Sex Roles, Dimorphism, Weapons & Fights

Question 1

2 kinds of sexual selection

Answer 1

intrasexual selection: traits that help members of one sex compete with each other
intersexual selection: traits that make individuals attractive to opposite sex

Question 2

mating competition =

Answer 2

intrasexual selection

Question 3

mate choice =

Answer 3

intersexual selection

Question 4

Bateman’s Principle

Answer 4

males: reproduction is limited by number of eggs fertilized, dictated by how many females they mate with. (Offspring restricted by access to females, proportional to mates)

females: reproduction limited by number of eggs produced and resources (can mate lots, offspring will not change. restricted by access to resources)

variance in offspring in males exceeds that of females.

Question 5

parental investment (typical)

Answer 5

males: more mating effort
females: more parental effort
members of least investing sex will compete among themselves to mate with members of sex investing most.

Question 6

OSR: operational sex ratio

Answer 6

ratio of receptive males to females in a population

Question 7

potential reproductive rate

Answer 7

how many young/day can a sex reproduce, differs from male to female

Question 8

factors that influence intrasexual selection

Answer 8

sexual dimorphism
evolution of weapons
fighting and contests
alternative reproduction tactics
sperm competition

Question 9

sexual dimorphism

Answer 9

physical differences between males and females of a species

Question 10

mating system of elephant seal

Answer 10

female produces one pup a year, males can go for dozens. males fight to become the beachmaster and they breed with all females on the beach. few males win big. prize is maternal investment. males have higher variance in fitness

Question 11

evolution of weapons

Answer 11

male-male competition and fighting

Question 12

two kinds of male dung/scarab beetles

Answer 12

type 1: horned, larger
type 2: hornless, smaller

Question 13

properties of weapons

Answer 13

1. structures used in combat with rivals
2. among species, weapons diverge in size, shape, use
3. weapons evolve when one sex (usually males) are able to defend spatially restricted critical resources
4. weapons are usually the most variable morphological structure and variation reflects differences in body size or quality

Question 14

fighting and contests

Answer 14

fighting is purposeful, sometimes violent, to establish dominance over a competitor. Higher mating competition means more intense fights.

benefits: win resource
costs: energy, time, risk, injury

Question 15

ritualized fighting

Answer 15

assessment tactics, threat displays, occur before contact or overt aggression

Question 16

factors that influence when to give up

Answer 16

resource holding power, resource value, aggressiveness

Question 17

resource holding power

Answer 17

absolute fighting ability of individual, measure of size/strength/weapons/etc. which would enable the individual to win a fight.

Question 18

aggressiveness

Answer 18

the readiness of an individual to engage or risk an escalated encounter. an inherent property of the individual

Question 19

how do animals fight?

Answer 19

minimize costs
threat displays
dominance hierarchies
ritualization
death/injury is rare