Download Chapter 8 - Life History Patterns

Chapter #8 Life History Patterns
(pg. 164 – 180)
8.1 – Reproduction May Be Sexual or Asexual
What are the goals for
living organisms?
8.2 – Sexual Reproduction Takes Many Forms
Parthenogenesis – born
w/o fertilization
Dioecious – Separate Males
and Females
Hermaphroditic –
Individual organisms with both
male and female organs.
Monoecious – separate
male and female flowers on the
same plant.
8.3 – Mating Systems Describe the Pairing
of Males and Females
Mating Systems Range from Monogamy to Promiscuity
8.3 – Mating Systems Describe the Pairing
of Males and Females
Polygamy – the acquisition by another individual of
two or more mates, none of which is mated to other
individuals. A pair bond exists between the
individuals and the individual having multiple mates
is generally not involved in caring for the young.
- Size of group depends upon synchrony
of fertility and receptivity.
- Small time period – fewer individuals.
- Longer time period – more individuals.
8.3 – Mating Systems Describe the Pairing
of Males and Females
Polygyny – Where an individual male pairs with
two or more females.
Polyandry – Where an individual female pairs with
two or more males (exception rather than the rule)
Access to
resources
Parental
Investment
8.3 – Mating Systems Describe the Pairing
of Males and Females
Relevance to Population Ecology
•
Life-history characteristics determine
–
Organization of individuals in space and time
•
–
How the population perpetuates itself
•
–
•
Examples…
discretely vs. continuously; rapidly vs. slowly, etc…
Which characteristics will be selected for and persist
within the population (due to sexual selection)
Conversely, selective pressures (abiotic factors,
distribution of resources, etc..) will affect the lifehistory patterns observed .
8.4 – Acquisition of a Mate Involves
Sexual Selection
What is the advantage to the individual and species by this display?
8.4 – Acquisition of a Mate Involves
Sexual Selection
Sexual Selection involves:
-Intrasexual selection: male:male competition or
female:female competition for access to potential
mates. The maintenance of traits that assist in
competition within the gender Æ successful
mating.
- Intersexual selection: differential attractiveness
of males to females and vice versa. The
maintenance of traits that are attractive to the
opposite gender.
Which gender determines the “winner”?
Intersexual Selection:
A Focus on Female Choice
• Material benefits: Nutrition Ex: hangflies)
– Length of mating time depends on quality and size of
“courtship gift”
Intersexual Selection:
A Focus on Female Choice
• Material benefits: Anti-predator substances
– Defensive compounds in arctiid moths
Photo: butterfly-conservation.org
Intersexual Selection:
A Focus on Female Choice
• Ability of males to provide sufficient sperm
– Female fruit flies (some species) choose virgin males.
Photo: San Francisco Exploratorium
Intersexual Selection:
A Focus on Female Choice
• Parental Ability
– Cannot assess directly
– May be correlated with
other features of the
male
– Example 1: Redwing
blackbirds
• “Epaulettes” correlated
with nest defense
• Courtship effort correlated
with feeding effort
Photo: Vancouverislandbirds.com
Intersexual Selection:
A Focus on Female Choice
• Parental Ability (Ex: sedge warbler)
– Size of song repertoire correlates with chick weight at
fledging
The Sedge Warbler (cont.)
• Female sedge
warblers choose on
the basis of repertoire
size.
– Thus they choose the
“most fit” males.
Intersexual Selection:
A Focus on Female Choice
• Health/Genetic Quality
– Example: song repertoire in great reed warbler where:
– Females chose males with larger repertoires.
– This was correlated with greater offspring survival
(unrelated to parental care).
Intersexual Selection:
A Focus on Female Choice
• Health/Genetic Quality
– Example: Bright coloration of sticklebacks
negatively correlated with low parasite loads
Intersexual Selection:
A Focus on Female Choice
• Health/Genetic quality (bright color
negatively correlated with parasite load)
– Advantages to females choosing these males
• Avoid getting parasites while mating Æ
• Avoid transferring parasites to young
• Are choosing healthier males; their health status
may be related to “genetic quality”
Origin/maintenance of Mate Choice
for “Exaggerated” Characteristics
•
In some species, why do males develop
what appear to be extreme traits that
actually can hamper their survival?
– Example: Peacock’s tail
Origin/maintenance of Mate Choice
for “Exaggerated” Characteristics
•
Hypothesis 1: Runaway selection (R.A.
Fisher - early 20th Century)
– Directional that takes on a life of its own
•
•
Starts as an “honest signal” Æ more extreme.
Mechanism: Females choose males with large
tails, multiple eyespots. Æ the next generation has
a higher proportion of these males.
–
–
Will work even if his traits are not honest signals of
quality. Why?
Evidence of arbitrary choices by females (bird band
example)
Origin/maintenance of Mate Choice
for “Exaggerated” Characteristics
•
Hypothesis 2: Handicap or “good genes”
hypothesis (R.A. Fisher)
– Exaggerated trait might decrease chance of
survival, only males with superior genes can
survive despite the handicap.
•
Example: peacock tail as a handicap.
– In this case, a female choosing a male with
these traits would be improving her fitness.
(His signal is an “honest signal” of fitness.)
Distinguishing Between Runaway
Selection and “Good Genes” (Petrie)
•
Methods
–
Males of different ornamentation/tail length randomly
bred with females
•
–
•
Young raised under identical conditions and then
released
Results
–
–
•
Why random?
Offspring of the “attractive” males weighed more at
day 84.
Offspring of the attractive males were more likely to be
alive after two years
Which hypothesis is supported by this data?
Marion Petrie’s Peacock Data
Source: http://blog.lib.umn.edu/denis036/thisweekinevolution/2008/06/guest_blogger_the_peacocks_tal.html
Origin/maintenance of Mate Choice
for “Exaggerated” Characteristics
•
How extreme can a characteristic become?
Under what conditions will directional
selection stop? (Think about costs vs.
benefits…)
Intrasexual Selection
- Adaptations to Gain Access to Females –
• Dominance behavior & characteristics
– Example 1: sexual dimorphism in elephant seals
Male-male competition and sexual dimorphism (seals)
NOTE: Each point represents a species
Intrasexual Selection
- Adaptations to Gain Access to Females –
• Weaponry for fighting with other males.
• Example: dung beetle!
Male dung beetle, Phanaeus vindex (Rattlebox photography)
Intrasexual Selection
- Adaptations to Gain Access to Females –
• Sneaker strategies
– Example: Plainfin
midshipmen
• Dominant male features
and behavior
– Nest building, singing,
guarding
• Sneaker male features and
behavior
– No nest, no singing, just
sex…
– Small fish, big balls!
Dung Beetles - Two Morphs
• Behavioral and
morphological differences
similar to midshipmen
– Large, dominant males with
horns defend burrows
– Small, hornless males with “big
balls” sneak
• Midshipmen
– Genetically-based differences
• Dung beetles
– Nutritionally-based differences
Intrasexual Selection
- Adaptations Favoring Use of Sperm • Displacing or inactivating rival sperm
– Damselfly “scooper” penis
Intrasexual Selection
- Adaptations Favoring Use of Sperm • Displacing or inactivating rival sperm
– Example: Chemical sperm inactivation in fruit
flies
Photo: San Francisco Exploratorium
Intrasexual Selection
- Adaptations Favoring Use of Sperm • Mechanisms to
avoid sperm
displacement
– Mate guarding
(Example: many
crab species)
Intrasexual Selection
- Adaptations Favoring Use of Sperm • Mechanisms to avoid sperm displacement
– Prolonged mating and cannibalism (example: redback
spider)
• Female less likely to mate
with another if she eats him
• He has low likelihood of
finding a new mate (high
predation)
– Andrade, 1996
Intrasexual Selection
- Adaptations Favoring Use of Sperm • Mechanisms to avoid sperm displacement
– Anti-aphrodisiac (Example: Heliconius erato)
8.5 – Females May Acquire Mates Based
on Resources
In sexual Selection, the female will select
mate(s) based on their physical characteristics,
because this is an indirect measure of their
health OR their (their mate’s) ability to acquire
and defend resources (e.g., food and space).
Territoriality - Monogamy
Sexual Selection
•
Defined:
– Selection for characteristics/behaviors that
maximize chances of mating and producing
the most, and highest quality, offspring.
– A category within “natural selection”
•
General pattern: Male-male competition
and female choice
– Common pattern with many exceptions!
Example: Satin bowerbird mating
behavior
• Each male builds an
elaborate bower where
he conducts his
courtship display
• Bowers located near
each other
• Each female visits
several times, finally
chooses a mate
#
Bowerbird Males: of Mates
• Some males are much more successful than others.
#
Bowerbird Females: of Mates
Only ~1/3 of females have >1 mate.
Why Do Males Usually Compete, While
Females Choose?
• Hypothesis 1, A.J. Bateman: “Eggs are expensive,
sperm is cheap!”
• Amount of energy
invested in a single
gamete is much
greater for females
(eggs) than for males
(sperm)
– Female bird may
invest up to 30% of
body weight in eggs.
“Eggs Are Expensive, Sperm is
Cheap.”
• Difference in investment per gamete
– Example: Fairy wrens
• Males have 8 billion sperm in testes at once
• Females lay six eggs maximum per clutch
• Female limited by egg production,
• Male limited by number of mates only
(presumably unlimited sperm)
• Operational sex ratio skewed toward males
But, Is Sperm Really Cheap?
•
It often takes a large number of sperm to
fertilize a single egg, due to
– Hostile environment within female
•
•
Acid
Attacks by the immune system
But, Is Sperm Really Cheap?
• Sperm competition among males
– Occurs when females have multiple mates
• Possibly the predominant situation
• Fitness advantages for female (will explore in next
lecture)
– Some males may actually run out of sperm…
• Garter snakes, zebra finch, blue crabs, rams…
What if there is No Sperm
Competition?
• In sea horses, eggs are
deposited into
pouches, and there is
not sperm competition.
– Why not?
• Male sea horses have
relatively low sperm
counts!
But, Is Sperm Really Cheap?
• Drosophila bifurca:
one sperm with long
tail
– Sperm tail is 20x
length of his body.
– His testes make up
11% of his body mass.
Why Do Males Usually Compete, While
Females Choose?
•
Hypothesis 2 (R. Trivers):
Competition vs. choice is
based on individual with
the most total parental
investment
–
–
Often the female (example:
mammals)
But in some species, male
makes a greater total
investment.
Gulf Pipefish
• While male cares for a single brood, a female can produce two
clutches of eggs Æ male has greater total parental investment
– Operational sex ratio skewed toward females.
• Males choose large, ornamented females over small, drab
ones.
Female
Male
Overview
•
A mating system includes
–
–
–
•
Types of mating systems
–
–
–
•
how members of a particular species (or population)
choose and bond with mates
how many mates per individual
how parental care (if it occurs) takes place.
Monogamy: One male mates with one female
Polygyny: One male mates with several females
Polyandry: One female mates with several males
“Social” vs. “genetic” monogamy
Key Principles
•
The system that evolves depends upon the individual
interests of each gender.
Male and female interests are often in conflict. Why?
•
–
–
–
•
Differences in gamete investment and/or total parental
investment
Male “default” system = ____________. Why?
Is there a female default system? Why?
Interests/behavior of one gender serve to constrain
options available to the other gender.
Polygyny
• Resource defense polygyny
– Example: African cichlid fish, Lamprologus
callipterus
• Defended resource = shells in which females lay eggs
Polygyny
• Female defense polygyny
– Example: Elephant seals (females aggregate)
Photo: www.driftersister.com
Polygyny
• Female defense polygyny
– Example: Elephant seals (males compete for
beachmaster status)
Photo: www.wetasschronicles.com
Polygyny
• Lek polygyny
– Males clump, but not due to another resource
• Males become the clumped resource!
– Example 1: satin bowerbirds
Satin Bowerbirds: multiple signals of health and
fitness (and good genes?)
Polygyny
• Lek polygyny
– Males clump, but not due to another resource
• Males become the clumped resource!
– Example 2: sage grouse (filoplumes and sound
in central area of lek determines mate
preference)
Polygyny
• Lek polygyny
– Example 3: bullfrogs
• Females choose males with longest, loudest and deepest calls
• But don’t forget the sneaky f--kers
www.tc.umn.edu
Polygyny: benefits/costs
•
Male:
– number of offspring (+)
•
Female:
– gets a high-quality male (+)
– gets less of the male’s time and attention for
•
•
raising young
being defended against predators
Monogamy
• Common or rare?
• In which group of
animals is it most
common?
• What hypotheses
would account for
it?
www.magicmud.com
Monogamy: alternate
hypotheses
•
Mate assistance: it
takes two parents to
raise the offspring
– Example: Adelie
penguins
– Both parents needed
for chick survival
Photo: Karen Haberman
Monogamy: alternate hypotheses
•
Mate guarding: guarding assures paternity;
not guarding jeopardizes it.
– Especially critical if females are rare or
receptive for a limited time
– Example: many crab species
Monogamy: alternate hypotheses
•
Female-enforced
monogamy
–
–
–
Similar to mate-guarding, but
done by female.
Example: Burying beetles
A female would lose
resources, and possibly her
offspring if she allows her
male to mate again.
www.royalbertmuseum.ca
Monogamy: alternate hypotheses
•
Danger “theory”
– Leaving Æ increases
chance of dying if
predation rates are
high.
– Example: The
mantis shrimp
Lysiosquilla sulcata
Lysiosquilla sp. Opencage.info
Mantis shrimp (another type)
Monogamy: alternate hypotheses
•
Pop ‘em out “theory”
– Highly fertile mate
– Not worth
time/energy to seek
another.
– Example: Djungarian
hamsters
bbs.petsky.com.cn
Social Monogamy and extra-pair
copulations
•
Extra-pair copulations can increase fitness of
participants.
Males: More mates Æ more offspring possible.
Females:
•
•
–
–
Historical (not current) ideas: no advantage for
females
Observational/experimental evidence: clear fitness
benefits documented for some species
•
Example: Yellow-toothed cavy
Yellow-toothed cavy: Offspring survival as a
function of multiple mates for females
Social Monogamy and extra-pair
copulations
•
Direct fitness benefits: genetically based
– Good genes
•
What does this mean?
– Genetic compatibility
•
What does this mean?
– Genetic variability among offspring
•
Why important?
Social Monogamy and extra-pair
copulations
•
Other benefits that may improve fitness for
females:
– More resources hypothesis
•
Example: Orange-rumped honeyguides swap food
for sex.
– Better protection/care hypothesis
•
Example: Dunnocks (European song bird)
–
Mate with two males Æ both care for young
– Infanticide reduction hypothesis
•
Example: chimpanzees (who’s dad?)
Polyandry (w/o polygyny)
•
Spotted sandpipers: near-complete sex-role
reversal
–
–
–
Females arrive on breeding grounds; compete with
other females for territories.
Initial male arrives, mates, cares for her first clutch.
Second male arrives later, mates, and cares for her
second clutch.
What Circumstances Promote
Polyandry?
•
Female: only lays 4 eggs at once
– Add eggs (experimentally) Æ decrease the
total young successfully raised
•
Related to incubation effort and protection
– Female can ↑ reproductive success by laying a
second broodÆ
•
•
Needs second mate
Reproductive success limited by mates
rather than gametes in this case
What Circumstances Promote
Polyandry?
•
Why would males “comply?”
– Operational sex ratio biased toward males
(related to absolute ratio for this species)
– She abandons Æ
•
•
He stays Æ offspring survive
He leaves Æ offspring die
– Male 1: Certain of paternity for clutch 1;
possibility of paternity for clutch 2
•
How is this possible?
– Male 2: Later arrivals less dominant, but still
have a chance of paternity if they stay.
What Circumstances Promote
Polyandry?
•
Food fluctuation hypothesis
– In food-poor years, females put all energy into
eggs and have no energy left for care of
eggs/young.
•
Mate assistance (by male) essential Æ monogamy
– In food-rich years (i.e. many mayflies), the
female “recovers” her body mass and can lay
another batch
•
Monogamy Æ Polyandry
What Circumstances Promote
Polyandry?
•
Heavy predation pressure on nests
– Multiple nests assure that at least some young
will survive.
•
•
Male is needed to prevent predation
Young will all be lost if he doesn’t stay.
Patterns of Reproductive Effort
Variations
•
Numbers of young produced at a time
–
•
More young = less parental
investment/individualÆ high mortality
among young
Care of eggs/larvae
–
•
Variability in parental investment
Type of young produced
–
Precocial vs. altricial offspring (What is the
difference?)
Patterns of Reproductive Effort
Variations
•
Number of reproductive events in a lifetime
–
Semelparous: one big reproductive event in
lifetime/many offspring
•
•
–
Itoparous: many reproductive events in lifetime/
fewer offspring per event.
•
•
Many are relatively short-lived (squid, annual plants)
But some are long-lived (periodical cicadas)
Common especially birds and mammals
Timing is an issue:
–
–
begin early Æ materials/energy into reproduction,
Begin later Æ materials/energy into survival and
growth
“r ” vs. “K” strategists
“r”-strategists
Semelparous
Many offspring
“K”-strategists
Itoparous
Few offspring
Little/no parental investment High levels of investment per
per individual offspring
individual offspring
Relatively short lifespan
Relatively long lifespan
Begin to reproduce relatively
early in life
Begin to reproduce relatively
later in life
Good colonizers of newly
Not usually colonizers, but
available habitat, but often
arrive later in succession,
not effective competitors
compete successfully