Week Four Flashcards
What are the consequences of Anisogamy?
Two main factors drive gender differences:
- Offspring energy and care requirements (egg size, shelter, post-hatching care)
- Mating system:
- Frequency of sex
- Probability of fertilization
- Paternity uncertainty
- Sperm competition
What are the implications of anisogamy for sperm production?
Production of vast numbers of microgametes
Evolution of ways to further enhance the probability of encounter between sperm and egg
- -High motility
- -Egg tracking systems
How does the egg attract sperm?
-Why must the ‘dialect’ be unique?
Eggs emit attractants, which cause chemotaxis in sperm.
- Language of attractant/receptor and sperm may be similar in many species, but the ‘dialect’ must be unique.
- -Being fertilized by wrong species’ sperm is a potential disaster for a female.
- -Being fertilized by more than one sperm (polyspermy) generally lethal.
Which is more common?
Strongylocentrotus franciscanus, or Strongylocentrotus purpuratus?
Strongylocentrotus purpuratus.
- Purpuratus, population……….common?
What is the mechanism of sperm binding to egg?
Sperm bindin protein binds to a receptor protein on the egg.
Which heterologous cross is more likely between purpuratus and franciscanus?
While purpurata eggs are very unlikely to encounter franciscanus sperm, the reverse will be more common.
- This predicts S.f. receptors should be ‘choosier’.
- Therefore, weak binding between S.f. bindin and S.p. receptor.
What is the relationship between male fertilization and ratio of mates to competitors.
As ratio of mates to competitors increases, male fertilization success increases.
-Individual male reproductive success (RS) increases with number of available females… decreases with competition from other males.
What is the effect of male density on female fertilization success in S. purpuratus?
As the male density increases (logarithmically), the female fertilization success increases proportionally.
-Purpuratus eggs are adapted to high sperm density!
What is the effect of male density on female fertilization success in S. franciscanus?
From 0.01 - 1 Male density (#/m2) it has sigmoidal increase in fertilization success.
As the male density increases past 1 male/ m2, the female fertilization decreases heavily.
franciscanus eggs suffer from polyspermy when males are common.
Why would reproductive genes be predicted to be highly conserved in evolution?
Is this correct?
They are so directly related to fitness.
Yet….sperm-egg proteins are among the most rapidly-evolving in the entire proteome.
Are eggs changing to….
- Avoid parasites?
- Avoid polyspermy?
- Select the best sperm?
Which two forms of sexual selection did Darwin envision?
Intrasexual selection –> male-male combat for control of females
Intersexual selection –> Female choice of males based on their charms.
What was Bateman’s experiment?
What was his goal?
Combine males with different dominant markers with virgin females in mating chambers.
Measure female fertility and count all offspring, scoring each brood for the frequency of each marker.
He wanted to identify a fundamental cause of intra-masculine selection, independent of mating system and probably inherent in the mechanics of sexual reproduction.
What are Bateman’s Principles
Males have higher variance in the number of offspring produced than females do.
Males have higher variance in number of mates than females do.
There is a closer correlation between the number of mates and reproductive success in males than in females.
What are the implications of Bateman’s Principles?
for males
Males are usually the more strongly selected sex:
- -> More intrasexual competition
- -> Greater expression of secondary sexual characteristics
- -> Bigger winners, bigger losers (again, more variance)
What are the implications of Bateman’s principles?
females
For females, energy is usually the limited resource for achieving fitness.
–>Mattes/sperm rarely a barrier to reproductive success.
Females should be choosier about who they share their gametes with:
- Wasted gametes are more costly to females.
- Females usually invest more in the offspring when there is parental care.
What are the mating habits of Rough-skinned Newts?
No parental care.
- Breed in ponds in spring.
- Males stake out ponds
- Females come to ponds to breed, then leave.
~300 eggs/female
What did Jones et al. 2002 find when they experimented with Rough-skinned Newts?
They collected females during breeding season.
–> Multilocus genotyping was used to assess the paternity of eggs.
Found that ~70% of males had zero fitness.
-Fitness was correlated with the number of matings in males, but was not significant in females.
