In the wild, female Red-Winged Blackbirds (Agelaius phoeniceus) lay egg clutches that vary in size from just two eggs per clutch to seven eggs per clutch. Clutch size is a genetic trait, so a single female will lay clutches of a set size throughout her reproductive life.
Prior to a seven-year-long drought, a population ecologist surveys a breeding population of birds in a two-mile radius and determines the average number of eggs per clutch laid by females in that population to be five.
The ecologist surveys the same breeding population of birds at the end of the drought and finds the average number of eggs per clutch laid by females in that population to be two.
Three years later, during which time the area receives normal amounts of precipitation, the average clutch size in the population of breeding females has returned to five.
Which of the following best explains these observations?
In the wild, female Red-Winged Blackbirds (Agelaius phoeniceus) lay egg clutches that vary in size from just two eggs per clutch to seven eggs per clutch. Clutch size is a genetic trait, so a single female will lay clutches of a set size throughout her reproductive life.
Prior to a seven-year-long drought, a population ecologist surveys a breeding population of birds in a two-mile radius and determines the average number of eggs per clutch laid by females in that population to be five.
The ecologist surveys the same breeding population of birds at the end of the drought and finds the average number of eggs per clutch laid by females in that population to be two.
Three years later, during which time the area receives normal amounts of precipitation, the average clutch size in the population of breeding females has returned to five.
Which of the following best explains these observations?
The correct option is A Directional selection shifted to favor females who laid fewer eggs during the drought and then shifted again after the drought to favor females who laid more eggs.
Directional selection favors or increases the frequency of a particular allele over other allele. During drought conditions when food is scarce the females that laid fewer eggs were favored, on return of favorable conditions the food became abundant so now the allele for a greater clutch size was preferred So, the correct answer is 'Directional selection shifted to favor females who laid fewer eggs during the drought and then shifted again after the drought to favor females who laid more eggs'
Directional selection favors or increases the frequency of a particular allele over other allele. During drought conditions when food is scarce the females that laid fewer eggs were favored, on return of favorable conditions the food became abundant so now the allele for a greater clutch size was preferred
