week 3- evolution of exaggerated traits

Question 1

what are the diffferent types of selection

Answer 1

artifical selection (breeders equation)
natural selection: viability selection,fecundity selection
sexual selection

Question 2

when does sexual selection occur

Answer 2

between adults and parents

Question 3

what are the three forms of selection

Answer 3

disruptive selection, stabilizing selection and directional selection

Question 4

what are examples of trait exaggeration

Answer 4

rhinoceros beetle horns, long-taied widowbird tail, elk antlers, stag beetle mandibles, fiddler crab chela

Question 5

what are secondary sexual traits

Answer 5

advantageous when competing for mating or fertilisation opportunities

Question 6

the primary sexual traits (body structures involved in reproduction)

Answer 6

affect fertilisaition success/ ability to mate irrespective of the presence of rivals,
economic and under natural selection

Question 7

what is the definition of sexual selection

Answer 7

favours investment in traits that improve fertilisation, given limited access to the opposite sex gametes due to competition with members of the same sex

Question 8

what are the consequences of anisogamy

Answer 8

Higher variance in reproductive success in males (resulting from male bias in gamete numbers)

Question 9

what happens if anisogamy variance is non-random

Answer 9

sexual selection occurs

Question 10

what further fuels competition for mates

Answer 10

sex bias in parental investment (PI), resukting in further shift in operational sex ration (ORS) from the adult sex ratio (ARS)

Question 11

what is the direction of sexual selection

Answer 11

male-biased ORS means lower, average mating rates for males, but direction of sexual selection unclear

Question 12

what is Batemans gradient

Answer 12

slope of the regression of offspring production on mating rate. less mates results in less offspring and too many mates results in less offspring

Question 13

what does a steeper batemans gradient mean

Answer 13

stronger sexual selection on the competing sex

Question 13

practicing batemans gradient: male parental care in phalaropes

Answer 13

-females are more brightly coloured than males
-the females pursue males, compete for nesting territory, and defend their mates
-after laying, females leave the males to incubate the eggs while she looks for another mate
-means that batemans gradient is steeper for females than for males

Question 14

what are the benefits (fitness gain) and costs (time out) in case of ORS

Answer 14

ORS captures consequences of differential access to mates between sexes but does not specify fitness gain from mating.
neither BG or ORS specify trade-offs between getting a mate and other fitness-enhancing options
Trade-offs are apparent in mate choice

Question 15

what is ORS

Answer 15

ratio of sexulaly competing males and females that both are ready to mate

Question 16

what does batemans gradient not consider

Answer 16

how an individual increases mating success

Question 17

when does mate choice occur

Answer 17

occurs when traits create mating biases that reduce set of potential mates

Question 18

when might mating rate not be maximised

Answer 18

in choosy sex, hence trade-off between offspring production and mating rate

Question 19

when does mate choice evolve

Answer 19

only if mating is costly (e.g. predation risk)

Question 20

What does Bateman’s gradient suggest/inform about mate choice

Answer 20

suggests which sex can be choosy,
mating costs are not defined in batemans gradient ,
Batemans’ gradient does not inform on the evolution of mate choice

Question 21

what are the two types of sexual selection

Answer 21

intraxexual selection and intersexual selection

Question 22

what is intrasexual selection

Answer 22

direct competition for mates between members of the same sex, usually male-male competition

Question 23

what is intersexual selection

Answer 23

differences in attractiveness to the opposite sex, usually non-random mate choice by females (mate choice)

Question 24

example of male-male competition (red deer)

Answer 24

red deer (stags), male red deer with the greatest success in combat can retain females for longer periods- directinal selection on antler size and thus have higher reproductive success stags have higher variance in reproductive success than hinds (batemans gradient)

Question 25

example of male-male competition (hercules beetles)

Answer 25

engage in titanic jousting matches using their elaborate horns to displace rival males. this competition has led to an exaggeration of body size and horn size disruptive selection on horn size.

Question 26

what can male-male competition explain

Answer 26

the evolution of many morphological and behavioural traits

Question 27

what does mate choice occur in response to

Answer 27

direct selection on genetic variation in choice Indirect selection that acts on genetically correlated traits

Question 28

females and direct selection, reproduction

Answer 28

Females may benefit from increased nutrition or provisioning, or paternal care that increases their reproductive output or the quality of their offspring

Question 29

explain the good genes hypothesis (indicator selection)

Answer 29

(indirect selection) a chosen mate might have genes that give male and female offspring fitness advantage

Question 30

explain the handicap principle

Answer 30

(indirect selection) some males may have a heritage;e trait that reduces viability, only males with 'good genes' can survive on handicap, females that mate with these males will have offspring with higher fitness

Question 31

explain fishers runaway process

Answer 31

(indirect selection) -starts with a genetic correlation between a trait and its preference, and an initial advantage of the trait in attracting mates -females that prefer males with the trait will produce sons that are more attractive and daughters will inherit the preference -both choice genes and chosen male trait (genes) have positive selection -this creates a positive feedback loop that drives the trait and the preference to extreme levels, even if the trait becomes costly or harmful

Question 32

what is the lek paradox

Answer 32

lekking males face strong directional selection imposed by female choice on display traits Therefore, we expect that selection erodes heritable variation in those traits, but that is not what is observed

Question 33

what is the hamilton-zuk hypothesis- assumptions

Answer 33

-female choice on male traits -male trait expression limited by parasite infection -females choose males with exaggeratied traits to obtain resistence genes for their offspring

Question 34

how is heritable variation in paraiste resistance maintained

Answer 34

due to co-evolution between parasites and hots that generates new genetic variation.

Question 35

what is the Hamilton-zuk hypothesis-prediction

Answer 35

Females should mate with the most ornate males available; these males should carry lower parasite loads than less showy males

Question 36

what is the immuno-competence handicap hypothesis

Answer 36

suggests that males with robust sexual signals (testosterone) are also more vulnerable to immune challenges due to immunosuppressive effects of T so increases parasite load

Question 37

what is postcopulatory sexual selection

Answer 37

sexual selection favours investment in traits that improve fertilisation, given limited access to the opposite sex gametes due to competition with members of the same sex. This means that traits favoured by sperm competition are also sexually selected

Question 38

what is intrasexual selection in postcopulatory sexual selection

Answer 38

sperm competition competition between the sperm from two or more males for the fertilisation of a given set of ova

Question 39

what is intersexual selection in postcopulatory sexual selection

Answer 39

cryptic female choice non-random paternity biases resulting from female morphology, physiology or behaviour that occur after coupling (requires female remating)

Question 40

what does net magnitude of sexual selection depend on

Answer 40

both precopulatory and postcopulatory processes (interactive effects)

Question 41

use of weapons

Answer 41

weapons are a precopulatory investment (male-male competition) but scramblers without weapons have higher reproductive output when their mates are starved (direct selection: nuptial gift)

Question 42

explain how sexual selection leads to male adaptations (reduce remating oppurtunity of female)

Answer 42

-prolonged copulation following insemination -post-insemination mating plugs and anti-aphrodisiacs -prolonged contact after copulation -guarding of the female by the male after copulation

Question 43

explain how sexual selection leads to male adaptations (to eliminate/impair sperm of rival males)

Answer 43

-large sperm volume/frequent copulations -induce females to eject rival sperm -penile strutures that remove sperm

Question 44

exaplin mating of black damselfly

Answer 44

-females mate with several males within a few hours -females store sperm in spermatheca -males use specially adapted penis to scrub away rival sperm -very successful males remove 90-100% of competing sperm

Question 45

how has evolution had consequence on testis size

Answer 45

increased ejaculation size in sperm competition more sperm, larger testes

Question 46

sperm in deer mice

Answer 46

sperm discriminate among relatives and cooperate with most closely related sperm