Chapter 18- Speciation – quiz 5
Ch. 18 (Speciation). These include:
Sections 18.1, 18.2, 18.3, 18.6 (intro, 18.6a, 18.6b), 18.7 (intro, 18.7a, 18.7b), and 18.8
(intro, 18.8a, 18.8b, 18.8c).
18.1 What’s in the name ?
speciation is known as the process of species formation.
- in this chapter- the concept of species is explored and the mechanisms involved in
speciation and appreciate the importance of names of organisms in biology.
- communication can affect both inter- and intraspecifc behaviour
18.2 Definition of species
what are species defined as? it can be described many different ways
1. Biological Species Concept (BSC)- group of species that can successfully interbreed
together and produce fertile offspring.
2. Phylogenetic Species Concept (PSC)- group of species bound by a unique ancestry,
3. Ecological Species Concept - defines species as a group of organisms that share a
distinct ecological niche.
NSERT- definition of niche.
Problems with the Biological Species Concept
- the definition seems to work for species that reproduce sexually but it doesn't make
sense for species that reproduce asexually.
- doesn't address species that hybridize
Androdioesous species: composed of males and hermaphrodites (which produce both egg
Gynogenetic Species - species of only females that go through internal fertilization but
still need sperm. They need mechanical stimulation by sperm donated by other male
species. Therefore, they have to mate with other species. This goes against what the BSC
Hybridization: when species interbreed and produce fertile offspring. When sterile
offspring are produced, it doesn't put them outside the definition of BSC.
Recombination- is a principle advantage of sexual reproduction = explains it's prevalence
among living organism. Sexual reproduction involves genetic recombination.
18.3 One size does not fit all
- More than one definition of species in biology. - The diversity of species and their lifestyles partly reflects the mechanisms
underlying the processes of speciation.
- Gene flow among individuals in a population of conspecfics mixes their genetic
material and is suppose to be like glue holding the species together.
- Individuals of different species are genetically isolated but spp that produce fertile
hybrids may not be naturally isolated. ( are they spp ??)
- The BSC explains why individuals of a species generally look alike = the
phenotype reflects the genotype = therefore individuals share similar genetic info.
Biologists use the similarities and differences in morphological traits as
- According to the MSC- individuals of the same spp share measurable traits that
distinguish them from individuals of other species.
- Paleonlogists use morphology to identify fossil to spp but also depend on info of
the fossils' age.
18.6 Geographic Variation
- subspecies: geographically separated pops of a species show a dramatic yet
noticeable phenotypic variation.
- Individuals from different spp usually interbreed where their geographic
distributions meet and their offspring often exhibit intermediate phenotypes.
18.6a Ring Species: Genes Flowing between Some Populations
- ring shaped geographic distribution that surrounds inhabitable terrain: pops next
to the ring species can still exchange material directly, but gene flow b/w distant
pops occurs only through intermediate pops.
18.b Clinal variation
- Clinal changes are smooth patterns of variation along a geographic gradient.
- Clines: when there is gene flow b/w adjacent pops that are adapting to slightly
18.7 reproductive Isolation
- important to BSC**
- reproductive isolating mechanism: biological characteristic that prevents the gene
pools of two species from mixing even when they are sympatric. ( note:
sympatric: occupying the same space at the same time.
- 2 ways to achieve reproductive isolation : 1. prezygotic isolation: exert their effects before the production of a zygote or
2. postzygotic isolation: operate after zygote formation
Time relative to fertilization Mechanism Mode of action
Prezygotic (pre mating) Ecological isolation Spp live in different habitats
mechanism Temporal isolation Spp breed @ diff times
Behaviourial isolation Spp can’t communicate
Mechanical isolation Spp can’t physically mate
Genetic isolation Spp have non-matching
receptors on gametes
Postzygotic (post mating) Hybrid inviability Hybrid offspring do not
mechanism complete development
Hybrid sterility Hybrid offspring can’t
Hybrid breakdown Hybrid offspring have
reduced survival or fertility
18.7a Prezygotic Isolating Mechanisms: Isolation before fertilization
- 5 mechanisms can prevent interspecific mating sot fertilizations and the production of
hybrid( mixed spp) offspring
1. Ecological isolation - spp tht may share the same geographic region but in
different habitats. (ex. lions and tigers in the 19 century: lions in open grasslands
and tigers in dense forest.)
2. Temporal isolation - spp tht may live in the same habitat but they mate at different
times of the day or different seasons of the year.
3. Mechanical isolation- differences in the structure of copulatory organs prevent
successful mating b/w two different spp.
4. Genetic isolation- refer to table
18.7b Postzygotic Isolating Mechanisms: Barriers after fertilization
- refer to table above for summary
18.8 Geography of Speciation
- Gepgraphy has a huge impact on whether gene pools have an opportunity to mix.
- 3 modes of speciation
1. Allopatric= different homeland
2. Parapatric = para: beside
3. Sympatric = sym: together 18.8a Allopatric speciation: new spp develop from isolated pops
- Allopatric speciationmost common) physical barriers subdivides a larger pop
or when a small pop becomes separated from a spp’ main geographic
- 2 stages
1. two pops become geographically separated preventing gene flow b/w them.
2. As the pops experience distinct mutations as well as different patterns of
natural selection and genetic drift, they may have genetic differences tht
isolate them reproductively.
- Geographic separation: occurs when a barrier divides a large pop in two or more
- In some cases, small pops become isolated at the edge of species’ geographic
distribution .( ex. oceanic pops )
- A spp cluster results from after founding pop colonize an island or isolated land
- AP (allopatric pop) may reestablish contact when a geographic barrier is
- The secondary contact provides a test whether or not the pop have diverged into
separate spp. If their gene pools did not differentiate much during their
geographic separation, the pops will interbreed and merge. If they are different
enough then they have become reproductively isolated.
- Hybrid zones can be created when individuals of one pop mates with an ini from
- If hybrid offspring have lower fitness than those produced from those who mated
from the same pop. Natural selection(NS) will favour the ones produced from ini
from the same pop.
18.8b Parapatric Speciation: new spp develop when pops span a barrier
- Parapatric isolation : speciation arising from adjacent pops may occur if hybrid
offspring’s have low relative fitness.
- PS occurs when a spp is distributed across a discontinuity in environment
conditions so tht NS favours different alleles and phenotypes on either side of