Transcript Sexual Selection and Mating Patterns

Name: ________
Period: _____
Can you look at another member of your species
and tell whether it has an egg or lots of sperm
cells to merge with your DNA?
No exchange of genetic material. Involves only ONE
parent. Offspring is a CLONE of parent (same DNA)
Sponges and coral
reproduce asexually by
“budding”
Parthenogenesis:
Type of asexual reproduction where a female’s eggs
develop into offspring without ever being fertilized by a male! “Virgin birth”
Ex: some fish, insects, and a few species of frogs and lizards
Komodo
Dragon
Hammerhead shark
Combination of genetic material from TWO parents
What defines reproductive success?
1. ability to produce healthy offspring 2. ability to spread your genes
Females
• Limited number of eggs (400 human life)
• Gestation period (takes time)
Males
• Unlimited sperm production
• Estrus period (sexual receptivity)
• 100’s millions per ejaculation!
• Parental care
• Sexual success is to fertilize
as many females as possible.
• If she fails, she must wait until next year
to try again!
• Menopause
• Contribute nothing more than
GENES.
• Therefore, females spend substantially
more time and energy in
reproduction…more to risk.
** Results in SEXUAL CONFLICT = (males and females acting differently)
Males spend substantially more time and energy competing against other
males for potential mates. Consequently, males are usually larger and more
aggressive.
This is called Sexual Dimorphism…Males and females looking differently.
It is caused by Sexual Selection… different traits affect each sex differently
pheasant
peacock
Lion
In areas of high competition, sexual dimorphism is high.
In areas with low competition, sexual dimorphism is low
An adaptation or trait (physical or behavioral) that
allows you to reproduce.
Ex: A peacocks bright feathers attract a female.
* Does not necessarily mean increased survival
advantage!! (which is why we like “reproduction of
the fittest”)
* Ex: A brightly decorated peacock is more easily
seen by predators!!
* Reproductive potential outweighs risk of predation!
• Members of one sex (usually male) compete for mates.
• Common for herding animals
• Male secures a herd of females and aggressively defends his “harem”.
• Males can impregnate 100’s of females, therefore high competition for
females….it’s worth the risk of injury!
• High success for alpha males
•Females “synchrony” determines whether
the male will protect the females all year or just during the mating season
Sexual Selection: Males are larger and better able to fight and defend
Natural Selection: Females are larger and better able to produce,
store, carry, and provide resources for eggs.
Male elephant seals are up to four times larger
than the females and are extremely aggressive to
defend a harem of about 30 females, all in a large
group on a beach.
What about the “little guy? What about the Beta and Gamma males
and their genes? Other evolved behaviors include…
1. Female Mimicry
2. Satellite Male
“pretend” to be a
female. Sneak into
harem and mate.
Alpha male cannot
attend to ALL females
all the time!
Beta male hangs out
on the edge of
territory and
“intercepts” females
as they enter
3. Guarding /
Repelling
Males stays with female
the whole time to ensure
his sperm’s “safety”.
* Some butterflies leave a
repellant smell on the female
so no other males will mate
with her!
4. Sperm Competition
5. Dual Male Forms (phenotypes)
Some male insects have
a devise on their penis
to remove existing
sperm from other males.
Coho Salmon either large aggressive or small docile.
Some can seal up the
female genitalia =
chastity belt!!
Mimic female; get other
male to release sperm
The balance each other out and are perfectly stable.
• If more large ones, they would fight over territory too
much and small ones would thrive.
• If more small ones, the big ones wouldn’t fight and
would dominate the small ones.
•Both strategies equally successful
• Female chooses her mate.
• Competition among males exists, but not fighting or aggression
• Bases her choice on a trait she finds attractive.
• Males make sounds, visual cues, or give gifts to gain her attention
• Females have much to lose, so they should be picky when selecting a mate!
• Male may not be the best male, but rather the one with the best territory, or
builds the best nest, or brings the biggest piece of food.
Results in:
Courtship rituals ~ male and female perform together
Courtship displays ~ one sex performs for the other.
bowerbird displays
1. Identification – ensures mating is with the same species
2. Reduce aggression – some larger females may recognize the
smaller males as a threat and attack. His display will prove his ID
and calm her down (often times he gives her a gift of food).
3. Fitness assessment – size up the potential mate.
4. Mating readiness – ensures she is physiologically ready for
sex…is she ovulating?
5. Bonding – some animals need to ensure their compatibility with
their partner
• A Lek is a gathering area for males to “perform” for a female’s attention.
• Males gather to dance, call, or display their talents (no fighting)
• Center of the Lek is reserved for dominant males
•Frogs and toads = chorus
• Possess both male and female organs
• Can exchange sperm and egg simultaneously
• Self fertilization rarely occurs
• Usually found in solitary, slow-moving animals
~ difficult to find a mate
~ therefore, everyone is a mate!
* Occurs in animals with simple sex organs ONLY and external
fertilization. Not possible in mammals that have placenta, nipples,
uterus, live young, etc.
• Protandry: born male, then change to female
Clown fish
• Protogyny: born female, then change to male
grouper
1. Monogamy – exclusive one male and one female
2. Polygyny – one male mating with several females
Polygamy
3. Polyandry – one female mating with several males
4. Polygynandry – both sexes having many partners
Are these patterns genetically programmed in each species?
• relatively rare in nature (only 3% mammals are monogamous)
• common where resources are low and offspring are helpless
• common in rodents, but mostly found in birds - helpless until flight
• functional for nest protecting and food gathering
• when both parents invest, higher survival rate for offspring
• name a species that will only mate in private? Can you suggest a
reason for this unusual behavior?
Swans and geese stay together for life,
even when not breeding!
* Extra pair copulations is a common behavior for monogamous
couples
• one male mating with several females
• when food is plenty, and competition and predation are low, monogamy is not necessary.
• advantageous for males because, unlike female, he can increase his reproductability, he has
no gestation period, and does not lactate.
• most common mating system in the animal kingdom (97% mammal)
4 types:
1.
Resource defense
Female’s reproductive
success depends on
availability of resources
– food, water, safety
2. Female Harem Defense
Females gather in
defendable areas –
benefits from mutual
defense, alarm calls,
and safety.
Fleshman response: Male
curls lip upward and smells
female genitalia to determine
if she is sexually ready.
Small territory – single male
Common in hoofed mammals
Large territory – few males
3. Male Dominance
Resources are plentiful
and NOT clumped.
Females are free to
choose whomever she
wants…such as males
that are most FIT.
• Lek systems
~ elephant seal
~ lions, chimps
Study:
6% of bats did 80% of the
mating
4. Scramble Competition
Males actively search for
females, but with little
competition or fighting.
Usually large groups of
females and large groups of
males gathering
together…fighting
unnecessary.
• One female mates with many males
• Very rare in nature
• Few birds, insects, sea horse
• Female success is how many males she can mate with
• Female will lay many clutches of eggs for males to
incubate
• Males have small territory, while female has larger territory
encompassing many males areas (jacana bird). She will
breed with ALL the males!
Multiple mating pairs for both sexes.
A combination of polygynous males and polyandrous females
Usually occurs when male territories overlap, and each contain at
least one female.
A Male weasel will travel to find females. He
will mate and continue to travel. The females
will mate with many traveling males, and the
males will mate with multiple females along his
travels.
(mammalian)
1. Courtship: male sniffs and performs for the female. Recognition.
2. Pursuit: Male chases the female
3. Mounting: the male mounts the female
4. Lordosis: arched back posture with tail to the side. Invites insertion
5. Intromission: penis insertion
6. Ejaculation: occurs after multiple intromissions (thrusts)
7. Rest: refractory period for males. “Coolidge Effect” – refractory period in lab
rats is decreased (or eliminated) if different female is introduced! Named after
President Calvin Coolidge.
As defined by William Masters and Virginia Johnson (1957)
Researched sex - best seller, translated into 30 languages
Masters and Johnson Institute, St Louis
Defined 4 stages of sex:
1. Excitement
Vasocongestion: increase blood
flow to tissues (swelling), including
face, cheeks, and lips. Also
causes fluids to seep through =
lubrication.
2. Plateau
Vasoconstriction peaks
Breathing, pulse, bp, and
hr increase
Increase in BP, HR, and pulse.
Breasts swell
Scrotum pulls toward body.
Clitoris retracts into body
Labia majora flattens, minora
swells and opens. Cervix and
uterus retract creating room for
penis insertion.
Labia darkens
“Sex Flush” in females – redness
3. Orgasm
4. Resolution
Breathing, pulse, bp,
and hr increase
dramatically.
Excitement and
plateau reverse.
Muscular contraction
across body, including
face
Rhythmic muscular
contractions of genitalia,
including vagina, uterus
in females and urethral
bulb (prostate) and
penis in males.
Body returns to
unaroused state
Decrease in muscle
tension
Males have refractory
period where they
cannot become erect
or orgasm. Ranges
from minutes to days.
Females do not
experience this
Nitric oxide: increase blood flow to penis (viagra targets this chemical)
Serotonin: contract smooth muscle in genitalia
Epinephrine: increase muscle contraction during sexual activity, increase
vaginal pulse amplitude.
Dopamine: “pleasure chemical”. Responsible for sexual arousal.
Prolactin: reduces sexual desire (after sex). Inhibited by dopamine, and
effects dopamine release (too much causes impotence)
Androgen: primary male hormone (testosterone). Causes sexual desire.
Made by the sex organs.
Estrogen: primary female hormone. Does not cause desire, but leads to
lubrication during sex. Progesterone aids the female libido (not estrogen).
** Can males “smell” estrogen from female? May cause instant sexual
arousal.
** Most sex hormones are controlled by thalamus, hypothalamus, and pituitary
in the brain.
• “Reproductive cessation”
• Experienced in females only
• In humans:
- Lower estrogen levels leads to thinning vaginal walls and labia, and
decrease in lubrication…sex can be painful.
- Usually occurs in women about 50 years. High sexual activity during
this time can reduce the symptoms. Can also be treated with hormone
therapy.
- Menopause does NOT occur in males, however, aging men
experience shrinking testicles, decreased sperm count, a reduction in
volume and force of ejaculation, and a longer refractory period. Erectile
dysfunction (ED) is common.
- People over 70 years old:
65% women and 59% men still sexually active.