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Behavioural Ecology

Mating patterns

QuestionAnswer
Evolution of Anisogamy 1. Competitive for fusions 2. Zygote provisioning
Anisogamy is males and females Primary gamete traits can explain many differences between males and females = Numerous, cheap sperm versus few expensive eggs
Potential reproductive rates Bateman principle - number of mates vs mean number of offspring reproduced
BATEMAN PRINCIPLE IN A PROMISCUOUS SPECIES TRIBOLIUM CASTANEUM = MORE SELECTION ON MALES TO MAXIMISE QUANTITY = MORE SELECTION ON FEMALES TO MAXIMISE QUALITY
The male:female OR sperm/egg phenomenon also dictates reproductive success variance = the (in)consistencies in reproductive success within either sex An individual male elephant seal can fertilise all cows on the beach In reality 75% are sired by only 5% of the males
Anisogamy + Parental care/investment = DICTATES THE POTENTIAL REPRODUCTIVE RATE BY EITHER SEX
Anisogamy 1. Differences in reproductive potential 2. Differences in reproductive success variance 3. Differences in parental investment
Anisogamy ALL three differences between males and females influence the evolution of animal mating patterns
Gamete traits underpin male:female general reproductive differences MALE: Invest less in zygote/offspring fitness (gamete/zygote/embryo/care) Compete for reproductive success High variance in reproductive success High reproductive potential
Gamete traits underpin male:female general reproductive differences FEMALE: Invest heavily in zygote/offspring fitness (gamete/zygote/embryo/care) Tend to be the ‘choosy’ sex Low variance in reproductive success Lower reproductive potential
A simple framework for understanding mating systems Males: cheap gametes, no care Females: expensive gametes, much care OPERATIONAL SEX RATIO = ratio of sexually receptive males to sexually receptive females
In general Males: High potential Highly variable Low paternal investment & confidence
In general Females: Low potential Low variability High maternal investment & confidence - shaped by selection from ecology into a MATING PATTERN
Mating patterns Mating patterns are descriptors of behaviour related to the acquisition of mates for reproduction Classifications are useful for understanding the evolution of mating patterns BUT Mating patterns are complex and can be plastic
Monogamy One male mates with one female Associated with biparental care Social vs genetic monogamy 90% of bird species ie. emperor penguins
Polygyny One male mates with several females Usually without paternal care Usually overt male:male competition Sometimes sneak/satellite males Often associated with male-biased sexual size dimorphism ie. gorillas
Leks Leks are organised displays of male secondary sexual traits for females to choose from – usually biased success to few males FEMALES GAIN NOTHING BUT SPERM=GENES
Lek system dynamics Females choose males signalling ‘good genes’ Male reproductive success is extremely skewed
Polyandry One female mates with several males With or without paternal care Generates sperm competition Common and can occur within social monogamy ie. Baboons
Polygamy/promiscuity Many males mate with many females No pair bonds formed Uniparental/parental care uncommon Common in non-bird/mammal taxa ie. tribolium
Alternative mating tactics Male mate choice
Males - intense mating competition, low mate choice Females - weak mating competition, high mate choice
ECOLOGY: DISTRIBUTION OF MATES IN TIME AND SPACE INFLUENCES THE EVOLVED MATING PATTERN TIME: High asynchrony of mates favours polygamy; high synchrony favours monogamy SPACE: Spatial and temporal pattern of resource dispersion -- food, breeding sites, mates
Distribution of fertile window influences mating system evolution Seasonal/simultaneous breeders encourage monogamy? Sequential/continuous breeders allow polyandry?
Spatial ecology = distribution = male potential for mate monopoly Widely spaced females = constrained to monogamy Aggregated females = potential for polygyny?
Created by: rose.coo
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