Mating systems: current AB Final 1

Mating System

1. The number of sexual partners an individual acquires during a breeding season. 

2. The strategy used to acquire those partners.

selection of a mating system is directed toward gaining_________________

fitness within the constraints of the environmental conditions.

males usually have

Polygynous” tendencies

females usually have

Monogamous” tendencies

conditions that favor monogamy in males?

why would a male be monogomous?

• Availability / distribution of females

• Mobility of individuals

• Forced monogamy

• mate assistance

• distribution of mates

• availability of mates

male assistance hypothesis

provides parental assistance which increases offspring survival

example of male assistance hypothesis

Male seahorse incubates eggs.

Female seahorse provides a new clutch once the first one is hatched and leaves the male.

Female cannot produce more than the male can handle, so no need for her to find other males.

Male gets a constant supply of eggs, so no need for him to find other females.

mobility of male causes this

Mate Guarding Hypothesis

Male guards his mate who would otherwise use the sperm of other males to fertilize all or some of her eggs.

example of mate guarding hypothesis

Male clown shrimp will spend weeks with one female

This strategy makes sense if the female is still receptive after breeding and the operational sex ratio favors males (more sexually receptive males than females).

why does mate guarding work

• this strategy makes sense if the female is still receptive after breeding and the operational sex ratio favors males (more sexually receptive males than females).

• • if females are scattered and hard to find, it makes sense to guard a single female.

• ecological factors that dictate how females are distributed spatially have major effects on the evolution of male mating strategies

female enforced monogamy

• Female blocks the male from mating with multiple females, thus gaining his parental assistance.

• Similar to mate guarding by the male

indirect female enforced monogamy

• Female chats attack intruder females

direct female enforced monogamy ex

Female burying beetle actively keeps the male from secreting pheromones and thus attracting other females

why does the female beetle care about recruiting another female?

• the first pair lay their eggs on a dead mouse, which will provide food for larvae

• Recruitment of another female could reduce fitness of the first female via offspring competition, because that second female will want to lay her eggs on the same dead mouse.

is male monogamy common?

no its rare in mammals, but there are exceptions

• can predict that if a male exhibits paternal behavior, he leans toward monogamy  

• wants to protect offspring 

ex of male monogamy in mammals

Djungarian hamsters who help with delivery, a behavior that likely increases pup survival.

advantages of male monogamy

helping keep pups warm, protecting them from infanticide

increases pup survival

what happens if males are monogamous but females are scattered?

• If a male ventures off looking for another female, other males may come into his territory (he is not there to guard it)

• ex. is rock haunting possum 

male monogamy in mammals is related to

male paternal behavior

an overall evaluation of mammalian sp shows that 

male paternal behavior occurs in monogamous species and polygynous species

polygynous

males can have multiple mates, while females may only have one

pair bonded birds are monogamous?

• female engage in extra pair copulations so male could be caring for someone else’s offspring 

• male at the same time could be mating with other female

• bonded pair but with potential polygynous behavior in the system 

advantage of above system with pair bonded birds

• female choice 

female choice

the female is driving the system, taking precautions to limit risk against loss of the male or other factors 

extra pair copulations

mating behaviors where a paired individual in a socially monogamous relationship mates with another individual outside of their social bond

so basically with male birds….

•Males may care for some of the neighbor's offspring, but the neighbor may be doing the same. 

monogamous voles?

Polyandry: what is it and why?

female has lots of males

• Lots of males for protection of offspring and resources.

costs of polyandry

• time & energy 

• losing primary partner 

• sexually transmitted disease

benefits of polyandry

• ensures all eggs are fertilized

• social partner has lower genetic quality than other sperm donors

• increases genetic variety of sperm available to the female, increasing chances that DNA of male will be very compatible with female 

• more paternal care/resources 

• more mates=confusion abt whos baby that is=less infanticide 

ex of material benefits hypothesis

Some female bees mate with other males to gain access to nectar in that male’s territory.

why would a female copulate more frequently with the males that normally spend less time with her?

encourages male to stick around and ultimately helps with rearing the young and probably protecting local resources  

an example of polyandry 

another example of polyandry

male tactics to achieve polygyny?

• Males of different species may “defend” different things in an attempt to monopolize the females.

• Males may defend the female herself or some resource attractive to the female

• males may opt for no defensive strategy at all, and rather simply try to outrace other males to receptive females

female defense polygyny

• fighting with other males to monopolize female

  • predictable based on females being distributed in defensible clusters.

  • male may seek out a cluster of females, and defend them against rival males.

  • a male may create his own cluster of females

Resource Defense polygyny

• defending a resource that females need (food, nesting sites, etc.).

• So females may not live in clusters, so males cannot control the cluster of females.

• So a male may seek out a resource needed by the females, and defend it against rival males

• Or…..a male may create or enhance the resource.

Scramble competition polygyny

• males skip competition and outrace one another to females

  • females and resources are widely dispersed, then they are hard to defend so the strategy becomes one of persistent searching by the male

    • required good spatial memory!

    • useful when breeding is highly compressed 

ex of scramble competition polygyny

• frogs

lek polygyny

• males defend a small piece of ground at a location where females will congregate.  The males display at this location.

hotspot hypothesis

• males congregate there because it is a good spot to find females

Hotshot hypothesis

subordinate males congregate around a dominant male and thus increase their chances of breeding

Female preference hypothesis

females prefer clusters of males so they can make quick and safe decisions about mates

So more males ≠ more mating opportunities unlessss

Unless….mating chances ≠ among males.