Mating systems can be defined by the number of copulatory partners per individual per breeding season.
They explain patterns of aggregation of males and females in the environment.
Types of Mating Systems
Monogamy: Individuals mate with one partner.
Polygamy: Individuals mate with multiple partners.
Polygyny: 1 male + multiple females.
Polyandry: 1 female + multiple males.
Monogamy
1 female + 1 male.
May occur when offspring require both parents, indicating a high degree of parental care.
Seen in > 90% of birds and < 10% of mammals.
Male assistance hypothesis: males help provision young (examples: canids, marmosets).
Mate guarding hypothesis: females are solitary, and males can defend only 1 female (examples: dik-dik, many rodents).
Very rare in herps, fish, and insects (example: carrion beetles).
Polygyny
> 1 female per male.
> 90% of mammals.
Males defend females when they can.
Males disperse further, presumably to find a female group.
Some birds:
Males defend food or nesting sites (examples: oropendolas, grouse).
Types of Polygyny
Female defense polygyny
Occurs when females are grouped, or when females have smaller territories than males.
Example: Sandperch
Common in mammals – elk, gorillas.
Some birds – Red-winged Blackbirds.
Some arthropods – marine amphipods.
Resource defense polygyny
Occurs when males defend a resource needed by females.
The resource is exchanged for matings (resource = direct benefit to females).
Examples:
Food – Streamertail hummingbird
Nest sites – Weavers (bird family: Ploceidae)
Scramble competition polygyny
Occurs when females are widely dispersed, and the breeding season is short (males can’t monopolize females).
Examples:
13-lined ground squirrel – explosive breeders (large numbers become reproductive simultaneously in a SHORT breeding season).
Many amphibians.
Horseshoe crabs.
Males with the greatest reproductive success are those that move around the most.
Males of the thirteen-lined ground squirrel cover much more ground during the 2-week mating period when receptive females can be encountered.
Males of this species do not attempt to defend mating territories.
Lek polygyny
Occurs when males defend a small breeding territory (no resources), which only includes a display area (lek).
Purest form of sexual selection – all male contributes to offspring are his genes (excellent system to test female choice).
Examples: (a few in several diverse groups)
Some birds (bowerbirds, manakins).
Some mammals (hammer-headed bat, some antelope).
Some insects (some butterflies).
Hypotheses for lek formation:
Hotspot hypothesis – males congregate where females are likely to travel and compete for the best sites (example: many insects that lek).
Hotshot hypothesis – males congregate around a few very attractive males in an attempt to gain matings by association/proximity (example: sage grouse).
Female preference hypothesis – males congregate because females are attracted to male groups (example: kob antelope).
Polyandry
> 1 male per female.
Occurs where resources are patchy and briefly available, or predation is high.
Sequential polyandry – female clutch size is limited (examples: phalaropes).
Simultaneous polyandry – females defend males from other females, clutch size is less restrictive (example: Jacana).
Rare in birds.
Very rare in mammals.
Common in fish, insects.
Promiscuity
Multiple males and females.
Some birds
Some mammals
Some fish
Common in insects
Genetically, many birds are promiscuous!
~ 75% of bird species have extra-pair offspring - Brouwer and Griffith 2019.
Conflicts Between the Sexes
Conflicts between the sexes may lead to multiple mating systems in the same species!
Example: Dunnock (Prunella modularis)
Group Discussion Questions
For each of the following groups of organisms, what is the MOST common strategy?
a) Birds
b) Mammals
c) Fish
In a mammal, what kind of strategy would you predict would be favored if:
a) Females are not solitary and males can guard multiple mates?
b) Resources are scarce and require multiple males to defend them?
c) A high parental investment is required per offspring?