E3: 3/27- Notes on Animal Form and Function Lecture (REC)(DOC)

Introduction to Animal Form and Function

• Discussion of oversized animals popularized in 1950s movies due to nuclear accidents.

• Question posed: Why don’t we observe such enormous animals in nature?

Evolutionary Trade-offs and Limits

• Animals are constructed within physical and evolutionary limits.

• Evolution arises from rare mutations and existing genetic variation.

• The framework of evolution sets the stage for traits that can respond to environmental conditions.

• Importance of Phenotypic Plasticity: Adaptation of traits in response to environmental conditions without genetic change (e.g., leaf size of trees).

Phenotypic Plasticity in Organisms

• Example of Plasticity: Shade leaves are larger as a response to low light conditions. When placed in sunlight, they grow smaller leaves.

• Organisms can exhibit size changes based on available resources (e.g., frogs grow larger with more food but max out at a point due to bodily support limitations).

Energy Acquisition and Survival

• Animals have trade-offs in their approach to acquiring and using energy, crucial for survival and reproduction.

Energy Acquisition Strategies

• Dietary Habits: Organisms are classified as:

  • Herbivores: Only eat plants (e.g., cows).

  • Carnivores: Only eat meat (e.g., lions).

  • Omnivores: Eat both plants and animals (e.g., humans).

  • Being omnivorous allows moderate success in both without being particularly good at either.

• Generalists vs. Specialists:

  • Generalists (e.g., jungle crow): Adaptability to many foods but subjected to competition.

  • Specialists (e.g., Violet-ear hummingbird): Highly effective at specific food sources but at risk if that source disappears.

Storage and Use of Energy

• Different adaptations for storing energy:

  • Example: Dromedary camels use fat in their humps as energy storage, not water.

  • Body temperature regulation is divided into two categories:

  • Endothermic Animals: Generate heat internally (e.g., mammals, birds) and require frequent food intake.

  • Ectothermic Animals: Regulate temperature through environmental conditions (e.g., reptiles, fish).

Size and Energy Use

• Trade-offs exist between being small or large:

  • Smaller animals lose heat and water faster and may be more preyed upon; however, they have more shelter options and need less food.

  • Larger animals have better heat retention and fewer predators; however, they require more food and have fewer options for shelter.

Surface Area to Volume Ratio

• Explanation of the surface area to volume ratio and its impact on heat loss and food requirements:

  • Smaller animals have a higher ratio and thus higher metabolic rates, needing more food relative to their size.

Strategies for Survival

• Methods to avoid predation:

  • Defense Mechanisms: Being too large (e.g., sea turtles), unpalatable, or toxic (e.g., poison dart frogs).

  • Aposematic Coloration: Warning coloration to signal toxicity to potential predators.

  • Mimicry: Batesian mimicry where a non-toxic species mimics a toxic one.

• Cryptic Coloration: Camouflage that helps in avoiding detection.

• Behavioral Strategies: Running away or using flight initiation distances influenced by environmental factors and predator behaviors.

Reproduction Strategies

• Importance of finding mates and the different signaling methods (e.g., visual, auditory, pheromones).

• Mating Systems: Monogamy, polygamy, or polyandry—strategies depending on mate availability.

• Fecundity vs. Survivorship: Trade-offs between having many offspring with low survivorship versus fewer offspring with higher survival rates.

• Examples:

  • High Fecundity: Mustard plants producing thousands of seeds with low survivorship.

  • Low Fecundity: Coconut palms with fewer seeds but high survivorship.

Environmental Fluctuations and Reproductive Strategies

• Strategies adapted for fluctuating environments, such as staggered egg-laying by red-tailed hawks to cope with food availability.

• Balancing energy expenditure and offspring survival is key to reproductive strategies in changing habitats.

Conclusion

• Emphasis on the balance between energy acquisition, survival, and reproductive strategies as fundamental trade-offs for animals.

Introduction
A. Limits and tradeoffs
Hollywood’s giant fire-breathing monsters with extra limbs, bugs the size of skyscrapers, giant
squids that can walk around on land – they would probably have a pretty easy time surviving.
So why don’t they exist?
1. Designs have plasticity (flexibility) within certain limits. Plasticity is the ability
for trait to change based on environmental conditions.
a) Amphibians like frogs and toads grow throughout their whole lives. The rate
at which they grow is dependent upon many factors including resource
availability and space. However, even with infinite resources, time, and
space, a frog could only ever get to be about the size of a dinner plate. This
is because they have no supporting structures on their ventral side. If they
were to become too large, they could not support their own internal organs.
2. There’s never just one selective pressure; as you get better at one thing, you often
have to sacrifice something else. Everything is based on compromise.
a) Example: Giraffes have very long legs and necks which help them reach the
tops of trees, avoid predation, and large necks are selected for in males to win
fights against other males. However, these long necks require specialized
vein systems in order to keep them alive while they drink, and even so they
have to put themselves in an extremely vulnerable position to do so. Large
males will often get on their knees in order to drink, making it much harder to
get away should a predator approach.
b) Environmental variability: Different environments demand different suites
of adaptations, e.g. an animal can’t master terrestrial life without
compromising aquatic life. A hippo is a comparatively slow swimmer
compared to a killer whale, but much more versatile on land.
c) Becoming larger to escape predation or to increase one’s competitive edge
against other species requires multicellularity, cell specialization, and organ
systems for transporting nutrients, water, energy sources and waste products
between the outer and inner environment of the organism.
II. Energy
A. Obtaining energy
1. For animals this means eating, but there are many different things out there to eat as
well as ways of getting them and converting them into energy.
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a) Generalists vs. Specialists: A generalist is good in everything, master of
nothing. There are advantages to both, but few organisms can shift between
being an effective generalist or specialist.
(1) Example: Corvids such as the jungle crow are opportunistic
omnivores capable of eating a wide range of foods including fruits,
insects, and human garbage. As such, they are widespread and can be
found in most habitats across the globe, except for South America.
Hummingbirds, like the sparkling violetear, live exclusively in North
and South America and almost entirely in the tropics, with many
being endemic to only small and very specific habitats.
Hummingbirds are known for their unique bills which mirror the
flowers from which they get their food. As a result, hummingbirds
rarely have to compete for nectar with other animals because they are
specifically suited to their local flowers. Even within hummingbirds,
some species specialize in specific flowers that only they can get
nectar from. Crows are in constant competition with other animals,
many of which are better at getting specific food items than they are,
but since they have so many options they can always find something
to eat.
b) Herbivores, Omnivores, and Carnivores
(1) Energy source variability: Different energy sources demand
different, mostly incompatible adaptations to access them, e.g.
evolutionary designs of plants vs. animals: no animal is able to
photosynthesize, and no plants eat other organisms. Carnivorous
plants kill insects but do so for a nitrogen supplement rather than a
calorie source. Plants have systems for accessing the glucose from
photosynthesis, but they have no mechanism for eating and internally
digesting other organisms to obtain glucose. Another example: a lion
can’t digest, much less chew, grasses like a cow (the interlocking
canines do not allow lateral grinding movements), nor could a cow
capture, kill and rip apart the flesh/meat of another herbivore (to
begin with, a cow has no upper incisors or canine teeth).
(2) Digestive System: Breakdown of larger compounds into smaller,
useable ones – digestive systems of carnivores are simpler than those
of herbivores.
B. Storing energy
1. Food isn’t always readily available, and even when it is you can’t spend your all
your time eating! (Though some animals devote a good chunk of time to it.) Energy
from food needs to be stored for later. How much of it and for what purpose depends
on the animal.
a) Example: Dromedary camels are large mammals that live in harsh
environments where energy is hard to come by. As such, they have
adaptations which allow them to store as much energy as possible over long
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periods of time. The hump on a camel is actually filled with fat stores; a well-
fed camel will have a large hump which it can use for energy when food is
harder to find. They can also drink up to 20 gallons of water at a time, and
their urine is extremely thick so as not to waste any more water than
necessary.
b) Endothermy vs. Ectothermy: Even endothermic animals that hibernate and
show a temperature near ambient need to periodically awaken to dump
metabolic wastes and restock energy supplies. Ectothermic animals (e.g.
snake) have a much lower energy lifestyle than endotherms (e.g.,
bird/mammal), and an ectothermic animal becoming endothermic would be
unlikely to obtain sufficient food to sustain it. Most reptiles rarely drink
water and find/need prey only once every few weeks.
(1) Respiratory System: Brings in O2, releases CO2. Endotherms have
more complex lungs for greater oxygen usage.
(2) Cardiovascular System: Transports nutrients, wastes and gases
throughout body. Most complex in endotherms.
C. Using Energy
1. Once you have the systems in place to get and store energy, you have to decide how,
when, and for what purpose you will use it. Some animals travel the circumference
of the earth every year while others barely move at all. Some animals put all their
resources into getting large or creating ornaments for sexual selection, others remain
small and relatively plain.
a) Example: Octopi generally have a “Live fast die young” life history, the
longest-lived octopus is the Giant Pacific Octopus and they have a lifespan of
only 3-5 years. In that short period of time they can reach up to 33 lbs. and
develop levels of intelligence and problem-solving skills on par with
primates. They also use chromatophores in their skin to change the color and
texture for camouflage and attracting mates. They only breed once before
they die. All of these things take energy to develop and maintain, and they
have to do it within a very short time, so they are using energy constantly.
b) Galapagos giant tortoises, on the other hand, are among the longest lived
species on the planet, regularly reaching over 100 years old. While they do
become very large, it takes them between 40 and 50 years before they reach
their full size. They devote most of their energy to developing those large,
thick, shells which keep them safe from predators.
2. Winter in seasonal environments: How different animals adapt to the same problem
a) In habitats where winters are very harsh, different animals adapt in different
ways. Woodchucks will dig a deep burrow and hibernate for most of the
winter, allowing their body temperature to decrease drastically so they do not
have to forage for food. Arctic terns spend half the year in Antarctica and
half the year in the Arctic. They do this so that they never actually have to
experience winter at all - when summer in the northern hemisphere ends, they
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fly to the southern hemisphere where spring is just beginning. This way there
are always plenty of small fish for them to eat, which in turn allows them to
make such an extreme migration. Coyotes don’t migrate or hibernate, but
instead grow a thick fur coat and hunt for small mammals and birds which
are also toughing out the winter.
3. Surface to volume ratio. Animals are multicellular organisms, and in the process of
becoming multicellular, their cells became dependent and specialized for a smaller
subset of functions, forming multiples of each specialized cell types (tissues) to
provide for a larger organism. Eventually clusters of different tissues formed to
perform a more refined subset of functions (organs), and, in turn, the organs became
designed to completely take over a subset of life processes (organ systems). Each
species of multicellular organism is structurally and functionally different from
others, and no one species can morph (adjust/acclimate) into another within a
lifetime, so there are limits on the ability of organisms to shift to somewhat different
ways of living outside the range of the evolved traits that make each species unique,
e.g., elephants can’t fly and birds can’t knock over Acacia trees to access food. In the
evolutionary design of each species from one to the next, there were losses of old
ways of doing things and gains in other ways of doing things, but there is no case
where gains were made without losses. Why is this so? The surface to volume ratio
(S:V) explains why.
a) The volume of a sphere increases with the cube of the diameter, while the
surface area increases with the square of the diameter, and so something can’t
get larger w/o reducing the S:V ratio. For cells/animals depending on the
diffusion of oxygen across their surface to supply their internal cell
organelles/tissues, there would be a lot less oxygen available per unit volume
of cell/body mass with an increase in size. How can cells/individuals
compensate for this loss of surface area with larger size? Animals can evolve
to be larger but very flat, as did amoebas and flatworms. However, that
adjustment increases the distances between different parts of the body, which,
if there is division of labor between these parts, eventually causes resource
distribution problems as well. What other things change with increases in size
(decreases in S:V ratio)?
(1) Heat loss rate decreases
(2) Dehydration rate decreases
(3) Number of predators decreases
(4) The number of shelter options decrease, but because of 1, 2 & 3, the
need for shelter decreases (an elephant doesn’t need much shelter, but
a mouse does).
(5) The absolute amount of food and water needed by a larger individual
increases, but 200,000 mice with the same combined weight as one
elephant need 12x more food and water; why? 200,000 mouse bodies
collectively have a much greater S:V ratio than one elephant of the
same mass, and therefore the mice lose more body heat and moisture
and must consume more calories and water to maintain their
collective body temperatures. With ectotherms, the problem is mainly
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with increased moisture loss at smaller sizes (e.g., young animals are
more likely to die of dehydration than larger ones).
III. Survival: We will go into much greater detail about predator avoidance in future lectures. Here, we
will only touch on a few of the concepts.
A. Being unappealing to predators
1. In addition to lowering your rate of heat loss, being large means that the ultimate
number of different predators that can kill/eat you decreases. This may also be
accomplished by being armored. Animals such as sea turtles combine both of these:
an adult loggerhead sea turtle can get up to 3.5 ft in length and weigh 375 lbs.
2. Some animals are unpalatable (unpleasant to taste), nausea-inducing or even toxic
when eaten. Many of these exhibit aposematic coloration, which acts as a warning to
predators. Aposematic coloration is often bright (e.g. poison dart frogs) and aimed at
making prey stand out (e.g. reverse countershading in skunks). Distasteful species
which may or may not be related often use similar coloration, which is known as
Müllerian mimicry.
3. Species that are not unpalatable can exploit the warning signals of other species to
make them appear dangerous in what is known as Batesian mimicry. For example,
cockroaches in the genus Prosoplecta mimic ladybugs, which are toxic to many
animals. This kind of mimicry is negative frequency dependent and relies on having
a small amount of the mimic. If there are too many mimics, predators will learn that
most animals with that particular appearance are not toxic, and the coloration will no
longer be an effective signal.
B. Being hard to find
1. Animals can avoid predators by blending into their environment and becoming
cryptic (camouflaged), reducing their chances of detection. Populations of the
oldfield mouse (Peromyscus polionotus), for example, have been selected to match
the background of their location. Mice that live closer to the beach have lighter coat
pigmentation, while mice that live further away and closer inland have darker
pigmentation.
2. Not all predators hunt by sight, so some animals have learned to be quiet. Gulf
toadfish are preyed upon by bottlenose dolphins, which orient towards “boat-
whistle” sound produced by male toadfish during breeding season. Dolphins produce
a variety of sounds when foraging, including low-frequency “pops” which are easy
for toadfish to hear. Toadfish exposed to “pop” sounds will reduce their call rate by
50% and maintain their reduced call for a period of around 5 minutes.
C. Running away
1. Fleeing may seem to be a relatively simple solution, but animals may have evolved
such that it will make it easier or more difficult for them to do so. The flight
initiation distance, or how close a predator can approach before prey flee, can be
affected by any of the following factors:
a) Prey condition: body size, reproductive state, sex, age, temperature, group
size, crypsis, hunger, morphological defenses
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b) Predator condition: speed, size, directness of attack, predator type, starting
distance, number of predators, predator intent
c) Refuge: distance to refuge, light, time of day, habitat type, patch quality
IV. Reproduction
A. Finding a mate
1. For an animal to have offspring, it (usually) must first find and secure a mate. This
tends to require a form of signalling, which in addition to indicating an animal’s
availability may also indicate their quality as a mate. Some examples of signalling in
courtship:
a) Visual: Male bowerbirds build a structure to attract females, decorated with
sticks and brightly colored objects. These objects sometimes have a theme
such as a single color.
b) Auditory: Birdsong has many functions including attracting and securing
mates. Male songbirds often have not one but many different songs, and the
size of their repertoire (how many different songs they can produce) has been
correlated with mating success.
c) Chemical: Pheromones are chemical substances produced and released into
the environment by animals and often used for the purpose of finding mates.
Male silk moths, for example, can detect them with their antennae and use
them to find unmated females.
d) Tactile: Water striders produce ripples on the surface of the water in
different patterns including specific signals for calling mates, courtship,
copulation and postcopulation.
2. The average animal’s ability to find a mate could affect which kind of mating system
evolves in the species. If finding a mate is very difficult, it may be more beneficial to
be monogamous (mate with only one male/female). If finding a mate is easy, you
may be able to produce more offspring by being polygamous (mating with more than
one female) or polyandrous (mating with more than one male).
B. Maximizing reproductive success
1. Animals are evolved to maximize reproductive success, i.e. the number of
reproducing offspring they have within their lifetimes. This means there is often a
trade-off of quality vs. quantity in offspring production. Organisms that devote a
great deal of energy to producing a large number of offspring will have less energy
available to allocate resources to each individual offspring. They also have less
energy available to devote to traits that would increase their own survival, e.g.
growth, their immune system. In mammals, the greatest litter size is 25 for tenrecs;
second is for opossum (17). Many mammals have just one offspring/litter (e.g.
zebra).
2. Trait evolution involves good compromises, not perfection. For example, a red-tailed
hawk lays two eggs at different times, resulting in one hatchling beginning
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development before the other and therefore being larger. When food supplies are low
or normal, the first born chick will claim all the food brought back to the nest
(insuring its survival), and the smaller chick will get little to eat and die. Why lay
two eggs? It seems maladaptive and a waste of maternal resources. Well, when food
supplies are plentiful, the older chick eats all it can, but not all of it, leaving enough
for the smaller chick to survive. This results in two offspring produced instead of
one. So, the trait for laying two eggs is imperfect: there is waste much of the time in
order to produce two offspring every now and then. Perfect would be a parental trait
that could predict food abundance ahead of time and produce only the number of
eggs and young that could survive. So, there is a trade-off: waste energy most of the
time to double production some of the time. Laying two eggs all the time is
imperfect, but it beats laying one egg all the time.