L13. Mechanism of Diversification: Sexual selection and co-evolution

Question 1

Maladapted traits

Answer 1

• traits that would seemingly decreased fitness
• usually related to sexual selection directly impacting the reproduction of individuals

Question 2

Primary sexual characteristics

Answer 2

difference in the biological sexes directly related to reproduction

Question 3

Secondary sexual characteristics

Answer 3

• traits which are used in sexual selection, but are not required for sexual reproduction
• ex. horns, pretty feathers
• can be for direct competition, or attractiveness

Question 4

Sexual dimorphism

Answer 4

difference in appearance between males and females of the same species

Question 5

Intrasexual selection

Answer 5

• direct competition between two members of the same sex
• more common in polygynous species (one male, many females) (lions?)
• typically seen as male to male competition for a female having limited to no choice in mate selection
• males typically don’t help care for the offspring
• common patterns: larger males, males have sexual ornaments used to fight other males (combat armour)(ex. antlers), males similar colour to females (they don’t need to win over females they just need to fight off other males)

Question 6

Epigamic (intersexual) selection

Answer 6

• males trying to be chosen by the female
• selective pressure form the member of one sex having complete choice over mate of the opposite sex
• common sexual dimorphism patterns: males that don’t help raise offspring are colourful and have extreme ornamentation and the females are often larger, males that help raise the offspring are the same colour and size

Question 7

Why are there difference in preferences between males and females?

Answer 7

• they invest different levels of resources into propagating their genes

males:
- sperm has low input, high output
- reproductive success comes from mating with as many females as possible
- they have many mates so they can afford to select a suboptimal mate

females:
- eggs have high energy investment and a fixed number
- pregnancy is energy intensive
- reproductive success comes from breeding with the best male (helps ensure offspring are as fit as possible)
- costly to choose poor mate

Question 8

Bateman’s Principle

Answer 8

“The sex which invest the most in producing offspring will become a limiting resource over which the other sex completes”
- can be the male in some cases

Question 9

Is there ever male competition in epigamic selection

Answer 9

yes through any system where mate choice exists it is considered primarily epigamic

Question 10

Fischerian Runaway Selection Hypothesis

Answer 10

• there is a positive feedback loop of passing down preferences
• females prefer a secondary sexual characteristic
• happens because female prefer some sexual characteristic, selects the mate and that trait gets passed down along with the desire for that trait
• increases the desirability and extreme nature of the character over generations

Question 11

Sexy son hypothesis

Answer 11

• females choose attractive mates because it means that their own male offspring will be better able to attract mates

Question 12

Handicap hypothesis

Answer 12

• extreme secondary sexual characteristics indicate that the individual can afford to waste resources on developing the secondary sexual characteristic
• they can handicap themselves and still survive, therefore good mate choice!!

Question 13

Sexual selection and speciation

Answer 13

• reproductive isolation
• more elaborate sexual practices and structures mean more common changes leading to reproductive isolation
• taxonomic groups with the greatest amount sexual dimorphism generally also have the largest species diversity

Question 14

Reproductive isolation example: Birds of Paradise

Answer 14

• 41 species, all descended from a common ancestor
• high sexual dimorphism between sexes
• extreme female choice
• many can still interbreed
• ## hybridization

Question 15

Evolutionary arms race

Answer 15

two species which develop adaptations and counter-adaptations in response to each other

• symmetrical arms race: selection pressure are identical on two species, two species whose interaction result in them co-evolving the same trait (ex. trees trying to be the tallest to get optimal sunlight)
• asymmetrical arms race: contrasting selection pressures, both species are con-evolving, however selection pressure is acting differently on them (ex. cheetah and Thomson’s gazelle)

Question 16

Coevolution through symbioses

Answer 16

symbiosis: a close and prolonged interaction between organisms of different species
- can be beneficial to both partners, or neutral to one, or harmful to one

Question 17

Mutualism

Answer 17

• interactions between two different species mutually benefit each other
• obligate mutualism: two species must co-operate in order for both to survive, survival of one depends on the survival of other
• facultative mutualism: both species derive benefit from each other, but one would survive if the other went extinct

Question 18

Parasitism

Answer 18

• interaction between two different species where one benefits at the expense of the other
• generally very finely tuned to preserve the life of the host since it needs the host to survive