Colautti et al. (2010) generated a model of evolutionary constraints on the abil
ID: 211943 • Letter: C
Question
Colautti et al. (2010) generated a model of evolutionary constraints on the ability of purple loosestrife to expand its range through invasions of new habitats. a) describe the constraints that the authors modeled. b) explain how these constraints are depicted in Figure 1 of the paper. Include in your response some mention of the differences in mean and variance between north and south populations in fitness and phenotype frequencies, and an explanation of the significance of the “threshold” value. c) given the results of this paper, in which latitudinal direction will invasion by purple loosestrife be most successful, and would you expect a north south invasion or a south north invasion by purple loosestrife to be more successful in the long term?
south threshold north pi: IE south north small plants, early flowering PCI large plants, late floweringExplanation / Answer
a) The authors modeled the genetic constraints pertaining to the flowering time and the size of the plant.
b) The figure depicts that an increase in the strength of selection on flowering time and size in a northern versus a southern population resulted in a correlated reduction in the mean and variance and an increase in the skew of PC1 in the northern population.The maximum fitness value (i.e. the fecundity of an individual with phenotype pc) was lower for the northern population, as a result of a trade-off between flowering time and size at maturity.
The extension of the model represents a latitudinal gradient in climate by considering a gradual change in the strength of selection on flowering time and size at maturity. This resulted in four predicted clines in PC1 with increasing latitude: (i) a decrease in the mean, (ii) a decrease in the variance, (iii) an increase in the skew, and (iv) a decrease in fecundity.
c) From the model, it can be seen that the flowering declined as the altitude increased. Thus the invasion will be more successful in the South. And a north-south invasion will be more successful in a long run.