Animals Reproduction Strategies

Question 1

Sexual Reproduction: Fertilization

Answer 1

sexual reproduction starts with the combination of a sperm + egg in the process called FERTILIZATION
1. Internal Fertilization
2. External Fertilization

Question 2

External Fertilization

Answer 2

usually occurs in aquatic environments where both gametes are released into the water, a process called spawning
- water protects gametes from desiccation during development
- species that use EF might be fully aquatic (fish + aquatic invertebrates) or partially aquatic and terrestrial (amphibians)
- there are environmental (water temp, length of daylight) OR biological (pheromones) cures that cause males + females to release gametes at the same time, who are often not interacting as individuals but massed together so the gametes are in the same location (fish, crustaceans, mollusks, invertebrates)
- individual males court individual females to induce the female to release eggs in which the male releases the sperm to fertilize that individual female’s eggs (amphibians)

Question 3

Internal Fertilization

Answer 3

usually occurs in terrestrial animals, although some aquatic mammals (whales, dolphins) and fish (some cartilaginous fish like sharks) also reproduce this way
- 3 ways that offspring are produced following IF: Inside, Hatching, Placenta
- advantage of protecting the fertilized egg from dehydration on land
- depending on the species, the embryo may also remain within the female, which protects the egg from predation
- IF increases the likelihood of fertilization by a specific male
- fewer offspring are produced but their survival rate is higher than EF

Question 4

Internal Fertilization: Ways Offspring are Produced

Answer 4

1. Fertilized eggs are laid outside the female’s body + develop, and the embryo receives nourishment from the yolk part of the egg (bony fish, reptiles, amphibians, cartilaginous fish, BIRDS)
2. Fertilized eggs are retained inside the female’s body, and the embryo receives nourishment from the egg’s yolk; the young are fully developed when they “hatch” within the female’s body and then exit (fish, sharks, lizards, snakes, invertebrates)
3. Fertilized egg is retained inside the female, and the embryo receives nourishment from the mother’s blood VIA a placenta. The offspring develop within the female’s body and may or may not be fully developed prior to birth (mammals)

Question 5

Choosy Females + Not so Choosey Males

Answer 5

• eggs are “expensive” and sperm is “cheap”
• generally a female maximizes her reproductive success by mating with the “best” male, while generally, a male maximizes his reproductive success by mating with as many females as possible
• EVOLUTION SELECTS FOR CHOOSINESS IN FEMALES
• females invest more in the offspring than males do since she has a limited # of eggs compared to the limitless number of sperm produced by males
• female puts more energy and resources into offspring’s survival success then the male does

Question 6

Sexual Selection

Answer 6

type of natural selection where one sex has a preference for certain characteristics in individuals of the other sex, thus leading to increased reproductive success of individuals with that particular characteristic
- adaptations occur without conscious though or intention !!!
- maximizes biological fitness

Question 7

Biological Fitness

Answer 7

reproductive success RELATIVE to others in the population

Question 8

Males Compete for Female Access

Answer 8

because of the typical sexual selection of females, males compete with each other for access to females/induce specific females to mate with them
- Sexual Dimorphism + Secondary Sexual Characteristics
- In Internal Fertilization species, competition is present since multiple males cannot mate at the same time
- In External Fertilization species, females control how + when her eggs are released, thus males compete for access to eggs outside her body

Question 9

Sexual Dimorphism

Answer 9

distinct differences in size/appearance between males + females caused by sexual competition
- can lead to specific behaviors in males that increase reproductive success (energy is spent locating, attracting, and mating with a partner)

Question 10

Secondary Sexual Characteristics

Answer 10

exaggerated or showy physical traits associated with mating behaviors + reproductive success
- EX: breasts, tail feathers

Question 11

Direct Male Competition

Answer 11

occurs when a female mates only with a single mate, typically the “winner” of a competition:
- Male-male aggression
- Courtship rituals
- Lekking

Question 12

Male-Male Aggression

Answer 12

mates fight with each other for access to females
- Direct Male Competition

Question 13

Courtship Rituals

Answer 13

males engage in “dances” or other displays to attract females
- Direct Male Competition

Question 14

Lekking

Answer 14

specialized form of courtship ritual where many males gather + display at the same time, allowing females to choose among them
- Direct Male Competition

Question 15

Female Choice / Intrasexual Selection

Answer 15

Females choose the “best” males to mate with based on direct male competition; Female choice and direct male competition (both intrasexual selection) usually lead to selection for extremely “showy” traits that:
- Have no benefit to survival
- Increase predation
- Higher reproductive success - IMPROVES biological fitness at the cost of decreasing its survival

Question 16

“Good-Genes” Hypothesis

Answer 16

hypothesis about why females “care” about showy male traits; these sexually-selected traits are “honest indicators” of good genetic quality

Question 17

Indirect Male Competition

Answer 17

AKA Sperm Competition: males compete for fertilization of a female’s eggs AFTER mating has occurred
- occurs in species where the female is likely to mate with multiple males
- if a female mates with 1+ male, then any male whose sperm end up fertilizing more eggs has more offspring than other males
- if there is a trait that makes this male’s sperm more successful than others, the trait will be passed on
- EX: First + Second Male Advantages

Question 18

First Male Advantage

Answer 18

the first male to mate with a female has a higher chance of fathering her offspring:
- Mate guarding
- Copulatory plugs

Question 19

Mate Guarding

Answer 19

a male remains close by the female after mating, preventing other males from mating with her until his sperm fertilized the eggs

Question 20

Copulatory Plugs

Answer 20

the male’s ejaculate includes a sticky residue that temporarily blocks entry to the female’s reproductive tract, making it difficult for other males to mate with her until some time has passed for the first male’s sperm to fertilize

Question 21

Second Male Advantage

Answer 21

the second male to mate has a higher chance to father, often occurring when the 2nd male’s sperm physically displaces the 1st male’s sperm:
- Elaborate penis morphology
- Large ejaculate volume + large testes

Question 22

Elaborate penis morphology

Answer 22

elaborate structures on the penis help remove the sperm of previous males from the female’s reproductive tract by essentially scraping out the previous ejaculate

Question 23

Large ejaculate volume + large testes

Answer 23

a large volume of ejaculate helps to flush out the sperm deposited in the female’s reproductive tract by the previous male; large testes are needed to hold all the sperm

Question 24

Cryptic Female Choice

Answer 24

a female is capable of preferentially using sperm from a specific male even if she has mated with multiple males
- female anatomy influences the success of sperm from specific males

Question 25

Parental Investment

Answer 25

any energy, effort, or resource that a parent provides to increase the offspring's chances of survival, but at the cost of the parent's ability to invest in other offspring - can include all types of parental care, as well as energy resources deposited in the egg of other nutrition provided to the developing embryo - occurs in IF and EF species

Question 26

Animal Mating Systems

Answer 26

- influenced by environmental/ecological factors and evolutionary history, and in turn, influences selection for different types of traits + behaviors - except in true sexual monogamy, there is ALWAYS competition for fertilization - differs in whether competition occurs before (direct male competition) or after (sperm competition) mating - mating systems are influenced by competition for mates and vice versa - 3 general mating systems: monogamous, polygamous, promiscuous

Question 27

Monogamy

Answer 27

one male + one female are paired for at least one breeding season - "Male-Assistance Hypothesis": males that remain with a female to help guard + rear their young will have more and healthier offspring. Many monogamous species live in environments with widely scattered resources meaning it requires the effort of more than one adult to forage to rear the young - True Monogamy VS Social Monogamy

Question 28

True Monogamy

Answer 28

AKA sexual monogamy; both partners mate only with each other - only mating system where there is likely no competition for males (assuming a perfect male-to-female ratio) - rare in biological systems

Question 29

Social Monogamy

Answer 29

2 individuals partner together to rear their offspring but also engage in "extra-pair copulations" (mating with other individuals) - more common than true monogamy - competition for males occurs

Question 30

Social Monogamy: Advantages

Answer 30

- male increases the survival of social partner's offspring but also mates with others, increasing his number of offspring - females have help from social partner in raising her offspring while still mating with genetically "better" males

Question 31

Social Monogamy: Disadvatnages

Answer 31

- male are more likely to raise offspring that are not their own - male may abandon female and her offspring if he detects she has mated with another male

Question 32

Polygamy

Answer 32

either one male mating with multiple females or one female mates with many males - Polygyny - Polyandry

Question 33

Polygyny

Answer 33

One male mates with multiple females - the female takes responsibility for most of the parental care as the single male is incapable for providing care for that many offspring - the female benefits by mating with a genetically fit male at the cost of no help raising the offspring - HAREM MATING STRUCTURE: type of polygynous system where certain males dominate mating while controlling a territory with resources - LEK SYSTEMS: the species has a communal courting area where males perform and females choose based on their skills

Question 34

Polyandry

Answer 34

one female mates with multiple males; rare as it involves sex role reversal where females invest less into the offspring and males invest more

Question 35

Promiscuity

Answer 35

occur when each female mates with multiple males, and each male mates with multiple females - occurs when a single male is unable to sexually monopolize a group of females because females range more widely than the territory size of a single male )so they interact with multiple males) OR because males + females live together in large social groups that a single male cannot monopolize - a single male cannot prevent others from mating with other females while he mates with one female - paternity is never certain