A note on mating systems in animals (monogamy and polygamy).

1. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
pg. 1
Mating Systems
A mating system is a way in which a group is structured in relation to sexual behavior, i.e.
in animals, the term describes how males and females mate – number of mates, etc.
There are two mating systems:
 Monogamy: in this case, an animal has only one mate.
 Polygamy: in this case, an animal has more than one mates (it includes polygyny,
polyandry, and polygynandry).
MONOGAMY:
Monogamy is a type of mating system in which an animal has only one mate during their
lifetime or only one mate at any one time. Monogamy is a rare phenomenon in animals.
There are three different types of monogamy:
 Sexual monogamy is the practice of having sex only with one mate at a time.
 Social monogamy is when animals form pairs to mate and raise offspring but still have
"extra-pair copulations".
 Genetic monogamy is used when DNA tests can confirm that a female's offspring are
from only one father.
An estimated 90 percent of all birds are socially monogamous, living, and raising young
together, but many frequently have sex with other partners. One famous experiment
found that female blackbirds paired with sterilized males were still laying eggs that
hatched.
A few animals stay with one mate for life, for example, the mouse-like prairie vole. A male
vole will prefer to mate exclusively with the first female that he mates with. A mated male
vole will even actually attack other females.

2. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
pg. 2
Another example is the black vulture: when extra-pair copulation (other than the one
mate) takes place nearby, vultures will attack that individual. Staying together provides
their babies with biparental care, since both parents incubate eggs, each taking a 24-hour
shift, and for eight months the babies get fed by both parents.
POLYGAMY:
Polygamy is a mating system in which one individual mates with more than one individual
of the opposite sex. It is of three types:
(1) Polygyny:
In polygyny, a single male mates with multiple females. It is the most common mating
system in the animal kingdom. In polygynous systems, the males fight for dominance over
a group of females, and whichever male is the biggest and strongest gets to mate with all
the females. Lions and elephant seals use this type of mating system.
Costs of Polygyny for Males:
 In polygynous systems, there is less genetic diversity because one male fathers all of
the offspring.
 It increases the chance of inbreeding and the passing on of genetic disorders.
 It is difficult for males to handle many females at once.
Costs of Polygyny for Females: Females sometimes encounter infanticide, which is when
a breeding male is overthrown and a new breeding male becomes dominant and kills all
of their current offspring, as he has not fathered them. Because the females no longer
have offspring to nurse, they will go into estrous sooner, which allows the new breeding
male to mate with the females earlier.

3. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
pg. 3
Advantages of Polygyny for Males:
 The largest advantage for males in a polygynous mating system is the increased
fitness and reproductive success of the lone male because he will father all the
offspring.
 The male also passes on his genes to more individuals.
Advantages of Polygyny for Females:
 Some females willingly choose polygyny to gain access to the best resources
available. In these cases, the benefits from superior resource access must outweigh
the opportunity cost of giving up monogamous parental care by a male.
 They also can get support from the same group of other females when in danger, like
a female lion.
 It is harder for females to find a partner better than their mate in polygyny as compared
to monogamy, unless he is beaten by another male (then that male is considered more
fit).
Female Choice: Female choice, the act in which a female chooses her mate based on
the attractiveness of his qualities, is very common in polygynous systems. In these cases,
females will choose males based on secondary sexual characteristics, which may indicate
access to better and more resources.
(2) Polyandry:
In polyandry, a single female mates with multiple males. It is much rarer as compared to
polygyny. Polyandry has direct benefits for females allowing fertilization assurance,
provision of resources, and parental care for their offspring. House mice (Mus musculus)
have shown indirect, genetic benefits, where females have increased offspring survival

4. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
pg. 4
through multiple mating, showing that practicing polyandry mating results in an increase
in offspring viability (survivability).
(3) Polygynandry:
In polygynandry, multiple males mate with multiple females, it is a combination of
polyandry and polygyny.