W9L3 maiting system Flashcards
Why do we have mating system
- It is all about maximizing the survivorship of offspring
- If the young require care, and a singly parent cannot provide for the brood/clutch then might select for monogamy or cooperative breeding
Ecology of sexual selection
- Males compete with one another for access to females
- Like competition for scarce resources, male reproduction is limited by the spatial and temporal availability of receptive females
- The intensity of sexual selection depends on the rarity of receptive females in relation to the abundance of competing males
- Sexual selection favours male attributes that permit their bearers to find and monopolize their mates
- Ecological constraints on male monopolization attempts leads to a species-specific pattern of male-female association, called a ʻmating systemʼ
What determines the spatial and temporal distribution of receptive females
- Abiotic factors: weather, latitude, seasonality
- Habitat and food availability
- Oviposition sites
- Species life history
- Genetic quality
- Other males and females
Which gender control repoduction
Key decisions mainly controlled by females:
* Egg investment: what material and how much
* Mate choice: which males will donate sperm
* Fertilization: which sperm to use for each egg
* Offspring investment: how much maintenance and care to each embryo and offspring
Male in reproduction control
- Resources transferred to females: may influence egg investment, mate choice, or fertilization
- Elaborate courtship: may influence mate choice and fertilization
- Sexual coercion: may overcome female preferences
- Infanticide: may overcome female decisions about offspring investment
Sex differences in fitness variance for the evolution of mating systems
- Male variance in fitness is often > females
- Directly affected by the distribution of receptive females in space and time
What influence the Classification of mating systems
- Based on number of mating partners and the number of reproductive events
- Influences the variance in mating success
- Impacts on the opportunity for sexual selection (Imates ) = variance in fitness of each sex/mean fitness for each sex
Calculation for opportunity for sexual selection
Important thing to remember for opportunity for sexual selection
We can measure the intensity of sexual selection from the spatial distribution of females
* The spatial distribution of females is only one component of the sex difference in the opportunity for sexual selection
* Other important factors are: sex ratio and temporal distribution
Effect of sex ratio
- Influence the number of receptive females on a patch
- Hence directly influence the spatial distribution of females
- Stronger sexual selection when males are abundant
Two components of variance in mating success exists when female are clumped in time
- The variance in mating success within the class of males that actually mate by defending females
- The variance in mating success among the mating and non-mating males
The effect of opportunity for sexual success when clump in time
Iteroparity
- Reproduce >once in successive years or breeding seasons
- Variation in number of clutches and number of offspring per clutch
Monogamy
- Male and female pair mate only with one another during a single breeding season
- When both sexes are needed for successful reproduction
- Could also evolve as a paternity assurance for males = mate guarding
- Males often help in raising young
Polyandry, polygyny and promiscuity
- Polyandry = females mate with >1 male during a breeding season
- Polygyny = males mate with > 1 female during a breeding season
- Promiscuity = both males and females mate with many partners during a breeding season
The effect of monandry on Imates
- When a female mates once and produces only one clutch of offspring, she awards her entire reproductive output to a single male
The effect of polyandry on Imates
When a female mates more than once, she partitions her clutch into several sub-clutches, equal in number to the number of sires
Overall effects of polyandry on Imates
- Each mating male sires only a fraction of the offspring of each mate he secures
- The variance in mate numbers among males Is reduced
The effect of iterparity on Imates
When a female produces more than one clutch, the variance in offspring numbers can be partitioned into within- and among-female components
* Multiple reproductive episodes by females erode I
* As clutch number increases, I becomes a smaller fraction of the total variance in offspring number
Protandry as a male strategy
- Related to temporal distribution of females
- Males emerge before females
- Maximize no. of mating with virgin females
- Increased fertilization returns
Leks courtship
- Leks are courtship arenas where males display
- Often involve intense male-male competition leading to a dominance hierarchy
- Dominance reflects male fitness and assessed by females
Effect of predation; examples from guppies
- Predation varies among streams
- High predation males less colourful, court less and females less choosy
- Female mate copying reduce the cost of choice?
Cooperative breeding and parental care
> 2 individuals care for the brood
* Variation in reproductive skew
* Habitat saturation?
* Increase survival of offspring?
* Low mortality and small clutch size
* Constant environments
Sex role reversal; bushcricket example
- Males provide a lot of nutrients
- female feed on Pollen which availability varies
- Females in large nutritional need
- Male donations >female investment
- Result in sex role reversal
Hermaphrodites
The condition of having both male and female reproductive structures
* Simultaneous hermaphrodites
* Sequential hermaphrodites; males first = protandry female first = protogyny
Evolution of hermaphroditism
- Low population density –hard to find a mate
- Sequential – the sex where max returns for small/large size
Alternative mating strategies
- Success is directly dependent on the strategy played by competitor
Example: male polymorphism in
Paracereis sculpa
a-, b-, g-male morphs
* males control resources
* b- and a- males prefer to invade large harems
* large a- males can defend against other
a- males
* b-males are female mimics
* g-males are tiny and hide among females
Alternative male tactics in lizards
Males have three mating strategies:
1. Territory holders, large, aggressive - several females (Orange)
2. Sneakers, mimic females, enter orange territories (Yellow)
3. Defenders, detect sneakers, defend small territories with one female (Blue)
Alternative male tactics in scorpion flies
Three male strategies
-equals fitness frequency dependent equilibrium
-cyclical dynamic
-not equal fitness
Consequences of alternative mating strategies
- When the number of mating males increases, the mean number of mating per male, the variance in male mating success, and the opportunity for sexual selection all must decrease
- Thus, alternative mating strategies erode the sex difference in the opportunity for sexual selection
