Chapter 24 practice problems Flashcards
Which species concept(s) could you apply to both asexual and sexual species? Which would be more useful for identifying species in the field? Explain.
All species concepts except the biological species concept can be applied to both asexual and sexual species becausenthey define species on other characteristics besides reproduction. The most useful/easiest species concept would be the morphological species concept, which only factors in morphological characteristics
Suppose two bird species live in a forest and are not known to interbreed. One species feeds and mates in the treetops and the other on the ground. But in captivity, the birds can interbreed and
produce viable, fertile offspring. What type of reproductive barrier most likely keeps these species
separate in nature? Explain
The reproductive barrier is habitat isolation, as the two species prefer drastically different habitats and most likely will not cross paths in the wild. (prezygotic)
Allopatric and sympatric speciation, and which is more common?
Allopatric is when there is a geographical barrier that separates two populations, and two species are thus formed given the absence of gene flow
Sympatric is when a new species forms without geographic isolation, and this is likely due to some other barrier.
Since gene flow is greatly reduced in allopatric speciation events and less likely to be impeded in sympatric speciation events, allopatric is the more common speciation event.
Describe two mechanisms that can decrease gene flow in sympatric populations, thereby making sympatric speciation more likely to occur
Changes in chromosome number (esp in plants) can block gene flow and thus create a new organism
Sexual selection (Victoria cichlids - fish choosing different color males)
habitat differentiation (apple maggot fly)
Is allopatric speciation more likely to occur on an island close to a mainland or a more isolated
island of the same size? Explain your prediction.
It’s going to occur on a more isolated island, given the larger geographical barrier between the two land masses thus making it harder for gene flow to continue between them (due to migration).
Describe how an error during meiosis could lead to polyploidy.
Homologs fail to separate in during anaphase 1, and some gametes end up with more or less than the usual number of chromosomes. When parents mate, the extra set of chromosomes is passed to offspring.
What are hybrid zones, and why can they be viewed as “natural laboratories” in which to study speciation?
Hybrid zones are where members of different species meet and mate, producing hybrid offspring. They serve as natural laboratories as they allow us to directly observe factors that cause (or fail to cause) reproductive isolation.
Consider two species that diverged while geographically separated but resumed contact before reproductive isolation was complete. Predict the outcome over time if the two species mated
indiscriminately and (a) hybrid offspring survived and reproduced more poorly than offspring from intraspecific matings or (b) hybrid offspring survived and reproduced as well as offspring from
intraspecific matings.
A) Natural selection would select for prezygotic barriers that would eventually eradicate the hybrid population thus amplifying speciation
B) It would create large amounts of hybrid population, and parent species would continue to breed, causing genetic pools to mix and reversing speciation
Speciation can occur rapidly between diverging populations, yet the time between speciation events is often more than a million years. Explain this apparent contradiction.
The time between speciation events includes 1) the length of time when newly formed species begin to reproductively separate themselves from one another and 2) the time it takes for speciation to be completed once this divergence begins. Although speciation can occur rapidly once populations diverge from on another, it make take millions of years for the divergence to begin
Summarize evidence that the yup locus acts as a prezygotic barrier to reproduction in two species of monkey flowers. Do these results demonstrate that the yup locus alone controls the barrier to
reproduction between these species? Explain.
Investigators transferred alleles at the yup locus (which influences flower color) from each parent species to the other. M. lewisii plants with an M. cardinalis yup allele received many more visits from hummingbirds than usual; hummingbirds usually pollinate M. cardinalis but avoid M. lewisii. Similarly, M. cardinalis with an M. lewisii yup allele received many more visits from bumblebees than usual; bumblebees usually pollinate M. lewisii but avoid M. cardinalis. Thus, alleles at the yup locus can influence pollinator choice, which in these species provides the primary barrier to interspecific mating. Nevertheless, the experiment does not prove that the yup locus alone controls barriers to reproduction between M. lewisii and M. cardinalis; other genes might enhance the effect of the yup locus (by modifying flower color) or cause entirely different barriers to reproductive (for example, gametic isolation or a post-zygotic barrier).
