Transcript Slide 1

Life History
Photo of size variation in seeds from Panama from http://www.tc.umn.edu/~hmuller/
Life History
Major events related to an organism’s
growth, development, reproduction & survival
Timing, duration, phenology, rate, allocation, allometry, etc.
shaped by natural selection
Life-history traits vary among individuals & populations
Wood duck w/ 5
Wood duck w/ 7
Mallard w/ 11
Life-history strategy is a population-level representation
Photos from: http://westboroughlandtrust.org/nn/nn54.php;
http://portlandbirds.blogspot.com/2010_05_01_archive.html;
http://www.rampantscotland.com/colour/supplement070519.htm
Asexual vs. sexual reproduction
Binary fission produces genetically identical clones
Paramecium
Image from http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=OLIH023P&File_type=GIF
Asexual vs. sexual reproduction
Sexual reproduction produces genetically variable offspring
Isogamous
gametes
Anisogamous
gametes
Cain, Bowman & Hacker (2014), Fig. 7.7
Chlamydomonas
Homo sapiens
Asexual vs. sexual reproduction
A “cost of sex” / “cost of males”
Assume each adult
female in a
population
produces 4
offspring, either
asexually or
sexually
Cain, Bowman & Hacker (2014), Fig. 7.8
Asexual vs. sexual reproduction
Benefit of sex: Genetic variation
E.g., Red Queen Hypothesis (coping with ever-evolving enemies)
From a statement the
Red Queen makes to Alice in
Lewis Carroll’s
“Through the Looking Glass”
(“Alice in Wonderland”):
“Now, here, you see, it takes all
the running you can do, to keep
in the same place”
Photo of harvestman with parasitic mites from Wikimedia Commons
Simple vs. complex life cycles
Complex life cycle – 2 or more distinct stages that differ in
habitat, physiology, or morphology
E.g., Alternation of Generations in plants
E.g., Holometabolous
insects
Larval, pupal
& adult wasps
E.g., Anadromous &
catadromous fishes
Anadromous
salmon adults live
at sea, but spawn
in freshwater
E.g., Metamorphic
amphibians
Photos from Wikimedia Commons
Herbivorous, aquatic
tadpole will become
carnivorous,
terrestrial adult
The Life Cycle of Animals – Illustrated for Humans
Generation 1
Generation 2
Specialized cells
undergo meiosis
to produce gametes
Gametes fuse
during fertilization
to become a zygote
AA
XX
Gen. 3
A
X
Aa
XX
AA
XY
a
X
A
Y
Aa
XY
a
X
From the single-celled zygote stage
onward, cells undergo mitosis to increase
the number of cells in the maturing individual.
Aa
XX
Multicellular individuals;
Diploid (2n) cells
Aa
XY
Unicellular
gametes;
Haploid (1n)
cells
Unicellular
zygote;
Diploid (2n)
cell
Muticellular individuals;
Diploid (2n) cells
The Life Cycle of Fungi – Illustrated for Bread Mold
Several
generations
Multiple rounds of
asexual reproduction
possible; all cell
divisions occur by
mitosis.
A
+
Multiple rounds of
asexual reproduction
possible; all cell
divisions occur by
mitosis.
Brief intergenerational
zygote stage
Several
generations
Zygotic
meiosis
Aa
a
+-
-
Fusion of
compatible hyphae
(plasmogamy and
karyogamy) to
form a zygote-like
structure
a
-
Multiple rounds of
asexual reproduction
possible; all cell
divisions occur by
mitosis.
a
-
Haploid (1n)
cells of hyphae
Multiple rounds of
asexual reproduction
possible; all cell
divisions occur by
mitosis.
a
+
Diploid (2n)
zygote
Haploid (1n)
spore
Haploid (1n)
cells of hyphae
The Life Cycle of Plants (Alternation of Generations) –
Illustrated for a Dioecious Flower
Generation 1
Specialized cells
undergo meiosis
to produce spores
AA
bb
A
b
Gen. 4
Generation 3
Generation 2
Gametes fuse
during fertilization
to become a zygote
Pollen
grain
a
B
aa
BB
A
b
Aa
Bb
a
B
Aa
Bb
Multicellular
sporophyte
Diploid (2n)
cells
Embryo
sac
A
b
Aa
Bb
a
B
Single-celled spores undergo mitosis
to increase the number of cells in the
maturing gametophyte. Mature
gametophyte produces gametes
by mitosis
Unicellular
spores
Multicellular
gametophyte
Haploid (1n)
cells
Unicellular
gametes
Specialized cells
undergo meiosis
to produce spores
Unicellular
zygote
Multicellular
sporophyte
Diploid (2n)
cells
Unicellular
spores of
gametophyte
Haploid (1n)
cells
Allocation Trade-offs, Costs & Benefits, Constraints
Resources
vs.
Photos from Wikimedia Commons
Allocation Trade-offs, Costs & Benefits, Constraints
There is no free lunch
A jack of all trades is master of none
E.g., offspring or propagule size-number tradeoff
Number
Size
Each dot represents the life-history strategy of a given species in a given clade
Allocation Trade-offs, Costs & Benefits, Constraints
Constraint lines and wedge-shaped distributions
Number
Size
Each dot represents the life-history strategy of a given species in a given clade
Design Trade-offs, Costs & Benefits, Constraints
Design: shape, function, etc.
vs.
Photos from Wikimedia Commons
Design Trade-offs, Costs & Benefits, Constraints
A jack of all trades is master of none
E.g., consider pond-breeding salamander species
in ephemeral pools vs. stable ponds
What life-history strategy would perform best in each habitat?
Is there a “one size fits all” solution?
Semelparous vs. Iteroparous
(Monocarpic vs. Polycarpic)
Often entails a reproduction – survival tradeoff
Monocarpic talipot palm
Polycarpic coconut palm
Photo of monocarpic talipot palm from http://www.etawau.com/Agriculture/IndexTrees.htm;
photo of polycarpic coconut palm from http://www.hawaii.edu/cpis/MI/plants/ni.html
r-selected vs. K-selected
General environmental or population-level correlates
Disturbance
Population growth rate
Stability
K-selected
r-selected
Correlated organismal traits
Body size
Life span
Parental investment in offspring
Developmental rate
Rate of maturation
Reproductive rate
The concepts of r-selection & K-selection originated with MacArthur & Wilson (1967)
Grime’s Triangular Model
Competitive
Ruderal (“weedy”)
Stress-tolerant
Competition = “tendency of
neighboring plants to utilize
the same quantum of light,
ion of a mineral nutrient,
molecule of water, or volume
of space”
Disturbance = “process that
destroys plant biomass”
Stress = “abiotic factor that
limits vegetative growth”
Image from http://hosho.ees.hokudai.ac.jp/~tsuyu/top/dct/lc.html;
original concept from Grime (1977) American Naturalist
Competition – Colonization Tradeoff
Colonization
Ability
Competitive Ability
The concept was elaborated by Rees & Westoby (1997) Oikos
Tolerance – Fecundity Tradeoff
Fecundity
Stress Tolerance
Original concept from Muller-Landau (2010) Proceedings of the National Academy of Sciences
Ontogenetic niche shifts
Occur routinely in organisms with complex life cycles,
but occur in other organisms as well
Aquatic larva
Winged adult
Photo of hellgrammite (larva) and adult Dobson flies (Order Megaloptera) from Wikimedia Commons
A Classic Example: Clutch Size
David Lack
“Lack Clutch Size” = clutch size that maximizes the number
of offspring that a parent can rear to maturity, given the tradeoff between
investment per offspring vs. number of offspring
Experimental evidence through clutch-size manipulation experiments
Original concept from Lack (1947) Ibis