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Mating systems
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Diverse types of mating systems in nature
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Lecture 11- Mating systemsHave we already come across ideas about mating systems?
Migration
Communication and signalling
Territoriality and aggression- dominant male
Cooperation- altruism,
Mating systems are hugely diverse…
Categorise systems
How often? – semelparous (once) or iteroparous (multiple events)
Terminal investment or trade-offs?
Semelparous- salmon
This alters costs and benefits of a particular mating
How much should an individual give
One mating event- give all resources
Multiple- trade off resources in current mating opportunities for future mating opportunities
Might depend on:
Sex ratio- st peters fish- dictate who deserts from nest
Environment- might not be good environment- reproduce now- not enough food for
offspring- save resources for future investment
When? – year round -> seasonal
When can they mate?
Crickets
Gryllus campestris- northerly areas- central Spain and northwards- seasonal reproductive
opportunity= once a year in May/June
Sister species
Gryllus bimaculatus- southern Europe- mate all year round
Small windows of mating opportunity
Pandas
1-3 days a year
Produce twins but look after 1 offspring
How many partners? – monogamy, polygyny, polyandry, promiscuous/ polygamous
How many partners in 1 mating opportunity?
Polygyny- many females
Polyandry- many males
Birds
, Oyster catchers- monogamous- maintain year to year
Dunnocks- polygamous birds
Not always the case
We think we see monogamy when its actually social monogamy
Male and female will pair up and care for offspring
Doesn't necessarily mean they mated only with each other
Make distinction between social monogamy and genetic monogamy
How do the gametes meet? Broadcast spawning to spermatophores to intromittent organs…
Coral broadcast spawinig- else gametes into water column
Newts- male leaves sperm packet- spermatophore- female picks up sperm
Male could have intermittent organ- deliver directly into female
Argentinean lake duke- coiled penis
How do offspring develop? - viviparous (inside mother), oviparous (outside of mother)
Costs and benefits of these strategies?
• Costly to have offspring inside her
• Feeding herself and providing nutrition for offspring
• Gets bigger- gets slower- more prone to predation
• Produce eggs
• Develop outside
• Less costly in terms of nutrition she has to provide
• Will offspring survive to hatching?
Parental care? One or both parents, related helpers, and none
• Who care for offspring?
• Burying beetles- both male and female care for larvae
• Reproductive pair with a group of helpers- meerkats
• Crickets- lay eggs, no parental care
Need to think about this in the context of sexual selection
• Same principles as natural selection, but the selection
pressure comes from the opportunity to reproduce
(often imposed on one sex by the other)
• How males and females do different roles
• Based on idea of anisogamy
• Sexual reproduction- 2 gametes to meet each other
• Most effective search strategy:
• 1 gamete that is large
• 1 gamete that’s smaller and searches for larger gamete
and there are lots of them
• This system is selected for
• Midsize gametes fail to find each other- selection acts
against middle sizes
, • Pushes gametes in direction of very small or very large
• Anisogamy leads to sexual dimorphisms and sex roles …females are a limiting resource
• Male spruce small sperm
• Females produce larger eggs
• Because female produce larger eggs per gamete- this is more costly
• Females are a limiting resource
• They are often able to be choosy
• Males often need to try to get access to resources- both attracts mates and defend resources
• Is reproduction less costly for males? Or are they spending the resources differently?
• Easy to think mating isn't costly for male due to small gametes
• Males spend resources differently
• When mating they provide not only sperm but also ejaculate
If females are the choosy sex, then there should be more variation in male reproductive
output…
One sex that can be choosy
If this is the case
There is more variation in reproductive output in the other sex that is being chosen
Some female will reproduce to constricted number- less variation
Some males more often chosen- high reproductive success
Other males not chosen at all- no reproductive output
Cricket study in wild
Amongst females there is less variation than amongst males
One males produced 17 offspring into next generation
Why be choosy?
Direct benefits (food, care, territory)
E.g. North American bullfrogs, males
compete to hold better territories (those
that are warmer or suffer less
predation), and these are preferred by
females.
Genetic benefits
• “sexy sons” (Fisher’s runaway hypothesis), requires covariation between female choice and
male trait
• Females identify male trait they're chose about
• Choose males that show trait in extreme form
• Their sons will be those males- more chosen in next generation
• Runaway of female preferences and male trait exaggeration
• Can be anything
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