Principles of Biology - Biology 102
Spring Quarter
Written by: Sue Kloss
Lake Tahoe Community College
Instructor: Ralph Sinibaldi
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Ch. 24 - Origin of Species
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Introduction
A. speciation - origin of species; appearance of new species is the source of biological diversity
B. microevolution - adaptations that evolve in a single gene pool, or population
C. macroevolution - evolutionary change above the species level - appearance of feathers, for example,
that defines higher taxa
D. 2 basic patterns of evolution (Fig. 24.2)
1. anagenesis - phyletic evolution - accumulation of changes that gradually transform a given
species into a species with different characteristics
2. cladogenesis- splitting of a gene pool into two or more separates pools, which each give rise to
one or more new species. can promote biological diversity by increasing numbers of species
I. Biological species concept emphasizes reproductive isolation
A. species - latin for kind or appearance
B. biological species concept - potential to interbreed and produce viable fertile offspring; reproductive
compatibility (Fig. 24.3)
1. reproductive isolation - biological factors that impede 2 members of a species from
interbreeding (fig. 24.4)
a. prezygotic barriers impede mating or hinder fertilization of the egg
1. habitat isolation
2. temporal isolation
3. behavioral isolation
4. mechanical isolation
5. gametic isolation
b. postzygotic barriers impede a hybrid zygote from developing into a fertile adult
1. reduced hybrid viability
2. reduced hybrid fertility
3. hybrid breakdown
2. limitations of biological species concept a. can’t evaluate fossils or asexual organisms for these traits
b. some species do hybridize, still not the same species
C. other definitions of species
1. morphological species concept - characterizes a species by body shape, size, etc.
a. in practice, this is how most scientists classify species
b. disadvantage - relies on subjective criteria
2. paleontological species concept - focuses on morphologically discrete species known only
in fossil record
a. forced to use this bc there is no way to get more info
3. ecological species concept - if similar in appearance, distinguish by ecological niche
a. two spp. of Galapagos finch similar in appearance but not in niche, what they eat eg.
4. phylogenetic species concept - set of organisms with a unique genetic history
a. can use physical characteristics or molecular sequences
b. difficulty may be in determining just how much difference indicates a new species
II. Speciation can take place with or without geographic separation (Fig. 24.5)
A. allopatric speciation - gene flow is interrupted when a population is subdivided into 2 geographically
distinct subpops (Fig. 24.6)
1. rivers, canyons, roads may all be formidable enough barriers depending on the species
mobility
2. geographic isolation is NOT by itself a biological isolating mechanism; these must be intrinsic
to the species
B. Sympatric speciation - speciation takes place in geographically overlapping populations; members are
not in isolation from others
1. mechanisms include chromosomal changes and nonrandom mating that reduces gene flow
a subset of the pop. is reproductively isolated bc of switch to a habitat, food source or other
resource not used by parent population
2. polyploidy - sometimes mistakes in cell division result in polyploidy - extra sets of chromosomes
a. if diploid cells become tetraploid, reproductive isolation can occur in one generation;
plants that are tetraploid can either fertilize themselves or with another tetraploid individual
b. when 2 different species mate, chromosomes from one species can not pair correctly
with chromosomes from a different species (homologs)
1. plants may propagate themselves asexually
2. various mechanisms can change subsequent generations to fertile polyploids
this is called an allopolyploid - they can be fertile with each other but not parental
species (Fig. 24.9) - represent a new biological species
3. many crop plants are allopolyploids
3. Habitat differentiation and sexual selection
a. polyploid speciation also occurs in animals, although it is less common than in plants
b. other mechanism of sympatric speciation - Lake Victoria in E. Africa - fills and dries over
evolutionary time
1. the current lake is only 12000 yrs old, home to more than 500 spp of cichlids
2. all very similar genetically (fig. 24.10)
a. different fish exploit different food sources
b. sexual selection may be occurring - based on color, breached in lab
setting. species began to diverge only recently. genetic drift may have
played a role; sexual selection reinforces the color difference
4. Adaptive Radiation - evolution of many diversely adapted species from a common ancestor
upon intro to various new environments; occurs when a few individuals make way to new, distant
area
a. mammals underwent huge adaptive radiation when dinos went extinct
b. Hawaiian islands - huge range of altitudes and rainfall - provide many opportunities for
evolutionary divergence (Fig. 24.12)
c. most species on Hawaii are found nowhere else on earth
5. genetics of speciation - we can pinpoint genes that account for species differences - in mimulus
2 gene loci have been identified as significant in 2 species - one pollinated by bee, one by hummer
one locus influences flower color, one amt of nectar produceda. no postzygotic barriers - can be cross-pollinated in greenhouse
b. allelic diversity has resulted in speciation
6. Tempo of Speciation (fig. 24.13)
a. gradulism model - Darwin - natural selection
b. punctuated equilibrium- apparent stasis punctuated by sudden change
1. may not necessarily be able to discern changes at the molecular level in fossil
record, so it may appear sudden when actually it may have taken 50,000 yrs.
2. also, changes to behavior, physiology or internal anatomy may not be
preserved in the fossil record.
III. Macroevolutionary changes can accumulate thru many speciation events
A. speciation can occur from changes as small as the color on a cichlid’s back
1. as species diverge, these changes can become more pronounced as they accumulate
2. changes accumulate in macroevolution just as they did in microevolution
a. natural selection,
b. mutation
c. genetic drift
d. gene flow
3. cumulative small evolutionary changes account for macroevolutionary change
B. Evolutionary novelties
1. e.g. human eye - how could it evolve in pieces, since you need all the parts for it to work
correctly?
a. in most cases, complex structures evolved from simpler versions that performed the
same basic function
b. then changes were added incrementally (Fig. 24.14)
c. sometimes, structures formed for one function become secondarily adapted for another
this is called exaptation (human skeletons originally designed for 4 legged movement;
feathers may have been a design to increase insulation; hollow bones of birds may have
aided a lifestyle for climbing and perching in trees in birds ancestors)
C. Evolution of genes that control development
1. “evo-devo” interface between developmental biology and evolutionary biology shows how
slight genetic differences can be magnified into major morphological differences btn species
2. genes that program development control rate, timing, spatial patterns of changes in
organisms as they change from zygote into adults
a. heterochrony - changes in rate and timing of developmental events
1. organisms shapes depend on relative growth rates of different body parts
2. allometric growth gives organisms specific body form (Fig. 24.15)
3. changing the relative growth rates will change the adult form dramatically
a. human and chimp skull start out pretty similar, change a lot
b. salamander foot design probably controlled by genes that control
timing of foot development (Fig. 24.16) . mutation in the regulatory
gene, turning it off a little sooner so that the bones were shorter,
allowed a form that would have been more well adapted for tree climbing
4. regulatory genes that accelerate the rate of development of reproductive
organs relative to development of somatic structures can result in paedomorphosis
sexually mature individual retains features that were once found only in juvenile
form (Fig. 24. 17)
a. so overall genetic change might be small, but deliver huge changes in
the finished product
b. in summary, heterochrony alters the rates at which various body parts
develop, or by changing the timing of onset or completion of part devel.
3. changes in spatial patterns
a. homeotic genes - control basic features - where wings or legs will develop or how flower
parts are arranged (fig. 24.18) (homeotic genes are called hox genes in animals - lots of
conservation of hox genes - humans have very similar hox genes to fruit flies, similar
sequences found in plants, yeasts, prokaryotes)
b. hox genes turn on and cause cells in a particular part of the embryo to start forming
into a particular structure or organ
1. tetrapods (4 leggeds) from which amphibs and reptiles evolved are thought to
have evolved from fishes - hox mutation turned fish fins into limbs?
2. tetrapods have digits - extensions that extend skeletal support to end of limb
3. same hox gene controls wing edge in chicken as fin edge in fish (fig. 24.18)
c. evolution of vertebrates from invertebrates was associated with changes in hox genes
and their regulatory genes (fig. 24.19)
D. Evolution is not goal oriented - what looks like a particular trend in evolution may just be incomplete info
1. (Fig. 24.20) - yellow line makes it appear that horses were the “end goal” but if you look at the
whole tree, you see that lots of paths were possible
2. apparent trends could arise because of changing environment - horses on grasslands adapted
for running may have been selected for ability to escape predation once mammals evolved
Obj. ch 24
1. Distinguish between anagenesis and cladogenesis.
2. Define biological species concept.
3. Distinguish between prezygotic and postzygotic isolating mechanisms.
4. Describe five prezygotic isolating mechanisms and give an example of each.
5. Explain a possible cause for reduced hybrid viability.
6. Explain how hybrid breakdown maintains separate species even if fertilization occurs. 7. Describe some
limitations of the biological species concept.
8. Define and distinguish among the following: ecological species concept, paleontological species concept,
phylogenetic species concept, and morphological species concept.
9. Distinguish between allopatric and sympatric speciation.
10. Explain the allopatric speciation model and describe the mechanisms that may lead to divergence of isolated
gene pools.
11. Describe examples of adaptive radiation in the Galápagos and Hawaiian archipelagoes.
12. Explain how reproductive barriers evolve. Describe an example of the evolution of a prezygotic barrier and the
evolution of a postzygotic barrier.
13. Define sympatric speciation and explain how polyploidy can cause reproductive isolation.
14. Distinguish between an autopolyploid and an allopolyploid species and describe examples of each.
15. Describe how cichlid fishes may have speciated in sympatry in Lake Victoria.
16. Define adaptive radiation and describe the circumstances under which adaptive radiation may occur.
17. Explain in general terms how a complex structure can evolve by natural selection. 18. Define exaptation and
illustrate this concept with an example.
19. Explain how slight genetic divergences may lead to major morphological differences between species.
20. Explain how the evolution of changes in temporal and spatial developmental dynamics can result in evolutionary
novelties.
21. Define evo-devo, heterochrony, allometric growth, and paedomorphosis.
22. Explain why extracting a single evolutionary progression from a fossil record can be misleading.
23. Explain why evolutionary change is not goal-directed.
Ch. 25 - Phylogeny and Systematics
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Introduction - Investigating the tree of life
A. Phylogeny - the evolutionary history of a species or group of species
B. Systematics - analytical approach to understanding the diversity and relationships of organisms
1. morphological traits
2. biochemical traits
3. molecular systematics - comparisons of DNA, RNA and other molecules to infer evolutionary
relationships - (Fig. 25.2)
I. Phylogenies are based on common ancestries - fossil, morphological, molecular evidence
A. Fossil record
1. sedimentary rocks are richest source of fossils
a. deposits of sand, silt pile up and compress in to layers called strata (fig. 25.3) with
fossils embedded in them
2. other types of fossils
a. bones
b. minerals seep in and preserve - petrification
c. embedded whole material
d. casts that form from dissolved minerals
e. footprints, burrows, etc
f. entire organisms in amber (insects)
g. ice or glaciers preserve bodies
B. Morphological and Molecular Homologies
1. homologies - similarities due to shared ancestry
a. forearm bones of mammals
b. genes and other DNA sequences are homologies if the nature of similarity suggests a
common ancestor
1. the more similar the DNA, the more closely related, generally speaking
2. in some cases, huge morphological difference does not indicate huge genetic
differences - silversword alliance Ch. 24 - similar gene structure
c. sorting homology from analogy
1. similar environments and nat’l selection produce analogies - similar
adaptations in organisms with different evolutionary lineages
a. eutherian vs. placental mammals often display convergent evo
lution (Fig. 25.5)
2. bats vs. birds vs. cats - bats share some characteristics with birds (flight) but
structurally (forelimb bones) are more like cats
a. fossil evidence shows bat and bird forelimbs arose independently
from walking forelimbs of different ancestors
3. therefore, bats wings are homologous to cats forelimbs and analogous to bird
wings (analogous structures from independent origins are called homoplasies.
4. the more points of resemblance btn 2 structures, the less likely they evolved
independently
5. similarity in genes or genomes indicates close relationship evolutionarily
2. evaluating molecular homologies
a. in 2 similar species, gene sequences may have similar length and bases, but the more
distant they are the more likely that the sequence will change and even length of sequence
(Why?) (Fig. 25.6)
b. have to take into account that insertions and deletions change reading frame
1. computer programs account for gaps, but there are molecular homoplasies
(Fig. 25.7)
2. in order to evaluate these, scientists have come up with mathematical tools
3. evidence that despite morphological differences, humans do share common
ancestor with bacteria
II. Phylogenetic systematics connects classification with evolutionary history
A. Intro
1. taxonomy is the ordered division of organisms into categories based on a set of characteristics
used to assess similarities and differences
2. developed by Carolus Linneaeus, though his system relied on resemblances not evolutionary
relations
B. Binomial nomenclature- 2 name naming system - language of taxonomy
1. common names can be confusing across or even within regions
a. do not reflect type of organism - jellyfish, crayfish, silverfish
b. different languages pose problems of a whole different nature
2. the binomial is composed of the genus and species designations and refer only to that species
a. second part is called the specific epithet - one species in the genus
b. Canis familiaris, or Canis familiaris and Homo sapiens, or Homo sapiens correctly
3. DKPCOFGS, a hierarchy (Fig. 28.8) - like a biological “address”
a. system was set up over time, and on morphological traits not molecular ones, so that
inconsistencies remain
1. order of mammals does not have same diversity as an order of snails
b. taxon (pl. - taxa) is a category within the hierarchy e.g. which taxon shows the highest
degree of relatedness? (answer would be species)
C. Linking Classification and Phylogeny
1. phylogenetic trees- branching diagrams depicting hypotheses about evo relationships (fig 25.9)
a. reflects hierarchy
b. does not reflect actual ages of speciation, eg. last common ancestor of wolf and dog
was more recent than common ancestor of otter and skunk; not wolves evolved more
recently than otters
III. Phylogenetic systematics informs the construction of phylogenetic trees based on shared characteristics
A. Intro
1. cladogram - patterns of shared characteristics depicted on a diagram (fig 2.5.11)
a. if shared characteristics are due to common ancestry, then cladogram forms
basis for a phylogenetic tree
b. within tree, a clade (branch) is defined as group of species that includes ancestral
species and all descendants
c. analysis of species groupings is called cladistics
B. Cladistics
1. monophyletic - ancestral species and all descendants
a. paraphyletic - ancestral species and some but not all descendants
b. polyphyletic - grouping of several species that lack a common ancestor
2. shared primitive and shared derived characteristics
a. shared primitive chars. - characteristic shared beyond the taxon we are defining
b. shared derived chars- characteristic found only in that taxon
c. e.g. - if we are trying to define mammals, vertebrae are a shared primitive char,
and fur is a shared derived char.
3. outgroups - comparisons that will allow scientists to distinguish btn shared primitive and derived
chars
a. outgroup - species closely related to group we are studying, called the ingroup
b. outgroup comparison is based on the assumption that homologies present in both
outgroup and ingroup must be chars that predate the divergence of both groups from a
common ancestor
c. outgroup comparison allows us to focus on just chars that were derived at various pts.
along the branch
d. fig. 25.11a tabulates those characters, Fig. 25.11b translates them into cladogram
C. Read up on Parsimony and Molecular Clocks later in the Chapter if you are interested in this topic
Ch. 25 Objectives
1. Distinguish between phylogeny and systematics.
2. Describe the process of sedimentation and the formation of fossils. Explain which portions of organisms are most
likely to fossilize.
3. Explain why it is crucial to distinguish between homology and analogy before selecting characters to use in the
reconstruction of phylogeny.
4. Explain why bird and bat wings are homologous as vertebrate forelimbs but analogous as wings.
5. Define molecular systematics. Explain some of the problems that systematists may face in carrying out molecular
comparisons of nucleic acids.
6. Explain the following characteristics of the Linnaean system of classification:
a. binomial nomenclature
b. hierarchical classification
7. List the major taxonomic categories from most to least inclusive.
8. Define a clade. Distinguish between a monophyletic clade and paraphyletic and polyphyletic groupings of
species.
9. Distinguish between shared primitive characters and shared derived characters.
10. Explain how shared derived characters can be used to construct a phylogenetic diagram.
11. Explain how outgroup comparison can be used to distinguish between shared primitive characters and shared
derived characters.
12. Define an ingroup.
13. Explain why any phylogenetic diagram represents a hypothesis about evolutionary relationships among
organisms.