LS 7B (Summer) Week 3 Launchpad 3e

Refer to Animation: Speciation: Speciation Depends on Random, Inherited Mutations in the Genome. Speciation has occurred when:

divergent populations evolve to the point where interbreeding does not produce viable, fertile offspring.

Refer to VS Map: Speciation—Genetic Drift Tour. A neutral mutation:

does not affect survival or reproduction.

For reciprocal altruism to work, individuals must be able to:

recognize one another and remember previous interactions.

Refer to Animation: Speciation. In order for the gene pools of two closely related species to remain distinct, there must be:

some form of reproductive isolation.

Imagine these genotype frequencies in a population: p2 = 0.49, 2pq = 0.42, q2 = 0.09. Now assume that there is nonrandom mating where individuals with one genotype will only mate with individuals that also have their genotype. Assume this pattern of mating goes on until the frequency of heterozygotes is effectively zero. What will the frequency of allele p be in the population?

0.7

Imagine these genotype frequencies in a population: p2 = 0.49, 2pq = 0.42, q2 = 0.09. Now assume that there is nonrandom mating where individuals with one genotype will only mate with individuals that also have their genotype. Assume this pattern of mating goes on until the frequency of heterozygotes is effectively zero. In addition, there is also inbreeding depression such that individuals with the genotype represented by p2 die before they can reproduce. What will be the eventual frequency of allele q?

1.0

Refer to VS Map: Speciation—Genetic Drift Tour. When a mutation is fixed in a population, what percentage of individuals have this mutation?

100%

In a population of Mendel's garden peas, the frequency of the dominant A (yellow flower) allele is 80%. Let p represent the frequency of the A allele and q represent the frequency of the a allele. Assuming that the population is in Hardy-Weinberg equilibrium, what are the genotype frequencies?

64% AA, 32% Aa, 4% aa

In a population of Mendel's garden peas, the frequency of green-flowered plants (genotype aa) is 49%. The population is in Hardy-Weinberg equilibrium. What are the frequencies of the AA and Aa genotypes?

9% AA, 42% Aa

Refer to Animation: Speciation. Indicate whether genetic drift, if it acted alone, could cause changes in the allele frequency(ies) of a population.

Acting alone could change allele frequency.

Refer to Animation: Speciation. Indicate whether natural selection, if it acted alone, could cause changes in the allele frequency(ies) of a population.

Acting alone could change allele frequency.

_____ is a special case of explosive speciation in which new species form rapidly in response to numerous "open" ecological niches.

Adaptive radiation

_____ is the gradual emergence of two or more species as a result of the geographic separation of two or more groups of animals of the same species.

Allopatric speciation

In some cases, the speciation process has not generated just two species, one in the Pacific and one in the Caribbean, but has resulted in a third species, in this case, in the Caribbean. How can you account for this extra species?

An additional speciation event, either sympatric or allopatric, occurred in the Caribbean.

Refer to VS Map: Speciation—Natural Selection Tour. The table lists the number of individuals with genotypes corresponding to fin size in generations 1 through 4 of a fish population. In this species, fin size is determined by two alleles, S and s. Refer to the data in the table to determine which statement describes what happened between generations 1 and 4 of this fish population.

An influx of fish with medium fin size entered the population.

Although it is easy to think of the formation of the isthmus of Panama as a geologically instantaneous event - at one moment there was a water connection between the two sides, and at the next there was not - it was likely not simultaneous from the perspective of inshore-dwelling species. As the land bridge slowly formed, so the marine channels became shallower and shallower. Populations of a species that specializes in deep water were, therefore, isolated from each other - Pacific/Caribbean - earlier than populations of a species that specializes in shallow water. Table 1 lists data on the depth tolerances for six species of another genus of shrimp, Beteus, which are found on either side of the isthmus. Which is the most likely phylogeny for the species in Table 1?

Diagram A

Refer to VS Map: Speciation—Natural Selection Tour. Which scenario(s) depict allopatric speciation in process? Select all that apply.

Humans set up a dam in the middle of a river, splitting a fish population in two. The two resulting fish populations accumulate different sets of mutations over time. A small portion of the population on the mainland moves to an island. Over time, the island population genetically diverges from the mainland population.

You identify five endemic species of mammals living on an island a short distance from the mainland. You also identify each species' closest relative on the mainland. Two alternatives exist to explain this group of species: Hypothesis 1. The ancestors of the current island species dispersed from the mainland to the island and subsequently diverged on the island (dispersal). Hypothesis 2. The island was originally part of the mainland but a rise in sea level resulted in its being cut off, with the result that the mammals on the island diverged from the ones on the mainland (vicariance). How would you distinguish between these two hypotheses after sequencing the same segment of DNA in representatives of all ten species?

If the level of genetic divergence for all five species pairs is similar, then vicariance is the likely cause.

Refer to Animation: Speciation. Which phrase best describes how natural selection results in evolution?

Individuals with particular traits leave behind more offspring than individuals with other traits.

Which of the statements are true regarding hybridization? Select all that apply.

Natural selection sometimes acts against progeny that result from hybridization. Hybridization occurs in plants more often than in animals. Hybridization involves the transfer of genetic material between members of similar species. Hybridization can result in fertile offspring.

_____________ is the primary force responsible for changes in allelic frequency of deleterious mutations. _______________ is the primary force responsible for changes in allelic frequency of neutral mutations.

Natural selection; Genetic drift

Imagine these genotype frequencies in a population: p2 = 0.49, 2pq = 0.42, q2 = 0.09. Now assume that there is nonrandom mating where individuals with one genotype will only mate with individuals that also have their genotype. Assume this pattern of mating goes on until the frequency of heterozygotes is effectively zero. Is this population in Hardy-Weinberg equilibrium?

No, because there is nonrandom mating.

Based on the phylogenetic tree of the snapping shrimp, which speciation event likely happened most recently?

Pacific 5 and Caribbean 5

You are an experienced naturalist and biologist and you observe two birds mating that you do not believe are members of the same species. The eggs from this breeding do not hatch, and when you obtain one of the eggs, you find embryonic development stopped not long after fertilization. Which of the conclusions is supported by these observations?

Post-zygotic factors prevented successful production of offspring.

Inbreeding depression is a serious concern in small populations of endangered organisms. Why is inbreeding depression a concern for such populations?

Related individuals are more likely to mate with one another and thereby increase the probability that two deleterious alleles will be present in the offspring.

Eight shallow water marine species - p, q, r, s, t, u, v, w - occur on either side of an isthmus thought to have been formed about five million years ago. Figure 1 is the phylogeny for the eight species. You sequence 10,000 base pairs of DNA for each species and analyze the extent of the difference between the members of each closely related species pair. The results are graphed in Figure 2. What can you conclude from Figure 2?

Species t and u live at a shallower depth than the others.

Refer to Animation: Speciation by Vicariance. Seven species of snapping shrimp are found on either side of the Isthmus of Panama. What data provides good evidence that this is speciation by vicariance?

The DNA of each current species is most similar to that of a species found on the opposite side of the current Isthmus.

In a study of multiple geological events in which an isthmus has formed, separating marine populations on either side, you collect the data in Table 2. What can you conclude from the data in Table 2?

The extent of genetic divergence among closely related taxa on either side of an isthmus is positively correlated with time of isthmus formation.

The fossil record indicates that three species of fish - a, b, and c - lived in an ancient lake in New Jersey. Their phylogeny is shown in Figure 3. Four million years ago, the lake dried out, creating two new lakes, Lk1 and Lk2. There is now a total of six species in the two lakes: d, e, and f in Lk1, and g, h, and i in Lk2. Which is the most likely phylogeny?

The phylogeny that pairs one species from Lake 1 with another in Lake 2; i.e., [d g] [e h] [f i]

What is the main hypothesis of this study?

The vicariance (physical barrier) created by Panama induced the divergence of an ancestral species into different species.

Mark true (A) or false (B) about the following statement relative to Hamilton's key insight about how natural selection works. Indirect fitness can only be gained by helping kin and not by helping unrelated individuals.

True

Although it is easy to think of the formation of the isthmus of Panama as a geologically instantaneous event - at one moment there was a water connection between the two sides, and at the next there was not - it was likely not simultaneous from the perspective of inshore-dwelling species. As the land bridge slowly formed, so the marine channels became shallower and shallower. Populations of a species that specializes in deep water were, therefore, isolated from each other - Pacific/Caribbean - earlier than populations of a species that specializes in shallow water. Table 1 lists data on the depth tolerances for six species of another genus of shrimp, Beteus, which are found on either side of the isthmus. A similar study to the one described in the figure is carried out on these six species of Beteus. You sequence 10,000 bp of DNA from multiple loci in each species. In a comparison of the number of base pair differences between each species pair (that is, A and B, C and D, E and F), which order is the most likely outcome?

[C-D]>[E-F]>[A-B]

The pattern shown in the phylogenetic tree of the snapping shrimp in this study is interpreted as evidence of a vicariance event-the formation of the Isthmus of Panama-that split marine shrimp populations, isolating Pacific individuals from the Caribbean, and vice versa, and resulted in isolated populations that diverged genetically to produce new species. What additional evidence would support this interpretation?

a phylogeny of inter-tidal mollusks from the Pacific and Caribbean coasts of the isthmus showing a similar pattern

Refer to VS Map: Speciation—Genetic Drift Tour. Within a population, several mutations appear, resulting in four alleles, A through D. Consider the graph of allele frequency. Which allele becomes fixed in the population?

allele A

Refer to VS Map: Speciation—Natural Selection Tour. The graph depicts changes in allele frequencies across several generations for four alleles, A through D. Which allele underwent negative selection?

allele D

Two species of antelope ground squirrels are separated by the Grand Canyon. They are hypothesized to have descended from a common ancestor population that was divided when the Grand Canyon formed. If this hypothesis is correct, it would be an example of:

allopatric speciation by vicariance.

You are a biologist on a trip to an island in the South Pacific. While there, you are allowed to collect DNA samples from a local species of rat that resembles a species seen on a nearby continent. If your DNA analysis also indicates the two species are closely related, you might conclude that the evolution of the two separate species was an example of _____ through _____.

allopatric speciation; dispersal

Sympatric speciation:

can occur instantaneously through formation of polyploid offspring.

Refer to Animation: Speciation by Vicariance. A good example of vicariance is a:

change in allele frequencies in two closely related populations that are isolated from each other by a geographic barrier.

Refer to VS Map: Speciation—Natural Selection Tour. A deleterious mutation:

decreases survival and/or reproduction.

Refer to VS Map: Speciation—Natural Selection Tour. The graph shows the frequency of individuals with a range of fish sizes for generation 1 (black dashed curve) and generation 100 (blue curve).

directional selection

Refer to Animation: Speciation. Over time, in a population, new mutations of a given gene may:

disappear, remain at low levels, or become fixed.

The reason that lions, which live in Africa, and tigers, which live in Asia, do not produce ligers (infertile offspring of lions and tigers) in the wild is likely the result of:

ecological isolation of lions and tigers.

Which species concept might differentiate species on the basis of specific dietary requirements?

ecological species concept

If a population is not in Hardy-Weinberg equilibrium, we can conclude that:

evolution has occurred because one or more of the assumptions of the Hardy-Weinberg equilibrium has been violated.

In general, allopatric species will evolve pre-zygotic isolating mechanisms more rapidly than sympatric species.

false

Refer to Animation: Speciation by Vicariance. Evidence indicates that a number of finches from Ecuador dispersed to the Galapagos Islands more than 300 miles away and ultimately gave rise to the different species of Galapagos finches that exist today. This is good evidence of speciation by vicariance.

false

Refer to Animation: Speciation: Neutral Mutations and Speciation. Mutations always result in either an increase or a decrease in an organism's reproductive fitness.

false

Refer to Animation: Speciation: Speciation Depends on Random, Inherited Mutations in the Genome. Once a mutation is introduced into a population, it will eventually be passed on until it is found in 100% of the individuals in that population.

false

You would expect similar species with a different number of chromosomes to be genetically compatible and, therefore, able to reproduce fertile offspring.

false

The accumulation of different mutations in genetically separated populations is known as _____ and is the key to speciation.

genetic divergence

Refer to Animation: Speciation: Speciation Depends on Inherited, Random Mutations in the Genome. In the animation, fish with a larger body size have a ____________ reproductive fitness than fish with a smaller body size because ____________.

higher; they are less vulnerable to predators

Refer to Animation: Speciation. A geologic barrier between two populations of one species can contribute to speciation because of:

lack of gene flow between populations.

Imagine a scenario in which a common population of animals is separated into two groups by a natural event. Over time, you might expect the two populations to become ______ genetically similar. This process is known as _____ speciation.

less; allopatric

Refer to Animation: Speciation: Neutral Mutations and Speciation. In the animation, fish with less streamlined fins have a ____________ reproductive fitness than fish with more streamlined fins because ____________.

lower; they are less able to escape predators

The process by which sympatric speciation might occur would most likely be the result of:

natural selection.

Refer to VS Map: Speciation—Genetic Drift Tour. Which type of mutation is most likely to undergo genetic drift in a population?

neutral

Refer to VS Map: Speciation—Natural Selection Tour. Which type of mutation does not undergo natural selection in a population?

neutral

Refer to VS Map: Speciation—Genetic Drift Tour. The table lists the number of individuals with genotypes coding for blue, red, and green coloration in generation 1 of a fish population in Hardy-Weinberg equilibrium. Fish coloration is determined by two alleles, B and G. The allele frequencies for alleles B and G are represented by p and q, respectively, and the genotype frequencies for genotypes BB, BG, and GG are represented by p2, 2pq, and q2, respectively. Refer to the data in the table to calculate the allele and genotype frequencies.

p = 0.70, q = 0.30; p2 = 0.49, 2pq = 0.42, q2 = 0.09

Refer to VS Map: Speciation—Genetic Drift Tour. Within a species, there is a given trait determined by two alleles. The allele frequencies for these two alleles are represented by p and q. If Hardy-Weinberg conditions are met, which is not a possible genotype frequency?

p2q2

Unlike the biological species concept, the morphospecies concept relies on:

phenotype.

Refer to VS Map: Speciation—Genetic Drift Tour. In a population in Hardy-Weinberg equilibrium, the relationship between the genotype and allele frequencies of two alleles, A and a, are shown in the graph. At which point is 100% of the population exhibiting the recessive phenotype?

point A

Refer to VS Map: Speciation—Natural Selection Tour. The relationship between the genotype and allele frequencies of two alleles, A and a, is shown in the graph. At which point are the frequencies of genotypes AA and aa equal?

point C

Refer to VS Map: Speciation—Genetic Drift Tour. Consider several species with varying population sizes. In which population are the effects of genetic drift most extreme?

population size = 4

In the southwestern desert of the United States there are temporary ponds that form only after heavy summer rains. As a naturalist, you visit these ponds and notice that female frogs mate with males of their own species, which are identified solely by listening to male calls. The lack of mating between species would be an example of _____ and _____.

pre-zygotic isolation; behavioral isolation

Two species of frog mate in the same pond. One breeds in early summer and one in late summer. This is an example of what kind of reproductive isolation?

pre-zygotic, temporal separation

Adaptive radiation is an acceleration of speciation and adaptation when there are a large number of ecological opportunities available.

true

Imagine that you had two populations of red-tailed hawks: one with long tail feathers and one with short tail feathers. Mating discrimination in this species could entail either hawks with long tail feathers preferentially mating with other hawks that have long tail feathers, or hawks with short tail feathers preferentially mating with other hawks that have short tail feathers.

true

In co-speciation, two groups of organisms speciate in response to each other and in a coordinated manner.

true

Speciation can occur in the absence of natural selection; for example, speciation resulting from genetic drift.

true

The longer two species have been separated, the greater the number of genetic differences between them.

true

While in South America, you come across what you think are two groups of birds in the same location. They are nearly identical aside from their color. After years of observation, you conclude that the birds eat similar diets and share similar behaviors but do not reproduce with each other. These groups of birds appear to be an example of:

two different species on the basis of reproductive behavior.

Refer to VS Map: Speciation—Natural Selection Tour. Speciation occurs when:

two populations become reproductively isolated from one another.

Refer to Animation: Speciation by Vicariance. Vicariance is defined as:

when a geographic barrier arises that isolates two populations.