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Lecture

Biology 2483A Lecture Notes - Neoteny, Anisogamy, Sexual Maturity

11 pages26 viewsFall 2013

Department
Biology
Course Code
Biology 2483A
Professor
Mark Moscicki

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Figure 7.23 Clownfish Size Hierarchies
Ecology-Lecture 7
Oct 3 2013
Life History
Sequence of live events in an organism. (growth/development/reproduction/death) We are
interested in all of these factors. For a human, you go through a period of growth and then you
reproduce. On average, you live to 80. Our perception of life history is biased based on our
experiences. However, many organisms experience very different life histories.
Life history characteristics include: age and size at sexual maturity, amount and timing of
reproduction, survival and mortality rates
Clown Fish Case Study-FINDING NEMO
Clown Fish hang in sea anemones for protection. Anemones sting the predators of clownfish,
but not the clownfish themselves. The fish also benefit the anemone by eating its parasites or
driving its predators away.
Usually 2-6 will hang out in one sea anemone for their entire adult lives. However, it is unlikely
that they are related.
Largest clownfish is female. Next largest is the breeding male. All other fish are immature non
breeders. They are simply biting their time waiting for the others to die off so that they can take
their place. (based on body size) In finding Nemo, his mom died. If this actually happened, his
dad would have turned into a female. If female died, breeding male would take her place and
the next fish in line will become the breeding male.
Hatchlings move out of the anemone, and
juveniles must find a new anemone to inhabit.
The reef is dangerous for them. They grow in
open water and then come back to the reef to
find open spots in anemones. When a juvenile
enters an anemone, they are only able to stay if
there is room.
Why do the Clownfish Maintain the
Heirarchy?
Clown fish are dependent on survival of being
around anemone. (colorful and slow) They are
easy prey outside of the anemone. If you are small and you try to change things, you get pushed
out of the anemone and get eaten. You see through natural selection that aggressive clownfish
do not end up reproducing.
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Therefore, there is strong selection pressure to avoid conflict. Sea anemones are a scarce
resource for clownfish.
Clown fish have growth regulation. They are able to avoid conflict by making sure they do not
grow too big at any one time. (allows them to ensure they live to an age in which they can
reproduce)
Life History Diversity
Within a species there is a lot of diversity. There are genetic differences, differences in their
environment and differences in their life history. Life history is a record of major events related
to its growth, development, reproduction, and survival.
Individuals within a species show variation in life history traits due to genetic variation or
environmental conditions.
The life history strategy of a
species is the overall pattern in
average timing and nature of life
history events. Life decisions are
made but these are genetically
decided. (How many offspring
and how big are they going to
be? Are you going to care for
offspring? How long to live? )
Natural selection favours
individuals whose life history
traits result in their having a
better chance of surviving and
reproducing. An organism
predisposed to do certain things
may or may not be selected for.
Optimal Life History
Most organisms you would think would converge on a certain optimal life history to maximize
their fitness (genetic contribution to future generations). However, it is not perfect. This comes
down to ecological tradeoffs.
Phenotypic Plasticity
A certain life strategy may be favoured under some conditions and not favoured under other
conditions. You can only allocate resources in one direction at any one time.
This is why there is environmental plasticity. There is a certain amount of plasticity in any
organism where they optimize how they grow/reproduce in respond to the environment
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Environmental conditions can produce different phenotypes from the same genotype. One
example is growth and development. You tend to grow faster at higher temperatures.
Individuals of a pine tree species are separated into 2 populations based on the environments in
which they grow. (Ones that grow in cool moist and ones that grow in desert.) For any given
height, you have a thinner diameter trunk for cool areas and a larger diameter trunk for desert
trees. This is due to species physiology. Dry environment trees need to conduct water so the
wide trunks allow them to have a lot of root/vessel elements so they can draw up water.
Morphs
Phenotypic plasticity may result in a continuous range of sizes; or discrete types called morphs
(ALL OR NOTHING) There is nothing in between. Depending on the environment, you assume
one of two phenotypes (another form of environmental plasticity)
You can call it a polyphenism in this case because you have one genotype that can produce
several distinct morphs.
An example of this is toad tadpoles. We have omnivore morphs and carnivore morphs.
(both from same genotype)What they develop into depends on the food they consume
in early development. Depending on the pond they are in, they can become omnivore
morphs and feed on detritus and junk at the bottom of the ponds, or they can become
carnivores (large jaws) that feed on fairy shrimp in the water column. Carnivore tadpoles
tend to grow very fast and they morph early. This is because they live in semi permanent
ponds (ephemeral ponds). It is to your advantage to get out of the pond as quickly as
you can so you do not dry up and die before you gain enough energy to turn to frogs and
get out. Omnivores grow slowly because they dwell in long lasting ponds. When they
eventually turn into toads, they are much better conditioned that toads from carnivore
tadpoles (better survival)
Different body morphs result from different growth rates of body parts in both the Ponderosa
pines and spadefoot toads. This is known as allometric growth. Allometric growth is when
Changes in life history traits can cause
change in adult morphology.
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