Suppose you find a new triploid life form that reproduces sexually by combining the haploid gametes of three different sexes
One of the sexes is female with large and "expensive" egg cells; the other two sexes are two forms of males that each produce minute and "cheap" sperm. Using Maynard Smith's reasoning, what would be the cost of sex in this system (when the proportion of asexually producing females is low)? Fill in the table below using the following data:
• n = number of asexually producing females in the population at time t
• Assume that at time t, both types of males and the sexual females occur in equal proportions: Nm1 = Nm2 = Nf = N
• In generation t, let k be the number of offspring produced by a female (k is the same for asexual and sexual females)
• Assume that all offspring survive
Adults in t genera-tion Offspring Adults in t + 1 generation
Asexually repro-ducing females
Sexually repro-ducing males Type 1
Sexually repro-ducing males Type 2
Sexually repro-ducing females
What is the proportion of asexual females in the population at t?
A. _____________________________________________________________________
What is the proportion of asexual females in the population at t + 1?
B. _____________________________________________________________________
How many fold is the cost of sexual reproduction in this system?
C. ________
What will be an ideal response?
ANS:
Adults in t genera-tion Offspring Adults in t + 1 generation
Asexually repro-ducing females n kn kn
Sexually repro-ducing males Type 1 N kN/3 kN/3
Sexually repro-ducing males Type 2 N kN/3 kN/3
Sexually repro-ducing females N kN/3 kN/3
A: n/(3N + n)
B: kn/(kN + kn) = n/(N + n)
C: 3X
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