You are the steward for our local land trust, the Fort Collins Area Land Trust (

Question

You are the steward for our local land trust, the Fort Collins Area Land Trust (also known as FALT). Land trusts acquire and manage land for various purposes including conservation, which is the principal goal of FALT. Among its other acquisitions, FALT has purchased various small tracts of land harboring populations of a rare plant, the Rocky Mountain trumpet. Trumpets occur only on rock outcrops with shallow soils. One of your principal assignments as the FALT steward is to study and manage populations of the trumpet. The plant is well known for its showy, trumpet-like flowers. Its fleshy fruits are eaten by birds, which disperse seeds. The plant has perfect flowers, but it is an obligate outcrosser, pollinated by butterflies and hummingbirds. Plants have red, white, or pink flowers, and a single gene controls flower color. There are two alleles of this gene, R and r. Plants homozygous for R produce red flowers, plants homozygous for r have white flowers, and heterozygous plants have pink flowers. Most populations apparently contain both alleles, because red, pink, and white flowers are commonly seen.

1.Among the tracts of rocky land you're managing is one that lacked trumpets until recently. The tract is isolated from others supporting subpopulations of the trumpet, but FALT acquired this land because of its potential to support a trumpet subpopulation. Last summer you indeed discovered a small trumpet subpopulation on this tract (three plants), probably established from seed transported by birds. All the plants flowered and all had white flowers. Because most subpopulations of this species have plants with all three flower colors, why does this one produce only white flowers?

2. There is a fairly large subpopulation of trumpets on a rock outcrop near the one where you've just discovered the new subpopulation of white-flowered plants (question 1). The large subpopulation was recently inventoried and found to have 36% red-flowered plants, 48% pink-flowered plants, and 16% white-flowered plants. What are the frequencies of the R and r alleles in this large subpopulation and is the subpopulation in Hardy-Weinberg equilibrium?

3.Because the large subpopulation (question 2) of trumpets is the only one located near the new white-flowered subpopulation (question 1), you suspect that seed from the large subpopulation probably established the new subpopulation. Given what you know about the large subpopulation, what is the probability that three seeds taken at random from this subpopulation would have the white genotype?

4.Although most of the long-established trumpet subpopulations on FALT holdings contain both the R and r alleles in some mixture, there are two subpopulations of moderate size that are each fixed for one of the two alleles. Thus one subpopulation currently has only red-flowered plants and the other has only white-flowered plants. Between them is a rocky area owned by FALT that lost its trumpet subpopulation several years ago because of illegal collecting. You decide to re-establish this subpopulation, and you do so by transplanting 50 red-flowered plants from one of the adjacent subpopulations and 50 white-flowered plants from the other, thus ensuring genetic diversity. Although this new subpopulation now has a 50:50 mix of the R and r alleles, it is not in Hardy-Weinberg equilibrium. How do you know this?

5.Over the years, you've had experience with several very small, isolated subpopulations of trumpets. Typically, such populations have declined in size, despite having excellent growing conditions. The plants have performed poorly and seed set has often been far less than that experienced by larger populations. What is your assessment of the probable cause of this poor performance?

6.A new invasive, yellow knapweed has been found to hybridize with the trumpet. The knapweed also thrives in the same rocky outcroppings as the trumpet. Less than 100 knapweed plants have been found in Larimer, Weld and Boulder Counties. What are the immediate implications for the genetics of the trumpet? If knapweed spreads quickly what would be a concern for the genetics and what measures do you think might address any problems?

Explanation / Answer

1. The three plants having white flowers should have the (recessive genotype)rr. Moreover the tract is isolated from other supporting subpopulation of the trumpet hence the chances of pollination occurred should be nil so there is no new genotypes produced. Any occurrence of mutation will also be not there. Therefore the flowers remain white coloured

2. Percentage of homozygous recessive individuals =16. Therefore q2 =0.16, then q=0.4

Frequency of r allele=0.4

According to Hardy-Weinberg equilibrium p + q=1

Therefore p=1-0.4=0.6

Frequency of R allele =0.6

4. This not following Hardy-Weinberg equilibrium because here migration of individuals has occurred out of the population and also selection has occurred

5. As the particular plant is an obligate crosser lack of pollination might be one of the reason for poor seed set and hence it multiplication is affected

6. As the knapweed plants hybridize with the trumpet plants, the genetic purity of the trumpet genotypes will be affected. Knapweed genes will be incorporated into the trumpet plants and it might develop characters that belong to knapweed plants. Removal of the Knapweed plants is the only option to preserve the genetic purity of trumpets

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