25. Mating systems: Polygyny

Quiz: in which mating system should

the strength of sexual selection be

greatest?

A. Monogamy

B. Monogamy with EPFs

C. Leks

C. Leks

bateman gradient when you have diff in mating success between males and female, in males positive relationship nbetween number of mates and number of offspring ptroduced

In terms of sexual selection, in most species…

• Males do best to __________ the number of matings.

Females are a limiting resource for males.

maximize

In terms of sexual selection, in most species…

• Males do best to maximize the number of matings.

Females are a limiting resource for males.

• Females do best to maximize number of successful

eggs/pregnancies. Males are ___ a limiting resource for

females.

not

Polygyny -one male, many females

• Very common in animal kingdom (97% of mammals)

• Categories of polygyny:

– Territorial defense

– Female defense

– Resource defense

– Scramble competition

– Explosive breeding assemblages

– Leks

Territorial defense polygyny

Territory

An area that is defended for exclusive use of the

defender against rivals.

Territories may be defended by males

or females and for multiple purposes.

What is being defended?

Sometimes territories are defended simply for resources:

food, basking sites, dens or hiding places, etc.

This may still be important for sexual selection, e.g., if females “_______” male territories based on the

resources within the territory

In many species, males set up territories around females (or vice versa) – in this case it becomes similar

to harem defense polygyny

choose

Female defense polygyny- male combat

Reproductive success is more variable in males than fem ales

Many stags ______ reproduce, some may sire up to 24 offspring!

never

Female defense polygyny

• Males ____ for access to females.

• Females are ________ or can be herded - easy to

monopolize/guard.

• At an extreme, males have ‘harems’ (elephant seals).

fight, clustered

Female defense polygyny

Elephant seals (Mirounga sp.) - breeding females cluster together on beaches

- allows males to defend a ‘_____’ of many females at once

harem

Female defense polygyny

But some females ‘_____’ on the

beachmaster!

7/cheating-beachmaster

Maybe we need a less male-centric view of

the natural world.

cheat

Female defense polygyny

The greater spear-nosed bat

(Phyllostomus hastatus). A large male

(bottom right) guards a roosting cluster

of smaller _______. A successful male

may sire as many as 50 offspring with

his ‘harem’ of females in a year.

females

Female defense polygyny

(A) Male Montezuma oropendolas attempt to monopolize females in (B) small colonies of nesting females. (C) As colony size increases, mating attempts are often disrupted by rivals. (D) As a result of these disruptions, frequency of copulations per hour at the colony site decreases.

Can only defend so many females at a time… and they might want other ______.

mates

Resource-defense polygyny

• Males have resource-rich territories to attract females.

• Best (most fit) males have ___ resources/territories.

• Cichlid fish: eggs laid in snail shells.

• Topi (African antelope): females gather on green patches

of grassland (lek).

• Female resources can be clumped, and males can guard

those.

best

_______________ polygyny

The African cichlid fish Lamprologus callipterus. (A) A territorial male bringing a shell to his midden. The more shells there are in a male’s midden, the more nest sites are available for females to use. (B) The tail of one of the territorial male’s very small mates can be seen in a close-up of the shell (lower left) that serves as her nest.

Resource-defense

Resource-defense polygyny

Resource defense polygyny in an Australian antlered fly. Males compete

for possession of egg-laying ____ that can be found only on certain

species of recently fallen trees.

sites

When females cannot be herded, or guarded in one place, males have to find them, or attract them from far away.

• Scramble competition polygyny

OR

• Explosive breeding assemblages

OR

• Lek polygyny

Scramble competition polygyny

• Males _______ to outrace rivals to find receptive females.

compete

An explosive breeding assemblage

An explosive breeding assemblage. A male wood frog grasps a female (upper left) that he has found before rival males, two of which are ____ the mating pair. Numerous fertilized egg masses float in the water around the frogs.

near

Lek Polygyny

whjere males gather together to display for females

Lek Polygyny

• Males display in groups on small territories, offer no resources or parental care, only “_____ ____” and a selection of males to choose from.

• Feeding ecology of females makes it hard to monopolize them.

Why the group display?

Who is the best male?

good genes

______- males aggregate in particular areas called leks, display for females

Lekking

Lekking - males aggregate in particular areas called leks, display for females

Combination of male competition… Males may fight for position in center of lek

…and female choice:

Females choose a mate…often dominant

male or male in the ______

center

Lek Polygyny

Mating success at topi leks. Each male topi

in a central position at his lek mates with

more females per capita than do males

forced to peripheral sites. The blue bars

represent the averages for the _____ leks

shown.

three

Leks in wire-tailed manakins

Each lek is made up of multiple males who dance together to attract females.

Leks in wire-tailed manakins- skewed

reproductive success

Within each lek, social

connectivity (the number of dance

partners a male has) is the best

predictor of number of offspring

sired. In other words, females

choose the most _________ males.

popular

The Lek Paradox

Since females usually mate with one male, why do other males bother to come to the lek at all?

With one male getting most matings, why is there still variance in traits?

Practice is most obviousous

What conditions favor the evolution of leks?

hot spots' - males gather at sites where females are ____ likely

to congregate

Females’ preferred spot

Reduced predation

Greater resources (undefendable)

Amplify sexually selected characteristics

'hot shots’ – display near dominant males. females prefer to

choose mates from aggregations of males (i.e., group displays

facilitate comparisons).

more

Hotspots or Hotshots?

Researchers divided a black grouse lek into 100-square-meter sectors and

recorded the total number of copulations in each sector over a 5-year period

from 1987 to 1991. The irregular polygons show the location of the top

territory for each of the 5 years. The shifts in the preferred territory suggest

that male attractiveness, rather than the territory itself, plays the key role in

reproductive success in this species, as required by the _______ hypothesis

hotshot

Hotspots or Hotshots?A)

The location of greater sage-grouse

(Centrocercus urophasianus) leks (numbered red

circles) in relation to sagebrush, meadows,

forests, and a lake. (B) The distribution of nesting

females in relation to the leks where males

gather to display. The darker the shading, the

more females present. So looks like ________ are

key.

hotspots

Do females aggregate where males are?

Do females aggregate where males are?

The relationship between mating females and calling males of the

barking treefrog. The _______ female barking treefrogs mating at a pond

on a given night, the more males found chorusing there. However, the

relationship stems not from the ability of large numbers of males to

attract more females with their calls but from the fact that both sexes

respond similarly to a set of environmental variables, including

temperature and rainfall.

more

Polygyny:

Some males in a population regularly have

two or more mates

So…

Why should a female pair with an already

mated male when there are still unmated

males available?

Best of a bad situation?

Best you can do for your

offspring?

Good genes?

The sons of successful males are more likely to be

successful themselves.

A father’s mating success can be transmitted to his ___.

In experiment 1, two male field crickets were given an

opportunity to compete for a female; one male (S) mated

successfully, while the other male (U) was unsuccessful.

When the sons of male S were placed in competition for a

female with the sons of male U (which had been given a

female to mate with after failing to win the initial

competition), the sons of S were about twice as likely to

mate with the female as were the sons of U. In experiment

2, a male that had won a mating competition was later

allocated a female at random for breeding, as was a male

that had lost the competition. The sons of the two males

were then placed in an arena with a female, and as

before, the sons of S were much more likely to mate with

the female than were the sons of U.

sons