Bio 101 Exam 2

Front 1

Adaptation

Back 1

process that improves survival and reproduction of an organism based on a specific environment. ie: a flower mantid in Malaysia had adapted to look like the flowers it lives on, while a stick mantid in Africa had adapted to look like the sticks of the plant it lives on. The two related species evolved to be able to be camouflaged in different environments.

Front 2

Evolution

Back 2

the change of gene frequencies over generations.

Front 3

Natural selection

Back 3

unequal success in the reproduction of different phenotypes resulting from the interaction of organisms with their environment. Evolution occurs when natural selection causes changes in relative frequency of alleles in the gene pool. i.e.: In the Galapagos Islands, there are dozens of species of closely related finches. They each have adapted various shapes to their beaks according to what it is they feed on.

Front 4

Artificial selection

Back 4

the selective breeding of domesticated plants and animals (by humans) to encourage the occurrence of desirable traits. i.e.: Broccoli, cauliflower, cabbage, brussels sprouts, kale, and kohlrabi have been artificially selected from one species of wild mustard.

Front 5

Vestigial structures

Back 5

remnants of features that served important functions in the organism’s ancestors. i.e.: the skeletons of some snakes retain vestiges of the pelvis and leg bones of walking ancestors.

Front 6

Endemic

Back 6

confined to a specific, relatively small geographic area. i.e.: many species of the Galapagos, a relatively small geographical area, are found no where else in the world.

Front 7

Biogeography

Back 7

the study of the past and present geographic distribution of species. i.e.: The sugar glider is a marsupial that evolved in Australia. While sugar gliders superficially resemble the eutherian flying squirrels of North America. The ability to glide though the air evolved independently in these two distantly related groups of mammals.

Front 8

Genetic assimilation

Back 8

a process by which a phenotypic character, which initially is produced only in response to some environmental influence, becomes, though a process of selection, taken over by the genotype, so that it is found even in the absence of the environmental influence which had at first been necessary.

Front 9

Canalization

Back 9

the ability of organisms to produce the same phenotype despite variation in genotype or environment by constraining developmental pathways. i.e.:

Front 10

Balancing selection

Back 10

selection that occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population. This type of selection includes heterozygote advantage and frequency dependent selection.

Front 11

Bottleneck effect

Back 11

a sudden reduction in population size due to a change in the environment. (i.e.: The loss of prairie habitat caused a severe reduction in the population of greater prairie chickens in Illinois. Surviving birds had low levels of genetic variation, and only 50% of their eggs hatched.)

Front 12

Cline

Back 12

a graded change in a trait along a geographic axis.

Front 13

Discrete characters

Back 13

characters that can be classified on an either-or basis. (i.e.: the color of a human’s eye.)

Front 14

Founder effect

Back 14

the result occurs when a few individuals become isolated from a larger population. (i.e.: 15 colonists founded a British colony on an island (Tristan da Cunha). One of the colonists carried a recessive allele for retinitis pimentosa. Of the 240 descendants living on the island many years later, 4 had the disease. The frequency of this allele remains ten times higher on this island than in the population form which the founders came from.)

Front 15

Gene flow

Back 15

the genetic additions to and/or subtractions from a population resulting from the movement of fertile individuals or gametes. Because of this gene flow tends to reduce differences between adjacent populations. (i.e.: pollen from one population of plants may be blown by the wind to pollinate plants from another population.)

Front 16

Frequency-dependent selection

Back 16

when the fitness of a phenotype declines if it becomes too common in the population. (Blue-jays learn to locate and eat moths that have the most common phenotype. This puts common moths at a disadvantage and the rare ones at an advantage.)

Front 17

Gene pool

Back 17

all of the alleles for all loci in a population.

Front 18

Genetic drift

Back 18

the unpredictable fluctuation of allele frequencies from one generation to the next. (i.e.: in a small wildflower population, one of the alleles for flower color can be lost by an indiscriminate event. Over time, genetic drift tends to reduce the genetic variation through such losses of alleles from the gene pool, and the flower population may look a lot more different than the original population.)

Front 19

Heterozygosity

Back 19

the average percent of loci that are heterozygous in a population. (a Drosphilia fly (fruit fly) population has and average heterozygosity of 14%, if a typical fruit fly is heterozygous at about 1,800 of its 13,300 gene loci and homozygous at all the rest.

Front 20

Heterozygote advantage

Back 20

an advantage that occurs when heterozygotes have a higher fitness than do both homozygotes. (i.e.: In areas where malaria is prevalent, the environment favors individuals that are heterozygous for a locus that codes for a subunit of hemoglobin, who are resistant to the severest effects if malaria, over homozygous dominant individuals who are more susceptible to malaria, and also over homozygous recessive individuals , who develop sickle-cell disease.)

Front 21

Microevolution

Back 21

change in allele frequencies in a population over generations.

Front 22

Mutation

Back 22

changes in the nucleotide sequence of DNA.

Front 23

Neutral variation

Back 23

genetic variation that appears to confer no selective advantage or disadvantage. Natural selection does not act on these alleles because the genetic variation in populations probably has little or no impact on reproductive success. (i.e.: variation in noncoding regions of DNA or in proteins that have little effect on protein function of reproduction fitness.)

Front 24

Polymorphisms

Back 24

the coexistence of two or more distinct forms in the same population.

Front 25

Population

Back 25

a localized group of individuals capable of interbreeding and producing fertile loci in a population

Front 26

Adaptive radiation

Back 26

The emergence of numerous species from a common ancestor introduced into an environment that presents a diversity of new opportunities and problems. i.e.: The Hawaiian archipelago was formed by volcanic eruptions. Each of the islands have such physical diversity, which provides for many opportunities for evolutionary divergence by natural selection. A group of varied Hawaiian plants, known collectively as the “silversword alliance” are all descended from an ancestral tarweed that arrived on the islands about 5 million years ago from North America.

Front 27

Quantitative characters

Back 27

characters that vary along a continuum within a population. (i.e.: the height of an individual.)

Front 28

Relative fitness

Back 28

the contribution an individual makes to the gene pool of the next generation, relative to the contributions of the other individuals.

Front 29

Allopatric speciation

Back 29

(“other country”), is a speciation in which gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations. i.e.: In the Grand Canyon, two closely related species of antelope squirrels have developed on opposite rims of the canyon due to allopatric speciation. Harris’s antelope squirrel inhabits the canyon’s south rim, while the white-tailed antelope squirrel inhabits the north rim. In contrast, birds and other species that can disperse easily across the canyon have not diverged into different species on opposite rims.

Front 30

Autopolyploid

Back 30

an individual with more than two chromosome sets, derived from one species. For example, a failure of cell division can double a cells chromosome number from diploid to tetraploid. This mutation prevents a tertraploid from successfully interbreeding with diploid plants of the original population (triploid). The offspring are sterile because of their unpaired chromosomes. However the tetraploid can still produce sterile offspring by self-pollinating mating with other tertaploids. Thus creating reproductive isolation within one generation. i.e.: Bananas are autotriploid of 2n= 33.

Front 31

Allopolyploid

Back 31

is a species with multiple sets of chromosomes derived from different species. i.e.: the wheat used for bread, Triricum aestivum, is an allohexaploid. The first polyploidy event was a spontaneous hybrid of an early cultivated wheat and a wild grass in the Middle East about 8000 years ago.

Front 32

Behavioral isolation

Back 32

courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. i.e.:blue-footed boobies, inhabitants of the Galapagos, mate only after a courtship display unique to their species. Part of the “script” calls for the male to high-step, a behavior that calls the female’s attention to his bright blue feet. The courtship display of a Red-footed booby male would not be recognized by a Blue-footed booby female.

Front 33

Biological species concept

Back 33

definition of a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are unable to produce viable, fertile offspring with members of other populations. i.e.: All humans belong to the same biological species because they are able to have viable babies that develop into fertile adults. In contrast, humans and chimpanzees remain in distinct biological species even where they share territory, because many factors keeps them from interbreeding and producing fertile offspring.

Front 34

Gametic isolation

Back 34

Sperm of one species may not be able to fertilize he eggs of another species. Many mechanisms can produce this isolation. For instance, sperm may not be able to survive in the reproductive tract of females of the other species, or biochemical mechanisms may prevent the sperm from penetrating the membrane surrounding the other species’ eggs. i.e.: Gametic isolation separates certain closely related species of aquatic animals such as sea urchins. The sea urchins release their sperm and eggs into the surrounding water, where they fuse and form zygotes. Gametes of different species, like the red and purple urchins, are unable to fuse.

Front 35

Habitat isolation

Back 35

two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers. i.e.: Two species of garner snakes in the genus Thamnophis occur in the same geographic areas, but one lives mainly in water, while the other is primarily terrestrial.

Front 36

Hybrid

Back 36

an offspring resulting from the crosses between different species. i.e.: The hybrid offspring of a donkey and a horse is a mule, which is robust but sterile.

Front 37

Hybrid breakdown

Back 37

is when some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile. i.e.: Hybrids of different species of strains of cultivated rice are vigorous and fertile, but plants of the next generation are small and sterile.

Front 38

Macroevolution

Back 38

evolution which refers to evolutionary change above the species level.

Front 39

Mechanical isolation

Back 39

Morphological differences can prevent successful mating. i.e.: The shells of two species of the Bradybaena spiral in opposite directions and therefore they are physically hindered from mating.

Front 40

Prezygotic barrier

Back 40

(“before the zygote”) impede mating between species or hinder the fertilization of ova if members of different species attempt to mate.

Front 41

Postzygotic barrier

Back 41

(“after the zygote”) often prevent the hybrid zygote from developing into a viable, fertile adult. i.e.: Hybrid breakdown.

Front 42

Reproductive isolation

Back 42

the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring.

Front 43

Speciation

Back 43

the origin of new species in evolution. i.e.: sympatric and allopatric.

Front 44

Sympatric speciation

Back 44

(same country) speciation which takes place in geographically overlapping populations. i.e.: lake Victoria cichlids.

Front 45

Temporal isolation

Back 45

species that breed during different times of the day, different seasons, or different years cannot mix their gametes. i.e.: In North America, the geographic ranges of the eastern spotted skunk (Spilogale putorius) and the western spotted skunk (Spilogale gracilis) overlap, but S. putorius mates in later winter and S.gracilis mates in late summer.

Front 46

1. Describe the four observations and two inferences that lead Darwin to propose natural selection as a mechanism for evolutionary change.

Back 46

a. Observation #1: Members of a population often vary greatly in their traits.
b. Observation #2: Traits are inherited from parents to offspring.
c. Observation #3: All species are capable of producing more offspring than the environment can support.
d. Observation #4: Owing to lack of food or other resources, many of these offspring do not survive.
e. Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.
f. Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Front 47

2. Distinguish between artificial selection and natural selection.

Back 47

a. Natural selection is unequal success in the reproduction of different traits resulting from organisms interaction with their environment. Evolution occurs when natural selection causes changes in relative frequency of alleles in the gene pool.
b. Artificial selection is the selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.

Front 48

3. Explain why an individual organism cannot evolve.

Back 48

Although individuals may change throughout their life course, they do not “evolve”. “Evolution” can be measured only as changes in relative proportions of heritable variations in a population over a succession of generations.

Front 49

4. Explain why natural selection can act only on heritable traits.

Back 49

a. Natural selection can amplify or diminish only heritable traits- that is, traits that are passed from organisms to their offspring. Though an organism may become modified though its own interactions with the environment during its lifetime, and these acquired characteristics may even adapt the organism to its environment, there is no evidence that such acquired characteristics can be inherited of offspring. We must distinguish between adaptations that an organism acquires during its lifetime and inherited adaptations that accumulated in a population over many generations as a result of natural selection.

Front 50

5. Discuss the importance of canalization and genetic assimilation to natural selection.

Back 50

a. Canalization is the ability of organisms to produce the same phenotype despite variation in genotype or environment by constraining developmental pathways. If a particular organismal morphology is particularly successful, mutations that make it robust and resistant to change would be advantageous. Canalization is a conservative process that opposes evolutionary change, over several generations. However, canalization can facilitate evolution over large time scales, due to the accumulation of variation. This variation will be exposed to selection only in extreme (i.e. rare) environments.

Front 51

6. Describe the experiments that supported Endler’s hypothesis that differences in color patterns in male guppies are due to selective pressure based on predation.

Back 51

a. Brightly colored male guppies are more attractive to females but more vulnerable to predation. Guppy populations with fewer predators had more brightly colored males. Ender transferred brightly colored guppies (with few predators) to a pool with many predators. As predicted, over time the population became less brightly colored. He also preformed the opposite experiment, transferring drab colored guppies (with many predators) to pool with few predators. As predicted, over time the population became more brightly colored.

Front 52

7. Describe how natural selection favors the evolution of drug-resistant pathogens.

Back 52

a. In natural selection, a drug will not create new traits, but edits or selects traits in resistant individuals that were already present in the population. Also, natural selection depends on time and place. It favors those characteristics in a genetically variable population that increase fitness in the current, local environment.

Front 53

8. Explain how the fossil record may be used to test our current understanding of evolutionary patterns.

Back 53

a. The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time. The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record. Paleontologists have discovered fossils of many such transitional forms.

Front 54

9. Explain how the existence of homologous and vestigial structures are explained by Darwin’s theory of natural selection.

Back 54

a. Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor. Vestigial structures are remnants of features that served important functions in the organism’s ancestors. The existence of these structures are explained by Darwin’s theory of natural selection because they help determine the evolutionary tree from which they came from. Some homologies are shared by all species and other homologies mark distinct forks in the tree as new species evolve.

Front 55

10. Explain how evidence from biogeography demonstrates evolution by natural selection.

Back 55

a. Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution.
b. Closely related species tend to be found in the same geographic region, whereas the same ecological niches in distant regions are occupied by very different (though sometimes similar-looking) species.

Front 56

11. Explain the concept of plasticity and give several examples. Explain why it may or may not be adaptive.

Back 56

a. Plasticity is the ability of one genotype to produce different phenotypes under different environments. (Examples) A phenotype may not be affected by environment or genotype, it may be affected by one and not the other, or it may be affected by both. In this last case plasticity is adaptive. In the other cases it is not.

Front 57

12. Explain how plasticity can be ‘selected for’ or ‘selected against’.

Back 57

a. Phenotype plasticity is not necessarily adaptive, however when it is, the genes that lead to plasticity can be selected for. Adaptive plasticity is heritable and can therefore be acted on by selection.

Front 58

13. How can plasticity be detected? Explain what is meant by a ‘Genotype by Environment’ interaction.

Back 58

a. The fact that each genotype has its own specific response to the environment is evidence of adaptive phenotype plasticity. ‘Genotype by environment interaction’ shows how the interaction between the environment and the genotype affect phenotype.

Front 59

14. Explain the concept of canalization. Explain why canalization is a form of plasticity.

Back 59

a. Canalization is the ability of organisms to produce the same phenotype despite variation in genotype or environment by constraining developmental pathways. It can be considered a form of plasticity because as the environment changes, instead of the phenotype adapting to the environment and changing, it does the opposite and “changes” its natural reaction to the changing environment in order to remain the same.

Front 60

1. Explain the statement “It is the population, not the individual that evolves.”

Back 60

a. Although individual organisms’ combination of traits affects its survival and reproductive success compared to other individuals, the evolutionary impact is only apparent in the changes in the population of organisms over time. Some traits become more common within the population, while other traits become less common, and thus a change is observed.

Front 61

2. Explain why the majority of point mutations are harmless.

Back 61

a. One reason is that much of the DNA in eukaryotic genomes does not code for protein products. Therefore the chances of a mutation occurring in a noncoding region of DNA is high, and it won’t result in any visible change.
b. Another reason is that many genetic codes can be redundant and therefore the mutation in a gene might not affect protein production. For example, UTA and UTC both code for Argenine.

Front 62

3. Explain how sexual recombination generates genetic variability.

Back 62

a. Sexual reproduction can shuffle existing alleles into new combinations every generation. A population contains a myriad possible mating combinations and fertilization brings together the gametes of individuals that are likely to have different genetic backgrounds.

Front 63

4. Explain why meiosis and random fertilization alone will not alter the frequency of alleles or genotypes in a population.

Back 63

a. Because mating within the same population with just meiosis and random fertilization, the genotype would remain constant not matter how many generations go by.

Front 64

5. List the five conditions that must be met for a population to remain in Hardy-Weinberg equilibrium.

Back 64

a. No mutations
b. Random mating
c. No natural selection
d. Extremely large population size
e. No gene flow

Front 65

6. Write the Hardy-Weinberg equation. Use the equation to calculate allele frequencies.

Back 65

a. p2 + 2pq + q2 = 1

Front 66

7. Explain the following statement: “Only natural selection leads to the adaptation of organisms to their environment.”

Back 66

a. This is because genetic flow and genetic drift occur totally randomly. However, natural selection will allow the genomes that are a good adaptation to the environment pass on to the next generation and cause the genomes that aren’t good adaptations die out.

Front 67

8. Explain the role of population size in genetic drift.

Back 67

a. Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next. In genetic drift, the smaller a sample of a group of species, the greater the chance of deviation from a predicted result.

Front 68

9. Distinguish between the bottleneck effect and the founder effect.

Back 68

a. The founder effect occurs when a few individuals become isolated from a larger population. The bottleneck effect is a sudden reduction in population size due to change in the environment. They are similar as in the surviving population of the bottleneck effect can be compared to the few individuals that are isolated in the founder effect. The difference is that in bottleneck only has that small group left, while in founder there still is a larger parent population that exists. Both of these small groups, the gene pool may no longer reflect that of the original population’s gene.

Front 69

10. Describe how gene flow can act to reduce genetic differences between adjacent populations.

Back 69

a. A population may gain or lose alleles by gene flow, the genetic additions to and/or subtractions from a population resulting from the movement of fertile individuals or gametes. Because of this gene flow tends to reduce differences between adjacent populations.

Front 70

11. Distinguish among directional, disruptive, and stabilizing selection. Give an example of each mode of selection.

Back 70

a. Directional selection favors individuals at one end of the phenotypic range. For example, fossil evidence shows that blackbears in Europe increased in size with each glacial period, and decreased as the temperature rose later on. Larger bears, with smaller surface-to-volume ratio, are better at maintaining body heat and surviving periods of extreme cold. Disruptive selection favors individuals at both extremes of the phenotypic range. For example, black-bellied seed cracker finches in Cameroon have two distinct beak sizes. Small-billed individuals feed on soft seeds, while large-billed individuals specialize in cracking hard seeds. Birds with intermediate-sized bills tend to be inefficient at cracking both types of seeds, and thus have a lower relative fitness. Stabilizing selection favors intermediate variants and acts against extreme phenotypes. It reduces variation and favors a particular phenotype. For example, the birth weights of most human babies are between 3-4 kg; babies who are much smaller or

Front 71

12. Explain how diploidy can protect a rare recessive allele from elimination by natural selection.

Back 71

a. Diploidy maintains genetic variation in the form of hidden recessive alleles.

Front 72

13. Describe how heterozygote advantage and frequency dependent selection promote balanced polymorphism.

Back 72

a. Heterozygote advantage occurs when heterozygotes have a higher fitness than do both homozygotes. In frequency-dependant selection, the fitness of a phenotype declines if it becomes too common in the population.

Front 73

14. Define neutral variations. Explain why natural selection does not act on these alleles.

Back 73

a. Neutral variation is genetic variation that appears to have no selective advantage or disadvantage. Natural selection does not act on these alleles because the genetic variation in populations probably has little or no impact on survival or reproductive success.

Front 74

15. List four reasons why natural selection cannot produce perfect organisms.

Back 74

a. Selection can act only on existing variations
b. Evolution is limited by historical constraints
c. Adaptations are often compromises
d. Chance, natural selection, and the environment interact

Front 75

1. Define Ernst Mayr’s biological species concept.

Back 75

a. A species is a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are unable to produce viable, fertile offspring with members of other populations.

Front 76

2. Distinguish between prezygotic and postzygotic reproductive barriers.

Back 76

a. Prezygotic barriers (“before the zygote”) impede mating between species or hinder the fertilization of ova if members of different species attempt to mate. Postzygotic barriers (“after the zygote”) often prevent the hybrid zygote from developing into a viable, fertile adult.

Front 77

3. Describe five prezygotic reproductive barriers and give an example of each.

Back 77

a. Habitat isolation: two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers. i.e.: Two species of garner snakes in the genus Thamnophis occur in the same geographic areas, but one lives mainly in water, while the other is primarily terrestrial.
b. Temporal Isolation: species that breed during different times of the day, different seasons, or different years cannot mix their gametes. i.e.: In North America, the geographic ranges of the eastern spotted skunk (Spilogale putorius) and the western spotted skunk (Spilogale gracilis) overlap, but S. putorius mates in later winter and S.gracilis mates in late summer.
c. Behavioral isolation: courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. Blue-footed boobies, inhabitants of the Galapagos, mate only after a courtship display unique to their species. Part of the “script” ca

Front 78

4. Explain how hybrid breakdown maintains separate species even if fertilization occurs.

Back 78

a. In hybrid breakdown, some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile.

Front 79

5. Distinguish between allopatric and sympatric speciation.

Back 79

a. In allopatric speciation (“other country”), gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations. In sympatric speciation (same country), speciation takes place in geographically overlapping populations.

Front 80

6. Define allopatric speciation. Describe the mechanisms that may lead to genetic divergence of isolated gene pools.

Back 80

a. The definition of a barrier depends on the ability of a population to disperse. Separate populations may evolve independently though mutation, natural selection, and genetic drift. Regions with many geographic barriers typically have more species than do regions with fewer barriers. Reproductive isolation between populations generally increases as the distance between them increases.

Front 81

8. Define sympatric speciation and explain how polyploidy can cause reproductive isolation.

Back 81

a. Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division. An autopolyploid is an individual with more than two chromosome sets, derived from one species. For example, a failure of cell division can double a cells chromosome number from diploid to tetraploid. This mutation prevents a tertraploid from successfully interbreeding with diploid plants of the original population (triploid). The offspring are sterile because of their unpaired chromosomes. However the tetraploid can still produce sterile offspring by self-pollinating mating with other tertaploids. Thus creating reproductive isolation within one generation. An allopolyploid is a species with multiple sets of chromosomes derived from different species. This hybrid is usually sterile, but it may be able to propagate itself asexually. As generations go by, various mechanism change a sterile hybrid into an allopolyploid that is able to interbreed with each other, but not with the either of the parent species, thus r

Front 82

10. Explain how habitat differentiation has led to sympatric speciation in North American maggot flies.

Back 82

a. The fly’s original habitat was native hawthorn trees, but about 200 years ago, some populations colonized apple trees. Apple mature more quickly than hawthorn fruit, and so the apple-feeding flies have been selected for rapid development. These apple-feeding populations now show temporal isolation from the hawthorn-feeding R. pomonela. Although the two groups are still classified as subspecies rather than separate species, speciation appears to be well under way.

Front 83

11. Explain how sexual selection has led to sympatric adaptive radiation in the cichlids of Lake Victoria. Explain how the process of speciation may be reversing, due to pollution in this lake.

Back 83

a. Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria. Pundomilia pundamilia has a blue-tinged back, and Pundomilia nyererei has a red tinged back. They are both closely related sympatric species. This mate choice by coloration is the main reproductive barrier that normally keeps the gene pool of these tow species separate. In natural light, females of each species mated only with males of their own species. However, this process of speciation may be reversible. In poor light (due to pollution) females of each species may mate indiscriminately with males of both species. These matings are viable and fertile.