Principles of Biology 2 Exam 3 Follow Up Questions

Explain what makes a phenotypic trait heritable. List at least TWO phenotypic traits that are heritable and TWO that are NOT heritable

A phenotypic trait is heritable if it is influenced by genetic information passed from parents to offspring through DNA.

• Heritable: Eye color and NATURAL height

• Non-Heritable: Language spoken, scars/tattoos

If every individual in a population had exactly the same DNA sequence, could the population evolve? Why or why not?

If every individual in a population had exactly the same DNA sequence, then the population could not evolve through natural selection. Evolution would only resume if new mutations were introduced that created variation in the gene pool.

Briefly describe the five forces of microevolutionary change we noted in class. Although they are not the focus of our discussions, explain why a basic understanding is important for understanding speciation.

• Natural Selection: Change due to differences in survival and reproduction

• Artificial Selection: Change due to human intervention

• Sexual Selection: Change due to mate preferences

• Gene Flow: Movement of individuals between populations

• Random Events (e.g. earthquake lol)

  Understanding these forces is important for understanding speciation because these forces contribute to our knowledge on how speciation may happen within species.

Explain why an individual (e.g. you) cannot evolve.

An individual cannot evolve because evolution is a process that happens at the population level, not the individual level. Evolution is about genetic changes in a population over time, and genetic changes can’t occur within an individual in their lifetime.

Explain why the statement, “Once the individuals in a population have adapted to their environment, the population stops evolving” is false.

Even after a population becomes well-adapted, it can continue to evolve due to:

• changing environments

• new mutations

• random events (genetic drift)

• new genetic input (gene flow)

Your friend tells you that snowshoe hares evolved to have white fur because it was necessary for them to hide from predators in snowy environments. Correct your friend’s misunderstanding.

Snowshoe hares with lighter fur survived better in snowy environments and passed on their genes, so white fur became more common over time. Natural selection has favored the lighter fur trait in this situation and therefore those with that trait bred with each other and made the lighter fur trait more prevalent.

Give at least two reasons that evolutionary change cannot lead to organisms perfectly suited for their environment. Use hypothetical (or real) examples to illustrate your reasons.

1. There are trade-offs between traits (pros and cons depending on environment/situation)

2. Evolution is limited by existing traits (it cannot create new traits upon demand to suit the environment)

Explain why evolutionary change can increase the percentage of individuals in a population with traits that are not beneficial for survival and reproduction. Use an example to illustrate your explanation.

Genetic drift (random chance) can result in any trait (beneficial or harmful) to become more common. For example, in rock pocket mice, two fur colors are prevalent among the species: light and dark, in which dark is advantageous for camouflage. A drought occurs and dries up the land, making the ground dry and lighter in color, favoring the light-colored mice. Predators then attack the dark-colored mice, all happening due to random chance.

In your own words, write a sentence that describes the connection between microevolution and speciation.

Microevolution is the small changes in heritable phenotypes within a population over time, and when enough of those changes build up, they can lead to speciation—the formation of a new species

Even though most scientists agree on the definition of a species, grouping organisms into species is challenging. Give at least two reasons why

1. Speciation is always occurring: our hypotheses on speciation are always changing as a result

2. Concepts (criteria) are not equally applicable/useful for all species

You are given a set of preserved (dead) butterflies. Which of the three species concepts we discussed could you use to categorize them?

Morphological: Categorize the butterflies based on physical appearance

What could lead to a group of bird species being classified differently by two different scientists using the phylogenetic concept?

The scientists each using two distinctively different sets of data (e.g., one may use morphological data, which may group the birds on way, while the other may use behavioral data, which may group the birds a different way).

Describe a hypothetical (or real) scenario in which two lizard populations could be organized into species differently by the biological vs. the morphological species concept.

• Biological: The lizards can successfully mate and their offspring are fertile; they would be considered the same species, because they can reproduce and pass on genes

• Morphological: Population A has bright green scales and long tails, while Population B has dull brown scales and short tails; they would be considered two separate species because they look so different

Explain why it is not possible to definitively prove that a particular group of organisms is a species.

• Different species concepts use different criteria that may yield different results

• Evolution is gradual and everchanging, so boundaries between species can be unclear and altering

Explain why speciation is described as a process, and not a discrete event

Speciation is a gradual process, as populations slowly accumulate genetic differences and become reproductively isolated over time.

When a new species arises, does that mean that another species is lost? Explain your answer

No, the original species still exists. Their genes are still in tact within their respected population and are simply a different species than the ones that evolved from them.

Explain why geographic separation does not guarantee that two populations will evolve into different species. What circumstances would make speciation more likely? Less likely?

Geographic separation doesn’t share a cause-effect relationship with populations evolving into different species.

• More Likely: Longer isolation, different environments, smaller populations with more genetic diversity

• Less Likely: Shorter isolation, similar environments, larger populations with less genetic diversity

Explain why a mechanism that limits gene flow between populations is a requirement for speciation. Explain why a mechanism that limits gene flow does not guarantee speciation will occur.

Gene flow keeps populations genetically similar; limiting gene flow is important to allow independent evolutionary changes to occur. Limiting gene flow doesn’t guarantee speciation as genetic differences must build up over time in order to create reproductive isolation; this results in speciation.

Explain the difference between prezygotic and postzygotic reproductive barriers. Which ones can be applied to hybrid offspring?

• Prezygotic Barriers: Before fertilization of egg

• Postzygotic Barriers: After fertilization of egg (applied to hybrid offspring)

Explain the difference between reduced hybrid viability and reduced hybrid fertility

• Viability: Hybrid offspring don’t survive well enough to have their own offspring

• Fertility: Hybrid offspring cannot successfully reproduce

Two populations of frogs become isolated from each other when human activities alter the course of a river. Several decades later, the river’s course is changed again, and the populations come into contact. The two frog populations have undergone different evolutionary changes so that they look quite different from each
other, however no reproductive barriers have evolved. What do you predict will happen when the two populations meet again?

The two frogs will still mate with each other as no reproductive barriers have evolved that prevents them from doing so.

In a forest, you observe a group of birds that look very similar. Some of the birds eat berries found on low shrubs, while others feed on insects that fly around high in the treetops. All male birds build nests in the same type of tree to attract females, and females choose males with brighter red chests over those that are more brown in color. Is there evidence to suggest that a habitat barrier exists in this group of birds? Explain your answer.

No, the male birds build nest in the same type of tree, and it’s never noted that the birds live in the shrubs or treetops where they find food. If that were the case, then a habitat barrier would occur.

Give at least one factor that would favor speciation between geographically isolated populations. Give at least one factor that would favor speciation between two groups that live in the same area.

• Isolated Populations: Different environments cause different adaptations

• Same-area Populations: Behavioral or mating preferences reduce gene flow

Review the analysis that used “starch” and “maltose” Drosophila (fruit flies). Based on the data collected in the analysis, what reproductive barrier(s) exist between the fly populations?

Behavioral

Why did the researcher use four different “starch” populations and four different “maltose” populations rather than just one of each?

Using four different populations for each food source provides more data that increases validity of the result.

Explain why Northern and Southern green-eyed tree frog populations are an example of an allopatric speciation process (or at least a likely one in progress).

There was a specific contact area where allopatric speciation occurred between Northern and Southern green-eyes tree frogs (the Northern females at that area preferred Southern male mating calls more than Northern male mating calls).

Explain how/why differences in habitat preferences and differences in mate preferences can favor sympatric speciation.

• Habitat Differences: Reduces interactions and mating between groups

• Mate Preferences: Leads individuals to choose certain traits, which isolates subgroups reproductively

Imagine a forest with low bushes and very tall trees. Describe how sympatric evolution could occur in a bird population living in this forest that relies on seeds as its primary food source (assume both the bushes and trees produce edible seeds)

In a scenario where a bird population lives in this forest…

• Some birds may prefer bushes for habitat, while other prefer tall trees

• The different habitats result in different feeding zones, isolating the bird population into mating groups that result in distinct traits and preferences developing over time (through evolution)

• Sympatric speciation occurs from this

Considering what we discussed about maggot flies, explain WHY variation in fruit scent preference could contribute to sympatric speciation in maggot fly populations.

Variation in fruit scent preference in maggot flies will draw the flies to that certain food with the scent, where flies with similar preference will mate with each other. This essentially divides the flies based on scent (in this case, apple vs. hawthorn) and with enough generational breeding, sympatric speciation could occur.

Based on the data from the study we discussed in class, 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 subspecies?

• Behavioral and temporal

• Hawthorns and apples grow at different times of the year, which influences the two subspecies’ mating patterns throughout the year

Describe how natural selection (evolution due to differences in survival and reproduction) could favor both large AND small varieties of sticklebacks in a single lake

Within the lake, there are different sizes of prey (little and big) located at different parts of the lake respectively. “Little” stickleback feed on little prey and “Big” stickleback feed on big prey, allowing the two varieties to coexist in the same lake.

Review the data from stickleback study we discussed. Based on the data, is there evidence that allopatric speciation has occurred (or is in the process of occurring) between stickleback species in different lakes? Why or why not?

No, while the two species of stickleback live at different parts of the lake, there is no physical barrier that’s preventing gene flow. In fact, both varieties mate in shallow waters near the shore, meaning that the two varieties could potentially interbreed.

Variation in food preference exists in a population of lizards that live in a meadow near a lake. Some lizards prefer flies, which are found in more open, drier areas of the meadow. Other lizards prefer slugs, which are most prevalent near the lake where the soil is moist. Lizards in the population mate in the shelter of bushes in the meadow, and females prefer males with brighter colors. Is sympatric speciation likely to occur in the lizard population? Explain your answer

Yes, but it’s not guaranteed to occur. There are differences in food preferences within the lizard species, meaning that there is potential for the lizards to mate collectively based on food preference (these lizards would be normally grouped with each other). This is a correlational effect however and is not causally related to speciation.

What does a phylogenetic tree show? Explain why phylogenetic trees are hypotheses

A phylogenetic tree shows evolutionary relationships and common ancestry. It’s considered a hypothesis because it’s based on current evidence and can change with new discoveries.

In your own words, describe what internal nodes on a tree represent. Explain why they do NOT (and cannot) represent extinct taxa.

Internal nodes on a phylogenetic tree represent common ancestors—the points where two or more lineages split from a shared ancestor in evolutionary history. Because internal nodes are not actual species, but rather hypothetical ancestors. They represent the branching point where one species gave rise to two or more new lineages, not a species that’s extinct.

A scientist is constructing a phylogenetic tree with twelve fox species of interest. Explain why the scientist also includes a species of wolf (outgroup) in their phylogenetic analysis.

The wolf (outgroup) is assumed to share all the traits that the common ancestor has, serving as a general baseline for comparison towards the fox species and good prediction for trait evolution.

If new evidence was obtained that suggested species D in the tree below was more closely related to species C than species A, would that change the tree? Why or why not?

Yes, the current tree shows that species D is (theoretically) as similar to species C as species A. This doesn’t reflect the new evidence obtained, meaning that the tree must change in order to reflect the most accurate hypothesis.

Put species A through D in order of relatedness to species E (from most related to least related) based on the tree below. If species are equally closely related to species E, indicate that.

• B (most related)

• D

• C and A (least related)

Can you state from the tree below that the common ancestor indicated by the letter X existed before the common ancestor labeled Y? Before the common ancestor labeled Z? Explain your answers

• X and Y: No, X and Y occur on different evolutionary paths, meaning that relative timing can’t be interpreted for these ancestors in relation

• X and Z: Yes, since X and Z occur on the same evolutionary path, relative timing can be interpreted for these ancestors in relation, and Z has X as a common ancestor, indicating that X came before Z

The tree below shows one hypothesis for primate evolution (a group of organisms that includes humans). Based on this tree, can you state that humans have undergone more evolutionary changes than rhesus macaques since the two groups split from their shared common ancestor? Explain your answer

No, while humans have more common ancestors compared to rhesus macaques (as noted by the number of internal nodes), this doesn’t constitute evolutionary change. This cannot be measured on a phylogenetic tree.

Give at least TWO reasons why you CANNOT state from the tree below that chimps are more similar in their features to bonobos than orangutans.

• We don’t know what exact changes have occurred in evolution within any of the species on the tree

• More closely related in ancestry doesn’t necessarily mean more similar in appearance

Horses and rhinos both have an odd number of toes on their rear feet. Horses are grazing animals that can run quickly. Rhinos are large, heavy animals that move slowly and eat thorny wood bushes, fruit, and branches. Based on these observations, predict whether odd-toed hooves in these species is most likely a homologous or an analogous trait. Explain your answer

Analogous Trait: These two species share a similar trait, but don’t reflect common ancestry

You observe that desert cacti species in America have a protective coating that helps to prevent water loss. Certain plant species found in the deserts of Africa have a similar protective coating. Do you think that the protective coating is most likely a homologous or analogous trait? Describe additional evidence that could
support your prediction.

Analogous Trait: There is no information given that hints at common ancestry between the two species in this scenario. Given that these two species are plants, they would be unable to move to one another and reproduce together, lacking possibility that they could share a common ancestor.

What three factors make characters useful for determining evolutionary relationships?

• When there is variation between species

• When taxa have different states of that character

• When shared traits reflect shared ancestry (homologous traits)

Explain why molecular characters are particularly useful for constructing evolutionary hypotheses for both very distantly related taxa AND very closely related taxa

• Closely related taxa: They reveal small genetic differences that might not be visible physically between taxa

• Distantly related taxa: They can trace long-term evolutionary relationships from conserved genes

List at least two challenges that scientists face when analyzing data in phylogenetic analyses.

• Evolved traits can be lost and revert back to what was present in the common ancestor of all taxa shown on a tree

• Shared traits between taxa may not reflect shared ancestry (analogous traits)

Explain/describe the differences between analogous and homologous traits. Which category is useful for constructing phylogenies? Why?

• Analogous Traits: Traits that were evolved independently in different lineages

• Homologous Traits: Traits that were evolved from a common ancestry (the common ancestry is why they are useful for constructing phylogenies)

In the context of phylogenetics, what does trait loss mean? Explain why trait loss can make building phylogenetic trees challenging.

Trait loss refers to when an evolved trait reverts back to what was present in the common ancestor of all taxa shown on a tree. This can make building phylogenetic trees challenging as it can mask true relationships between taxa and can possibly be mistaken for never having the trait in the first place.

Describe the basic process used to construct phylogenetic trees

The basic process of building phylogenetic trees involves grouping taxa by shared unique traits (i.e. traits shared by some, but not all, taxa). Upon grouping, it’s best to construct a tree with the least evolutionary changes (maximum parsimony).

Why is maximum parsimony a reasonable approach for comparing phylogenetic trees? When comparing two trees, how do you determine which is more parsimonious?

Maximum parsimony assumes that the hypotheses (trees) requiring fewer evolutionary changes are more likely to be true. When comparing two tree, the tree with the least changes is the most parsimonious.

Give TWO reasons why it is NOT always possible to construct one tree that is most parsimonious for all traits
assessed

• There is a frequent huge number of possible trees that express maximum parsimony

• Convergent evolution and trait loss do happen, which distorts true evolutionary relationships between taxa

A tree depicting one hypothesis for mammal evolution is included at the end of the study guide. List all of the taxa on the tree that are part of the smallest clade that includes bats and pigs.

Bats, pangolins, carnivores, perissodactyls, pigs, hippos, whales

Still looking at the mammalian evolution tree, would armadillos be considered a clade? What about lemurs and primates? Aardvark and sirenian? Explain your answers.

• Armadillos: Yes, a singular taxa can be a clade

• Lemurs and primates: No, tree shrews would be included in that clade

• Aardvark and sirenian: No, a bunch of other taxa would be included in that clade

Teeth with high crowns are good for grazing. High crowned teeth are present in rabbits, pigs, elephants, and some rodents. Based on the mammal tree at the end of the study guide, do you think that high crowned teeth in these species is most likely a homologous or an analogous trait? Explain your answer.

Analogous Trait: All of the above species are distantly related, meaning that they most likely developed this trait on their own and not from a common ancestor