1
Q
primary sexual characteristics
A
the genitalia and organs of reproduction
2
Q
secondary sexual characteristics
A
morphological differences between the sexes that are not directly involved with reproduction
3
Q
explain how secondary sexual selection traits puzzled Darwin
A
- exaggerated morphological and behavioural traits should be energetically expensive to produce and maintain and make more obvious to predators (reducing survivorship)
- why only found in males?
4
Q
what did Darwin hypothesize as to why secondary sexual traits were present?
A
- because of sexual selection - represents the advantage certain individuals have over others of the same sex and species solely in terms of reproduction
- is subset of natural selection
5
Q
what did Darwin propose as to how sexual selection explains the evolution of exaggerated male traits?
A
1) mate competition or intrasexual sexual selection
2) mate choice (intersexual selection)
6
Q
what is mate competition/intrasexual selection
A
situation in which members of the same sex compete for access to the other sex for reproduction (often males)
7
Q
what is mate choice/intersexual selection
A
selection by one sex (usually males) for members of the other sex for reproduction
8
Q
what is sexual selection
A
represents the advantage certain individuals have over others of the same sex and species solely in terms of reproduction
9
Q
what is anisogamy
A
the existence of differently sized gametes (small and large) in the different sexes
10
Q
what is isogamy
A
the production of gametes of the same size by all individuals
11
Q
what question did Geoff Parker’s model focus on?
A
why two sexes?
12
Q
what were the assumptions of Geoff Parker’s model?
A
- in the ancestral marine environment, individuals in a population that retain reproductive compatibility produce different-sized gametes
- each parent has a fixed amount of energy allocated to gamete production, resulting in a size-number trade-offs: as the number of gametes produced increases, their size will decrease
- Zygote viability is related to its size. Larger zygotes have higher viability because they contain more resources for survival
13
Q
what were the predictions of Parker’s model?
A
- small gametes will produce the most zygotes
- large gametes will produce zygotes of highest survival
- intermediate-sized zygotes will have no advantage so lowest fitness - disruptive selection acting against
result: - proto-females - produce fewer large gametes
- proto-males - produce fewer large gametes
14
Q
how did Bateman conduct the fruit fly experiment and what did he infer from it
A
- conducted mating trials with male and female fruit flies
- observed progeny from both sexes
- more females produced progeny than males
- inferred that intensity of sexual selection measured by variation in reproductive success was generally higher in males than females due to male male competition
15
Q
What else did Bateman’s experiment suggest
A
- a male’s reproductive success increases more strongly w/number of mates obtained than female reproductive success
- female rs limited by by egg production because sufficient sperm from single mate
- male rs limited not by sperm depletion by by # of mating single male obtains
- female has fewer gametes so more intense competition among males for fertilization of female gametes
16
Q
what is Bateman’s hypothesis
A
hypothesis that female reproductive success is most strongly limited by # and success of eggs that a female can produce, while male reproductive success is limited by # of mates a male has
16
Q
what is parental investment
A
any investment by the parent in an individual offspring that increases the offspring’s chances of surviving (and hence reproductive success) at cost of the parent’s ability to invest in other offspring
- may be: gestation, incubation, defense, food provision, etc.
17
Q
who focused on parental investment as a key difference between the sexes?
A
Robert Trivers
18
Q
what is the parental investment theory
A
the hypothesis that the sex that pays the higher cost of parental investment should be choosier when it comes to mates
19
Q
what is the operational sex ratio
A
the ratio of the number of sexually receptive males to sexually receptive females in a population
20
Q
is the sex with higher cost of parental investment always receptive?
A
no - changes operational sex ratio
21
Q
what are weapons
A
exaggerated morphological traits used in competition with individuals of the same sex
22
Q
what are ornaments
A
exaggerated morphological traits used to attract mates
23
Q
explain the weapon size and mating success experiment in dung beetles
A
- wanted to see role of horns in competition for mates in male dung beetles
- staged fights between 2 males in artificial nesting arena with female in arena
- 2 males matched in body size, not horn size
- body size and horn size measured
- winner was male who entered and remained in tunnel w/female more than 24h, likely mated w/female
- between small beetles, male size and horn lenght mattered more
- between big males, horn size alone was biggest factor
- overall, longer horn lenght = more likely winner
- concluded maintenance of long horns in male dung beetles can be explained by sexual selection driven by male-male competition
24
explain the ornaments and mate choice in peafowl experiment
- males fight for status and preferred spots on the lek
- researchers captured and marked males and females
- measured each male's tail lenght, body size, counted ocelli, male-male interactions during breeding season, number and duration of male tail displays to females, number of vocalizations and number of copulations
- results showed intense competition for display sites, larger males and w/longer tails had more success in getting site
- females were very picky w/makes to mate w/
- in general, males w/highest ocelli and display rates got most copulations but were not exactly the largest
- both male competition (for defending display site) and mate choice (female choosing) favoured evolution of males w/long, ornamented and high display rates
25
who do peahens prefer to mate with
peacocks with most ocelli - most ornamented tail
26
what is a lek
a location where males aggregate and display to females
27
explain a bit about pipefish
- males invest more in offspring because males get pregnant
- sexual selection theory predicts males should be choosy and female-female competition would be intense
- females have secondary sexual ornament which is a temporary striped pattern on the side of the body displaying only during competition - AKA courtship dance
- ornament makes female stand out so likely to increase predation risk making it costly
28
what is a sex role-reversed species
a species in which females compete for males that invest heavily in parental care
29
explain the male mate choice in pipefish experiment
- wanted to see if males spend more time and mate more often w/females that display temporary striped pattern (ornament) the most
- Day 1: did choice test to see which female the male spent most time with dividers in place
- recorded amnt of time male spent in front of each female, how often ornament was displayed, how often male engaged in courtship dance w/each female
- Day 2: no dividers, recorded:
- total time dancing, latency to dance, copulations with each female
- counted all eggs from male's brood pouch
- resulted showed males spend more time w/, time dancing, more copulations, shorter latency to dance w/ female that displayed ornament more
30
what is the sensory bias hypothesis
the hypothesis that female mating preferences are a byproduct of preexisting biases in a female's sensory system
31
what are two possible benefits of females being choosy about picking a partner?
direct material benefits and indirect genetic benefits
32
what are direct material benefits
material resources obtained by a female from mating with a particular male
33
what are indirect genetic benefits
genetic benefits females can obtain for their offspring by mating w/males that have high genetic quality
34
what is a nuptial gift
a physical resource such as a food item that an individual provides to a potential mate to enhance mating success
35
explain the female choice and nuptial gifts in butterflies experiment
- wanted to see whether nuptial gifts enhance female reproductive success in butterflies
- saw if female's egg production (representative of her fitness) varied with size of nuptial gift received from male
- tagged leafs w/C13 or H3 and tracked it in spermatophore and release into female to quantify how much resource transferred from male incorporated into egg production
- female eggs, abdomen and thorax tested for radioactivity to quanitfy
- results showed females received more resources from males (larger spermatophores) produced more eggs - direct benefit of male nuptial gift on female fecundity
36
what is one method females can assess the genetic quality of potential males?
selecting males based on their secondary sexual traits
37
explain Ronald Fisher's model about evolution of exaggerated secondary sexual traits
- assumed females select mates based on a particular trait that varies among males
- trait could evolve bc 1) fitness advantage independent of female choice or 2) female preference
38
what is the runaway process
an evolutionary process in which a male trait co-evolved with a female preference for it and becomes increasingly exaggerated
39
when should the runaway process continue till?
until the benefit it provided through sexual selection was outweighed by the advantage it entailed through natural selection
40
what is linkage disequilibrium
when genes for the trait and for female preference for the trait are genetically linked even if trait is unrelated to male fitness
- occurs when genotype at one locus is not independent of genotype at another locus
41
how often is Fisher's runaway process?
review suggests that runaway selection may help to explain the evolution of a variety of sexual traits and mating preferences in diverse taxa
42
Who suggested the handicap principal
Amotz Zahavi
43
what is the handicap principle
the hypothesis that well-developed secondary sexual characteristics are costly because they handicap survival
44
what are good genes
the alleles of a high-quality individual
45
what are the similarities between Fisher's and Zahavi's model
- in both models, male trait initially preferred by females indicates a high degree of male vigor and survivorship
- in good gene models, correlated between female preferences for male trait and male good genes
- in Fisherian runaway selection, is presumed genetic correlation btn female preference for male trait and male trait itseld
46
what is the Hamilton-Zuk hypothesis
The hypothesis that parasites and pathogens play an important role in sexual selection when secondary sexual traits are costly and condition dependent
47
explain the good genes and the Hamilton-Zuk hypothesis experiment in field crickets
- tested Hamilton-Zuk hypothesis
- quantified variation in male courtship song and immunocompetence and examined female choice for different males
- lab-reared individuals captured, nymphs raised in isolation
- at sexual maturity, courtship song analyzed to quantify rate of production and duration of HF and LF ticks
- immunocompetency was assayed and encapsulation rate quantified by using an implant (higher degree of encapsulation means higher immune system function and vice versa)
- female preference assessed by seeing which speaker she goes to first (both speakers played courtship song of two size-matched males whose immunocompteence level was known
- results showed females preferred males that produced a higher frequency and duration of HF ticks; also had higher encapsulation rates
- encapsulation ability is heritable, suggests females can obtain indirect genetic benefits by mating with males with high HF tick rates and durations
48
what is sperm competition
a situation that occurs when the sperm of different males compete to fertilize eggs
49
can postcopulatory male competition and postcopulatory female choice occur after gamete transfer?
yes
50
what is mate competition?
a behaviour in which a male remains close to his mate to prevent her from mating with rivals
51
what is an extra-pair young
offspring of a pair bonded female produced outside the pair bond by a third party male
52
what are ways a male can reduce mate competition to enhance likelihood of success when sperm competition occurs?
mate guarding and high copulation frequency
53
explain the sperm competition in tree swallows experiment
- wanted to see if frequent copulation with a mate will enhance male fitness in tree swallows
- focal bird pairs observed for 3 hours for over 2 weeks at dawn when most copulations start
- results showed about half of young sired from extra pair copulations
- an increase in frequency of copulations by male increased the percentage of young he sired
- in this species, males can reduce the likelihood of paternity loss from sperm competition by increasing their copulation frequency
54
explain a bit about tree swallows
- extra-pair fertilization is common
- males spend significant time on parental care, so selection should favour behaviours that minimize loss of paternity
55
what are two behaviours that enhance a male's likelihood of success in mate competition and result in higher rates of fertilization
high copulation frequency and mate guarding
(high copulation frequency could act as a type of mate guarding bc frequency copulations prevent other males from mating)
56
what is cryptic female choice
a situation that occurs when a female influences the fertilization success of sperm from one male over that from others (after multiple copulations w/different males)
57
what is often the result of cryptic female choice?
one male's sperm fertilizes a disproportionate number of her eggs
58
what is inbreeding depression?
a close relative being a low-quality mate because such mating often produce low fitness for offspring
59
why does cryptic female choice exist?
- cryptic female choice will benefit a female that matches with several males that differ in quality
- she can enhance the fitness of her offspring by biasing fertilization success in favour of the higher quality male
60
explain the inbreeding avoidance via cryptic female choice in spiders experiment
- wanted to see if female orb spiders avoid inbreeding depression by cryptic female choice
- conducted double mating trials
- females mated w/either 1) two siblings 2) non siblings 3) sibling and non sibling
- each male around same size, each pair male only had one pedipalp (one had right, other had left)
- hatchlings kept seperate to identify siblings and non siblings
- males and females also kept seperate
- males put in female cage, given time to copulate
- estimated the number of sperm transferred to each spermathecae by sacrificing some females
- to determine paternity for each male, second experiment - irradiated one male to make his sperm inviable - saw which eggs were not fertilized and did not hatch
- results showed no difference in mating w/sibling and non sibling
- number of sperm in spermathecae did not differ based on relatedness to female
- females stored more sperm from non sibling male in comparison
- found proportion of eggs fertilized by non sibling male much higher than sibling male
- females store more sperm from non sibling than sibling and thus bias paternity towards him as well
- both aspects of choice reduce inbreeding within a brood
61
explain a bit about orb spiders
- females have two independent sperm storage organs AKA spermathecae on each side of the body that are filled as a result of two separate mating by either same or different male
- male inseminate females using paired pedipalps (filled with sperm) - usually used one per mating attempt (right pedipalp for right spermathecae, same for left)
62
what are alternative reproductive tactics
the existence of multiple behavioural mating phenotypes in a population
63
what are the two commonly observed behavioural strategies?
- bourgeois tactic
- parasitic tactic
64
explain the bourgeois tactic
competitive males (bourgeois males - large, older, best physiological condition) defend a nest or territory to monopolize its resources for females or else possess traits attractive to females
65
explain the parasitic tactic
- used by less competitive males to usurp mating from bourgeois males
66
what are two types of parasitic behaviours?
satellite males - associate w/bourgeois males by remaining close to them to intercept females that are attracted to the bourgeois male
sneaker males - attempt to avoid detection so they can quickly enter a bourgeois territory to fertilize eggs being deposited in a nest
67
how can two behavioural tactics exist in a population?
1) conditional strategy
2) tactics coexist in an evolutionary stable strategy (ESS) maintained by frequency-dependent selection
68
what is conditional strategy
a strategy that an individual chooses based on its condition
69
how can a behavioural tactic exist in a population through ESS maintained by frequency dependent selection?
neither tactic leads to higher fitness, but an average fitness of each tactic increases as the tactic becomes less common
70
what is mate choice copying?
a situation in which one individual observed and copies the mating decisions of another individual
71
explain the mate copying in fruit flies experiment
- wanted to see if females will change mate preference after observing another female associate with a previously nonpreferred male
- created high and low quality males by feeding rich and poor nutrient food
- conducted female choice test with one high and low quality male - most chose high quality
- allowed half females to observe model female with high quality male, other half with low quality male
- repeated mate choice trials (posttest)
- results showed posttest, females that observed other female w/low male spent more time near low male
- concluded female fruit fly mating behaviour is affected by observing the mating decisions of other females
72
why might an individual copy the mate choice of another individual rather than making a decision on its own (in females specifically)?
- one model says:
- may be difficult for female to determine which male is of higher quality if the males are similiar or if she has little experience discriminating between males
- can make own decision or copy decision of another females which may be better discriminator
- model predicts that young females should mate copy more often than older females since worse discriminators
73
explain the nonindependent mate choice by male mosquitofish experiment
- wanted to see if risk of sperm competition affects mate choice in male eastern mosquitofish
- 3 stage experiment w/two choice test
1st stage: saw male preference btn 2 random females
2nd stage: focal male constrained, half males observed rival male next to preferred female, other half saw rival male close to un preferred female
stage 3: rivals removed and focal allowed to associate w/females again
- results showed the control fish (rival near unpreferred female) spend more time with same preferred female (larger) in stage 3
- treatment males (rival close to preferred female) spent less time w/same female in stage 3
- demonstrate mate choice of individuals often affected by social environment and observations of mating behaviour of others
74
how do Club-Winged Manakins sing to attract a mate?
male club-winded manakins flick wings striking feathers together to produce bright buzzing sound telling females they are ready to mate
75
what does sexual selection favour?
characteristics that enhance reproductive success
76
what is sexual selection
a form of natural selection that acts on heritable traits that affect reproduction via mate competition (intra-) and mate choice (inter-)
77
what is mate competition
selection in which one sex competed with other members of the same sex for access to the other sex for reproduction
78
what is mate choice
selection by one sex for members of the other sex for reproduction
79
what is parental investment theory
the sex that pays the higher cost of parental investment should be choosier in selecting mates. The other sex will experience more intense sexual selection
80
what are direct material benefits
material resources obtained by a female from mating with a particular male
81
what are indirect material benefits
genetic benefits females can obtain for their offspring by mating with males that have high genetic qualities
82
what is a nuptial gift
a physical resource such as a food item that a male provides to a female to enhance his mating success
83
what is a spermatophore
a structure or package containing sperm which is transferred from a male to a female during reproduction in some animal species
- specific structure and function can vary among different species but their primary purpose is to deliver sperm to the female's reproductive organs
84
explain a bit about spermatophore
- male produces as part of his reproductive strategy
- may contain not only sperm but also other substances that provide nutrients or protection for the sperm
- when male encounters a receptive female often transfers spermatophore through specialized reproductive organs or structure
- female takes spermatophore ands its contents which can fertilize her eggs when she is ready to reproduce
85
what are the different ways for transfer of spermatophores
direct insertion, capsule placement, transfer via a spermatophore structure, sperm web or sperm packet
86
explain direct insertion
in some species, such as certain insects, male reproductive organs can directly insert the spermatophore into the female's reproductive tract. This is a common method in many insects like beetles and some butterflies
87
explain capsule placement
in other cases, the male places the spermatophore in a location where the female can access it. the female may then take up the spermatophore on her own. this method found in certain arachnids, such as some scorpions.
88
explain transfer via spermatophore structure
In some species of squids and octopuses, the male transfers a spermatophore by using specialized structures, such as an elongated arm called a hectocotylus, to place the spermatophore into the female's reproductive tract.
89
explain sperm web or sperm packet
Certain spider species create a sperm web or sperm packet, which is essentially a silk structure containing the spermatophore. The male deposits the spermatophore on the web or packet and then guides the female to it, where she retrieves and takes it up.
90
what are indirect genetic benefits
genetic benefits females can obtain for their offspring by mating with males that have high genetic quality
91
explain runaway process
An evolutionary process in which a male trait co-evolves with a female preference for it and becomes increasingly exaggerated
92
explain handicap principle
Well-developed secondary sexual characteristics are costly to survival but reliable signals of fitness
93
explain good genes
The alleles of high-quality individuals
94
what are captive breeding programs used for
to increase the population size of endangered species
95
what should be considered in captive breeding programs
mate choice and genetic diversity
96
what are some ways sexual selection can happen after mating
mate guarding extra pair young, sperm competition, cryptic female choice, inbreeding depression
97
what is mate guarding
when a male follows his mate to prevent her from mating with rivals
98
what are extra pair young
offspring of a pair bonded female produced outside the pair bond by a third party male
99
what is sperm competition
Competition between sperm of different males to fertilize eggs (after mating has occurred)
100
what is cryptic female choice
When female influences the fertilization success of sperm from one male over others
101
what is inbreeding depression
A reduction in fitness as a result of mating with close relatives
102
what are alternative mating tactics
Multiple behavioural mating phenotypes in a population
103
what is a satellite male
Alternative, parasitic mating tactic in which a male remains near a bourgeois male to intercept females that are attracted to the bourgeois male
104
what is a sneaker male
Alternative, parasitic mating tactic in which a male attempts to avoid detection so that he can quickly enter a bourgeois territory to fertilize eggs being deposited in a nest
105
what is a conditional strategy
The flexibility with which one chooses a particular strategy based on an individual’s condition
106
what is an evolutionary stable strategy (ESS)
A strategy that, if adopted by individuals in a population, cannot be trumped by another strategy because it yields the highest fitness
LifeSci 2D03
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