These graphs show variation in lifetime reproductive success for male and female
ID: 41886 • Letter: T
Question
These graphs show variation in lifetime reproductive success for male and female elephant seals (note difference in x-axis scale). The most successful male had >90 offspring; the most successful female had 10 and many others did nearly as well.
Male elephant seals are 4 times larger than females.
What is the most likely mechanism underlying evolution of this sexual dimorphism? Explain with reference to different modes of sexual selection.
These seals lived but had no offspring 100 75 75 Males Females These seals died before 50 freq 50 adulthood 25 25 0 01- 11- 21- 31- 41- 51- 61 71 81 9 0 1 2 3 4 5 6 7 8 9 10 10 20 30 40 50 60 70 80 90 100 Number of offspring Number of offsprii Number of offspringExplanation / Answer
The variation in sexual dimorphism might have arised due to various modes of sexual selection like competition, choice of female, competition of sperm, etc.
The type and degree of sexual dimorphism, related features like relative size of testis, pattern of scars on the body, and many more provide evidence of extent of sexual selection in the seals and responsible mechanisms of sexual selection.
Sexual dimorphism in size, attacking body parts (like teeth, big head) helps in competition for mates and this is could be important for male mating success. Also it is not necassary that due to smaller sexual size there will be less male-male competition for mates. But then, other characters come into play, like making sounds, how quick or active they are, or how they look.
At times female choice is also critical.
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