In speciation lies the __________________________, and the study of speciation
bridges ___________________________
origin of diversity
microevolution and
macroevolution
Evolution of diversity occurs by
cladogenesis
anagenesis
cladogenesis
branching of lineages
anaenesis
evolution within a species
Speciation Time
Long process to be observed by _________________________ of scientists
one or a few generations
Speciation Time
too ___________________________ to find it well documented in the fossil record
short for geological time
scales
Species - latin for "_______"
kind
What is a Species
Highly dependent on
the context of the definition used
Species can be defined to
#1
Enable us to classify organisms
Species can be defined to
#2
Correspond to discrete groups of similar
organisms
Species can be defined to
#3
Help us understand how discrete clusters of
organisms arise in nature
Species can be defined to
#4
Represent products of evolutionary history
Species can be defined to
#5
Apply to the largest possible variety of
organisms
No two of these possible goals always coincide thus it is unlikely that
any one species concepts will serve most of these purposes
The Crow Story
The two european
crows look more
different from one
another than crows do
from ravens - however
there is
a clear hybrid
zone between the
carrion crow and the
hooded crow
Species Concepts
biological
evolutionary
phylogenetic
genealogical
cohesion
Biological Species Concept (BSC)
Mayr (1942) - "Species are groups of actually or
potentially interbreeding natural populations that are ___________________________
from other such groups"
reproductively isolated
Phylogenetic Species Concept (PSC)
Cracraft (1989) - "An irreducible (basal) cluster of organisms that is diagnosably distinct from other such clusters, and within which there is a
___________________________________________".
Applies to _________________________ organisms
parental pattern of ancestry and descent
sexual and asexual
Phylogenetic Species Concept (PSC)
de Queiroz and Donaghue (1990) - "The _________________________ of common ancestry"
smallest monophyletic group
Evolutionary Species Concept (ESC)
Wiley (1978) - "A species is a ___________________________ that maintains an identity
separate from other such lineages and which has its ________________________".
single lineage of populations
own evolutionary fate
Most widely used species concepts today:
Biological Species Concept
Phylogenetic Species Concept
_____________________________________ emphasizes species as the outcome of evolution, the products of
divergence
Phylogenetic Species Concept
_____________________________________ emphasizes the process by which
species arise
Biological Species Concept
Regardless of which concept is used,
some populations will not be
unambiguosly assigned to one species or another
Most frequently used by evolutionary biologists concerned with process
Biological Species Concept
"Species are groups of actually or potentially
interbreeding natural populations that are
reproductively isolated from other such groups".
Biological Species Concept
Biological Species Concept
Reproductive isolation means that biological
differences between populations ___________________________ even in the absence of geographic
isolation
reduce gene exchange
Biological Species Concept
Advocates of BSC recognize that there can be
some _________________________.
gene exchange "leakage"
Development of the Biological Species Concept
variation within populations
Development of the Biological Species Concept - Variation Within Populations
White and blue color morphs of the snow goose
from the same mother represent _________________________.
a genetic polymorphism
Development of the Biological Species Concept
Geographic Variation
human populations
Development of the Biological Species Concept
Sibling species are _________________________ but _____________________ ____________________.
reproductively isolated
indistinguishable morphologically
Development of the Biological Species Concept
Sibling species are reproductively isolated but indistinguishable
morphologically. Recognized by differences in
ecology, behavior,
chromosomal number
Some Terms Used in the Species Literature
geographic isolation
reproductive isolation
Geographic Isolation
Reduction/prevention of gene flow between
populations by
an extrinsic barrier to movement
Reproductive Isolation
Prevention of gene flow by
genetically determined differences
Terms Used in the Species Literature
Population Types
Allopatric
Parapatric
Sympatric
Allopatric Population
located in separate geographic areas
Parapatric Populations
adjacent, meeting at the border
Sympatric Population
in the SAME location
Sibling Species
reproductively isolated but difficult to distinguish morphologically
Sister Species
derived from an immediate common ancestor
Hybrid Zone
region where genetically distinct populations interbreed to some extent
Introgression
movement of genes from one distinct population into another
Semispecies
parapatric populations nearly but not quite different species
Fitness
reproductive success
Pleiotropy
multiple effects of a single gene
Epistasis
when the action of one gene is modified by one or more others that assort __________________________ (i.e. the two genes may be quite tightly linked, but their effects must reside at __________________________)
somewhat independently
different loci in the
genome
Restricted to sexual, outcrossing
organisms as well as short intervals (not
useful in long geologic time intervals)
Domain of Biological Species Concept
Borderline Cases
Hybrid Zones
example of sympatric hybridization in oaks
Borderline Cases
Geographic Variation in Status
genetically different populations or conspecific in certain areas and different species elsewhere
Difficulty of Biological Species Concept
assessing if allopatric populations belong to the same species since
it requires assessment of potential interbreeding
Conflict between Phylogenetic Species Concept and Biological Species Concept
in classification
Conflict between Phylogenetic Species Concept and Biological Species Concept
In Classification - distinct allopatric populations would be considered species by the _______ but if the differences were only slight they would be
considered
PSC
variants of the same species under the BSC
Conflict between Phylogenetic Species Concept and Biological Species Concept
In Classification - when making trees with new species, the PSC would require
renaming old species while the BSC would consider one paraphyletic
Gene Flow Barriers
aka
isolating mechanisms
isolating barriers
Gene Flow Barriers
under the BSC speciation consists of
the evolution of biological barriers to gene flow
Premating Barriers
Ecological Isolation
different breeding seasons
habitat isolation
Premating Barriers
Behavioral Isolation
sexual isolation
Premating Barriers
Behavioral Isolation (Sexual Isolation)
Important among ______________ __________
sympatric species
Premating Barriers
Behavioral Isolation (Sexual Isolation)
Specific Mate Recognition Signals
signals and responses between potential mates
one sex will not respond to inappropriate signals
Behavioral Isolation
Morphologically
indistinguishable insect
species with ___________________________.
Females discriminate
against ____________________________.
distinct mating songs
other species as well as hybrids
Behavioral Isolation
Visual signals are
often used in
combination with
__________________________
signals in courtship
behavior
chemical and acoustic
Plants
Behavioral isolation does not exist per se. Different pollinating animals respond
to differences in
color, form or scent
Postmating Prezygotic Barriers
conspecific sperm precedence
gametic isolation
Conspecific Sperm Precedence
insects and pollinated plants
Gametic Isolation
important in free spawning marine invertebrates
Orbicella species complex
__________ sibling species
three
Orbicella species complex
combination of premating and postmating barriers
different spawning times
lower hybrid viability
Population Collapse in Early Pleisocene
mass extinction of Orbicella species between 1 and 2 Mya
share evolutionary history for all species until 700 ky
Postzygotic Barriers
hybrid inviability
hybrids sterility
Postzygotic Barriers
Hybrid Inviability
hybrids have LOWER survival rates than nonhybrids
Postzygotic Barriers
Hybrid Sterility
differences between the genes from two parents
Hybrid Sterility
Structural differences between the ______________ producing gametes with an
__________________________ of chromosomes
chromosomes
unbalanced complement
Haldane's Rule
Hybrid sterility is limited to the heterogametic sex →
the one with two different chromosomes
MALES in mammals, insects
FEMALES in birds, butterflies
Hybrid Sterility is manifested in
F1, F2 and backcross offspring
In Drosophila, both prezygotic and
postzygotic isolation increases gradually
with time since
the separation of populations (speciation is gradual)
Prezygotic isolation
measured by
mating success (or failure)
Postzygotic isolation measured by
survival and fertility of hybrids
In Drosophila, prezygotic isolation is STRONGER among
sympatric than among
allopatric pairs of taxa
Genetic Basis of Reproductive Barriers
Hybrid Sterility measured by
sperm motility
Genetic Basis of Reproductive Barriers
Every chromosome arm
derived from D.mauritania had ____________ sperm
motility compared
to D. simulans
reduced
Epistasis
Interactions between genes that contribute to hybrid sterility do NOT have
the same interactions in the two parent species
Ancestral Species
↓
Independent Divergence
↓
Deleterious interactions in hybrids
↓
hybrid ________________
inviable
because the genes have diverged in the two species
Early acquisition of hybrid sterility requires
few gene differences
The X chromosome has
a GREATER effect than any autosome
Genes that cause reproductive isolation are
poorly known
one of the best known examples of genes that cause reproductive isolation
Nup96
Nup96
Encodes for a _____________
protein in the nuclear pore complexes which regulate passage between _____________________________
nucleoporin
cell nucleus and cytoplasm
Chromosomes & Isolation
Reciprocal Translocation
can cause aneuploidy (abnormal numbers of
specific chromosomes)
Chromosomes & Isolation
In Animals - chromosomal heterozygotes have __________ fitness probability due to aneuploidy
LOWER
mole rats in Israel
Dobzhansky-Muller
Incompatibility
Reproductive isolation is usually due to
differences in multiple loci
Dobzhansky-Muller
Incompatibility
Reproductive isolation requires populations/species
diverge by at least two allele substitutions
Dobzhansky-Muller
Incompatibility
AABB (ancestral)
↓ ↓
AAbb aaBB
(derived) (derived)
a and b are incompatible
AaBb are low fitness hybrids
Coalescence
A population with two alleles
at time 0 - by chance
(genetic drift) some
individuals fail to leave
descendants
Coalescence
At time t all copies of a gene are descended from a single
ancestral gene copy - they
coalesce back to a single
common ancestor
Coalescence
Lineage sorting is
____________ in smaller
populations
FASTER
Lineage Sorting
when the gene tree reflects the species tree
Ancestral Polymorphisms
often shared in closely related species
lineage sorting is incomplete
Lake Malawi's cichilds
Branches
haplotypes
Lake Malawi's cichilds
Color Acronyms
different species with same haplotype
Hybrid Zone by
divergent selection
secondary contact
Yellow Bellied Toads
secondary contact
