Study Guide 7 Question 8 Flashcards
describe what type of reproductive barrier might be present and
whether this barrier is pre-zygotic or post-zygotic
a) Two species of frogs belonging to the same genus occasionally mate, but the embryos stop developing after a day and then die.
Reduced hybrid viability (post zygotic) because the hybrids do not complete development
describe what type of reproductive barrier might be present and
whether this barrier is pre-zygotic or post-zygotic
b)Rocky Mountain juniper (Juniperus scopulorum) and one-seeded juniper (J. monosperma) have overlapping ranges. Pollen grains (which contain sperm cells) from one species are unable to germinate and make pollen tubes on female ovules (which contain egg cells) of the other species
mechanical isolation (prezygotic)
-males and females reproductive structures cannot successfully interact
-note: this is not gametic isolation, as the issue lies between the structures that produce sperm and those that produce eggs, rather than fertilization itself
describe what type of reproductive barrier might be present and
whether this barrier is pre-zygotic or post-zygotic
c)Beetle pollinators of a particular plant are attracted to its flowers’ bright orange color. The beetles not only pollinate the flowers, but they mate while inside of the flowers. A mutant
version of the plant with red flowers becomes more common with the passage of time. A particular variant of the beetle prefers the red flowers to the orange flowers. Over time, these
two beetle variants diverge from each other to such an extent that interbreeding is no longer possible.
ecological habitat isolation (prezygotic)
-different species use distinct parts of the habitat, preventing contact
-example: beetles attracted to different flower colors (orange vs red)
-note: behavioral isolation could also apply, as beetles recognize mates by flower color preference, but ecological habitat isolation is stronger since the species do not encounter each other
describe what type of reproductive barrier might be present and
whether this barrier is pre-zygotic or post-zygotic
d)Three populations of crickets look very similar, but the males have courtship songs that sound very different. Females of each population prefer the song of the males in their population.
Behavioral isolation (prezygotic) as this relates to identifying possible mates
describe what type of reproductive barrier might be present and
whether this barrier is pre-zygotic or post-zygotic
e)Many songbirds breed in North America in the spring and summer and then migrate to Central and South America in the fall. They spend the winter in these warmer areas, where they feed and prepare for the spring migration north and another breeding season. Two hypothetical species of sparrow, A and B, overwinter together in mixed flocks in Costa Rica. In spring, species A goes to the east coast of North America, and species B goes to the west coast.
Geographic habitat isolation (prezygotic) because they breed in nonoverlapping regions of the
continent
describe what type of reproductive barrier might be present and
whether this barrier is pre-zygotic or post-zygotic
f)The common edible frog of Europe is a hybrid between two species, Rana lessonae and Rana ridibunda. The hybrids were first described in 1758 and have a wide distribution, from France
across central Europe to Russia. Both male and female hybrids exist, but when they mate among themselves, they are rarely successful in producing offspring.
Hybrid breakdown (postzygotic) because the F1 hybrids themselves are viable and fertile, and
the barrier only arises in the F2 generation
describe what type of reproductive barrier might be present and
whether this barrier is pre-zygotic or post-zygotic
g)On the Bahamian island of Andros, mosquitofish populations live in various, now-isolated, freshwater ponds that were once united. Currently, some predator-rich ponds have mosquitofish that can swim in short, fast bursts; other predator-poor ponds have mosquitofish that can swim continuously for a long time. When placed together in the same body of water, the two kinds of female mosquitofish exhibit exclusively breed with males that have the same swimming phenotype as the female.
behavioral isolation(prezygotic)
-relates to mate identification among species
-example: two types of fish may be in different ponds (geographic habitat isolation) but prefer distinct mating behaviors, limiting interbreeding
-note: behavioral isolation is the stronger argument since it interbreeding even when fish occupy the same habitat
