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)
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
1) Why aren’t hybrids more common?
2) How do overlapping (sympatric) species remain distinct species?
Real Example: Reproductive isolation + Sexual Selection+ Natural Selection
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)
Real Example: Reproductive isolation + Sexual Selection+ Natural Selection
Results: Assortative mating in both species and their hybridMales prefer to mate with females of their “type”
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
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) =
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 moreby predators. The parent
species are favored by N.S.: Disruptive selection
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
=
Darwin & The Modern Synthesis (Natural Selection, Heredity & Genetics)
•Allopatric speciation: evolution of reproductive isolation and divergence between populations that are geographically separate
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
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
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
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
Allopatric Speciation
Allopatric speciation: - requires geographic separation,
Geographic separation of one population into two occurs by:
(A) vicariance –separation of a population by geological forcesExamples:
- a new river, glacier, or mountain range forms- a land bridge forms or is submerged- plate tectonics and continent movements
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 foundersExamples:
- islands- postglacial lakes (Canada), rift lakes (Africa)
Allopatric Speciation
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
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
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
(Step 3: the populations become reproductively isolated)
mountain range
Differences accumulate BY CHANCE in allelescontrolling mate preference: mating signals, genital shapes, etc.
Allopatric speciation : Vicariance + Genetic drift
... 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
Consider a species found in a desert and a neighboring forest
Hot, dry desert
Cool, rainy forest
Allopatric speciation : Vicariance + Disruptive Selection
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
After selection, the two populations will be genetically different
Hot, dry desert
Cool, rainy forest
forest-adapted individualshave survived here
desert-adapted individualshave survived here
Allopatric speciation : Vicariance + Disruptive Selection
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
Now: a barrier to gene flow arises between the 2 habitats
Hot, dry desert
Cool, rainy forest
mountains
Allopatric speciation : Vicariance + Disruptive Selection
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
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
Hawaiian Drosophila
Allopatric speciation : Dispersal & founders
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
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
Speciation and the Isthmus of PanamaKnowlton 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
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
What is a species?• Species are the fundamental units of
biodiversity• Note: one species, two species
http://carabidae.pro/carabidae/elaphrinae.htmlElaphrus beetles
Importance of recognizing species
• Survival depends on our ability to recognize species
What is a species?
Universality of recognizing species
What is a species?Ti
me
Amount of divergence (morphology)
What is a species?• Races • Varieties• “kinds”• Incipient species • Ecotypes• Morphs• Subspecies• Cultivars (Artificial Selection)
• Breeds (Artificial Selection)
Tim
e
Amount of divergence
What is a species?
What is a species?
What is a species?
1) speciation by cladogenesis
2) speciation by anagenesis between a & b
a
b
anagenesis
Anagenesis: no cladogenesis
cladogenesis
Cladogenesis: speciation
Anagenesis + Cladogenesis
A B C D E
A
B
CD
Most of the time we don’t know the ancestral states for
sure
What is a species?• Biologists do not agree on ONE way to define a species – thus, “species concepts”
Why?
At least 22 different definitions have been proposed to explain what a “species” is.
Three main ones:1. Morphological2. Biological3. Phylogenetic
Species concepts
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
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
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
Fertile Hybrids: Violations of both the Morphological v. Biological species
Concepts
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!
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
Phylogenetic species concept
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
High level of cryptic species diversity revealed by sympatric
lineages of Southeast Asian forest frogs
Bryan L Stuart, Robert F Inger, and Harold K VorisBiol Lett. 2006 September 22; 2(3): 470–474.
Odorrana livida
Cryptic species by the phylogenetic species concept
cf. = similar to
High level of cryptic species diversity revealed by sympatric
lineages of Southeast Asian forest frogs
Bryan L Stuart, Robert F Inger, and Harold K VorisBiol 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
High level of cryptic species diversity revealed by sympatric
lineages of Southeast Asian forest frogs
Bryan L Stuart, Robert F Inger, and Harold K VorisBiol Lett. 2006 September 22; 2(3): 470–474.
Odorrana livida
Cryptic species by the phylogenetic species concept
cf. = similar to
Odorrana livida
Rana chalconota
cf. = similar to
Cryptic species by the phylogenetic species concept
Cryptic species by the phylogenetic species concept
Morphology + DNA
Forest habitat Savanna habitat
Cryptic species by the phylogenetic species concept
Lox
odon
tia
afri
cana
Ele
phas
max
imus
Cryptic species by the phylogenetic species concept + extinct organisms!
6 mya
Ring species by the phylogenetic & morphological & biological species concepts
Ring species by the phylogenetic & morphological & biological species concepts
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