Fitness and Life Histories

Download Report

Transcript Fitness and Life Histories

A Simple Life
• Bacteria cells
reproduce by simple
• A cell is either
developing toward
reproduction or,
• The meaning of life is
clear – fitness is in
terms of reproduction
Life History
of Bacteria
• LAG PHASE: slow growth as the bacteria
acclimate to the food and nutrients
• LOG PHASE: metabolic machinery is running,
exponentially multiplication of population
density, doubling in number every few minutes.
• STATIONARY PHASE: competition for food
and nutrients causes number of bacteria to
• DEATH PHASE: Toxic waste products build up,
food is depleted and the bugs begin to die.
How many “Broods” per year?
• Univoltine - organisms having one brood per
• Bivoltine - organisms having two brood per
• Multivoltine organisms having more than two
brood per year ,
• How many times in its’ life does a bacterium
Semalparous – reproduce once
Many plants live for one
year – we plan them
each spring
Salmon grow for 3-6 years, first
in the river of their birth and
then in the sea. They then
return to spawn in the
headwaters of the river, and die.
Link – reproduction in Salmon
Fitness of a semelparous organism
• The product of viability and fecundity
w = vf
We know when they are
Univoltine fitness
• The reproductive “Burst” must be
synchronized to environmental factors
– The organism must start development early
enough to allow for growth and eventual
reproduction by the progeny
– Instead of “hibernating – the univoltine
organism can just die  no loss to the
– Many insect species have Univoltine and
Bivoltine representative
• Breeding many time in the lifetime
– Trees
– Most vertebrates
– Many marsupials
– Many arthropods
– Many flowers
Semelparous vs Iteroparous
• Energy for
production &
support of
• Energy for
• Energy for
• Energy for
metabolism to
support life
• Energy for future
Iteroparous fitness
• How do you tell if the species is fit?
• Long term “fitness” does not necessarily
mean an exponential burst of growth
• However – over evolutionary time,
species that do not “go forth and
multiply”, and been replaced by those
that do
Age structured life histories
• Each age group has a
unique probability of
survival and an age
specific fertility
• When all age classes
are growing at the
same exponential rate
– the population is in a
stable age- distribution
Age structure in Human
Why are these two
age structures
What can we predict
about the future
population growth of
these countries?
Offspring Size and
Offspring Survival
Reproductive Restraint
(fecundity = number of offspring)
More Eggs =
An intermediate
number of eggs is
best for fitness
Ageless organisms
Organisms that reproduce by fission or budding do not
age – there is no such thing as “an adult”
Organisms that reproduce only by eggs or ovules do
not follow conventional aging. They are “ambiguous”
Evolution of Aging
• Really long lived
trees can live
thousands of years.
• We are incapable of
studying aging
• These trees are
from very harsh
Link to trees of the Methuselah trail
Semelparous mortality
• In annual
plants– when
is over –
• There is no
advantage to
Interesting fact: Salmon that are castrated
live a lot longer than those that are allowed
to breed? Why to you think this is so?
Survival & Fertility
• Studied in cohorts
• Measured by
mortality and
fecundity per age
• At 2 weeks the
plateau= low
mortality high
Iteroparous aging
• Long-lived Animals
with "Negligible
• Turtles (video)
Sexual maturity at 30 years
Lifespan of 80-100 years
What should a lifespan be?
• Human aging
– Between 30 and 50
– Gray hair & Hair loss
– Reduced sexual
– Loss of muscle tone
– Unreliable memory
Aging is based on a decline in the
force of natural selection
• If natural selection eliminates an immature
organisms – the effect is complete (no viable
• If natural selection eliminates a young, but
reproducing organism the effect is to reduce the
reproductive potential of that organism
• If natural selection eliminates an organism that is
some producing – there is not biological effect.
Iteroparous aging and evoloution
• For some species,
there is an
advantage to longer
lifespan beyond the
time of fecundity
• Where does this
advantage end?
An experiment in changing in
aging patterns
• Forced selection for
deferred breeding
• All eggs laid before the
preferred age of
reproduction are
– 100 generation  major
physiological changes
– Resist stress better
– Fly longer
– Longer fecundity
Evolution and Aging
Food for thought
• There are no “ageless
vertebrates” – just longer
lived ones
• The life expectancies of longlived vertebrates seem to be
remarkably constant