TOPIC 13: MATING SYSTEMS Flashcards
Asexual Reproduction
Originally organisms would have reproduced using binary fission
Similar to mitotic cell division
All new individuals would have been clones of the original
Evolution could only have occurred due to mutations of the original cell line (NO GENETIC
DIVERSITY!
Major Advantage of sexual reproduction
genetic diversity within a population of a species
List some Disadvantages of sexual reproduction
1) Only half of an individuals genes are passed to the next generation
2) Growth rate is half that of asexual reproduction (takes two to make one)
3) Some unfavourable recombinations
All of these factors can serve to reduce fitness
Gender Biases in Animals typical pattern
Typical Pattern: Males do the courting and females do the choosing
Male fitness is often dependent on acquiring multiple mates
Female fitness is often dependent on access to abundant resources
Anisogamy
Gender biases are a result of unequal investment in gametes (Anisogamy)
explain anisogamy
Egg cells are much more energetically costly to produce than sperm cells
Theoretically a single man could fertilize all the eggs of all the women in the world
Males fitness increased by fertilizing multiple eggs
Females fitness increased in continued investment in costly egg
Also results in females having already invested more in gamete production to continue
to invest in parental care
Secondary Sex Characteristics
Males evolution driven by sexual selection imposed by limited female partners
Traits to enhance attractiveness
2) Traits to enhance competitive ability with other males
Traits to enhance attractiveness
hypothesized that displays advertise good genes and a healthy condition.
Further enforced through runaway selection
- males inherit genes for impressive display
-females inherit preference for display
Traits to enhance competitive ability with other males
impose dominance hierarchy
- sneaky male strategy
- mate guarding
- sperm competition
- nuptial gifts
Mating System
the number of partners that males and females have
* Can vary among and within species
* Also includes aspects of parental care
4 General Categories
- 1) Polygyny*
- 2) Polyandry
- 3) Monogamy
- 4) Promiscuity
Polygyny
a single male takes multiple female mates
Most commonly observed of the mating systems
Female Defense
Where females cluster together for predator defense or resource
patches
Resource Defense
Where resources are clumped and male will control area that is
attractive for females
Lek Polygyny
An area where a male will set up an often elaborate mating
display to attract mates (no resources involved)
) Scramble Competition
Where timing window for mating may be short, so it is a first
come first served basis
Polyandry
Rare in nature.
When something limits the brood size of the female below that of which it is capable it may
take multiple mates
Eg. Spotted sandpiper
Gender role reversal
Monogamy
a single pair bond between one male and one female
Somewhat common in some animal groups like fish and birds
When there is a high risk that female may take multiple partners in absence of mate guarding
When male offers up energetically costly support
Eg. Seahorse
Brood pouch means that male seahorse bears the burden of “pregnancy”
Promiscuity
females and males both take multiple mates
Likely the result of coevolution of other mating systems between males and females
Both sexes increase their fitness by having multiple mates
