UNIT 5 DAY 2 - Feisty Females Flashcards
When males are scarce, sexual selection can favour female adaptations —> Darwin’s 3 classes
- When adult males “more beautiful or conspicuous” than females because males compete or females choose
- When adult females “more beautiful or conspicuous” than males because females compete or males choose
- When adult males resembles adult females
Examples from Darwin’s 3 classes
- Most abundant in nature (widowbirds and sticklebacks)
- Jacanas, both genders have territories but females are more fierce and compete more
- Blue-footed boobies, both display condition to mate, both parents share responsibilities
Successful females, whose territories can encompass as many as 4 female territories
Polyandrous
When parental invest,meant increases and abundance of egg/sperm decreases
Sexual selection on opposite gender strengthened
Precopulatory sexual selection
- males compete
- male-male competition yields selection on features of male bodies (size, weapons) that allow them to win contents for access to females
- females choose
- female choice yields selection on features of male bodies (ornaments, dance, song) that appeal to female sensory bias or provide direct benefits or good genes
Postcopulatory sexual selection
- males compete
- sperm competition yields selection on features of sperm (numbers, speed, longevity) that allow them to win competition to fertilise eggs
- females choose
- cryptic female choice yields selection on features of sperm that appeal to female sensory bias or provide direct benefits or good genes
When do pre- and post- copulatory selection occur
Occurs after sperm are released
Sperm competition
Sperm injected into female reproductive tract (more than 1 sperm) —> achieve fertilisation
Cryptic female choice
Females control which sperm they allow to reach their eggs —> happens out of sight
—> eg. Insects have spermatheca that allows them to control when and which sperm are released to fertilise eggs
What traits are favoured by sperm competition
- increased sperm number
- increased sperm speed
- increased sperm longevity
Sperm number
All else being equal, the male who emits the most sperm with fertilise the most eggs
Speed
If the sperm that reaches an egg are the ones most likely to fertilise it, sperm speed might outweigh sperm number
Longevity
If sperm must endure long waits before they can reach the eggs, the sperm longevity might matter the most
Parental males
Defend nests against other males
Sneaker males
Strategy blast out sperm into nest with eggs
Bluegills
- large testes, large bodies, mimics female submission to gain access to nest
Female hierarchy
- high status means you get to breed
- low status regulates you to babysitting
Female-female competition
- compete for resources to nurture their offspring, gives natural, as well as, sexual selection, a role in shaping female-female competition
Meerkats
- dominant female and male procure all offspring
- dominant female prevents subordinate females from breeding by killing any offspring that manage to bear and by evicting the, when become old enough to threaten rule —> dominance also increased success of female offspring
Dung beetles
- horn males: fight access to females, females fight for food for their offspring
Sexual selection only favours traits related to breeding opportunity, natural selection shapes all traits that increase reproductive success
- “sex selects les rigorous, as a result isn’t death, but fewer offspring”, Darwins fault, reproductive success more important to species than survivors
Clutton-brock et al - meerkats
- live in groups of 2-30 in arid South Africa, groups have dominant females —> oldest and heaviest
Are the subordinate females able to breed?
- subordinate females are physiologically capable of breeding but they aren’t allowed too
What are the effects of the presence/a sense of unrelated males on subordinate breeding?
- many subordinate females live in groups that contain no males unrelated dap them
- these animals show lower levels of fecal oestrogen are less likely to breed than are subordinates living in groups including unrelated males
- subordinates living in groups without unrelated males commonly mate with roving males from other groups and are clearly capable of breeding although dominate females may more easily restrict their access to females
