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2nd half Lecture 5

Course Code
Darryl Gwynne

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Lecture 5
Sexual selection: What is it?
Why are Males Masculine, Females Feminine and Occasionally Vice-Versa?
• Operational Sex Ratio
• Relative Parental Investment
In sea horses, females provide t he eggs and the males care + protect the eggs.
Sexual selection on female katydids Body size:
Heavyweights preferred by males
Sexual selection for large males
The most prolific father of all time is believed to be the last Sharifian Emperor of Morocco,
Mulai Ismail (1646-1727). In 1703 he had at least 342 daughters and 525 sons and by 1721
he was reputed to have 700 male descendents. “
said to be the father of 888 children through a harem of 500 women.
"The greatest number of children produced by a mother in an independently attested case is 69
by the first wife of Fyodor Vassilet (1816-72) a peasant of the Moscow Jur isdiction, Russia,
who in 27 confinements, gave birth to 16 pairs of twins, 7 sets of triplets and 4 sets of
quadruplets. Most of the children attained their majority. Mme. Vassilet became so renowned
that she was presented at the court of Czar Alexander II" [1975 edition Guiness Book of Records]
theor y that Ganges Kan spread his Y chromosome to 10-12% of Asian amles.
Sexual Selection
• Variation in male reproductive s uccess is greater than in females
Typical species with sexual selection gets all females to mate but not all males mate!
Sexual selection has to be related to a trait and has to involve mating!
Sexual selection: Bateman curves
More Number of mates => Number of offspring for males ONLY!
More than 1 mate for a female does not increase her number of offspring. More than 1 mate can
decrease her number of offspr ing (STD risk, sexually transmitted disease). But her number of
offspring can increase if she gets a nutritional food packet!
Why do females mate multiply?
When there is no material benefit from the male multiple mating can enhance offspring survival
Male marsupial mice that ejaculate more competitive sperm, sire more viable offspring (3-fold
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