All the information is provided in the attachments to answer the questions [1.1]
ID: 192613 • Letter: A
Question
All the information is provided in the attachments to answer the questions [1.1] [2.1] [3.1] [4].
Exercise 7 (created by NMS) [1] Whittall and Hodges (2007) published a paper in the journal Nature to determine what mechanisms was behind spur length evolution in columbines. As stated in the introduction to this virtual lab, the match between a flower visitor's tongue length and flower tube depth determines how effective a visitor is as a pollinator. The more compatible the match, the more beneficial the relationship is for both partners. The plant gets more pollen, and the pollinator gets more nectar. If this match is poor or if the traits of the pollinator change, populations of plants may experience rapid evolution and/or diversification in flower traits. To explain the exceptionally long nectar spur of Angraecum sesquipedale, Darwin (1862) argued that a coevolutionary race resulted in directional selection for increased length in the orchid's flower spur and its pollinator's tongue. No pollinator was known for this plant at the time, but in 1903, a moth with a 22 cm tongue, Xanthopan morgani ssp. praedicta, was found - validating Darwin's prediction. However, many scientists argue that this coevolutionary race is relative uncommon, and that floral traits evolve as plant populations adapt to novel pollinators or as they specialize on a subset of more effective pollinators To shed light on this debate, Whittall and Hodges (2007) tested two hypotheses of spur length evolution in the columbine genus, Aquilegia H1: A coevolutionary race between columbines and their pollinators led to longer spurs H2: Spurs evolved as plants adapted to a series of unrelated pollinators, each with greater tongue length Figure 1 Two contrasting hypotheses for the evolution of exceptionally long nectar spurs. Darwin's coevolutionary race model (a, b), which posits a gradual increase in both the pollinator's tongue and the plant's nectar spur, and the pollinator shift model (c, d), where spur length evolves owing to a switch to a new pollinator with a longer tongue. These models differ in whether adaptive peaks are constantly increasing (b), or whether they are relatively fixed optima based on pollinators' pre-existing tongue lengths (d). They also differ in whether spur-length evolution occurs gradually (b) or in a punctuated fashion a Darwin's coevolutionary race Individuals with the Selection altemates longest tongues are between plant and Plants with the longest spurs are selected for selected for because they obtain the greatest food pollinator, causing a because their reproductive continual and gradual organs optimally contact the Spur and tongue length elongation of the pollinators' body, providing pollinator's tongue the greatest reproduction and the flower's spur c Pollinator shift In part of the species range, an unrelated longer-tongued pollinator (blue) becomes the Rapid evolution of longer spurs owing to selection for improved pollen transfer In the rest of the species' range, the original shorter- tongued pollinator remains the predominant visitor If pollinators cannot reach nectar, then they will not visit flowers and thus reversals to short spurs are less likely Spur length [1.1] After examining Figure 1, explain what the predictions are for each hypothesisExplanation / Answer
1.1 Hypothesis 1 predicts that there is a coevolutionary relationship between flower`s spur and pollinator`s tongue length. selection alternates between the spur and tongue length. Individuals with longest tongue were selected over individuals with shorter tongue as they obtained greater nectar rewards. Simultaneously there is an increase in flowers spur length and flowers with longest spur were selected as there reproductive organs contact optimally with the pollinator`s body leads to increased reproduction. This hypothesis suggests that there is a direct relationship between Pollinator`s tongue length and flower`s spur. It suggested that spur length evolution occured gradually.
Hypothesis 2 suggests that spur`s length evolved as plants adapted to pollinators with increased tongue length. If longer tongue pollinators becomes predominant visitor of the flower then there is a rapid evolution of longer spurs to improve pollination of these flowers.It suggests that spur length evolved in a punctuated manner.
2.1 This graph shows that floral traits including spur length adapted to different pollinators ( bumble bee, humming bird, Hawkmoth) who visited the flower. Species that are pollinated by different pollinators clustered together in PCA analysis as they possesd similar floral traits.
3.1 This data supports Hypothesis 2 as the transition of pollinators from bumble bee to Humming bird and then to Hawk led to the evolution of long spurs in the flowers. this observation matches with hypothesis 2 which suggests that Flower`s spur length evolved as plants adapted to unrelated pollinators.
4.1 By combining the data presented by Whittal & Hodges, it is suggestive that columbine spur length evolved as a result of transition in the pollinator who visited the flower.