Sexual Selection Flashcards
What are the 2 kinds of sexual selection?
Intrasexual selection - mating success determined by within-sex interations
- often seen in male-male combat
Intersexual selection - mating success determined by between-sex actions
- female choice of males or vice versa
What are the main types of mating systems?
Monogamy - one male forms pair bond with one female
Polygamy 3 types, all form exclusive relationships
- Polygyny - 1 male mates with > 1 female
- polyandry - one female mates with > 1 male
- polygynandry - several males mate with several females
Promiscuity - no pair bond, males and females meet briefly to copulate
What are the mating success rates of indvs. in the three types of mating systems?
Monogamy - 1 male = 1 mate
Moderate Polygyny - some males = 0 mate some = 1mate some = 2 mate
Strong Polygyny - Most males = 0 mate 1 male = 8 mate
Describe monogamy
Single male breeds with single female
Mostly rare in animal groups but common in birds with >90% showing this behaviour
Typical monogamous birds: male and female remain apart during non-breeding season and pair up shortly before breeding
Cooperate in nest preparation, incubation and care of offspring
Describe harem based polygyny
Also referred to as female defense polygyny
Groups of females, their offspring and generally one male
Southern elephant seals - single dominant male
- central females more closely associated with dominant males
- peripheral females less so
- juvenile males leave the herd - solitary of bachelor herds
What are the benefits and costs of polygyny?
Benefits
- dominant male has access to several females
- females gain protection
- can reduce energy required for vigilance
- social behaviours like grooming and cooperation
Costs
- energetically costly for males and females
- males engage in battles from invaders
- reduced reproductivity success
- offspring frequently killed
What is lekking polygyny?
Males aggregate and establish dominance relationships among themselves
Females then choose males on basis of competitive ability
Result - few males end up with most matings
Leks commonly formed before or during the mating season
Combination of inter and intra selection
Why lek?
Aggregation at hotspots - males aggregate around ares where female frequent
Aggregation at hotshots - cluster around more attractive individuals
Reduced risk of predation
Less time seeking out males
Name another type of polygyny in which it is not the individual that is sought after but something else
Territorial defence polygyny - territory is the prize
Describe polyandry and its benefits
One female mates with numerous males
Often accompanied by reversal of sexual roles where males take on most parental duties
Females are often larger
Exclusive polyandry is rare occurring in ~1% spp.
Benefits - females gain fertilisation assurance
- sperm competition can result in better genes
- potential for multiple paternity
Costs
- increased disease and predation risk
- Energy costs due to multiple matings
- harm due to sexual harassment
Why are males fundamentally promiscuous and females selctive?
Bateman’s principle suggests that typically females have a larger investment in the producing of offspring due to the difference in size of the gametes
Sperm are cheaper than eggsss
single male can easily fertilise all female eggs but single female will not produce more offspring by mating with >1 male
Males limited only by the number of females he can mate with whereas females are limited by the amount of eggs they can produce
What are the three main types of intrasexual selection?
Male-male combat
Sperm competition
Infanticide
Give an example of male-male combat
Red deer stags - males grow antlers each year - females herded into harem by single male
3 stages
- 1st males challenge each other and challenger can be intimidated by roar
- 2nd challenger persists and both walk in parallels of assessment
- 3rd fight with interlocked antlers, 25% of permanent injury
Antlers are made of bone and are a huge cost but are advantageous in sexual selection but disadvantageous in natural selection
What three methods do males use to improve chances of sperm fertilisation?
Mate guarding - males stay close and ward off opponents
- may attach to female before and after copulation until eggs have been fertilised
Female damage - adapted penis may rake out stored sperm (dragonflies) or female tract may be sealed via a plug formed from ejaculate (bats and rodents) or spines on
penis may damage female reproductive tract
Amount of sperm - increased (crickets) decreased (fruit fly)
What are the 2 principles associated with intersexual selection?
Sexy son hypothesis
The handicap principle
