Transcript Sexual Selection and Reproductive Behaviour

Mating Systems
Mating System
Species typical pattern of mate-finding, reproduction
and parenting of offspring
Kinds of mating systems
Number of
females
Number of
males
Monogamy
Polygyny
Polygynandry
Polyandry
Polygamous
Kinds of mating systems
Monogamous Mating Systems
-a mating system in which one male and one female for and
mate with only each other during a given breeding
season
To put it another way
-neither sex is able to monopolize more than
one member of the opposite sex
Kinds of mating systems
Monogamous Mating Systems
First question - why should a male be monogamous?
If the particular niche dictates that a male will do better
reproductively staying with one mate - will do so.
-mates are scarce
-resources are scarce or non-defendable
Kinds of mating systems
Monogamous Mating Systems
1. Mate assistance hypothesis
-male stays with one female because it is to his
advantage to help raise offspring
Hippocampus whitei
-male carries offspring
-brood pouch contains 1 clutch
-no point to new matings
Kinds of mating systems
Monogamous Mating Systems
2. Mate guarding hypothesis
-male spends time with mate to ensure fertilization
Assumes
1. Females are scarce (highly male-biased OSR)
2. Females will mate multiply
Hymenocera elegans
-male stays with female
for weeks
-female receptive every
3 weeks
Kinds of mating systems
Monogamous Mating Systems
3. Female-enforced monogamy
-female blocks polygamous moves by mate
Icteria virens (yellow-breasted chat)
- aggression by females
More
aggressive
0
Less
aggressive
Toward
males
Toward
females
Toward
wrens
Kinds of mating systems
Polygamous Mating Systems
1. Polygyny - males mate with several females
a. Female Defense Polygyny
-females live in permanent groups that males defend
Male
Kinds of mating systems
Polygamous Mating Systems
1. Polygyny - male mate with several females
b. Resource Defence Polygyny
- males defend resource females need
Lamprologus -males gather and defend oviposition sites - mollusc shells
Kinds of mating systems
Polygamous Mating Systems
1. Polygyny - male mate with several females
c. Lek Polygyny
- males compete for high rank
Kinds of mating systems
Polygamous Mating Systems
1. Polygyny - male mate with several females
c. Lek Polygyny
- males compete for high rank
Upper limit on lek effectiveness
Mating
rate
0
Lek size
10
Kinds of mating systems
Polygamous Mating Systems
1. Polygyny - male mate with several females
d. Scramble competition
-females are available for a short period
-males mate with as many as possible
Kinds of mating systems
Polygamous Mating Systems
Polygamous
1. Polygyny
a. Female Defence Polygyny
b. Resource Defence Polygyny
c. Lek Polygyny
d. Scramble Competition
Male controls access
to resources
Male can’t control
access to resources
Kinds of mating systems
Polygamous Mating Systems
2. Polyandry - one female mates with several males
Jacana
Male
territories
Female
territory
Kinds of mating systems
Polygamous Mating Systems
2. Polyandry - one female mates with several males
Kinds of Polyandry
1. Sperm replenishment
-females mate multiply to get extra sperm
e.g. Drosophila
1 mate
Multiple mates
# of eggs
Time
Kinds of mating systems
Polygamous Mating Systems
2. Polyandry - one female mates with several males
Kinds of Polyandry
1. Sperm replenishment
2. Prostitution - females mate with males to get access to resources
3. Resource Defense - females control access to resources
4. Lek Polyandry - females compete for dominance
- some primate troops
Kinds of mating systems
Polygamous Mating Systems
2. Polyandry - one female mates with several males
Benefits of Polyandry
1.
Sperm replenishment
- add to a depleted supply of sperm
- avoid cost of storage
2. Material benefits
3. Genetic benefits
-replace ‘inferior’ sperm
- increase genetic variance in offspring
4. Convenience
- avoid cost of fending off copulatory attempts
Kinds of mating systems
Are mating systems ‘fixed’?
- do all members of a species conform to one mating system
How monogamous is monogamy?
Indigo bunting
Within pair
Extra-pair
0
12
Days before egglaying
Kinds of mating systems
Are mating systems ‘fixed’?
- do all members of a species conform to one mating system
How monogamous is monogamy?
Indigo bunting
Rate of extra pair copulation - 27 - 76%
Kinds of mating systems
Are mating systems ‘fixed’?
- do all members of a species conform to one mating system
How monogamous is monogamy?
Humans
U.S.-10 - 18%
Yanomama - 9%
!Kung - 2 - 3%
Summary
Mating Systems
Monogamous
1. Mate assistance hypothesis
2. Mate guarding hypothesis
3. Female-enforced monogamy
Polygamous
1. Polygyny
a. Female Defence Polygyny
b. Resource Defence Polygyny
c. Lek Polygyny
d. Scramble Competition
2. Polyandry
a. Sperm replenishment
b. Prostitution
c. Resource Defence
d. Lek