Transcript EXAM 1 next Tuesday 12:30 here Lectures/Chapters thru Thursday

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