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Bio Exam 3
Terms in this set (83)
Why are some phenotypic differences heritable and some are not heritable?
B/c some phenotypes are homologous traits and inherited from one's ancestors, and other traits analogous traits and have evolved independently due to selective pressures, causing convergent evolution.
Biological evolution definition
change in the distribution of heritable phenotypes (physical and physiological characteristics)
variation in the phenotypes of individuals
specific sequence of DNA that encodes instructions to make particular product (ex: protein), transmitted from parents to offspring
changes in the gene pool of a population from one generation to the next
prevent mating or fertilization between species
operate after hybrid zygotes have formed
- reduced hybrid viability
- reduced hybrid fertility
- hybrid breakdown
splitting of one species into 2
- separation mechanism that limits/prevents gene flow
-accumulation of diff evolutionary changes leading to reproductive isolation
group of populations that are evolutionary independent of other population (heritable traits change independently of one another)
Morphological species concept
Smallest group of organisms that share similar physical traits (suggests common evolutionary history)
Advantages: widely applicable, works for asexual and extinct species
Challenges: traits change during lifetime, not all features as preserved as fossils, *subjective
Phylogenetic species concept
Smallest group of organisms that contains all known descendants of a common ancestor
- distinguishes by unique traits
- gene sequences used to construct trees
Advantages: applies to all organisms & testable, works for asexual and extinct species
Disadvantages: requires data on evolutionary histories, which traits to use?
Biological species concept
smallest group of organisms that mate or could potentially mate in nature and create viable, fertile offspring
Advantages: objective, populations evolutionarily independent by default, easily applied and tested in many cases
Challenges: difficult to classify extinct species, hybrid species, asexual reproduction, difficult to observe, some don't mate in nature but produce offspring in captivity
Reasoning for classifying species
- conservation and policy
- daily life
- disease treatment
Variation is a result of what?
- mutations: random changes in a DNA sequence
- sexual reproduction
What are requirements of evolution?
- heritable variation
- a force of change: natural selection, artificial selection, sexual selection, movement of individuals between populations, random events
Examples of heritable and non-heritable traits
heritable: earlobe attachment, tongue rolling, dimples, handedness, freckles, hair qualities, colorblindness, hairline, PTC tasting, some behaviors
non-heritable: abilities (learned), behaviors
If every individual in a population had the same DNA sequence, could the population evolve?
No, because there must be a change in in the distribution of heritable phenotypes
1) find/identify mate
4) adult offspring
Why can't an individual evolve?
Because one's genes can't change over a lifetime. Selection acts on individuals, creating evolution in a population.
Is the statement "Once the individuals in a population have adapted to their environment, the population stops
evolving" true or false?
False, because the environment is always changing
Your friend tells you that snowshoe hares evolved to have white fur because it was necessary for them hide
from predators in snowy environments. Correct your friend's statement/misconception.
Evolution doesn't have goals
Give at least two reasons that natural selection cannot lead to "perfect" organisms and use hypothetical (or real)
examples to illustrate your reasons.
- environments are constantly changing
- traits have trade-offs
- we can't create variation, it alters the proportion of existing traits
Explain why evolutionary change can sometimes increase the percentage of individuals in a population with
traits that are NOT beneficial for survival and reproduction.
Evolution can lead to hybrids that are not viable or fertile because they don't do well in their environment and can't reproduce.
What are the forces of microevolutionary change?
Microevolution: changes in the distribution of heritable phenotypes in a population
- artificial selection
-movement of individuals between populations
Write a sentence that describes the connection between microevolution and speciation.
Microevolutionary change is required for speciation - but, microevolutionary change does NOT always lead to the evolution of new species
Why is identifying species so challenging?
Because there are many species concepts and they vary greatly
Why isn't it possible to definitely prove that a particular group of populations (organisms) is a species?
Because each species concept uses different methods and they don't always agree on which group of organisms is a species
Different species share similar traits because of variation within species
Which species concept(s) can be applied to fossils?
Morphological & Phylogenetic
What types of organisms cannot be identified as species by the biological species concept?
- extinct species
- asexual species
- hybrid species
- bacteria (asexual reproduction)
In the speciation video we watched, what species concept(s) did they use to identify bird species?
Morphological and biological?
You are given a set of preserved (dead) butterflies. What species concept(s) could you use to categorize them?
morphological and phylogenetic
Describe a scenario in which two scientists could reach different conclusions regarding the identification of a species.
Describe a scenario in which two lizard populations could be organized into species differently by the
biological vs. the morphological species concepts.
Biological - organized based on ability to mate
Morphological - Organized based on physical appearance
As we develop more tools to assess the characteristics of organisms, do you think that it will become more or
less challenging to identify species?
More challenging because we will discover many new traits, making it more difficult to identify the relationship between different species.
Explain why speciation is described as a "process," and not a discrete event.
Speciation occurs over time, not rapidly
Explain why geographical separation is neither necessary nor sufficient for two populations to evolve into different species.
Dispersal can still occur, and populations must still undergo evolutionary changes that lead to reproductive isolation
Explain why a mechanism that limits/prevents gene flow between populations is a requirement for speciation
By limiting gene flow it prevents the population from reproducing, creating a reproductive barrier between the two populations
Explain why a mechanism that limits/prevents gene flow is NOT sufficient for speciation.
Because there are many other forces of change besides gene flow
Imagine two populations of crickets. For each of the reproductive barriers we discussed, describe at least one
observation that would support the hypothesis that a particular reproductive barrier exists between the two
Describe the difference between reduced hybrid viability and reduced hybrid fertility.
viability - not born, significant development defects, or can't survive well in current environment
fertility - can't get a mate or physically unable to produce offspring
Write a sentence that explains why reproductive barriers are not "all or nothing."
They can vary in strength, multiple can exists between a species, and they can prevent/limit ability of individuals to mate and produce viable offspring
Do you think that prezygotic barriers or postzygotic barriers tend to be evolutionarily favored? Why?
geographically separate populations
populations that live in the same are
List at least two reasons why identifying the category (mode) of speciation for a particular speciation process is challenging.
Explain the difference between allopatric and sympatric speciation. Is it possible for a speciation process to be
an example of both categories?
Allopatric - Geographically isolated populations that undergo different evolutionary changes that lead to reproductive isolation (dispersal or barrier)
Sympatric - populations inhabit same area but subject to selective pressure
Explain why geographical isolation does NOT always lead to speciation. What conditions could increase the
chance that reproductive barriers will evolve between geographically isolated populations?
Populations must undergo different evolutionary changes that lead to reproductive isolation
- diff env conditions
-diff genetic variation in populations when they're separated
Many biologists predict that allopatric speciation is more common than sympatric speciation. Based on what
you know about speciation, propose an explanation for this prediction (i.e. why does it make sense?).
- Different conditions such as environmental conditions and genetic variation in the populations when they are separated can favor allopatric speciation
- Variation in habitat and mate preference favor sympatric speciation (selective pressure)
Review the analysis performed by Diane Dodd using "starch" and "maltose" Drosophila. Based on the data collected in her analysis, what reproductive barrier(s) exist between the fly populations?
- Behavioral barriers, different food sources can lead to the evolution of reproductive barriers between allopatric populations in 40 generations
Would you classify the starch and maltose Drosophila as two different fruit fly species? Why or why not?
What other information would be helpful in assessing whether they should be classified as different species? What species concept(s) could be applied?
- yes, because diff food sources can lead to evolution of reproductive barriers between the populations
- flies from one of the starch populations with flies from a different starch population
- Biological species concept
Explain why Northern and Southern green-eyed tree frog populations are an example of allopatric speciation.
They're separated by glaciers, only 2 areas of contact w/few hybrid offspring
- DNA sequences shown northern frogs more sim to each other than to southern pop & vice versa
Looking back at the observations and data collected by Hoskin, et al. on the green-eyed tree frog populations,
what species concept(s) would categorize the frogs as the same species? Different species? For what
concept(s) would you need additional data (be sure to specify what data you would need!)?
- speciation occurred in the north, but not the south
Based on the analysis we discussed, what reproductive barrier(s) have evolved between green-eyed tree frog
populations? What other barriers could exist?
Describe at least two factors that could contribute to different evolutionary changes occurring in the new
population of green iguanas on Anguilla compared to the green iguanas on Guadeloupe.
If scientists continue to study the iguana populations on Anguilla and Guadeloupe, and the populations
eventually evolve into different species, will the scientists be able to define an exact time at which speciation
has occurred? Why or why not?
No because speciation occurs over time, not in one instance
What conditions could increase the chance that reproductive barriers will evolve within a population? Explain how/why each of these conditions can favor sympatric speciation.
- behavioral: diff mating behaviors, don't recognize each other as potential mates
- habitat: live in same area but occupy diff habitats, don't encounter frequently
- temporal: breed diff times, don't encounter at right time
- mechanical: organs not compatible, (pollinators cant transfer)
- gametic: sperm cant fertilize egg (fish)
- reduced hybrid viability: don't dev past zygote, dev defects, don't survive well in env
- reduced hybrid fertility: cant get a mate (behavior), sterile
Imagine a forest with bushes that have either small, soft seeds or large, hard seeds. Explain how sympatric
evolution could occur in a bird population living in this forest that relies on the seeds as its primary food
Beak size and characteristics could change -> behavioral & habitat barriers -> live in same area but b/c selective pressures don't mate
Based on the data obtained by Linn, et al., what reproductive barrier(s) exist(s) between hawthorn and apple maggot flies? What evidence would support the hypothesis that a temporal barrier exists between the two
behavioral - preference of diff fruit scent heritable
- the apple and hawthorn maggot flies mate at different times & don't encounter each other at the right time
Describe how natural selection (evolution due to differences in survival and reproduction) could favor both large AND small varieties of threespine stickleback fish in a single lake.
Review the data from Rundle, et al.'s experiments with sticklebacks. Based on their data, can you state that
allopatric speciation has occurred (or is in the process of occurring) between stickleback species in different
Explain why phylogenetic trees are hypotheses.
Because they can change based on new data and be tested, relationships are hypothesized not known facts.
Describe in your own words what internal nodes on a tree represent. Explain why they do NOT (and cannot) represent extinct taxa or taxa used to construct the tree
A scientist is constructing a phylogenetic tree for twelve fox species. Explain why the scientist also includes a species of wolf in the phylogenetic analysis.
Explain why it is NOT possible to make predictions about the number of evolutionary changes undergone by
any particular taxa on a tree.
Can a single taxon be considered a clade? Why or why not?
yes, a single taxon can be a clade and a whole tree can too
Describe one situation you might encounter in your life where an ability to "read" (interpret) phylogenetic trees
would be beneficial
- public policy
Give one reason why the number of internal nodes along a branch CANNOT be used to make predictions about the degree of evolutionary change.
Internal nodes are common ancestors, not necessarily evolutionary changes
Explain why humans
are NOT more highly evolved than any other species.
Because humans have been evolving for the same amount of time as other species that exist today
Why must character traits be heritable to be useful for developing hypotheses regarding evolutionary
relationships between groups of organisms (phylogenies)?
- must be heritable to be able to be influenced by evolutionary change
- determining ones genes necessary for a character and useful for phylogenies
Explain why molecular traits are useful for constructing evolutionary hypotheses for both very distantly related taxa and very closely related taxa.
- not subjective
- provides lots of data
- useful for distantly related groups
- can detect small differences
Homologous vs. Analogous traits
homolgous - similarities between taxa due to shared ancestry
analogous - evolved independently in 2 different lineages, but look similar b/c sim selective pressures (convergent evolution)
Explain the difference between a homologous trait and a vestigial trait. Are both useful for constructing
Homolgous trait - sim between taxa due to shared ancestry
Vestigal trait: no known current function, but did in the past (link groups closely related)
Yes, both helpful because they suggest taxa share a common ancestor
Describe the basic assumption used to construct phylogenetic trees.
taxa that are more closely related share more unique traits that are not present in other taxa
What makes a character state "ideal" for grouping related taxa? Describe at least TWO challenges to grouping
taxa by unique shared traits. Describe at least ONE way you could overcome, or at least minimize the impact,
of one of these challenges.
- evolved only once
- present in all descendant taxa
- only present in descendant taxa
Challenges: some traits not due to shared ancestry, traits can be lost in descendant taxa, order of trait evolution not always clear
overcoming: use lots of traits, choose homologous traits, use outgroup to help determine traits of common ancestor
Why is maximum parsimony a reasonable approach for comparing phylogenetic trees? When comparing two
trees, how do you determine which is more parsimonious?
- generates all possible trees
- maps evolution of traits on each tree using fewest changes
- compares trees to determine most parsimonious overall
fewest evolutionary changes = maximum parsimony
Explain why, in some cases, it is NOT possible to construct the most parsimonious tree for all traits.
Because some trees are equally parsimonious
defined groups of organisms at the end of trees
lineages evolving through time
- represent shared evolutionary history
common ancestors of taxa
-population that existed at one time
-branching represents hypothesized splitting event (speciation)
- populations that split do not go extinct because they have descendant species
lineage from which all taxa on the tree evolved
- help to interpret relationships
- can also be unrooted
a distantly related taxon
- useful for rooting the tree
- can help predict patterns of trait evolution
all taxa that are descendants of a specific common ancestor
- can be separated by one "cut"
- can include a single taxon or a whole tree
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