral forms not common to all members 3) paraphyletic – excludes species that share a common ancestor that gave rise to species included in the taxon

homology – likeness attributed to shared ancestry analogy – likeness due to evolutionary convergence – unrelated species developing similar features due to similar adaptations to be selected for

Modern systematics tools: (to determine homology) 1)Protein comparison 2)DNA comparison a) DNA – DNA hybridization b) restriction mapping c) DNA sequencing – order of nucleotides d) analysis of fossilized DNA 3) Molecular clocks – determining protein evolution to see where branches occur

Figure 25.7 Hierarchical classification

3 taxonomic schools of thought 1)phenetics – determines taxa strictly based on phenotypic similarities & differences for as many characteristics as possible 2)cladistics – classifying orgs. According to the order in which clades (evolutionary branches) arise 3)classical evolutionary systematics – considers both divergence of structures & sequence of branching

Chapter 26 Early Earth and the Origin of Life

Formation of the Earth geological events shape biological evolution, & organisms change the planet in turn episodes initiate new ways of life ex: evolution of photosynthetic organisms totally changed Earth’s atmosphere between 4.6 – 5 bya our solar system formed from a cloud of matter Earth formed ~ 4.6 bya due to ice & dust gravitationally pulling together

Figure 26.0x Volcanic activity and lightning associated with the birth of the island of Surtsey near Iceland; terrestrial life began colonizing Surtsey soon after its birth

began as a cold world which melted due to heat, radioactive decay, & impact of meteorites hot, molten mass separated into layers of varying density Life began when atm. had little O 2 & the mixture of gases comprised a reducing atm. prokaryotes only for 1 st few billion years after Earth’s crust cooled & solidified stromatolites – banded domes of sediment similar to bacterial mats in Fig Tree chert (rock formation in Africa) – oldest available fossils ~ 3.5 bya

Figure 26.3 Early (left) and modern (right) prokaryotes

Figure 26.3x1 Spheroidal Gunflint Microfossils

Figure 26.4 Bacterial mats and stromatolites

Origin of life One hypothesis (most scientists agree) – nonliving materials became ordered into molecular aggregates eventually capable of self-replication & metabolism

1 st organisms were products of chemical evolution in 4 stages 1) abiotic synthesis & accumulation of small organic molecules (monomers) such as AA’s & nucleotides 2)joining of these into polymers, including proteins & nucleic acids 3)aggregation of abiotically produced molecules into droplets, protobionts that had chemical characteristics different from their surroundings 4) origin of heredity (maybe before the droplet stage)

1920’s Oparin/Haldane – independently hypothesized Earth’s early atm. provided conditions not possible today 1953 Miller/Urey – tested Oparin’s hypothesis in lab & produced diverse organic molecules from inorganic precursors

Figure The Miller-Urey experiment