Name: ____________________________________________ Date: __________________________________________ Period: ___________
Reproductive Barrier Worksheet
1) Throughout the wet years, small seeds were more common and there was such a large supply of the small seeds that the
finches rarely ate large seeds. During the dry years, none of the seeds were in great abundance, but the birds usually ate more
large seeds. The change in diet of the finches affected the depth of the birds’ beaks in the future generations. Their beaks range
from large and tough to small and smooth. What type of selection am I?
A) Directional
B) Disruptive
C) Stabilizing
2) Some Central American Acacia species have hollow thorns and pores at the bases of their
leaves that secrete nectar (see image at right). These hollow thorns are the exclusive nest-site
of some species of ant that drink the nectar. But the ants are not just taking advantage of the
plant—they also defend their acacia plant against herbivores. The plants would not have
evolved hollow thorns or nectar pores unless their evolution had been affected by the ants,
and the ants would not have evolved herbivore defense behaviors unless their evolution had
been affected by the plants. What type of evolution am I?
A)
B)
C)
D)
Convergent evolution
Divergent evolution (Adaptive radiation)
Co-Evolution
Parallel Evolution
3) The illustration shows four different animals from around the globe. They may look similar, but it's not because they're
close relatives. Instead, they've evolved similar adaptations because they occupy similar niches -- dining on ants, hunting in
the high grass, or swimming in the dark -- although their evolutionary origins are quite different. What type of evolution am I?
A)
B)
C)
D)
Convergent evolution
Divergent evolution (Adaptive radiation)
Co-Evolution
Parallel Evolution
4) A plant that is too short may not be able to compete with other plants for sunlight. However, extremely tall plants may be
more susceptible to wind damage. Combined, these two selection pressures select to maintain plants of medium height. The
number of plants of medium height will increase while the numbers of short and tall plants will decrease. What type of
selection am I?
A) Directional
B) Disruptive
C) Stabilizing
5) Two closely related skink species, Eumeces skiltonianus and Eumeces gilberti are very different in their habitat preferences.
E. skiltonianus tends to live in forested and woodland habitats whereas E. gilberti is an inhabitant of drier and more open
habitats like grasslands. The two also differ in coloration. It turns out, however, that some E. gilberti populations are closer to
E. skiltonianus than they are to another E. gilberti populations. What type of evolution am I?
A) Convergent evolution
B) Divergent evolution (Adaptive radiation)
C) Co-Evolution
D) Parallel Evolution
6) Specialization may subdivide a single niche into many new niches. For example, cichlid fishes have diversified in East
African lakes into more than 600 species. This diversification may have been possible because different fish lineages evolved
to take advantage of different foods (including insects, algae, mollusks, small fish, large fish, other fishes’ scales, and even other
fishes’ eyes!). What type of evolution am I?
A)
B)
C)
D)
Convergent evolution
Divergent evolution (Adaptive radiation)
Co-Evolution
Parallel Evolution
Use the Key Box to match the following examples with the appropriate term.
A. Habitat Isolation B. Temporal Isolation C. Behavioral Isolation D. Mechanical Isolation E. Gametic Isolation F. Reduced
Hybrid Viability G. Reduced Hybrid Fertility H. Polyploidy I. Bottleneck Effect (Genetic Drift) J. Founder Effect (Genetic
Drift) L. Gene Flow M. Sexual Selection N. Allopatic speciation O. Sympatric speciation
_______1. Imagine an isolated population in which fifty people have sickle cell anemia, thirty people are carriers of the disease
(meaning that they have one disease-causing allele and one regular one) and twenty people who do not have sickle cell anemia
nor are they carriers of it. One day, a tremendous tidal wave hits the population and half of the people die. Now, just ten people
have sickle cell anemia, twenty-two people are carriers of it, and eighteen do not have nor carry it. You can see how genetic
drift has caused the predominant allele, which causes sickle cell anemia, to become less present in the population.
_______2. Different frog species live and breed in the same pond, but they reproduce at different times of the year. Explain if it
is a PRE-ZYGOTIC BARRIER OR a POST-ZYGOTIC BARRIER and WHY?
_______3. Occurs in some animals, such as goldfish, salmon, and salamanders, but is especially common among ferns and
flowering plants, including both wild and cultivated species. Wheat, for example, after millennia of hybridization and
modification by humans, has strains that are diploid (two sets of chromosomes), tetraploid (four sets of chromosomes) with
the common name of durum or macaroni wheat, and hexaploid (six sets of chromosomes) with the common name of bread
wheat. Many agriculturally important plants of the genus Brassica are also tetraploids. This is a mechanism of sympatric
speciation because they are usually unable to interbreed with their ancestors.
_______4. Different species of frog and salamanders are able to mate with each other, but most hybrids are not even born, while
those that do are weak and usually do not survive long. Explain if it is a PRE-ZYGOTIC BARRIER OR a POST-ZYGOTIC
BARRIER and WHY?
________5. In general, the people in Africa today, descendants of the original large gene pool have the highest genetic diversity in
their population, followed by people on the Indian subcontinent (one of the first places humans settled when they left Africa)
and so on. Places like Iceland, which was settled late and is also an isolated area, have some of the least genetic diversity on the
planet and a high incident of recessive traits like blonde hair and blue eyes.
_______7. The genus Bradybaena has different spiraled shells. This keeps the two species of snails from successfully mating
because the snails’ genitals cannot be properly aligned. Explain if it is a PRE-ZYGOTIC BARRIER OR a POST-ZYGOTIC
BARRIER and WHY?
_________ 8. One of these native plants, Ulmus pumila, demonstrated a lower prevalence of genetic differentiation than the
plants Vitex negundo, Ziziphus jujuba, Heteropappus hispidus, and Prunus armeniaca whose habitat is located on the opposite
side of the Great Wall of China where Ulmus pumila grows. This is because Ulmus pumila has wind-pollination as its primary
means of propagation and the latter-plants carry out pollination through insects. Samples of the same species, which grow on
either side, have been shown to have developed genetic differences.
______9. Sea urchins of different species release both their eggs and sperm into the same water. But because there are different
proteins on the surface of the egg and sperm, the two different species cannot produce a fertilized egg. Explain if it is a PREZYGOTIC BARRIER OR a POST-ZYGOTIC BARRIER and WHY?
_______10. There are two different species of cricket that would be indistinguishable unless you heard their mating song: they
are of a noticeably different pitch. A creature will only be able to conduct successful mating with an animal with similar mating
songs. Explain if it is a PRE-ZYGOTIC BARRIER OR a POST-ZYGOTIC BARRIER and WHY?
_______11. Mules and hinnies have 63 chromosomes, a mixture of the horse's 64 and the donkey's 62. The different structure
and number usually prevents the chromosomes from pairing up properly and creating successful embryos, rendering most
mules infertile. Explain if it is a PRE-ZYGOTIC BARRIER OR a POST-ZYGOTIC BARRIER and WHY?
________12. It is known that males will often neck with other males in order to exhibit dominance. Theoretically, the
characteristic should be more exaggerated in one of the sexes; it must be used to indicate dominance; have no direct survival
benefits; help the organism gain survival costs; positive allometry should be observed. For instance, evolution history shows
increased neck length not correlated to increases in other parts of the body, which is what would be expected in foraging
selection.
_______13. This isolation impedes the meeting of potential pairs occurs in two fish species of the
family Gasterosteidae (sticklebacks). One species lives all year round in fresh water, mainly in small streams. The other species
lives in the sea during winter, but in spring and summer individuals migrate to river estuaries to reproduce. The members of
the two populations are reproductively isolated due to their adaptations to distinct salt concentrations. Explain if it is a PREZYGOTIC BARRIER OR a POST-ZYGOTIC BARRIER and WHY?
_______ 14. Lives in same habitat but cannot breed because there is a reproductive barrier. Genetic isolation without a
geographical barrier.
_______ 15. A genetic isolation with a geographical barrier; a new group is isolated from its parent population.