Polygyny
Males: Lower PI
and
Greater Variance Reproductive Success
Male-Male Competition
Female Choice
Polygyny
White-bearded Manakin
(Manacus manacus)
Male-dominance polygyny
Lek
Males Display, Interact Aggressively
Females Choose Mates
White-bearded Manakin Male
Polygyny
Lekking Systems
High Variance in Male Mating Success
Females Prefer “Central” Males
Lekking Common: Birds, Mammals
Found in Some Insects
Polygyny
Lekking Systems
Male Dominance
Obtain Central Position
Direct/Intrasexual Competition
Female Choice: Indirect Male Competition
White-bearded Manakin
Shorey, L. 2002. Behavioral Ecology and
Sociobiology 52:451-457.
Northern Trinidad
White-bearded Manakin
Concentrated Lek
Each Male Displays on “Court”
Clears Court of Leaves
Emergent Saplings: Acrobatics
Males Fight: Dominance, Position
Males Display: Attract Females
White-bearded Manakin
Correlates Male Mating Success
Size (Tarsus Length, +)
Condition (Extra Mass, +)
Distance from Lek Center (-)
Large Males at Lek Center ?
White-bearded Manakin
White-bearded Manakin
Males Compete for Central Positions
Larger Males More Likely
Dominant, More Likely Central
Lek Centrality: Cue for Female Choice
Polyandry
Female PI < Male PI
Dichromatism: Female Brighter
Females Larger, More Aggressive
Polyandry
Polyandry Relatively Rare
“Test” of General Concepts
Jacana spinosa
Jacana: Polyandry
Some Females: Large Territories,
Contain 2 – 10 Male Nesting Territories
Females Provide Eggs;
Males Care for Brood
Jacana spinosa
Polyandry
Females More Aggressive, Slightly Larger
Than Males
Younger Females: Excluded from Breeding
New Female Territory Holder:
Infanticide, Free Males for New Clutch
Polyandry
PI Pattern, Intrasexual Selection
Follows Conceptual Construct
Female Variance in Reproductive Success
> Male Variance
Polyandry
Jacana: Many Clutches Lost to Predation
Abundant, Year-Round Food
Females Free of Caring for Young
Replace Lost Clutch Quickly
Males Take Brood Care
Monogamy
Common in Birds, Rare Otherwise
Obligate Monogamy: Offspring Very Low
Survival in Absence of Biparenal Care
Facultative Monogamy: Females Avoid
Already-Mated Males
Social Monogamy: Mated Pairs,
Promiscuity
Monogamy
Obligate Monogamy: Offspring Very Low
Survival in Absence of Biparenal Care
Common in Raptors
Found in Rodents, Canids
Foraging Demands of Reproduction,
Protection of Young
Monogamy
Social Monogamy:
Snapping Shrimp (Alpheus angulatus)
Females Brood Eggs Until Larvae Disperse
No Parental Care by Males
Male PI Lower (?)
How Does Social Monogamy Evolve?
Monogamy: Snapping Shrimp
Territorial Mutualism: Both Sexes Benefit
by Sharing a Territory
Females Invest In Burrow Construction;
Both Occupy
Males Aggressively Defend Territory;
Both Sexes Avoid Eviction
Monogamy: Snapping Shrimp
Mate-Guarding by Males
Females Molt, Release Eggs, Brood
Cycle Repeated
Male May Stay with Female Through
Multiple Episodes of Reproduction
Monogamy: Snapping Shrimp
Economics Monogamous Mate-Guarding
Population Density: Low Density, Search
Time for Mate Extended, Stay & Guard
Sex Ratio: Male-Biased, Stay & Guard;
Female-Biased, Desert?
Monogamy: Snapping Shrimp
Mathews, L.M. 2002. Behavioral Ecology
and Sociobiology 51:426-432.
Field: Population Density
Fort Pierce, FL
Lab: Sex Ratio
Monogamy: Snapping Shrimp
Proportion of Males Paired with (Guarding)
Females Independent of Shrimp
Population Density
Social Monogamy Unresponsive to
Population Density
Monogamy: Snapping Shrimp
Sex Ratios Lab: 1, 0.2
Equal Frequency Sexes: Males Stayed
with Female
1 Male/5 Females: Males More Likely to
Leave Recently Mated Female;
Reduced Tendency for Mongamy
