2 - Sex and the sex ratio Flashcards
What is sexual reproduction?
The coming together of a male (smaller) and female (bigger) gamete
How do limits on reproduction differ between male and female fruit flys?
- Males can quickly produce sperm, and therefore produce more offspring with more mates. Limited by access to females.
- Female reproductive rate slowed down because of production of a larger gamete. More mates don’t necessarily increase offspring number (until she produces more gametes)
What are the main reproductive limits for males and females, and the strategies they use to overcome these?
Males: Access to females/competing with males
Females: Access to resources/choosig high quality mates
List four mechanisms of sex determination for offspring/brood.
- Producing different levels of X or Y chromosome sperm
- Diferential implantation or abortion
- Environmental sex determination (eg. heat)
- Differential neglect (eg. don’t feed certain sex)
What is the Coolidge effect? When does this effect not work in populations? When does it work best?
The ability to copulate with many different mates.
Doesn’t work in monogamous mating or when there are lots of males
Works best when there are few males:females
What is the payoff to producing males over females?
None! Should produce both equally, even though males can impregnate many mates.
Son production versus daughter production. Males favoured when there are few females and females favoured when there are few males (evolutionary stable strategy), assuming the cost of producing males and females is equal (which is not usually true, leading to a shift, such that if females are bigger (eg. fish) than there will be more males to females, which will balance out because the large females can hold more eggs and produce more offspring)
Why might you might not want to invest in the two sexes equally?
- Local mate competition (producing lots of suns leads to competition)
- Local resource competition (if one sex consumes too much resources in one territory)
- Local resource enhancement (resources are enhanced by one sex or another)
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Are sons or females favoured (reproductive value) in:
- Poor environments
- Good environments
(for most species)
Poor: Daughters favoured
Good: Sons favoured
This is the basic idea behind conditional sex allocation. This can also be switched around.
What are two factors that conditional sex allocation can be based on?
- Attractiveness (resulting from environment quality?)
- Maternal condition
Fish can change their sex through their lifetime. What influences their ‘decision?’
- Reproductive value changes throughout the lifetime (as they get older, they get bigger)
- If males compete intensely for females (only get a female if you’re really big) than they will be favoured late in life when much bigger
- If there is not much competition, females are favoured later in life because their larger size can bear more offspring
Example of conditional sex allocation, but in a direct manner.
The sex ratio is not usually the stable 1:1 that might be expected. Why?
Because the investment into either sex might differ.
Stable investment ration: equal investment in males and females
What are three biased sex allocation interaction types (among relatives)?
- Local mate competition
- Local resource competition
- Local resource enhancement
What are three biased sex allocations conditions (conditional sex allocations)
- Better environment quality produces more males, worse quality produces more females
- Attractiveness (eg. tarsus length can be correlated with proportion of sons)
- Maternal condition (eg. better body condition can produce more males)
Attractiveness and maternal condition can be consequences of good quality environment
How is sex change in fish dependent on age or size?
Age: More females to more males (from young to old)
Size: More males to more females (from small to big)
