EXAM 1 next Tuesday 12:30 here
Lectures/Chapters thru Thursday
Practice exam with answers:
6
On course website on Exam date
Format: Choice of ?s to answer
Longer: 4 of 5 (interpret figures)
Shorter: 4 of 6
Questions?
Next week’s lab: Stream Ecology
Next lecture: Ch 12 Family, Society, and Evolution
Next lab: Group Proposal Worksheet
due 3 days BEFORE lab
TA help with writing paper/data analysis
Where: 164 Burrill Computer Rooms
Use WEST door closest to Bio Library + NHB
When:
LAB
M
T
R
W
F
DATE/DAY
27S WED
27S WED
28S THURS
28S THURS
28S THURS
TIME
4-6
6-8 or…
4-6
6-8
8-10
Read: Guidelines: Scientific Writing (pg 33-39)
Guidelines: A Sample Manuscript (pg 41-51)
Chapter 11:
Sex and Evolution
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Objectives
Why sex?
Costs of sexual vs. asexual reproduction
Sex ratio
Mating systems
Plants
Animals
Sexual selection
Size important for offspring success
Male-male competition
Female choice
Sample Exam Question:
• The mean number of offspring is the same
for males and females in elephant seals, a
polygynous species. Individual male and
female seals differ greatly in their mating
success during any one breeding season.
• 1. Graph the results found in the first
sentence. Label axes.
• 2. In this species, which gender has the
more variable mating success? Write the
answer; then add this result to the graph.
• 3. What basic asymmetry of reproduction is
responsible for this difference? Explain.
Sexual reproduction
• mixes genetic material of
individuals---> variable offspring
• Meiosis --> variable gametes
• Fertilization ----> variable offspring
Asexual reproduction produces offspring
usually identical to parent and to one another.
Sexual reproduction is costly.
• Need a partner (takes time, energy,
resources)
• Lose good combinations of genes via
recombination
• Cost of meiosis: contribute only 1/2 of
genes
***The ‘cost of meiosis’: How many genes
does a female contribute via sexual vs.
asexual reproduction? Which mode of
reproduction does this cost favor?
***Explain how ‘cost of meiosis’ is avoided by:
• hermaphrodites (both male and female in one
individual)
• male parental care
Asexual reproduction….
• If advantageous, it should be common and
widely distributed among many lineages.
• Most asexual species are in genera with
sexual species.
• So no long evolutionary history
• Asexual lines die out over time…because
of reduced genetic variability?
What is the advantage of sexual
reproduction?
Asexual-->
Identical
offspring;
OK in
unchanging
environment
Sexual--->
offspring
differ from
parents--->
adaptive
in changing
environment?
Sex: any short-term advantage?
• Models on environmental variability fail to find
enough advantage to overcome cost of meiosis.
• An alternative hypothesis:
• Genetic variability is necessary to respond to
biological changes in the environment, especially
pathogens/parasites that can evolve virulence
rapidly and drive host species to extinction.
• The Red Queen Hypothesis:
• continual selective pressure from pathogen
requires continual evolution of populations --->
• need variable offspring and sex to stay ahead.
Sex ratio when sexes are separate
• modified by evolution to maximize
individual fitness. It balances the
contribution of genes to progeny
through male and female function.
• Usually 1:1 ratio of male : female
offspring at evolutionary equilibrium
• What happens if deviate from 1:1 ratio
that returns it to 1:1?
• Frequency-dependent selection:
– genes are selected for when at low
frequency and against when at
high frequency
***Explain how the rare-sex advantage
leads to a 1:1 sex ratio via frequencydependent selection.
Why do sex ratios deviate from 1:1?
When there is inbreeding and local mate
competition (e.g. competition among
brothers)---> favors production of daughters.
16 sets of genes in grandkids
49 sets of genes in grandkids
***Mother’s condition and skewed sex ratio
• Males must be large to be successful.
• Females mate regardless of size.
• Should stressed mother switch
nourishment to daughters or sons?
• Should well-fed mother switch
nourishment to daughters or sons?
MATING SYSTEMS: Individuals may have
female function, male function, or both.
• Hermaphrodites: both functions
•
simultaneous or sequential
• Monoecious: separate male and female flowers
• Dioecious: separate male and female
individuals
• ***How do plants and animals differ?
• Perfect flowers: both male and female
parts
• Can be outcrossing or selfing
depending on compatibility genes
***What is the pattern of pollen:ovule ratios?
Explain the pattern.
***Separate sexes versus hermaphroditism:
Is it advantageous to add a second sexual
function in A or B?
B
A
• Hermaphroditism when male or female
function can be added with little
depressing effect on opposite sexual
function.
***Sequential hermaphroditism: How does sex
change with body size? How is fitness
increased by changing sex? Why?
Protandry
Protogyny
Mating systems: patterns of pairing of
males and females within a population.
• Asymmetry in sexually reproducing
organisms:
• Female:
•
success depends on ability to make eggs
•
eggs require large amount of resource
•
ability to gather resources determines
•
her fecundity
• Male:
•
success depends on number of eggs he
can fertilize
•
small gametes require few resources
•
ability to mate with many females
determines his fecundity
Mating systems
Promiscuity:mating at large in population; no
bonds arises when males contribute little,
other than genes, to number or survival of
offspring
(all outcrossing plants and most animals)
Polygamy:
•
Polyandry: female mates with more than 1
male
•
Polygyny: male mates with more than 1
female
•
arises when males can monopolize
either resources or mates through malemale competition
Male-male aggression in polygyny; male
guards his harem.
• Monogamy: male and female mate only
with each other; strong pair bond
•
Males can increase fitness more by
caring for offspring than by seeking
additional matings.
Rare in mammals; common in
birds
• BUT can be extra-pair copulations
which leads to mate guarding by male
If females gain greater fitness by joining
already mated male that holds a superior
territory--> switch from monogamy to
polygyny.
Sexual selection: selection by one sex
for specific characteristics in the other
sex. It leads to:
sexual dimorphism
secondary sexual characteristics
Sexual dimorphism
Arises from:
1) dissimilar sexual functions of male
and female (e.g. larger body of
female-->more offspring)
2) male-male competition for female access
3) female choice among potential mates
females choose and males compete as a
consequence of asymmetry of parental
investment.
Male-male competition can result in malemale conflict and elaborate male
ornamentation (secondary sex traits).
Female choice based on male vocal display
No.
displays
by female
Male song repertoire size
Date of pair
formation
Repertoire size
Female choice when males compete for mates and
females choose among them ---> leads to elaborate
structures and courtship displays in males that
indicate their fitness.
***Is male-male competition or female
choice driving development of this
secondary sexual characteristic?
***Explain how female
choice can lead to
runaway sexual selection?
Do such traits represent
a handicap (and thus
demonstrate a superior
genotype?)(the handicap
principle)
Parasite-mediated sexual selection
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Parasites reduce host fitness.
Parasites alter male showiness.
Parasite resistance is inherited.
Females choose less
parasitized males.
• Parasite-mediated sexual selection:
• Lice produce feather damage.
• Doves with lice have reduced insulation and
are lighter in body mass.
• Females prefer clean to lousy males.
Sexual selection in plants
Male-male competition:
• extremes in floral display to attract
pollinators and get pollen moved to
other plants
Female choice among pollen:
• some males get selected during
germination of pollen tubes
Female choice among offspring:
selective abortion of developing seeds
and fruits on basis of paternity
***How is pollen germination a period of
female choice?
Sample Exam Question:
• The mean number of offspring is the same for
males and females in elephant seals, a
polygynous species. Individual male and female
seals differ greatly in their mating success during
any one breeding season.
• 1. Graph the results found in the first sentence.
Label axes.
• 2. In this species, which gender has the more
variable mating success? Write the answer; then
add this result to the graph.
• 3. What basic asymmetry of reproduction is
responsible for this difference? Explain.
Objectives
•
•
•
•
•
•
•
•
•
•
Why sex?
Costs of sexual vs. asexual reproduction
Sex ratio
Mating systems
Plants
Animals
Sexual selection
Size important for offspring success
Male-male competition
Female choice
Vocabulary
Chapte r 11 Sex and Evolution
gametes
meiosis
diploid
cost of meiosis
hermaphrodite
dioecious
outcrossing
fertilization
gonads
asexual reproductio n
pathogens
simultaneous
monoecious
sex ratio
inbreeding
local mate competition
promiscuity
monogamy
polyandry
polygyny
mate guarding
sneak
polygyny threshold
sexual selection
secondary sex characteristic male-male competitio n
runaway sexual selection handic ap princip le
zygote
haploid
clone
Red Queen hypothesis
sequential
perfect flowers
frequency-dependent
selection
haplodiploidy
polygamy
extra-paircopulations(EPC)
lek
sexual dimorphism
female choice
parasite-mediated sexual
selection