From an original population \(P\) of a butterfly species, two experimental populations \(X\) and \(Y\) were established. In \(X\), males and females were maintained in standard conditions, and females were allowed to mate and lay eggs. Only eggs from females laying small clutches (i.e., \(S\) eggs or fewer) were allowed to hatch and the rest were not utilized. In \(Y\), males and females were maintained in standard conditions and females were allowed to mate and lay eggs. From each female, \(S\) eggs were randomly selected and allowed to hatch, and the rest were not utilized. After 20 generations of these experimental conditions, relative to the original population \(P\), and assuming that clutch size is under genetic control, we expect clutch size to be ______________________in \(X\) and ___________________ in \(Y\).
The question asks to predict the change in clutch size for two experimental butterfly populations, \(X\) and \(Y\), relative to the original population \(P\), after 20 generations. Clutch size is assumed to be under genetic control, and different selection methods are applied.
Clutch Size in Population X
Population \(X\) employs truncation selection. Only eggs from females laying small clutches (i.e., \( \le S \) eggs) are allowed to hatch. This selection directly favors the genetic traits associated with smaller clutch sizes.
Over 20 generations, this consistent pressure will lead to an increase in the frequency of genes promoting smaller clutches. Consequently, the average clutch size in population \(X\) is expected to be reduced relative to the original population \(P\).
Clutch Size in Population Y
Population \(Y\) uses a different method: \(S\) eggs are randomly selected from each female. This limits the number of offspring per female but does not specifically target the genetic basis of clutch size for reduction.
For example, a female genetically prone to large clutches still contributes offspring if \(S\) eggs are selected from her clutch. This random selection of a fixed number of eggs does not apply consistent directional selection pressure against genes for larger clutches, unlike in population \(X\).
Therefore, the genetic variation influencing clutch size is less likely to be significantly altered in a directional manner, and the average clutch size in population \(Y\) is expected to remain relatively same as the original population \(P\).
Expected Clutch Size Comparison
Summarizing the effects:
- Population \(X\): Clutch size is expected to be reduced.
- Population \(Y\): Clutch size is expected to be same.
Thus, clutch size is expected to be reduced in \(X\) and same in \(Y\).
Important Questions from Natural selection
- Which one or more of the following is/are NOT essential for evolution by natural selection to take place in a population?
- Two bacterial variants are growing together in the same flask. At any relative frequency of the two variants, the population growth rate of the rarer variant is higher. The above is an example of ________.
There are two species, X and Y, with abundances $x$ and $y$, respectively. Species X has growth rate $\alpha$, and species Y has growth rate $\beta$. Assume that the sum of the species abundances is constant over time, i.e., $x + y = 1$. Let $x$ and $y$ follow the rate equations:
$$\frac{dx}{dt} = \alpha x - \varphi x,$$
$$\frac{dy}{dt} = \beta y - \varphi y,$$ where $\varphi$ is the average species fitness.
Which one of the following options correctly represents the expression for $\varphi$?The figure illustrates the soil zinc tolerance of the grass species Anthoxanthum along a transect from inside a mine to the middle of a pasture outside the mine.
Which one or more of the following processes explain(s) the observed pattern of zinc tolerance in this grass species?- In which of the following four plots, showing reproductive fitness versus a trait, is the strength of selection MAXIMUM?
