EVOLUTION (BIOL 318) BIOLOGY EXAM
2 (Turbeville) STUDY NOTES COMPETE
AND ACCURATE LATEST GUIDE
VIRGINIA COMMONWEALTH
UNIVERSITY
, Exam 2 Study Guide Species
Concepts and Speciation
• Species: Fundamental unit of biological diversity
o Speciation: Processes that generates species
o Two components to realities
▪ Spatial – how they’re distributed across geographically and across landscapes
▪ Temporal – phylogeny
• Space and time contribute to evolutionary processes
• Not a single concept of a species
• Evolutionary Species Concept (ESC): Lineage of ancestral-descendant populations which maintains
its identity from other such lineages and which has its own evolutionary tendencies and historical fate
o Lineage = set of ancestral descended populations
o Umbrella concept; not precise
o Proposed by G.G. Simpson, architect of Modern Synthesis
o Ex: Two different species of mosquitos breed in different places, mate differently, prefers
different hosts, produces eggs differently, and has a different life cycle
▪ Evolved different life history
o Vague - No guidelines to determine species boundaries or limit species
▪ Refinement of the ESC emphasizes different aspects of the evolutionary histories that
underlie the species as real units of biological diversity
• Morphological Species Concept (MSC)
o Morphology: Study of form and structure of organisms, like shape and structural traits
▪ Traits vary because of evolutionary processes
▪ Can use morphology to define species
• After species converge evolve independently
• Morphology differences that evolve afterwards allows us to define a species
o Ex: Hypothesize that 3 different populations of butterflies are likely different species
▪ Measure two phenotypic traits – antenna length and wing length plot the traits
▪ Quantify the morphological diversity forms clusters in phenotypic space
• Can use the clusters to assign species boundaries
▪ Phenetics: Quantification of morphological diversity
• If you measure phenotypes of individuals from different populations, should see
cluster in phenotypic data if the populations represent different species
• Separate clusters = separate species; clusters define species boundaries
o After species diverge from a common ancestor evolve independently
• Would separate individuals into clusters in an extremely diverse species, even if
it’s one species
• Biological Species Concept (BSC): Requires evolution of differences that prevent successful mating
between populations (reproductive isolation)
o No gene flow between populations – can be used to limit a species
▪ Only the same species can reproduce with one another
o Methods of study
▪ Patterns of gene flow
▪ Tests of crossing individuals from different populations lacking connection via gene flow
• Seeing if individuals can produce viable, fertile offspring
o Focused on reproduction, specifically sexual reproduction
▪ Focuses on reproductive isolation in gene pools
• What if studying organisms that reproduce asexually?
o How bad must the reproductive capabilities be before considering a population two species?
o Ex: Two species of Meadowlark – overlapping ranges and similar morphologies
▪ Evolved behavioral isolating mechanism – their song separates them by keeping them
from mating
• Only responds to calls of their own species
• Phylogenetic Species Concept (PSC): Evolutionary history results in an underlying tree-like structure
describing this history
o Phylogenies used to delimit species
▪ Clades = monophyletic groups
• Defined by shared derived characters = synapomorphies
▪ Phylogenetic Species: The smallest subset of individuals distinguished by a
synapomorphy
, o Useful if there is little morphological differences, can collect molecular data to construct
phylogeny
o Convergent evolution can result in misleading delimitations
• Modes of speciation – based on how populations are distributed spatially
o Allopatric Speciation: Involves geographical isolation of populations
▪ Geographical, physical barriers
• Ex: Water, distance
▪ Tied closely to the BSC
▪ Vicariance Model: Division of a population
• Original population is subdivided into two large populations by geographic barrier
prevents gene flow between subpopulation
o If reproductive isolation evolves delimits the subpopulations as two
biological species
• Ex: Geological processes caused Panama to form
o The closing of the isthmus of Panama isolated populations of various
shrimp species
▪ No gene flow across the isthmus
o Produced 6 pairs of sister species – one on each side of the isthmus
▪ Peripheral Isolate Model: Colonization of a new habitat
• Only a small subset of original population is isolated
o Limits gene flow between subset population and original population
o Subset diverges over time reproductive isolation evolves
• Drift plays a bigger role in smaller populations
o Diversity of original population isn’t represented in the smaller
subpopulation
o Greater sensitivity to drift more than larger population
• Ex: Red spruce likely diverged from black spruce recently
o Recent speciation events result in progenitor (black) and derivative (red)
species
o Genetic diversity found in derivative species only a subset of what you find
in the progenitor species
▪ Diversity is reduced in red spruce
o Parapatry Speciation: Adjacent populations diverge into separate species without being
separated by a geographic barrier
▪ Results from different selection pressures ends in environmental gradient
• Separation along an environmental gradient sorts genotypes based on their
fitness
▪ Initial step = divergent selection across a cline
• Leads to evolution of reproductive isolation
• Occurs across a hybrid zone – there’s gene flow across the divergent populations
o The hybrids have reduced fitness
• Ability to hybridize is considered to be lost over time because of reduced fitness
isolating mechanisms evolve to isolate the two species reproductively
▪ Sorting results in a cline
• Cline: Spatial gradient in frequency of genotypes and phenotypes
• The ends of the cline diverge because of the accumulation of genetic changes
due to selection
▪ Ex: Vernal grass
• Incipient speciation
• Mine grass > self-fertilization
• Mine grass flowers earlier – limits gene flow
o Isolates reproductive the species living in area pasture vs mine soil
o Sympatric Speciation: Does not involve geographical separation
▪ Genetic isolation occurs in the same place
• There’s genetic differentiation but it’s in the same location (in situ)
• If reproductive isolation evolves different species
▪ Character Displacement: The evolution of different trait values in different lineages
• Ex: Beak size in Darwin’s finches
o Beak size affects ability to eat – directly related to fitness
2 (Turbeville) STUDY NOTES COMPETE
AND ACCURATE LATEST GUIDE
VIRGINIA COMMONWEALTH
UNIVERSITY
, Exam 2 Study Guide Species
Concepts and Speciation
• Species: Fundamental unit of biological diversity
o Speciation: Processes that generates species
o Two components to realities
▪ Spatial – how they’re distributed across geographically and across landscapes
▪ Temporal – phylogeny
• Space and time contribute to evolutionary processes
• Not a single concept of a species
• Evolutionary Species Concept (ESC): Lineage of ancestral-descendant populations which maintains
its identity from other such lineages and which has its own evolutionary tendencies and historical fate
o Lineage = set of ancestral descended populations
o Umbrella concept; not precise
o Proposed by G.G. Simpson, architect of Modern Synthesis
o Ex: Two different species of mosquitos breed in different places, mate differently, prefers
different hosts, produces eggs differently, and has a different life cycle
▪ Evolved different life history
o Vague - No guidelines to determine species boundaries or limit species
▪ Refinement of the ESC emphasizes different aspects of the evolutionary histories that
underlie the species as real units of biological diversity
• Morphological Species Concept (MSC)
o Morphology: Study of form and structure of organisms, like shape and structural traits
▪ Traits vary because of evolutionary processes
▪ Can use morphology to define species
• After species converge evolve independently
• Morphology differences that evolve afterwards allows us to define a species
o Ex: Hypothesize that 3 different populations of butterflies are likely different species
▪ Measure two phenotypic traits – antenna length and wing length plot the traits
▪ Quantify the morphological diversity forms clusters in phenotypic space
• Can use the clusters to assign species boundaries
▪ Phenetics: Quantification of morphological diversity
• If you measure phenotypes of individuals from different populations, should see
cluster in phenotypic data if the populations represent different species
• Separate clusters = separate species; clusters define species boundaries
o After species diverge from a common ancestor evolve independently
• Would separate individuals into clusters in an extremely diverse species, even if
it’s one species
• Biological Species Concept (BSC): Requires evolution of differences that prevent successful mating
between populations (reproductive isolation)
o No gene flow between populations – can be used to limit a species
▪ Only the same species can reproduce with one another
o Methods of study
▪ Patterns of gene flow
▪ Tests of crossing individuals from different populations lacking connection via gene flow
• Seeing if individuals can produce viable, fertile offspring
o Focused on reproduction, specifically sexual reproduction
▪ Focuses on reproductive isolation in gene pools
• What if studying organisms that reproduce asexually?
o How bad must the reproductive capabilities be before considering a population two species?
o Ex: Two species of Meadowlark – overlapping ranges and similar morphologies
▪ Evolved behavioral isolating mechanism – their song separates them by keeping them
from mating
• Only responds to calls of their own species
• Phylogenetic Species Concept (PSC): Evolutionary history results in an underlying tree-like structure
describing this history
o Phylogenies used to delimit species
▪ Clades = monophyletic groups
• Defined by shared derived characters = synapomorphies
▪ Phylogenetic Species: The smallest subset of individuals distinguished by a
synapomorphy
, o Useful if there is little morphological differences, can collect molecular data to construct
phylogeny
o Convergent evolution can result in misleading delimitations
• Modes of speciation – based on how populations are distributed spatially
o Allopatric Speciation: Involves geographical isolation of populations
▪ Geographical, physical barriers
• Ex: Water, distance
▪ Tied closely to the BSC
▪ Vicariance Model: Division of a population
• Original population is subdivided into two large populations by geographic barrier
prevents gene flow between subpopulation
o If reproductive isolation evolves delimits the subpopulations as two
biological species
• Ex: Geological processes caused Panama to form
o The closing of the isthmus of Panama isolated populations of various
shrimp species
▪ No gene flow across the isthmus
o Produced 6 pairs of sister species – one on each side of the isthmus
▪ Peripheral Isolate Model: Colonization of a new habitat
• Only a small subset of original population is isolated
o Limits gene flow between subset population and original population
o Subset diverges over time reproductive isolation evolves
• Drift plays a bigger role in smaller populations
o Diversity of original population isn’t represented in the smaller
subpopulation
o Greater sensitivity to drift more than larger population
• Ex: Red spruce likely diverged from black spruce recently
o Recent speciation events result in progenitor (black) and derivative (red)
species
o Genetic diversity found in derivative species only a subset of what you find
in the progenitor species
▪ Diversity is reduced in red spruce
o Parapatry Speciation: Adjacent populations diverge into separate species without being
separated by a geographic barrier
▪ Results from different selection pressures ends in environmental gradient
• Separation along an environmental gradient sorts genotypes based on their
fitness
▪ Initial step = divergent selection across a cline
• Leads to evolution of reproductive isolation
• Occurs across a hybrid zone – there’s gene flow across the divergent populations
o The hybrids have reduced fitness
• Ability to hybridize is considered to be lost over time because of reduced fitness
isolating mechanisms evolve to isolate the two species reproductively
▪ Sorting results in a cline
• Cline: Spatial gradient in frequency of genotypes and phenotypes
• The ends of the cline diverge because of the accumulation of genetic changes
due to selection
▪ Ex: Vernal grass
• Incipient speciation
• Mine grass > self-fertilization
• Mine grass flowers earlier – limits gene flow
o Isolates reproductive the species living in area pasture vs mine soil
o Sympatric Speciation: Does not involve geographical separation
▪ Genetic isolation occurs in the same place
• There’s genetic differentiation but it’s in the same location (in situ)
• If reproductive isolation evolves different species
▪ Character Displacement: The evolution of different trait values in different lineages
• Ex: Beak size in Darwin’s finches
o Beak size affects ability to eat – directly related to fitness
