L3 - Sexual Selection Flashcards
What are the two sub-categories of sexual selection?
Pre-copulatory (before mating)
Post-copulatory (after mating)
What are the two types of pre-copulatory sexual selection?
Intra-sexual selection = same sex competition
Inter-sexual selection = mate choice
What are the two types of post-copulatory sexual selection?
Sperm competition = same sex competition
Cryptic female choice = mate choice
Why do males compete for females?
Their fitness increases the number of females they mate with
Why are females so selective with the males they mate with?
Their fitness is increased with the quality of their mate
How do the production costs of gametes differ between sexes?
Much higher for females - eggs much larger than sperm (can be 20% of body mass)
What leads to competition between males, and females choosing between males?
Because males gain more than females by multiple matings
What does sexual selection and natural selection interact to produce?
Trait distributions
How does intra-sexual and inter-sexual selection show in behaviour?
Intra-sexual = out compete rivals
Inter- sexual = be more attractive
What percentage of male California elephant seals father 85% of pups?
4%
What is sexual weaponry?
Weaponry that is used to fight off competition for mates, usually males fighting/ competing for females
Give two examples of the cost of sexual weaponry:
(Emlen 2000) - developmental cost in beetles, trade off between horn size and eye size
(Johnston et al,. 2013) - shorter lifespan in Soay sheep, larger horns increase reproductive success but reduce survival
Give two examples of pre-copulatory sexual selection
Courtship displays
Elaborate architecture
Give two examples of pre-copulatory sexual selection which have a direct benefit
Oral gifts - nutrients to consume e.g Great Grey Shrike (aka Butcher bird)
Seminal gifts - protein rich ejaculate to nourish female e.g bush crickets
What is the “sexy son hypothesis”?
Females choose males based on producing offspring with the best chance of reproducing
What is Zahavi’s Handicap principle?
Females choose males because he was able to survive with a costly sexual trait (assumes sexual signals are costly – ‘honest signals’)
What is runaway sexual selection?
When the choosing sex (usually female) prefer a version of a trait, despite the fitness cost of that version. The trait originally gave a survival advantage but now it is too extreme e.g peacock tails
What experiment did Malte Andersson (1982, 1992) carry out which showed runaway sexual selection?
Experimented on long-tailed widow birds, artificially manipulated tail length by cutting and sticking feather
Results showed males with elongated tails had more active nests
What is sperm competition?
Competition between sperm from rival males to fertilise a female’s egg(s), extended form of male-male competition
What are ways in which males reduce their risk of sperm competition?
- Mate guarding
- Removing rival male sperm during mating (Odonata have complex male genitalia which can remove rival sperm)
- Increase investment in sperm production
For which animal, do testes make up the largest percentage of body volume? And what is that percentage?
Northern giant mouse lemur, 5.5%
For which animal, do testes make up the largest percentage of body weight? And what is that percentage?
Tuberous bush cricket, 14%
In primates, what does the size of the testes correlate with?
Whether it is a multi-male breeding system or not: if multi-male the testes are bigger
Similar effect seen in butterflies
What increases in males when presented with a new female?
Sperm investment/ count
How can females still be in control of which male fertilises her eggs after mating?
In some species, females are able to use physical or chemical mechanisms to control a male’s success in inseminating her eggs
E.g in red jungle fowl, females eject more sperm after mating with subordinate males
