1. Heliconius butterflies
Real Example: Reproductive isolation + Sexual Selection
+ Natural Selection = sympatric species
• live in various habitats in South America
• Müllerian mimics to other Heliconius
species in or close to their range, all are
unpalatable (taste bad to predators)
2. Heliconius butterflies
Real Example: Reproductive isolation + Sexual Selection
+ Natural Selection = sympatric species
• live in various habitats in South America
• Müllerian mimics to other Heliconius
species, all unpalatable (taste bad to predators)
• (incomplete) pre-zygotic isolation
by habitat isolation
H. cydno: live in forest understory
H. melpomene: live in disturbed re-growth forest
Species overlap in intermediate habitats and found
flying together: rare hybrids found in wild
3. 1) Why aren’t hybrids more common?
2) How do overlapping (sympatric) species remain distinct species?
Real Example: Reproductive isolation + Sexual Selection
+ Natural Selection
4. Experiment
Real Example: Reproductive isolation + Sexual Selection
+ Natural Selection
• Mating confirmed by identifying male spermatophore
in female via dissection
• Mate choice (and sexual selection pressure) is by
MALES (male choice) & based on female color pattern
• A male mates with a newly hatched female before
her first flight
• Males and females
exposed to each other in
no-choice trials (1 hr)
5. Real Example: Reproductive isolation + Sexual Selection
+ Natural Selection
Results: Assortative mating in both species and their hybrid
Males prefer to mate with females of their “type”
6. Results: Sexual Selection against hybrids because they don’t have
attractive traits (in this case color pattern)
Real Example: Reproductive isolation + Sexual Selection
+ Natural Selection
Hybrids females are mated with 50% less often by males of
either “parent” species
7. Results: Natural Selection: hybrids eaten by Jacamar birds
(and other predators) more than parent species are.
Real Example: Reproductive isolation + Sexual Selection
+ Natural Selection
Hybrids aren’t protected
from predators by Müllerian
mimicry, thus more eaten
by predators (N.S) =
8. Results: Natural Selection: hybrids eaten by Jacamar birds
(and other predators) more than parent species are.
Real Example: Reproductive isolation + Sexual Selection
+ Natural Selection
Hybrids are eaten more
by predators. The parent
species are favored by N.S.:
Disruptive selection
9. Darwin & The Modern Synthesis (Natural
Selection, Heredity & Genetics)
• Speciation was introduced by Darwin, in On the
Origin of Species by Natural Selection (1859)
• Darwin didn’t discuss allopatric
speciation or genetic drift
• The Modern Synthesis focused on
geographical isolation and genetic
drift (isolation + time )
Allopatric speciation
=
10. Darwin & The Modern Synthesis (Natural
Selection, Heredity & Genetics)
•Allopatric speciation: evolution of reproductive
isolation and divergence between populations that are
geographically separate
11. Allopatric speciation: - requires geographic separation.
- Most documented kind of speciation
In this model, speciation results from differences in mating preference
that arise from 2 possible sources:
(1) genetic drift:
Allopatric Speciation
http://evolution.berkeley.edu/evosite/evo101/IIIDGeneticdrift.shtml
12. Allopatric speciation: - requires geographic separation.
- Most documented kind of speciation
In this model, speciation results from differences in mating preference
that arise from 2 possible sources:
(1) genetic drift: Change in allele frequencies due to chance.
(2) disruptive selection: Natural Selection and/or Sexual
Selection that favors more extreme phenotypes over the original
average phenotype
Allopatric Speciation
13. Allopatric speciation: - requires geographic separation.
- Most documented kind of speciation
Secondary contact: occurs after evolving in isolation, two
populations come back into contact with each other
•If the divergence is recent, these two species (or populations) may
hybridize producing fertile offspring
•If the divergence is substantial, the two species may hybridize
producing unfertile offspring or may not hybridize at all
Allopatric Speciation
14. Allopatric speciation: - requires geographic separation,
Geographic separation of one population into two occurs by:
(A) vicariance –separation of a population by geological forces
Allopatric Speciation
15. Allopatric Speciation
Allopatric speciation: - requires geographic separation,
Geographic separation of one population into two occurs by:
(A) vicariance –separation of a population by geological forces
Examples:
- a new river, glacier, or mountain range forms
- a land bridge forms or is submerged
- plate tectonics and continent movements
16. Allopatric speciation: - requires geographic separation, which
causes reproductive isolation.
Geographic separation of one population into two occurs by:
(B) dispersal - colonization of a new habitat by founders
Examples:
- islands
- postglacial lakes (Canada), rift lakes (Africa)
Allopatric Speciation
17. Initially, there is migration between 2 nearby populations of a
forest-dwelling animal with two alleles controlling color
Allopatric speciation : Vicariance + Genetic drift
because of gene flow, the allele frequencies will be the same
in the two populations
18. Over time, a barrier to migration arises between populations:
mountain range
The allele frequencies in each population will start to change
due to genetic drift
(Step 1: gene flow has been interrupted)
Allopatric speciation : Vicariance + Genetic drift
19. The populations will slowly diverge as different alleles become
fixed at many loci throughout the genome
(Step 2: populations differentiate)
mountain range
Different alleles may eventually fix in the 2 populations
Allopatric speciation : Vicariance + Genetic drift
20. (Step 3: the populations become reproductively isolated)
mountain range
Differences accumulate BY CHANCE in alleles
controlling mate preference: mating signals, genital shapes, etc.
Allopatric speciation : Vicariance + Genetic drift
21. ... but because of assortative mating, the two types do not interbreed
have formed sister species that will now evolve separately
If the mountain range disappears, the
two populations can mix = Secondary Contact.
(Step 4: speciation has occurred)
Allopatric speciation : Vicariance + Genetic drift
22. Consider a species found in a desert and a neighboring forest
Hot, dry
desert
Cool,
rainy
forest
Allopatric speciation : Vicariance
+ Disruptive Selection
23. Selection will favor different alleles in the desert and forest
Hot, dry
desert
Cool,
rainy
forest
Natural selection will favor
forest-adapted individuals
Natural selection will favor
desert-adapted individuals
Allopatric speciation : Vicariance
+ Disruptive Selection
24. After selection, the two populations will be genetically different
Hot, dry
desert
Cool,
rainy
forest
forest-adapted individuals
have survived here
desert-adapted individuals
have survived here
Allopatric speciation : Vicariance
+ Disruptive Selection
25. However, migration will keep mixing alleles between the populations
Hot, dry
desert
Cool,
rainy
forest
Allopatric speciation : Vicariance
+ Disruptive Selection
Maybe some evolution, but NO SPECIATION unless
there is reproductive isolation
26. Now: a barrier to gene flow arises between the 2 habitats
Hot, dry
desert
Cool,
rainy
forest
mountains
Allopatric speciation : Vicariance
+ Disruptive Selection
27. Now: a barrier to gene flow arises between the 2 habitats
Hot, dry
desert
Cool,
rainy
forest
Natural selection will favor
forest-adapted individuals
Natural selection will favor
desert-adapted individuals
mountains
Allopatric speciation : Vicariance
+ Disruptive Selection
28. Each population evolves into a distinct, well-adapted species
Hot, dry
desert
Cool,
rainy
forest
Forest-adapted population Desert-adapted population
mountains
Species #1 Species #2
Allopatric speciation : Vicariance
+ Disruptive Selection
No migration
31. Speciation and the Isthmus of Panama
RESULTS of mating experiments:
(1) Sister-species shrimp snapped at each other instead of mating!
This is pre-zygotic reproductive isolation (sexual isolation): mating
signals not understood by potential mates
(2) when a male of one species was held with a female of
its sister species [from the other side of Panama] for a month,
no offspring were produced except for one single pair
This is either pre-zygotic isolation (gamete isolation) or post-zygotic
reproductive isolation: zygote does not develop.
For snapping shrimp: 3.5 million years is enough time for
complete reproductive isolation to occur
Allopatric speciation: Vicariance
32. Caribbean and Pacific oceans were linked until the Isthmus
of Panama formed ~3.5 million years ago
Prevented any more
gene flow between
marine organisms
on each side of the
new land barrier
Did this result in the
evolution of new
sister species pairs
separated by the
Isthmus?
Speciation and the Isthmus of Panama
Google
maps
Allopatric speciation : Vicariance
33. Speciation and the Isthmus of Panama
Knowlton et al. studied pairs of snapping shrimps that were
morphologically similar, where one member of the pair was
found on the Caribbean side and the other on the Pacific side
Knowlton & Weight 1998
Alphaeus cylindricus
The sister species still closely
resembled each other –
were they different species?
Sequenced part of a gene
and also compared
allele frequencies
Finally, did mating crosses to assess reproductive compatibility
would shrimp mate or fight with their sister species?
Allopatric speciation : Vicariance
34. Knowlton & Weigt 1998
• based on DNA sequences, the
members of each pair were
indeed each other’s closest
relatives
- That is, each sister-group
pair were were descendants
of a common ancestor
Allopatric speciation: Vicariance
35. What is a species?
• Species are the fundamental units of
biodiversity
• Note: one species, two species
http://carabidae.pro/carabidae/elaphrinae.html
Elaphrus beetles
36. Importance of recognizing species
• Survival depends on our ability to recognize species
What is a species?
46. What is a species?
• Biologists do not agree on ONE way to
define a species – thus, “species concepts”
Why?
47. At least 22 different definitions have been proposed to
explain what a “species” is.
Three main ones:
1. Morphological
2. Biological
3. Phylogenetic
Species concepts
48. Morphological species concept
: Two organisms that display “substantial”
and consistent morphological differences
are different species
• Advantages: Easy to apply, can be used with fossil
species
– Disadvantages: It is not testable, the definition of
“substantial” is subjective. Problems with
convergence, cryptic species, hybridization (= gene
flow) & intermediate phenotype
49. Morphological species concept
: Chronospecies: a morphology that can be
identified as a stage in an evolving lineage
(anagenesis)
Note increasing number of
pleura (or “ribs”) on
trilobites
50. Biological species concept
: a group of actually or potentially inter-
breeding individuals
• Advantages: testable in many cases, objective
• Disadvantages: difficult to apply and test
(impractical), cannot be used with fossils, irrelevant
to asexual populations
52. Phylogenetic species concept
: Lineages with different evolutionary histories
are different species – these lineages must be
the smallest units of evolution
• Advantage: it is testable, objective and can be applied to
living and fossil species
– Disadvantage: it requires comprehensive phylogenetic
analyses = need a cladogram!
53. Phylogenetic species concept
: Lineages with different evolutionary histories
are different species – these lineages must be
the smallest units of evolution
•Instead of depending on reproductive isolation, this concept
revolves around fixed differences between populations
•Species are the smallest population that you don’t have any
reason to divide into even smaller clades or populations
55. Issues & Solutions
Issue: How genetically different do species have to be?
Solutions:
- from a single DNA base change that only exists in one
population, to many consistent genetic differences across
genes, also consistent measurable phenotypic differences
- Ideally, multiple fixed differences should be used
- Need a well-supported cladogram.
Phylogenetic Species Concept
56. High level of cryptic species
diversity revealed by sympatric
lineages of Southeast Asian
forest frogs
Bryan L Stuart, Robert F Inger, and Harold K Voris
Biol Lett. 2006 September 22; 2(3): 470–474.
Odorrana livida
Cryptic species
by the phylogenetic species concept
cf. = similar to
57. High level of cryptic species
diversity revealed by sympatric
lineages of Southeast Asian
forest frogs
Bryan L Stuart, Robert F Inger, and Harold K Voris
Biol Lett. 2006 September 22; 2(3): 470–474.
Odorrana livida
Cryptic species
by the phylogenetic species concept
Cryptic species: organisms that
appear identical or almost
identical to close relatives, but
are genetically distinct- they are
their own lineage
Odorrana livida
58. High level of cryptic species
diversity revealed by sympatric
lineages of Southeast Asian
forest frogs
Bryan L Stuart, Robert F Inger, and Harold K Voris
Biol Lett. 2006 September 22; 2(3): 470–474.
Odorrana livida
Cryptic species
by the phylogenetic species concept
cf. = similar to
Odorrana livida
59. Rana chalconota
cf. = similar to
Cryptic species
by the phylogenetic species concept
60. Cryptic species
by the phylogenetic species concept
Morphology + DNA
Forest habitat Savanna habitat
63. Ring species
by the phylogenetic & morphological & biological species concepts
64.
65. Ring species
by the phylogenetic & morphological & biological species concepts
66. How do you describe a species?
1. Compare it to all similar described species
2. Name it
• Must be latinized & binominal
3. Designate a type
• Designate a holotype
• Designate paratypes (if possible)
4. Describe it
5. Provide a picture or illustration
6. Designate a type locality
7. Deposit it (the type or types) into a museum
8. Publish the description in a peer-reviewed journal
Hinweis der Redaktion
Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
The model of allopatric speciation says nothing more is needed
for 2 populations to evolve into separate species but
geographical isolation + time
- this remains the dominant view of how most speciation has
taken place over earth’s history
- notice: there is no requirement for natural selection to
play a role in species formation
Because drift is a random process, it may take a very long time
for enough fixed differences to build up to prevent two
populations from interbreeding
- according to this model, species should only co-exist if
they were 1st isolated from each other for a long time
As these photos of Drosophila suzukii, D. macrothrix, and D. nigribasis (top to bottom) show, the Drosophila found in Hawaii are remarkably diverse in body size, wing coloration, and other traits.
All human cultures recognize and name species. Because we eat other species of living organisms it is very important that we can properly recognize species with different characteristics and that we have names for them, so we can communicate about the characteristics of the different species.
A wholphin or wolphin is a rare hybrid, born from a mating of bottlenose dolphin. Polar-Grizzly Bear Hybrid. An example of a sheep-goat chimera. A Cama is a hybrid between a camel and a llama. A jaglion, Jaguar-Lion Hybrid. Würdemann's Heron, a great blue heron white egret hybrid.
The taxa labeled A-G on the tips of this phylogeny represent distinct species. Groups labeled G1, G2 etc. represent populations of the same species.
In West Africa, elephants that live in forest habitats (left) have morphological characteristics that distinguish them from savanna-dwelling elephants (right) from west, central, and east Africa.
This evolutionary tree indicates that forest-dwelling elephants are a distinct phylogenetic species.