Biol 2107K Chapter 22

hybridization

Interbreeding between two different varieties or species.

morphospecies concept

The idea that members of the same species usually look like each other more than like other species.

Over time, in a population, new mutations of a given gene may:

disappear, remain at low levels, or become fixed.

Speciation has occurred when:

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

A neutral mutation is a mutation that _____ increase the reproductive fitness of an organism.

does not

A neutral mutation is one that:

does not affect survival or reproduction.

Speciation due to genetic drift is typically a very _____ process.

slow

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

some form of reproductive isolation.

Rarely, hybridization has occurred between polar bears and grizzlies. The presence of grolars and pizzlies:

suggests that the time since divergence may not be sufficient for complete reproductive isolation to have occurred.

geographic isolation

Spatial segregation of individuals.

Neutral mutations can decrease in frequency to a minimum of what percentage of the population?

0%

mainland population

The central population of a species.

speciation

The process whereby new species are produced.

Did Polar bears arise from a vicariant event?

Yes

biological species concept

(BSC) As described by Ernst Mayr, the concept that "species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups." The BSC is the most widely used and accepted definition of a species, but cannot be applied to Bacteria or Archaea.

Neutral mutations can increase in frequency to a maximum of what percentage of the population?

100%

ecological niche

A complete description of the role a species plays in its environment.

species

A group of individuals that can exchange genetic material through interbreeding to produce fertile offspring.

adaptive radiation

A period of unusually rapid evolutionary diversification in which natural selection accelerates the rates of both speciation and adaptation in a single lineage.

peripatric speciation

A specific kind of allopatric speciation in which a few individuals from a mainland population disperse to a new location remote from the original population and evolve separately.

Given a group of organisms, describe how you would test whether they all belong to one species or whether they belong to two separate species.

According to the morphospecies concept, organisms of the same species often have very similar appearances, so careful observation of the phenotypic characteristics of the organisms could provide insight into how many species were represented in the group. If possible, a more rigorous test would be to determine whether the organisms could breed with one another to produce viable, fertile offspring.

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.

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.

Which of the following is true regarding adaptive radiation?

Adaptive radiation is more likely to occur in a population produced by a dispersal event than in a long-established population on a continent.

subspecies

Allopatric populations that have yet to evolve even partial reproductive isolation but which have acquired population-specific traits.

_____ 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

Differentiate between allopatric speciation by dispersal and by vicariance, and give an example of each.

Allopatric speciation can occur if a subset of a population moves to a new location far from the original population (dispersal), much like what would happen if a hurricane blew a group of beetles to a distant island off the coast of the mainland. Allopatric speciation can also occur by vicariance, which is when a change in the environment effectively separates a population into two distinct groups. An example of allopatric speciation by vicariance would be if a lake receded and began to dry out leaving only smaller, isolated ponds behind. Fish from a single species might be split among several different ponds, each of which would then be subject to genetic divergence based on the conditions in their respective pond and genetic drift, which over time could lead to speciation.

Differentiate between allopatric and sympatric speciation, and state which is thought to be more common and why.

Allopatric speciation occurs after a geographic barrier physically separates two populations from one another, which limits gene flow and promotes genetic divergence of the two populations as they adapt to their different environments. Sympatric speciation is the divergence of one group of organisms into two distinct species within the same geographical area, so that although the organisms inhabit the same area and come in contact with one another, gene flow is limited because of strong selection against hybrid offspring. Allopatric speciation is thought to happen more often than sympatric speciation because genetic divergence between geographically isolated populations is inevitable, whereas sympatric populations will only diverge when strong disruptive selection is operating.

Define the term "species."

Although no one definition is able to perfectly describe the genetic boundaries between different organisms, the biological species concept defines a species as a group of organisms that can share genetic material by interbreeding with one another to generate viable, fertile offspring. By this definition, organisms that cannot successfully reproduce with one another are therefore considered different species.

island population

An isolated population.

The following numbers represent the numbers of genotypes coding for blue, red, and green coloration in the fish population. The numbers are shown for three successive generations of the population. Blue color (Genotype=BB) Red color (BG) Green color (GG) Generation 1 25 50 25 Generation 2 30 40 30 Generation 3 50 25 50 The allele and genotype frequencies in Generation 3 are:

B = 0.50, G = 0.50; BB = 0.40, BG = 0.20, GG = 0.40.

post-zygotic isolation

Describes factors that cause the failure of the fertilized egg to develop into a fertile individual.

pre-zygotic isolation

Describes factors that prevent the fertilization of an egg.

behaviorally isolated

Describes individuals that only mate with other individuals on the basis of specific courtship rituals, songs, and other behaviors.

allopatric

Describes populations that are geographically separated from each other.

sympatric

Describes populations that are in the same geographic location.

partially reproductively isolated

Describes populations that have not yet diverged as separate species but whose genetic differences are extensive enough that the hybrid offspring they produce have reduced fertility or viability compared with offspring produced by crosses between individuals within each population.

True or False: If the environmental conditions change, a neutral mutation can become advantageous or disadvantageous.

True

Post-zygotic reproductive isolation may be due to temporal or ecological separation.

False

True or False: Mutations always result in either an increase or a decrease in an organism's reproductive fitness.

False

True or False: 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

True or False: When individuals of a parent species are separated geographically, one population of separated individuals is more likely to acquire neutral mutations than the other.

False

genetic incompatibility

Genetic dissimilarity between two organisms, such as different numbers of chromosomes, that is sufficient to act as a post-zygotic isolating factor.

There are hundreds of species of cichlid fish in Lake Victoria in Africa. Some scientists argue that they evolved sympatrically, but recent studies of the lake suggest that it periodically dried out, leaving a series of small ponds. Why is this observation relevant to evaluating the hypothesis that these species arose by sympatric speciation?

If populations of fish became separated from other populations of fish in different ponds during dry periods, this scenario suggests that speciation was more likely to be allopatric rather than sympatric. The allopatrically evolved species became sympatric only when the lake flooded again, combining all the separate ponds into a single body of water.

Describe how genetic divergence and reproductive isolation are related to each other.

In order for populations to genetically diverge from one another, they must have limited gene flow between them. Reproductive isolation limits the production of hybrid offspring, limiting genetic exchange between populations, and divergence continues as each population is subjected to the selective pressures of its environment and genetic drift. In addition, if populations begin to diverge through genetic drift or disruptive selection, these differences can result in establishment of a reproductive barrier, which would then work to further limit gene flow and promote reproductive isolation.

gametic isolation

Incompatibility between the gametes of two different species.

What phrase best describes how natural selection results in evolution?

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

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. Is this good evidence of speciation by vicariance?

No, there is nothing separating these finches and they just decided to live elsewhere so this isn't vicariance.

temporal isolation

Pre-zygotic isolation between individuals that are reproductively active at different times.

ecological isolation

Pre-zygotic isolation between individuals that specialize ecologically in different ways.

Name four reproductive barriers and indicate whether each is pre- or post-zygotic.

Reproductive barriers that prevent fertilization (pre-zygotic) include differences in mating behaviors like courtship rituals, mechanical blocks to fertilization such as differences in the genitalia required for mating, and biochemical incompatibilities in the gametes that can limit the fusion of sperm and egg. After fertilization has occurred, post-zygotic barriers limit the ability of the zygotes formed from gametes of different species to develop into fertile adults because of differences at the genomic level, such as an improper number of chromosomes.

Describe how genetic drift can result in speciation.

Since genetic drift acts randomly to alter allele frequencies, the alleles that become fixed or extinct in a given population will be different in each population. These differences, accumulated over time, can result in genetic incompatibility that will limit gene flow and lead to the establishment of two different species.

Explain how ecological and phylogenetic considerations can help inform whether or not a group of organisms represents a single species.

Since resources are limited in every habitat, each species must have a unique niche within its environment in order to avoid competition with other species. Thus, organisms with overlapping ecological requirements are likely members of a single species. In addition, organisms of a single species will have a high degree of genetic identity due to a shared ancestral lineage, so information about the evolutionary history of an organism can suggest whether a group of organisms is indeed a single species or whether they have genetically diverged from one another to form two separate species.

Name two types of organism that do not fit easily into the biological species concept. What species concept would work best for these organisms?

Since the biological species concept defines species based on their ability to interbreed to generate viable, fertile offspring, those organisms that reproduce asexually (such as bacteria) and those that are extinct cannot be easily characterized by this definition. A combination of phylogenetic and ecological species concepts would work best for these organisms.

Describe how natural selection can result in speciation.

Speciation is the result of genetic divergence between two populations to the point where they are no longer capable of producing fertile offspring. Natural selection can drive genetic divergence of populations based on the characteristics that are favorable in each population's environment, which may also influence their reproductive compatibility with other populations. The characteristics that allow for optimal survival and reproduction in one population will be specific for its environment, so two populations that have lived in different locations for a long time, both being adapted to their environments by natural selection, will likely encounter reproductive barriers, limiting gene flow between the populations and reinforcing speciation. In some cases, natural selection contributes directly to the process of speciation, when individuals better at choosing appropriate mates (i.e., from their own group) are selectively favored over those that frequently mate with members of the wrong group.

instantaneous speciation

Speciation that occurs in a single generation.

Why haven't we been able to come up with a single, comprehensive, and agreed-upon species concept?

Species change over time, making it difficult to craft a single definition that can be applied in all cases. Also, a species concept has to apply to such an astonishing variety of living and dead biological forms—everything from a living microbe to a long-extinct dinosaur—that it seems impossible to find an ideal one-rule-fits-all definition. Thus, though the BSC is useful in many cases, it is not applicable to asexual organisms and organisms known only from fossils.

ring species

Species that contain populations that are reproductively isolated from each other but can exchange genetic material through other, linking populations.

mechanical incompatibility

Structural configuration of the genitalia that prevents mating with another species.

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.

ecological species concept (ESC)

The concept that there is a one-to-one correspondence between a species and its niche.

The similar pattern of the phylogenies (five species of related flowers that hold nectar as a reward for their pollinators, five related species of moths, in their spur) suggests the characteristics coevolved with one another. What is an accurate statement reflecting this pattern?

The flowers and moths coevolved, so that spur-length and tongue-length each evolved because of changes in the other.

phylogenetic species concept (PSC)

The idea that members of a species all share a common ancestry and a common fate.

When visiting Hawaii on vacation, a tourist notices that there are many different species of birds that look similar to one another, but are distinct in their ecology and in the morphology (beak size and shape) that helps make them successful in different habitats on the island. The tourist supposes they are closely related and result from an adaptive radiation. What would provide the STRONGEST evidence they are the result of an adaptive radiation?

The phylogeny of the birds shows a single common ancestor for the group.

Which of the following represents genetic incompatibility?

Two groups of snakes do not produce fertile offspring because they have a different number of chromosomes.

reinforcement of reproductive isolation (reinforcement)

The process by which diverging populations undergo natural selection in favor of enhanced pre-zygotic isolation to prevent the production of inferior hybrid offspring.

vicariance

The process in which a geographic barrier arises within a single population, separating it into two or more isolated populations.

dispersal

The process in which some individuals colonize a distant place far from the main source population.

A population of rare frogs is reduced by 90% in number when a large dam is constructed that obliterates most of their prior habitat. Which of the following is probably true?

The remaining frogs have reduced genetic diversity.

Which of the following scenarios could not explain the changes in genotype frequencies above?

There is random mating among all of the fish genotypes.

Imagine that a scientist wants to create a new species of minion—one that is a cross between a shark and a wolf. To his dismay, when he introduces shark sperm and wolf eggs into a petri dish, no viable embryos form. Why?

This could be an example of pre-zygotic isolation, where the proteins of the shark sperm and wolf eggs do not interact properly; however, this could also be an example of genetic incompatibility, where genomic differences between sharks and wolves prevent the formation of viable embryos.

Imagine that a zoo in Sri Lanka has started an elephant-breeding program. Zookeepers have introduced an Indian and Sri Lankan elephant into the same enclosure. What will be the result of this mating?

This mating will demonstrate that these elephants are members of the same species and will produce fertile offspring.

True or False: An allele that has acquired a mutation at a particular nucleotide position is just as likely to acquire a subsequent mutation as an allele which has not been previously mutated.

True

Why do we see so many wonderful examples of adaptive radiation on mid-ocean volcanic archipelagos like the Galápagos?

Volcanic island chains offer many examples of adaptive radiation because they are dependent on the serendipitous process of colonization. This means that only some plants and animals are able to get there. In addition, because of the absence of competitors on these islands, there are often many available ecological opportunities for the colonizers. For example, there may be no insect-eating birds on the islands, providing an ecological niche to be filled.

The origin of polar bears was the result of:

allopatric speciation.

It is difficult to apply the biological species concept to bacteria because:

bacterial reproduction is asexual.

You observe two groups of frogs that are closely related. Males from each group "sing" with a species-specific song to attract a female frog. Females only respond to songs sung by males of their species. This is an example of _____ separation and _____- zygotic reproductive isolation between two species.

behavioral; pre

* See above * Which of the following is the most likely mechanism operating to produce the results shown for the three generations in the table?

disruptive selection

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.

If two populations are reproductively isolated from one another (like certain populations of Russian warblers), they must be genetically isolated from each other and therefore cannot belong to the same species.

false

Natural selection is always the driving force of speciation.

false

When two populations have undergone divergence in allopatry long enough to have a difference of one fixed allele between the two populations, they are always then sufficiently different to be considered two different species.

false

New species can form through allopatric or sympatric speciation. What mechanism will act more strongly on populations that are initially separated in allopatry than on those initially separated in sympatry?

genetic drift

If the frequency of the blue trait changes randomly in the population from generation to generation, the most likely cause for this is:

genetic drift.

Neutral changes in a physical trait of an organism are most commonly fixed in a population by:

genetic drift.

The Biological Species Concept is least useful for:

identifying species represented by fossils.

A geologic barrier betwen two populations of one species can contribute to speciation because of:

lack of gene flow between populations.

In animals with alleles for a given trait of A and a, if Hardy-Weinberg conditions are met, what are possible genotype frequencies?

p2 q2 2pq

Which of the following species concepts might differentiate species on the basis of descent from a common ancestor?

phylogenetic species

When taxonomists recognize subspecies, they are identifying:

populations with restricted enough gene flow to develop some population-specific traits, but that can still interbreed with members of other such populations.

You observe two groups of freshwater fish that spawn at the same time of the year and in the same pond. After females lay their eggs on the pond bottom, males of both species attempt to fertilize them. After some investigation you realize that sperm from both species fertilize the eggs, but embryonic development stops shortly after fertilization when the eggs are fertilized by one species of males, but not by the other. This is an example of ______- zygotic reproductive isolation between the two species.

post

Male birds of different species sing species-specific songs to attract mates. Females only mate with males that sing their species-specific song. This is an example of:

pre-zygotic isolation.

Biochemical recognition systems within the stigma of a flowering plant prevent the pollen from a different species from developing a pollen tube and fertilizing its eggs. This is an example of what kind of reproductive isolation?

pre-zygotic, lock and key

Characteristics of a species

the ability of all members to exchange genetic material with one another a common evolutionary ancestry among all individuals shared characteristics such as shape, size, and color (in individuals of the same life stage and sex) the ability to produce fertile progeny

Which of the following factors would be least likely to affect the mutation rate in a population?

the level of recombination in a population

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.

Speciation is said to occur when:

two populations become completely reproductively isolated from one another.

Vicariance is defined as:

when a geographic barrier arises that isolates two populations.

What additional information would assist you in determining whether polar bears and grizzlies are different species, based on the biological species concept?

whether the F1 is fertile whether F1 offspring are viable