Bio 501 Evolution exam I

There are 14 marmot species in the world, of which 6 species live in North America, and 4 species live in Canada. The Vancouver Island marmot (Marmota vancouverensis) is the only species listed as "endangered". Marmots live in small colonies, generally consisting of an adult male, 1 adult female, some sub-adults ("teenagers"), and pups ("young-of-the-year") with a 1:1 sex ratio in the population. Marmots live in underground burrows. These can be quite elaborate, including sleeping chambers and multiple entrances. Vancouver Island marmots hibernate for about seven months each year, from late September to early May. Adults mate underground in the spring, and produce an average litter of three pups that first emerge in early July. Most marmots don't breed until they reach 4 years old, and thereafter usually breed only every second year. Vancouver Island marmots can easily live to be 10 or more years old. Unfortunately, few animals today live past 3-6 years of age, and this reduced survival is why the population is declining. Vancouver Island marmots are very social creatures. They communicate by physical contact and by whistling. Their most frequent call is a high-pitched whistle, which warns colony members of danger. Hence one local nickname, " whistle pig ".

It's impossible to provide a one-sentence answer to the question of why Vancouver Island marmots are endangered. Certainly the immediate problem is clear: there just aren't enough marmots left to go around! In fact, the population collapsed from over 300 animals during the mid-1980s to fewer than 100 today (including some now in captivity).

 

It now appears likely that forestry contributed to the recent downfall of Marmota vancouverensis . One effect of clearcut logging was to create new habitat that encouraged dispersing "teenagers" to stop in nearby "easy" (fresh clearcuts resemble the natural sub-alpine meadows). By doing so these individuals didn't get to more far-flung places, where they might have provided new mate-choices for residents. Scientists would describe this as "altering the landscape connectivity" for marmots. This wouldn't be a bad thing if marmots were as successful in clearcuts. But for a variety of reasons they're not (they apparently die more often during hibernation and/or are killed more often by predators). Scientists would decribe this as creating poor quality habitats that function as a population "sink".

1. 
   What are the expected Hardy-Weinberg genotype frequencies for the Vancouver Island Marmot in the next generation at locus 1?
   

2. 
   Produce a graph showing the census population size, the demographic based estimate of N_e, an estimate based on the change in heterozygosity (assume all loci are in Hardy-Weinberg Equilibrium) and the change in allele frequencies, and the equilibrium heterozygosity estimate (assume that the 1988 population represents the original stable frequencies). Do your estimates differ based on the different methods? Why? What does this tell you?
   

3. 
   What is the inbreeding coefficient for the Vancouver Island marmot? Given this, what is the expected Hardy-Weinberg genotype frequencies for the Vancouver Island marmot?
   

4. 
   If you look at the map on page 1, you will see that is one current center of distribution (pink circles) and a second core area that is now inactive (red squares). Based on the microsatellite data, how isolated were these two populations and how much dispersal occurred between them? Support your answer.
   

5. 
   Is this population undergoing evolution? If so, which force is likely to be the most powerful? Support you answer.
   

6. 
   The Vancouver Island marmot feed mostly on seeds and grasses which they detect using their sense of smell. Assuming the Vancouver Island marmot population has two alleles (p = 0.44) in the population that influence the ability of the animal to pick up scents, with the respective selective values of s = 0.6 and t = 0.3 and mutation rates of µ_pq = 0.00002 and _qp = 0.00008, what will be the frequency of q in 100 generations? Is this value different than that expected at equilibrium if mutations were not occurring? Support your answer. Are either of these answers different from the equilibrium frequency of q if mutation were the only evolutionary force?
   

7. 
   Describe an experiment you would conduct to determine if the above trait really is under the influence of selection.
   

8. 
   What is the average time to loss, fixation, and persistence for the allele 2 in the Vancouver Island marmot population at locus 4 based on the current data? Assuming there the 4 alleles remain in the population at that locus and the population size stays stable at 32 animals, what is the probability that a new allele would drift to fixation? Are these numbers the same? Describe why or why not.
   

9. A recessive trait exists in the population where marmots have a more acidic cecum, reducing the animal’s ability to support the bacteria needed for digesting cellulose. This severely limits their ability to obtain the energy needed for reproduction and reduces their average reproductive success to 1.

If the individual completely forgoes its own reproduction and contributes all of its reproductive effort to helping a sibling, the sibling will have on average an additional 1.8 offspring compared to wombats without helpers. Should the homozygous recessive animal help its sibling? Support your answer.

DATA TABLES

Table 1: Population size of the Vancouver Island Marmot.