Polyandry
• Usually characterized by
sex-role reversals
• Factors favoring
polyandry include
– Male-biased sex ratio
– Precocial offspring
– Superabundant food
jacana
Wilson’s
phalarope Polyandry
spotted
sandpiper
x
Clutch manipulations
reveal incubation
constrained at four eggs
Selects for production
of two clutches Monogamy
Given sex differences in gamete
production, why monogamy? Monogamy
Duration may be variable
Rare in mammals (<5%)
common in birds (>90%) Monogamy
Occurs in species where females
are widely distributed, rarely encountered
mantis shrimp Mate assistance
Important when young are
energetically demanding
cotton-top tamarins
Important where habitat is
harsh or offspring survival is low
emperor penguins Mate assistance
Female + male
Female only
Mating Systems and Parental Investment Part 3
of 7
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