chapters 11-15

In order to understand the origin of life on Earth, evolutionary biologists collaborate with__________.

-chemists -geologists -atmospheric scientists

Young marsupials are born underdeveloped and with a number of adaptations to life in their mother's pouch. One adaption is particularly important for their survival since it enables the jaw structure for suckling the mother's milk at this early stage of development. What have experiments revealed about the neural crest development in regard to this adaptation?

Analysis of marsupial embryos found that neural crest cells begin their migration much earlier in marsupials than in other mammal groups and this promotes early jaw development.

One of the first studied Hox gene mutations in Drosophila was a mutation in the Antennapedia gene, which controls leg formation. This mutation is abbreviated as Antp. What is the phenotypic effect of this mutation?

Antennae are replaced by legs.

Why did the role of horizontal gene transfer ultimately become diminished over evolutionary time?

As cells became more complicated, they also became more integrated, less modular and less likely to take up new genes by horizontal gene transfer.

In the cliff swallows studied by Charles and Mary Brown, it is common to find a blood-sucking parasite, an insect known as the swallow bug. This bug often clings to the feet of birds, can move from swallow to swallow within colonies, and is responsible for most of the nest failures and juvenile mortality in these birds (Brown and Brown 1996). The graph shows a correlation between the colony size and the number of bugs per nest. What conclusion(s) can we make based on this study?

As group size increases, the fitness cost of parasitism increases.

Karl Ernst von Baer, a German naturalist, biologist, and embryologist, rejected both the scala naturae and the Meckel-Serres law. Instead, von Baer's law states which of the following?

General characteristics of embryos in closely related species develop before specific characteristics, and embryos of higher taxa do not resemble the adult form of ancestral lower-taxa species

The Hawaiian Islands have gone through at least two waves of human colonization (in prehistoric times and again starting in the seventeenth and eighteenth centuries). Of the approximately 125 to 145 bird species that once inhabited the Hawaiian Islands before human colonization, 90 to 110 are now extinct. Which of the following is most likely TRUE when it comes to the first wave of extinctions?

Human colonization introduced nonnative species, which killed the larger birds first.

By 10,000 years ago, two-thirds of 150 genera of the Pleistocene megafauna that were present just 40,000 years earlier had gone extinct. What seems to be the reason for this relatively recent extinction of so many large mammal species?

Hunting by humans, habitat fragmentation, and the ice age played a large role in this extinction.

The painted turtle (Chrysemys picta) has an amazing physiology that tolerates wide swings in temperature and oxygen levels and has a wide geographic distribution in North America. In the winter, it goes into hibernation under the ice of the ponds in which it lives and has been observed to tolerate anoxic conditions for up to 170 days at 3oC. What would you predict about this species' ability to survive environmental perturbations that can lead to an extinction event?

This species has a high probability of surviving.

What is the meaning of the phrase "dead clade walking," which was coined by David Jablonski in 2002?

Many of the clades that survive a period of mass extinction go extinct during the following geological time period.

Which gas was most likely the LEAST abundant in early Earth's atmosphere?

O2

Which of the following is an important evolutionary implication of a gene having many regulatory enhancers?

Regulatory enhancers can increase morphological variation within a population and hence the amount of variation that natural selection has to act on.

In the common bluegill sunfish, foraging in small groups increases success in finding food. They feed on small, aquatic insects that live in underwater vegetation, and when bluegills forage together, they are able to flush out many more insects. Which of the following is correct in this case of group foraging?

The bluegill example illustrates a "passive" benefit of group foraging.

German biologist and naturalist Ernst Haeckel disagreed with Karl Ernst von Baer and further expanded on the Meckel-Serres law with his biogenetic law. What does the biogenetic law claim?

The developmental progress of an organism (its ontogeny) recapitulates its evolutionary history (its phylogeny).

What would be an appropriate evolutionary explanation of the fact that the ordering of some homeotic genes (such as Hox genes) on vertebrate chromosomes parallels the ordering of homeotic genes on fruit fly chromosomes?

The similar ordering of homeotic genes in animals, both vertebrate and insect, is due to ancient homology.

Which of the following suggests that sympatric speciation is occurring in Rhagoletis pomonella (the apple maggot fly)?

The sympatric races of the apple maggot fly are diverging, and potentially on the path to becoming separate species as evidenced by fruit preference documented in the maggots.

Which of the following describes the phenetic species concept?

This concept looks at organisms that are clustered together in a phenotype space and is often used by numerical taxonomists.

The famous Cretaceous-Paleogene (K-Pg) extinction occurred about 65 million years ago, close to the boundary between the Cretaceous and Paleogene periods, with profound effects on many different taxa, including the dinosaurs. Which of the following is widely accepted as the cause of this extinction?

This mass extinction occurred as a result of an impact with an extraterrestrial body, such as an asteroid, as evidenced by the layer of clay demarcating the K-Pg boundary that contains iridium

Fossils are the remains of past-living organisms that can form in several different ways. Which of the following describes fossilization by dissolution?

Water seeps into a fossil and breaks it down, but the shape of the fossil is preserved in the sediment around it, providing a rough outline of the organism.

The famous radiation of Galápagos finches from the common ancestor species on the western coast of South America is probably a result of __________.

allopatric speciation

In a study of red spruce trees and black spruce trees, scientists found that the red spruce was living in a smaller geographic area and had much less genetic variation than the black spruce. They proposed that the red spruce might have arisen from a southern population of black spruce, which became geographically isolated from other black spruce populations at some point during the Pleistocene glaciations. What is this an example of?

allopatric speciation with the peripheral isolate model

In a hypothetical scenario, imagine that you have discovered a rare species of bird on a remote Pacific island. You spend some time studying their ecology and habitation and discover that although these birds look alike, they are indeed two distinct populations with very different mating calls. You propose that these two populations must be two species since they are no longer able to mate with one another. Which of the following species concepts would you use to defend your statement?

biological species concept

In 1970, Lynn Margulis proposed that the origin of two eukaryotic organelles, mitochondria and chloroplasts, occurred through endosymbiosis. According to more recent phylogenetic analyses based on molecular genetic data, which of these prokaryotic lineages is a candidate for the ancestral source of mitochondria?

proteobacteria

Paleontological studies on a lineage of bryozoans (whose fossils preserve many of their morphological characteristics) show a pattern of evolution with little or no change for long stretches of time. Occasionally, however, speciation occurred in a burst of change and diversification. This is an example of __________.

punctuated equilibrium

Which of the following is TRUE regarding the evolution of multicellularity?

-The evolution of multicellularity represents one of the major transitions in the history of life on Earth. -The transition has occurred independently many times, in many taxa, over evolutionary history -In the early steps toward an obligate multicellularity, cells may have often joined together temporarily and then disbanded.

Which of the following statements regarding the benefit of making the switch from an RNA- to a DNA-based genetic system during the evolution of life is correct?

DNA is a more stable molecule because deoxyribose is less reactive than is ribose.

The Dobzhansky-Muller model explains hybrid infertility in crosses between two close species (such as the fruit flies D. simulans and D. melanogaster). Which of the following is the best explanation of this model?

Epistatic interactions between the alleles of two or more loci, undergoing different evolutionary paths in the two speciating groups, lead to the fitness costs of hybridization.

Which of the following correctly defines "homeotic genes"?

Homeotic genes are "master-switch" genes that control other genes in a set sequence and thereby affect cell size, shape, division, and the positioning of the cells within the organism.

This figure illustrates the results of selection for yeast strains that are well adapted to either high-salt or low-glucose environments. Over the course of selection, many mutations have occurred in populations in both environments. If the Dobzhansky-Muller model applies to this experiment, what do you predict will happen if the two strains produce a hybrid?

Matings between individuals from the two strains will have reduced reproductive success compared to the controls.

In all of the extinctions that have ever occurred on Earth, the majority of species loss was due to __________.

background extinctions

When we say that a cell is totipotent, we refer to a cell that __________.

could differentiate into any of the cell types that make up the adult organism

Which of the following best represents the definition of an individual, as proposed by evolutionary biologist Rick Michod?

integrated and indivisible wholes that can reproduce and pass heritable variations on to their offspring

In paleobiology, one of the main concepts is that fossils found lower down in the sediment at a particular locality are older than those found closer to the surface. This often is called __________.

the law of superposition

Over the last few decades, there has been a major decline in amphibian populations worldwide, including the extinction of many amphibian species. Which of the following is true regarding the amphibian decline?

-The current rate of extinction in amphibians is much higher than typical background extinction rates. -One of the major factors driving these extinctions may be infectious disease. -Extinction of an endemic amphibian species results in global extinction of that species

Which of the following statements best explains secondary reinforcement?

If the reproductive isolating mechanisms that developed during the geographic isolation are somewhat weak but the hybrids between two populations have lower fitness, then the speciation process may continue.

Biologists have documented asexual reproduction in some animal lineages. Even in certain vertebrates, such as reptiles, a few species reproduce only with parthenogenesis (development from unfertilized eggs). However, parthenogenesis has never been documented in mammals. What is the current genetic explanation for this difference between mammals and other vertebrates?

Mammals evolved a process of genetic imprinting and therefore some genes from the father's genomes need to be expressed.

The origin of cell structures might be hypothesized to have involved a hypercycle, based on mutualism at the molecular level. Which of the following is correct regarding the hypercycle model?

Natural selection will favor a hypercycle that is enclosed in a membrane.

Identify which of the given examples is the best match for the following statement. "Individuals give up the ability to reproduce independently, and they join together to form a larger grouping that shares reproduction."

Solitary individuals start living together in colonial groups, sometimes even giving up the possibility of independent replication, as we see in many species of social insects.

Eugene Koonin and his colleagues used the distributions of genes in the minimal gene sets of Haemophilus influenza and Mycoplasma genitalium to predict the distribution of a minimal gene set for Bacillus subtilis (Koonin 2003). What did they conclude from their comparison?

The predicted distribution of genes in B. subtilis was a close fit to the minimal gene sets observed.

Many species of mammals and birds are known to live in close communities, while other species live solitary lives. What do we know about the benefits of sociality, such as that observed in cliff swallows?

There is often a significant positive correlation between group size (such as colony size in cliff swallows) and survival rate of the population.

When a reproductive trait appears earlier in development or when some somatic traits of an adult are retarded, we define this type of development as __________.

paedomorphosis

In some species of fruit flies, males have black spots on the edges of their wings, which they use for visual displays during courtship dances with females, while in other species these spots are completely absent. A gene called yellow plays a role in the development of these visual features in all of the species. Differences in the amount and spatial distribution of the yellow protein are due to which of the following?

the effects of regulatory enhancers on the yellow gene

Which of the following is TRUE regarding the evolution of chloroplasts?

-Chloroplasts are derived from ancient free-living photosynthetic cyanobacteria. -Cyanobacteria are related to algal plastids -RNA shows that the chloroplasts of plants are closely related to cyanobacteria.

Which of the following statements about LUCA is correct?

-It represents a base to the tree of life -The acronym stands for "last universal common ancestor" -It represents a phylogenetic event horizon

It is very difficult to find the fossil remains of an entire organism. Which of the following is a factor that paleontologists use when choosing sites to search for the best fossils?

-Paleontologists typically focus on the sites that best match the geological and abiotic conditions in which fossilization may have occurred. -Paleontologists are unlikely to be the first researchers to be searching for fossils from their organism of interest. Instead, they often choose sites where others have already uncovered related fossils. -Paleontologists often use predictions derived from phylogenetic reconstruction, biogeography, or molecular genetics to explore a particular area.

Among the oldest fossils yet discovered on Earth are microfossils from 600 meters below the Agnes gold mine of South Africa, which are __________ years old.

3.2 billion

Itay Budin and Jack Szostak sought to understand how cell membranes composed of single-chain lipid molecules could possibly evolve to the more complex phospholipids seen in modern cell membranes (Budin and Szostak 2009). Which statement best summarizes their results?

Adding a small fraction of phospholipid molecules resulted in vesicles with higher phospholipid content; these cells tended to grow in size conferring a selective advantage.

In light of recent achievements in the field of genomics, would it be reasonable to expect that the use of comparative genomics might shed light on the extinct genomes of early life?

Comparative genomics and studies of bacteria with very small genomes shed light on a common ancestor, and researchers can estimate the minimal characteristics that a cell would need to operate as a living organism.

A number of evolutionary studies show a strong phylogenetic link between prokaryotic and eukaryotic cells. Which of the following is the best statement about the evolutionary origins of eukaryotic cells?

Eukaryotic "informational" genes are most closely related to archaeal genes, while their "operational" genes are most closely related to bacterial genes.

What do we know about horizontal gene transfer (HGT) in the evolution of early life?

HGT was probably a powerful force during early cell evolution, leading to complex cellular organisms.

How does the dominance theory explain why the heterogametic sex is at a disadvantage in Haldane's rule?

If a recessive allele linked to a sex chromosome has a negative effect on the fitness of hybrids, that allele will always be expressed in the heterogametic hybrids that possess that allele because they only have one copy of the sex chromosome that carries the allele.

Which of the following defines Haldane's rule and its predictions?

If among hybrid offspring one sex is absent, rare, or sterile, that sex is heterogametic (has two different sex chromosomes).

Deep homology of homeotic genes is also seen in plants. For example, the MADS-box genes have been used to work out phylogenetic relationships within flowering species of plants. What was also documented in these studies across many plant lineages?

The MADS-box genes are also instrumental in nonflowering plant species, where they are involved in developmental pathways in leaf and root systems.

One of the main features of a eukaryotic cell is the nucleus. Recent evidence suggests that the cell nucleus may have evolved from archaeal ancestors and that the organelles may have evolved from bacterial ancestors, but there is another important factor that has shaped the evolution of nuclear genomes. Which of the following is a source of some eukaryotic nuclear genes?

both mitochondrial and chloroplast genes

In the early 1980s, studies of fruit flies led to the discovery of the master-switch genes involved in animal development. Which of these genes are essential for the development of different body segments of fruit flies?

hox genes

Why is the higher fidelity of DNA proofreading and repair (compared to RNA) evolutionarily important?

A lower mutation rate allows for longer genes and more storage of information in the genome.

After confirming that Amphilophus citrinellus and Amphilophus zaliosus were indeed two species that originated from a single colonization of Lake Apoyo by their common ancestor, what evidence explained this was a sympatric speciation event rather than an allopatric speciation event?

Although Lake Apoyo is a very homogeneous habitat, body morphology in the two species supported speciation based on habitat and ecological specialization, rather than geographic separation.

Why did the human introduction of feral pigs on Santa Cruz Island accelerate the extinction of the native island fox and increase the population of skunks?

Increased pig numbers attracted the golden eagle, which is a fierce predator of foxes, and skunks (the main prey of island foxes) therefore increased in population size.

Which of the following statements about the Lincoln and Joyce experiment on self-replicating ribozymes is most likely correct?

The self-replicating ribozymes that had more efficient catalytic activities would soon began to dominate their populations.

The apicoplast is an organelle found only in species in a phylum called Apicoplasta. This phylum includes a deadly human parasite, Plasmodium falciparum, which is responsible for malaria. Which of the following is TRUE regarding the apicoplast organelle?

-Apicoplasts are unique organelles with a quadruple membrane. -The primary endosymbiosis occurred when one prokaryotic host engulfed a cyanobacterium, giving rise to the initial eukaryote, which was subsequently engulfed in a secondary endosymbiosis. -Apicoplasts in Plasmodium falciparum and related species are involved in the production of at least 500 different gene products.

Thyroid hormone (TH) has been identified as one of the factors promoting phenotype development in the Mexican axolotl salamander. Which of the following statements regarding the impact of TH is TRUE?

-Axolotls maturing in water with high concentration of TH (thyroxine; T4) metamorphose into a terrestrial form. -Most salamander species produce a burst of TH when they move from water to land. -A genome-wide scan of both the axolotl and its sister species found a large reduction in the number of mRNA transcripts that regulate the production of TH.

Which of the following is TRUE regarding the evolution of group living?

-Group living includes benefits associated with safety from predators. -Group living requires new levels of coordination and communication between individuals. -A group is defined as a set of conspecific individuals that affect each other's fitness.

Which of the following statements regarding the Midas and Arrow cichlids in Lake Apoyo does suggest that the speciation event responsible for forming these two species occurred in sympatry rather than allopatry?

-The Midas and Arrow cichlids are a monophyletic clade. -Lake Apoyo is small, shallow, and homogeneous. -Not even one mitochondrial haplotype was found in any other Nicaraguan lake that was the same as those found in the two Lake Apoyo species.

Which of the following statements regarding the complexity of living organisms is TRUE?

-The body size of the largest living organisms has increased over evolutionary time -The complexity of multicellular organisms, as measured by the number of cell types, has increased over evolutionary time. -Modern bacteria and archaea are not always more complex than their ancestors that lived before the origin of multicellular life.

In the ancestral lineage leading to land plants, a gene duplication in the developmental gene OEP16 is known to have been followed by the process of neofunctionalization. Which of the following statements is TRUE regarding these genes?

-The duplication in the OEP16 gene took place in the lineage that led to the land plants. -The neofunctionalization of the OEP16 gene may have been partly responsible for the explosion of plant diversity and the evolution of flowering land plants. -The genes produced by neofunctionalization are OEP16L and OEP16S.

Which of the following is TRUE regarding studies on volvocine algae to explore the evolution of individuality?

-There is exceptional variation found within this group. Some species are unicellular; some species are made of cells that live in groups but do not have specialized germ and soma lines; and some species show well-differentiated germ cell and somatic cell lines. -The division of labor between germ and soma lines has evolved on at least three separate occasions in this group -Volvox carteri individuals are made up of many small somatic cells and few large reproductive cells.

Which of the following statements is TRUE about Hox genes experiments?

-When a Hox gene product from an appropriate chromosomal region in chickens is inserted into a fruit fly embryo, it results in normal regulation of the fruit fly development. -When the mouse Hox-2.2 gene is experimentally inserted into the fruit fly genome and expressed in the head of developing fruit flies, adults produce legs in place of antennae. -Homeobox regions of the Hox genes allow the transcription factor of one species to function in the other species.

Which of the following is considered a type of heterochrony (change in the rate and timing of development)?

-hypermorphosis -acceleration -neoteny

Which one of the following is a major transition in the evolution of life, according to biologists John Maynard Smith and Eörs Szathmary?

-origin of self-replicating molecules capable of heredity -evolution of sexual reproduction -evolution of multicellular organisms from single-celled ancestors

All of the following are true regarding Sol Spiegelman's experiment on the origins of life

-the most common size of the RNA strand in the final test tubes was a little over 200 nucleotides long -variation in the length of the RNA strands occurred at each round of replication -shorter RNA sequences were favored by selection because they took less time to replicate

Radiocarbon dating (14C) is a useful tool for measuring absolute age for about __________ years into the past.

50,000

The human parasite Mycoplasma genitalium, with one of the smallest genomes of any organism that can be grown in a laboratory, as well as Chlamydia trachomatis, an obligate intracellular parasite, are examples of the types of organisms that functional genomics researchers have focused on. What is the main purpose of the study of such genomes?

By studying such genomes, researchers try to discover the basic and essential cellular functions of early life.

Evolutionary biologists are very interested in understanding the patterns and processes that guide the tempo and mode of evolution. In specific clades, they sometimes point to trends (patterns of directional change over time). One such trend is also known as Cope's rule. Which of the following statements is TRUE?

Cope's rule states that species in mammalian clades tend to increase in body size over evolutionary time.

An analysis by Maria Rivera and James Lake suggests that ancient eukaryotic cells emerged from the fusion of an archaeal cell (most likely from the phylum Eocyta) and a bacterium (Rivera and Lake 2004). Which of the following is correct regarding this working hypothesis?

Eukaryotic cells probably evolved through endosymbiosis, in which either the archaeal or bacterial cell was engulfed within the other.

In 1977, Sidney Fox tried a different approach to testing the prebiotic synthesis of biological molecules. He mixed a number of different amino acids together at a high temperature (120°C) in an environment lacking water. When he subsequently placed the mixture into water to investigate what the amino acids would form, what happened next?

He found some peptide-like structures, but the bonds between the amino acids were weak and unstable.

Two parapatric subspecies of sagebrush (mountain big sagebrush and basin big sagebrush) produce hybrid sagebrush, which often is found in the intermediate elevation. In the following graph, you can see a relative composite fitness for each of them, raised in three different environments (below 1800 meters in the basin zone, above 1900 meters in the mountain zone, and in the hybrid zone between 1800 and 1900 meters). Which of the following best explains the findings in this experiment?

Hybrids had significantly better fitness than the other subspecies in the hybrid zone, supporting the bounded hybrid superiority model.

Which of the following is correct regarding the endemic species as they relate to the study of background extinction?

It is much easier to study extinction in endemic species because such local extinction becomes synonymous with global extinction for that species

Which two scientists elaborated on Darwin's idea of the "warm little pond" and formulated the "prebiotic soup hypothesis" as the first hypothesis for the abiotic origin of life on Earth?

Oparin and Haldane

As opposed to background extinction, a mass extinction typically refers to the loss of many groups of organisms over a broad geographic range. Which of the following mass extinctions in Earth's geological history was the most devastating for the marine families?

Permian

The first genetic material on Earth was most likely __________.

RNA

Slime molds are unusual eukaryotes. They spend most of their life cycle as single-celled organisms, and yet under certain conditions, they form a slug-like multicellular stage and then a fruiting body composed of both somatic cells and reproductive spores. The best known species of slime mold is a soil dweller, Dictyostelium discoideum. Why is it important to study this and related species of slime molds?

Slime molds provide clues as to how multicellularity may have evolved.

Which of the following is TRUE for the ancient Greek view of ontogeny (the development of an individual over its lifetime), which was later developed as the concept of scala naturae (the "great chain of being") in the European natural sciences?

The ancient Greeks argued that the ontogeny of an individual was built up from simple traits early in development to more complex traits later in the developmental process.

During the 1990s, Nancy Knowlton and her colleagues studied pairs of sister species of the genus Alpheus (snapping shrimp) (Knowlton 1993). In each of these sister species, one species in the pair lived on the Caribbean side of the Isthmus of Panama, while the other species lived on the Pacific side. What type of speciation might be responsible for this speciation?

allopatric speciation with the vicariance model

Stanley Miller and Harold Urey developed and conducted experimental tests for a "prebiotic soup" model of the origin of life, which had been proposed a few decades earlier by Aleksandr Oparin and J.B.S. Haldane. What did Miller and Urey show could be synthesized abiotically?

amino acids

What type of infectious disease is devastating populations of frogs in North America, Alaska, and Australia today?

chytridiomycosis, which interferes with the ability of amphibians to transport chemicals across the epidermis

In the slime mold species Dictyostelium discoideum, single-celled individuals gather in the migratory slug stage of development, in response to environmental cues. Which molecule is associated with this signaling?

cyclic adenosine monophosphate (cAMP)

A species is a lineage of populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate." This definition best represents the __________.

evolutionary species concept

Which of the following molecules involved in membrane structure was likely favored by natural selection in the evolution of early cells?

fatty acids

Neural crest cells in vertebrates are cells that are initially positioned near the neural tube during early development and then migrate to new locations. The development and positioning of these cells is controlled by a set of __________.

homeotic genes

In the late 1800s, William Bateson documented, both in insects and in vertebrates such as frogs, many cases where one body part had replaced another, which resulted in unusual forms. Bateson believed that his studies could teach us something about evolutionary changes. He named these changes __________.

homeotic transformations

Heterochrony is well studied in amphibians. One of the famous examples is in the Mexican axolotl salamander species, Ambystoma mexicanum, where reproductively mature individuals still live in the water and have external gills and flat tails, as in the salamander embryos. This phenomenon is best defined as __________.

neoteny

Two common species of frogs from the genus Bombina (B. bombina and B. variegata) live in similar latitudes and ecological conditions, but in two different regions, Central and Eastern Europe. In a narrow strip between these regions, scientists have observed a third species, which might be a hybrid between the former diverging populations of the ancestral species. What evolutionary process might be responsible for the speciation in Bombina?

parametric speciation

A researcher is trying to determine if populations of a butterfly seen on the eastern slope of the Rocky Mountains in Colorado are actually separate species. The researcher and her graduate students spent a summer capturing the butterflies at several locations, carefully documenting traits such as color, wing span, antennae length, proboscis length, etc. Which species concept could be applied using these data?

phenetic species concept

David Jablonski and his coworkers found that for gastropods (slugs and snails) of the late Cretaceous period, the key to a broad geographic range at the species level—and thus increased chances of surviving the mass extinction near the K-Pg boundary—was the nature of their larval stage. Which of the following best describes a stage that contributes to the increased geographic ranges of the gastropod taxa?

planktotrophic larvae that feed in the open water on very small prey and develop into adults at a relatively slow rate

Different races of the apple maggot fly have different breeding seasons depending on the host species they prefer (downy hawthorn or apple trees). Because of this temporal difference in breeding, which type of reproductive isolating mechanism is occurring?

pre zygotic

In a hypothetical flowering plant species, one population evolves a different response to environmental stimuli and begins to bloom significantly later in the season than nearby populations. What type of reproductive isolating mechanism would this be?

pre zygotic