Sex and Reproduction

Question 1

Costs of sexual reproduction

Answer 1

• loss of 50% genes
• energetic cost of producing gametes
• time & energy invested in courtship & mating

Question 2

Asexual reproduction species

Answer 2

• New Mexico whiptail
• some invertebrate animal species
• some fish, amphibians, reptiles

Question 3

Benefits of sexual reproduction

Answer 3

• offspring more varied
• mutations reduced

Question 4

Isogamy

Answer 4

identical gametes

microorganisms

Question 5

Anisogamy

Answer 5

different gametes

most plants & animals

Question 6

Why two sexes?

Answer 6

• Sexual reproduction X require (only needs gametes)
• Small gametes (sperm): increased probability of encountering & fertilizing large gametes
• Large gametes (eggs): can carry more nutrients & resources

Question 7

Why is the sex ratio typically 1:1? (Fisher)

Answer 7

• Frequency-Dependent selection acting upon the individual
• female dominated –> advantage to produce males
• male dominated –> advantage to produce females
• a female-biased sex ratio X evolutionarily stable

Question 8

Alligator sex determination (Ferguson & Joanen)

Answer 8

• temp of egg determines sex of offspring during 2nd & 3rd week of incubation
• 30 C below –> all females
• 34 C above –> all males
• ~32 –> lean females

Question 9

Red deer (Clutton-Brock)

Answer 9

• maternally-sub sons less reproductive success than maternally-dom
• daughters equal reproductive success regardless of maternal dominance
• hypothesis: natual selection might favor ability to adjust progeny sex ratio in relation to parents’ ability to invest in offspring (dominance = more resources for offspring)

Question 10

Cameron (2004) (more on the red deer shit)

Answer 10

• mothers in good condition have more sons
• higher uterine glucose levels favor the development of males
• reveals a potential mechanism for sex-ratio variation in relation to maternal condition around conception

Question 11

Viviparous mite

Answer 11

• mom produces brood of 1 son & ~20 daughters
• son mates w/ sisters inside & dies before born
• no selfish mutants for rare sex to take advantage (limited by environment)

Question 12

“Ideal” (optimal) mating systems

Answer 12

• male acquires as many mates as possible & invests little in parental care
• females select “fit” male & leaves parental duties to him while acquiring resources required to produce more offspring (female is more “selective” sex)

Question 13

Bateman Effect

Answer 13

• as mates increase, mean # of offspring increases for males increases; stays the same for females –> no advantage to increasing mates EXCEPT genetic diversity
• mean # offspring range much wider for males than females

Question 14

Moulay Ismail

Answer 14

• Emperor of Morocco
• 548 sons & 340 daughters in his harem of 500 women during his life (~1.2 copulations/day for 62 years)
• unlikely due to following factors:
• ovulation frequency combined w. sperm survival (women fertile only 12.5% of time)
• female infertility
• conception likelihood
• prenatal mortality

Question 15

Mating systems

Answer 15

• Polygyny (male w. multiple females) –> baboon, safe grouse, elk
• Promiscuity (both sexes have multiple partners) –> Japanese macaques, bonobos
• Polyandry (female w/ multiple males)–> seahorses
• Monogamy (1 male, 1 female) –> only ~5% of species

Question 16

Ecological factors influence how animals are distributed in space

Answer 16

• Polygyny –> small groups of females
• Promiscuity –> large groups of females or lack of male dominance
• Polyandry –> male reproductive output limited by time/energy constraints or female behavior
• Monogamy –> environmental demands require both male and female input for offspring survival

Question 17

Polygyny types

Answer 17

• Female defense polygyny: males directly defend several females from other males (greater spear-nosed bat, elk, lions)
• Resource defense polygyny: males w/ multiple females that are attracted to resources under his control (polygyny threshold model) (red-winged birds)
• Lek polygyny: multiple females attracted to male display territory (topi bulls, hammer-headed bat, leaf-cutting ant)
• Scramble competition: male acquires multiple widely scattered mates by being the first to encounter them (horseshoe crab, 13-lined ground squirrel)

Question 18

Polygyny threshold model (lark buntings)

Answer 18

• shade important to keeping nestlings cool
• females may choose a “polygynous territory” of a male” w/ good shade cover of a “monogamous territory” w/ less shade, even if the polygynous male restricts aid in rearing nestlings to first female

Question 19

Cock-of-the-rock

Answer 19

• Lek Polygyny
• males assemble in dozens & squabble amongst themselves
• female spotted –> males spread out & claim plot of land –> try to persuade female to land next to him by competitively bouncing
• peck neck –> chosen –> immediate fornication
• female will lay eggs alone
• another female may choose same male
• increases chance of displaying to females even in few actually mate

Question 20

Scramble competition polygyny

Answer 20

• female usually mates once
• males X need to display or compete

Question 21

Jacana

Answer 21

• 1 female, male harem
• female guards territory, need male to watch over nests
• ~4-5 nesting males
• predation stresses female in protecting eggs –> recruit males to help + increase in female size to produce more eggs

Question 22

Sexual selection (first proposed by Darwin)

Answer 22

selection for traits that are attractive to mates/ traits that concern competition for mates

subdivision of Darwinian selection that concerns mating

Question 23

Long-tailed widow bird (Andersson)

Answer 23

• females preder longer tails even if diff performance areas are weaker
• dangerously low flights & jumping competitions (in other widow bird species)

Question 23

Intersexual selection

Answer 23

• involves exaggerated traits that one prefers in the other
• ex. sage grouse, magnificent frigate bird: puffed chests
• ex. bats: male perfumes scent onto female, female chirp to determine male fitness

Question 24

Bower birds

Answer 24

males w/ more decorations @ nest get more females (tend to match colors)

Question 25

Sexual selection hypotheses

Answer 25

* "Runaway" selection (Fisher) * Disease/parasite avoidance (Hamilton & Zuk) * Handicap principle (Zahavi)

Question 26

"Runaway" selection (Fisher)

Answer 26

* tail length increases due to combination of both survival advantage & female choice * optimal tail length for survival heightened largely due to female choice * what else promotes a certain trait to "run away" & succeed? --> female choice

Question 27

Female sticklebacks

Answer 27

* use male coloration to identify healthy mates and avoid parasite-infected males * brighter red males chosen * effect disappears under green light

Question 28

European blackbirds (Biard)

Answer 28

* eating foods w/ carotenoids results in darker beaks --> more sexually attractive to females * plant pigments: involved in antioxidant activity & conversion to vitamin A --> increased perceived immune system health

Question 29

House finches (Oh & Badyaev)

Answer 29

* duller-colored males more appealing by being **more social** prior to mating season * by mating season, less attractive male have = success as brightly colored males

Question 30

Disease/parasite avoidance hypothesis (Hamilton & Zuk)

Answer 30

some traits signal good health ## Footnote sticklebacks, house finches, European blackbirds

Question 31

Handicap principle (Zahavi)

Answer 31

cost of the trait assumed is cannot be faked by lower-quality males --> effective mechanism for secual selection

Question 32

Results of intrasexual selection on males

Answer 32

* guarding behavior * sperm plugs * biochemical substances that reduce female receptivity * low threshold for mating attempts * monopolization of females * postponement of mating attempts * "sneak" copulations * forced copulations * sexual interference * female mimicry by males * assaults on male competitors * assaults on offspring of competitors * size of testes

Question 33

Guarding behavior

Answer 33

* **damselfly**: similar to dungflu copulation guarding; use appendage to hold onto female * **lovebugs**: 56 hour copulation tie

Question 34

Sperm plugs

Answer 34

* **green anaconda** * **dragonfly**: barbs & flagella allow for 2nd male to remove sperm of first * **primates**: penile morphologies - adaptations for sperm removal? * **orb-weaving spider**: male self-destructs during mating --> corpse remains wedged in female

Question 35

Biochemical warfare that reduce female receptivity

Answer 35

* **Postman butterfly**: during copulation, male deposits scent into female that makes her unattractive to other males

Question 36

Low threshold for mating attempts

Answer 36

* **Cock-of-the-rock**: presented w/ opportunity --> male proceeds quickly

Question 37

Postponement of mating attempts & "sneak" copulations

Answer 37

* **Baboons**: sub males may wait for mating opportunity when alpha male unaware

Question 38

Forced copulations

Answer 38

* **Scorpionflies**: courtship --> female reject --> male use appendage to grasp onto female & mate --> female may try to escape * **Orangutans** * **Ducks**: some female ducks' vaginas spiral in opposite direction of male phallus & longer (species w/ fewer forced copulations tend to have shorter & simpler genitalia)

Question 39

Female mimicry

Answer 39

* **Garter snakes**: late male may represent self as female via pheromones * **Sticklebacks**: non-territorial male behaves like female --> allowed into territorial male's nest --> may deposit sperm into female instead of actual male * **Western marsh harrier hawk**: female-like males may access breeding resources while avoiding costly fights w/ typical territorial males (fem hawks attacked & attack less, may be adaptive)

Question 40

Size of testes

Answer 40

* **Primates**: tend to be relative to body weight * **Yellow-toothed cavy** * **Bushcrickets**: largest testes to body-ratio --> deposit only small amounts of sperm/mating --> likely for mating w/ many females vs. competitively intrasexually

Question 41

*The Evolution of Animal Weapons* (Emlen)

Answer 41

* tendency for weapons to begin small --> more ornate * smaller = more damaging (only role to attack other males) * more elaborate = less injury/death (use as signal to females/ritualized combat)