BIO 345 EXAM 3 QUESTIONS AND ANSWERS
How were species delineated before DNA sequencing was available? - Answers -The
Biological Species Concept and the Phylogenetic Species Concept were used
Explain how species are distinguished according to the Biological Species Concept
(BSC): - Answers -Species are groups of actually or potentially interbreeding
populations, which are reproductively isolated from other such groups
Explain how a scientist might determine whether there is reproductive isolation between
populations. - Answers -Reproductive Isolation means that any of several biological
differences between the groups greatly reduce gene exchange between them, even if
they are not geographically separated. Does not require that species be 100 percent
reproductively isolated—there can be a little genetic "leakage" between species through
hybridization.
What are some weaknesses of the BSC? - Answers -Reproductive isolation evolves
gradually, as we will see. So interbreeding versus reproductive isolation is not an
either/or, all-or-none distinction.
The greatest practical limitation of the BSC is in determining whether populations that
are geographically separated (allopatric) belong to the same species.
Another limitation of the BSC is that it does not apply to organisms that do not
reproduce sexually.
Explain how species are distinguished according to the Phylogenetic Species Concept
(PSC): - Answers -Emphasizes species as the outcome of evolution—the products of a
history of evolutionary divergence. A phylogenetic species is an irreducible (basal)
cluster of organisms diagnosably different from other such clusters, and within which
there is a parental pattern of ancestry and descent
What are strengths of the PSC? - Answers -Unlike the BSC, it can be applied to
allopatric populations, such as those on different islands, in which reproductive isolation
is difficult or impossible to assess.
What are some weaknesses to the PSC that you can think of? - Answers -Most
evolutionary biologists use one or another variant of the BSC, because they view the
evolution of reproductive isolation as the key event that enables sexually reproducing
lineages to evolve independently and generate biological diversity. Without the evolution
of reproductive isolation, there would be only one (or at most a few spatially separated)
species of cichlid in each of those African lakes.
Sympatric - Answers -In the same location
,Parapatric - Answers -Adjacent populations
Hybrid Zone - Answers -Exist where genetically distinct populations meet and
interbreed to a limited extent, but in which there exist partial barriers to gene exchange
Why does the species problem still exist? Why might it be useful to have multiple
species concepts? - Answers -There are limitations to the different concepts that we
use. It's not clear cut how we define species. Often when we're study different species
in nature, there is this gray area in the middle- speciation is a gradual process.
Define Ecological Species Concept (ESC): - Answers -Ecology is causing speciation
event. Ex. Favor different plants
Define Morphological Species Concept (MSC) (this is also sometimes broadened to the
Phenotypic Species Concept): - Answers -Look at physical differences in the different
species.
Define prezygotic barrier: - Answers -Isolation types that prevent sperm from fertilizing
an egg
List the prezygotic barriers and rate them on the strength of isolation (low = in the future,
barriers could break down vs. high = barriers are most likely to remain permanently): -
Answers -Ecological: Separation by geographical features or great distances
Behavioral: Individuals only mate with those with specific courtship rituals or songs
Mechanical: Reproductive organs are incompatible
Temporal: Individuals are active or reproduce at different times
Gamete Incompatibility: Sperm from one individual cannot fertilize the egg of another
Define postzygotic barrier: - Answers -A zygote forms but something happens that
prevents the successful existence of that individual. These barriers can be classified as
either extrinsic or intrinsic, depending on whether or not their effect depends on the
environment. Intrinsic isolation is based on interactions between genes from two
populations, and is often more permanent than extrinsic isolation.
List the post-zygotic barriers and rate them on the strength of isolation - Answers -
Hybrid Inviability: Hybrid embryo forms but does not develop properly.
Hybrid Sterility: Hybrid offspring are healthy but cannot successfully reproduce.
How do reproductive barriers contribute to the process of evolution? - Answers -
Speciation is the evolution of biological barriers to gene flow, and so understanding the
evolution of reproductive isolating barriers tells us how new species evolve.
Why is the distinction between pre- and post-zygotic barriers useful? - Answers -Since
prezygotic isolating mechanisms act before postzygotic mechanisms, they have a
greater opportunity to restrict gene flow. A second reason why the distinction between
,prezygotic and postzygotic mechanisms is useful is that different kinds of selection act
on them.
Is it possible to know whether pre- or post-zygotic barriers were the original catalyst to
speciation? Why or why not? - Answers -Often difficult to tell which isolating barrier was
the original cause of speciation. A character difference that contributes to reproductive
isolation now may have evolved partly in geographically segregated populations before
they became different species, partly during the process of speciation, and partly after
the reproductive barriers evolved. Because genetic differences continue to accumulate
long after two species achieve complete reproductive isolation, some of the genes, and
even some of the traits, that now confer reproductive isolation may not have been
instrumental in forming the species in the first place.
Explain Dobzhansky-Muller incompatibilities: - Answers -Explains how incompatibilities
between populations can originate without ever producing incompatibilities within a
population.
DMIs have many causes. Gene regulation can be anomalous due to a mismatch
between cis- and trans-regulatory elements from the two species. Intragenomic conflict
appears to be a common cause. DMIs can also be manifestations of cytonuclear
incompatibility. For example, hybrids between different geographic populations of a
marine copepod have reduced survival and fecundity if their mitochondria and nuclear
genome come from different populations
Section 5.1: Critical Thinking: Suppose the Phylogenetic Species Concept (PSC) were
preferred over other species concepts, such as the Biological Species Concept (BSC).
What would be the implications for:
(a) discourse on the evolutionary mechanisms of speciation - Answers -In contrast to
the biological species concept (which focuses on reproductive isolation), the
phylogenetic species concept focuses on clusters of diagnostically distinct organisms
that share common ancestry.
Mechanisms of reproductive isolation are important to the BSC (such as whether
isolating barriers are premating, prezygotic, or postzygotic). If the PSC were used, there
would be less focus on reproductive isolation and greater emphasis on the identification
of clades. Research on mechanisms of speciation would be focused on how population
differences arise by mutation, drift, and selection.
Section 5.1: Critical Thinking: Suppose the Phylogenetic Species Concept (PSC) were
preferred over other species concepts, such as the Biological Species Concept (BSC).
What would be the implications for:
(b) studies of species diversity in ecological communities - Answers -If the PSC is used,
phenotypic and DNA sequence data would be sufficient to identify the species that
make up a community. Comparisons of species differences among communities, or
among samples from different localities, might be affected because more allopatric
, populations might be called different species, hence lower species overlap between
regions would be recognized.
Section 5.1: Critical Thinking: Suppose the Phylogenetic Species Concept (PSC) were
preferred over other species concepts, such as the Biological Species Concept (BSC).
What would be the implications for:
(c) estimates of species diversity on a worldwide basis - Answers -Estimates of species
diversity are likely to change if the PSC is used. In particular, one would expect the
number of species to increase. This is because individuals from divergent allopatric
populations that can potentially interbreed would belong to the same species under the
BSC. These same organisms would be classified as members of different species under
the PSC.
Section 5.1: Critical Thinking: Suppose the Phylogenetic Species Concept (PSC) were
preferred over other species concepts, such as the Biological Species Concept (BSC).
What would be the implications for:
(d) conservation practices under such legal frameworks as the U.S. Endangered
Species Act - Answers -The choice of species concept affects conservation biology.
Distinct populations that belong to the same species under the BSC can belong to
different species under the PSC. Each of these populations could potentially be
classified as an endangered species. Also, hybridization between populations has
different ramifications, depending on which species concept is used. Because
individuals that belong to divergent populations are not considered part of the same
species under the PSC, conservation efforts that involve introducing individuals from
different populations are less likely to be utilized. The U.S. Endangered Species Act
actually provides for protection of "distinct populations," so in many cases it is used to
protect organisms that might be considered "sub-species" under the BSC, but would be
classified as separate species under the Endangered Species Act.
What class of barrier to gene flow would we be observing if we noted that the offspring
of a lion and a tiger (two different species) are awkward, gangly beasts that have poor
survival in the wild?
a. Premating barrier
b. Geographic isolation
c. Prezygotic barrier
d. Temporal isolation
e. Postzygotic barrier - Answers -e. Postzygotic barrier
The structure and morphology of the genitalia of many insects sits in the gray area
between pre- and post-mating isolation. The analogy most similar to the functional use
of genital structures in these insects is a _____________________.
a. ratchet that moves one direction
b. bottlebrush similar to lab cleaning supplies
c. traffic light that can show red, yellow, or green
How were species delineated before DNA sequencing was available? - Answers -The
Biological Species Concept and the Phylogenetic Species Concept were used
Explain how species are distinguished according to the Biological Species Concept
(BSC): - Answers -Species are groups of actually or potentially interbreeding
populations, which are reproductively isolated from other such groups
Explain how a scientist might determine whether there is reproductive isolation between
populations. - Answers -Reproductive Isolation means that any of several biological
differences between the groups greatly reduce gene exchange between them, even if
they are not geographically separated. Does not require that species be 100 percent
reproductively isolated—there can be a little genetic "leakage" between species through
hybridization.
What are some weaknesses of the BSC? - Answers -Reproductive isolation evolves
gradually, as we will see. So interbreeding versus reproductive isolation is not an
either/or, all-or-none distinction.
The greatest practical limitation of the BSC is in determining whether populations that
are geographically separated (allopatric) belong to the same species.
Another limitation of the BSC is that it does not apply to organisms that do not
reproduce sexually.
Explain how species are distinguished according to the Phylogenetic Species Concept
(PSC): - Answers -Emphasizes species as the outcome of evolution—the products of a
history of evolutionary divergence. A phylogenetic species is an irreducible (basal)
cluster of organisms diagnosably different from other such clusters, and within which
there is a parental pattern of ancestry and descent
What are strengths of the PSC? - Answers -Unlike the BSC, it can be applied to
allopatric populations, such as those on different islands, in which reproductive isolation
is difficult or impossible to assess.
What are some weaknesses to the PSC that you can think of? - Answers -Most
evolutionary biologists use one or another variant of the BSC, because they view the
evolution of reproductive isolation as the key event that enables sexually reproducing
lineages to evolve independently and generate biological diversity. Without the evolution
of reproductive isolation, there would be only one (or at most a few spatially separated)
species of cichlid in each of those African lakes.
Sympatric - Answers -In the same location
,Parapatric - Answers -Adjacent populations
Hybrid Zone - Answers -Exist where genetically distinct populations meet and
interbreed to a limited extent, but in which there exist partial barriers to gene exchange
Why does the species problem still exist? Why might it be useful to have multiple
species concepts? - Answers -There are limitations to the different concepts that we
use. It's not clear cut how we define species. Often when we're study different species
in nature, there is this gray area in the middle- speciation is a gradual process.
Define Ecological Species Concept (ESC): - Answers -Ecology is causing speciation
event. Ex. Favor different plants
Define Morphological Species Concept (MSC) (this is also sometimes broadened to the
Phenotypic Species Concept): - Answers -Look at physical differences in the different
species.
Define prezygotic barrier: - Answers -Isolation types that prevent sperm from fertilizing
an egg
List the prezygotic barriers and rate them on the strength of isolation (low = in the future,
barriers could break down vs. high = barriers are most likely to remain permanently): -
Answers -Ecological: Separation by geographical features or great distances
Behavioral: Individuals only mate with those with specific courtship rituals or songs
Mechanical: Reproductive organs are incompatible
Temporal: Individuals are active or reproduce at different times
Gamete Incompatibility: Sperm from one individual cannot fertilize the egg of another
Define postzygotic barrier: - Answers -A zygote forms but something happens that
prevents the successful existence of that individual. These barriers can be classified as
either extrinsic or intrinsic, depending on whether or not their effect depends on the
environment. Intrinsic isolation is based on interactions between genes from two
populations, and is often more permanent than extrinsic isolation.
List the post-zygotic barriers and rate them on the strength of isolation - Answers -
Hybrid Inviability: Hybrid embryo forms but does not develop properly.
Hybrid Sterility: Hybrid offspring are healthy but cannot successfully reproduce.
How do reproductive barriers contribute to the process of evolution? - Answers -
Speciation is the evolution of biological barriers to gene flow, and so understanding the
evolution of reproductive isolating barriers tells us how new species evolve.
Why is the distinction between pre- and post-zygotic barriers useful? - Answers -Since
prezygotic isolating mechanisms act before postzygotic mechanisms, they have a
greater opportunity to restrict gene flow. A second reason why the distinction between
,prezygotic and postzygotic mechanisms is useful is that different kinds of selection act
on them.
Is it possible to know whether pre- or post-zygotic barriers were the original catalyst to
speciation? Why or why not? - Answers -Often difficult to tell which isolating barrier was
the original cause of speciation. A character difference that contributes to reproductive
isolation now may have evolved partly in geographically segregated populations before
they became different species, partly during the process of speciation, and partly after
the reproductive barriers evolved. Because genetic differences continue to accumulate
long after two species achieve complete reproductive isolation, some of the genes, and
even some of the traits, that now confer reproductive isolation may not have been
instrumental in forming the species in the first place.
Explain Dobzhansky-Muller incompatibilities: - Answers -Explains how incompatibilities
between populations can originate without ever producing incompatibilities within a
population.
DMIs have many causes. Gene regulation can be anomalous due to a mismatch
between cis- and trans-regulatory elements from the two species. Intragenomic conflict
appears to be a common cause. DMIs can also be manifestations of cytonuclear
incompatibility. For example, hybrids between different geographic populations of a
marine copepod have reduced survival and fecundity if their mitochondria and nuclear
genome come from different populations
Section 5.1: Critical Thinking: Suppose the Phylogenetic Species Concept (PSC) were
preferred over other species concepts, such as the Biological Species Concept (BSC).
What would be the implications for:
(a) discourse on the evolutionary mechanisms of speciation - Answers -In contrast to
the biological species concept (which focuses on reproductive isolation), the
phylogenetic species concept focuses on clusters of diagnostically distinct organisms
that share common ancestry.
Mechanisms of reproductive isolation are important to the BSC (such as whether
isolating barriers are premating, prezygotic, or postzygotic). If the PSC were used, there
would be less focus on reproductive isolation and greater emphasis on the identification
of clades. Research on mechanisms of speciation would be focused on how population
differences arise by mutation, drift, and selection.
Section 5.1: Critical Thinking: Suppose the Phylogenetic Species Concept (PSC) were
preferred over other species concepts, such as the Biological Species Concept (BSC).
What would be the implications for:
(b) studies of species diversity in ecological communities - Answers -If the PSC is used,
phenotypic and DNA sequence data would be sufficient to identify the species that
make up a community. Comparisons of species differences among communities, or
among samples from different localities, might be affected because more allopatric
, populations might be called different species, hence lower species overlap between
regions would be recognized.
Section 5.1: Critical Thinking: Suppose the Phylogenetic Species Concept (PSC) were
preferred over other species concepts, such as the Biological Species Concept (BSC).
What would be the implications for:
(c) estimates of species diversity on a worldwide basis - Answers -Estimates of species
diversity are likely to change if the PSC is used. In particular, one would expect the
number of species to increase. This is because individuals from divergent allopatric
populations that can potentially interbreed would belong to the same species under the
BSC. These same organisms would be classified as members of different species under
the PSC.
Section 5.1: Critical Thinking: Suppose the Phylogenetic Species Concept (PSC) were
preferred over other species concepts, such as the Biological Species Concept (BSC).
What would be the implications for:
(d) conservation practices under such legal frameworks as the U.S. Endangered
Species Act - Answers -The choice of species concept affects conservation biology.
Distinct populations that belong to the same species under the BSC can belong to
different species under the PSC. Each of these populations could potentially be
classified as an endangered species. Also, hybridization between populations has
different ramifications, depending on which species concept is used. Because
individuals that belong to divergent populations are not considered part of the same
species under the PSC, conservation efforts that involve introducing individuals from
different populations are less likely to be utilized. The U.S. Endangered Species Act
actually provides for protection of "distinct populations," so in many cases it is used to
protect organisms that might be considered "sub-species" under the BSC, but would be
classified as separate species under the Endangered Species Act.
What class of barrier to gene flow would we be observing if we noted that the offspring
of a lion and a tiger (two different species) are awkward, gangly beasts that have poor
survival in the wild?
a. Premating barrier
b. Geographic isolation
c. Prezygotic barrier
d. Temporal isolation
e. Postzygotic barrier - Answers -e. Postzygotic barrier
The structure and morphology of the genitalia of many insects sits in the gray area
between pre- and post-mating isolation. The analogy most similar to the functional use
of genital structures in these insects is a _____________________.
a. ratchet that moves one direction
b. bottlebrush similar to lab cleaning supplies
c. traffic light that can show red, yellow, or green
