Bio 3950 Autumn
2007 – Mullin
Vertebrate
Natural History
Introduction
A. How does science work?
Hypothetico-deductive reasoning:
1. Observation
2. Hypothesis -- this proposes a possible
cause (or several causes)
3. Test hypothesis
4. Retain/Refute/Revise hypothesis
(5. Retest revised hypothesis)
All hypotheses: (a) should be testable; and,
(b) can be eliminated via testing.
Biological phenomena are based on a
hierarchical organization of living things, the structures within them, and the
roles they play in the environment -- subatomic particles & atoms >
molecules > organelles > cells > tissues > organs > systems >
multicellular organisms > populations > communities > ecosystems >
biomes > biosphere
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Distinction & Classification
Taxonomic hierarchy:
Kingdom, Phylum, Class, Order, Family, Genus,
species
The hierarchy is based on a system called
binomial nomenclature. This system assigns each organismal species with a
two-part Latin name -- a Genus name, and a specific epithet. However, no two
species have the same binomial epithet.
Why is there so much diversity? Why are there
two different types of bacteria/mushrooms/snakes/etc. in a particular place on Earth, when there just as
easily could be one?? Historical changes in environmental conditions have
caused changes in ancestral forms of organisms which produced more than one
type of descendant.
Evolution by process of natural selection --
: the environment changes
: organisms produce far more offspring than
are capable of surviving
: some of those offspring possess traits
which are better suited for the current environmental conditions than others.
: those offspring better adapted to current
environmental conditions will out-compete those which are not for available
resources, and hence survive to reproduce (this passes their genes on to future
generations).
An important concept to grasp about evolutionary
processes is TIME, and an appreciation for how much of it must elapse in
order to produce evolutionary change.
One global concern is human activities
accelerating the rate of environmental change to a level where other organisms
cannot keep pace and thus go extinct.
How do you tell the difference between
taxonomic groups?
a) morphology: similar measurements on
variety of char's = relatedness
b) behavior: similar
postures/displays/strategies = close relatedness
c) ecology: similar habitat req's, interspp.
assoc. = close relatedness
d) biochemical: genetic similarity =
relatedness
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Evolutionary History & Biogeography
Global conditions past & present –
4.8 bya = formation of Earth
3.5 bya = oldest recognizable biotic forms;
atmosphere 02-deficient.
2.6 bya = 1st algæ, beginning of 02
build-up in atmosphere
1.6 bya = 1st eukaryotes; Pangæa
formation begins
680 mya = 1st multicellular
organisms, rapid radiation during Cambrian
525 mya = 1st vertebrate ancestor
500 mya = 1st fish ancestor
440 mya = 1st land plants
415 mya = 1st land invertebrates
360 mya = 1st amphibians, trees;
beginning of coal deposit formation
320 mya = 1st reptiles; Pangæa
formation complete; Permian-Triassic extinction (of 83% of known Genera)
210 mya = Triassic-Jurassic extinction (of 48
% of known Genera); 1st marsupials, birds
140 mya = 1st angiosperms; Pangæa
breaks into Laurasia (N hemisphere) and Gondwonaland (S hemisphere)
65 mya = Alp and Rocky Mtn orogeny; 1st
placentals; Cretaceous-Tertiary extinction (of 50 % of known Genera)
4.8 mya = 1st hominids; polar ice
cap formation
1.2 mya = Homo erectus, tool use;1st of repeated glaciations
10 - 0.5 kya = anthropogenic extinction of
Australian (85 %), North American (60 %), Madagascan/New Zealand (99 %) fauna.
The climate (temp., precip., photoperiod,
wind) on any particular region affects the organisms found there. Local
climates can be affected by (a) latitude, (b) proximity to ocean, and (c)
altitudinal barriers. Global climates have changed during Earth's history
(& effected taxa distribution) b/c:
a) plate tectonics –continents are
"floating" on viscous mantle pool. @ time 1st vertebrates,
1 of 2 major continents of Pre-Cambrian (Laurasia) 6 broken up into 5 smaller
continents; this facilitated taxa radiation.
b) glaciation – changes in polar ice area
affect sea level, and therefore, climate & exposed land area.
Biogeographic Rules affecting extant
endothermic taxa.
1. Bergman's Rule: greater indiv. size @
higher latitude, b/c lower temp. means indiv's should have lower SA:V to
conserve heat.
2. Allen's Rule: shorter extremities in areas
w/ greater temp. fluctuation b/c indiv's should have lower SA:V to conserve
heat.
3. Gloger's Rule: indiv. w/ darker color in
warm/humid areas, b/c there is more shading in tropics
4. Fahrenholz's Rule: symbiotic spp. (e.g., parasite-host) tend to evolve together, so similar
spp. should have similar symbionts.
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If these rules can be used to explain size
variation between popln's of indiv's w/in spp., then what explains sexual size
dimorphism?
1. F needs to eat more prey to produce larger
gametes
2. F needs to be larger to produce larger
clutch size
3. F needs to be larger to avoid injury
during ritualized courtship display
4. F needs to be larger to incubate clutch
(oviparous taxa only)
5. M needs to be larger to defend resources
6. dichotomy exists to reduce competition for
other resources.
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Phylum Chordata – four common features
(a) notochord - attachment site for muscles
(b) nerve cord - nervous system, may have anterior
development (brain)
(c) pharyngeal gill slits - may form
respiratory structures or be vestigial
(d) post-anal tail - may be vestigial
Subphylum Urochordata – filter-feeding
tunicates w/ "tadpole" larvæ; paedomorphic larval form gave rise to
other chordates.
Subphylum Cephalochordata – lancelets w/
segmented myomeres that aid in movement; gill slits for feeding (not
respirat'n) & open circulatory system.
Subphylum Vertebrata – shared features
(a) vertebrae – serially arranged along
dorsum = cartilage, bone (or absent)
(b) cranium – a skull surrounding brain =
fibrous, cartilage, or bone
(c) neural crest – embryonic tissue that
forms novel structures (esp. in head)
(d) enlarged, tripartite brain
These structures manifested increased size
and activity levels in vertebrates which in turn promoted other adaptations:
pharyngeal gills (fewer in #, but more complex) for respirat'n, true heart,
muscularized g.i. tract, & discrete visceral organs (e.g., kidney, liver, pancreas).
Based on fossil evidence & physiology of
extant forms, the 1st vertebrates arose in marine environments.
Among early taxa, ostracoderms were 1st to have bone (head plates)
and glomerular kidney for Ca+2 and P+2 uptake. Extant
analogy = Superfamily Myxinoidea (extant hagfish) w/ equal ion concentration as
seawater but w/out bone seen as proto-vertebrate condition.
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The Unity of Structure
Embryological system development
1. zygote — fertilized egg
2. blastula — formation of primitive coelom
(hollow ball of many cells)
3. gastrula — formation of three tissue
layers (3-layered ball)
a) ectoderm forms superficial layers, g.i.
tract, nervous/sensory organs
b) endoderm forms g.i. tract & assoc.
glands (e.g., liver, pancreas).
c) mesoderm forms muscle, skeletal,
circulatory, urogenital organs
4. neurula — formation of notochord &
dorsal nerve chord from ectoderm.
The germ layers lead to different tissue
types:
1. Epithelial -- (a) membranous, func. for
coverage
(b) glands: i. Endocrine glands secrete
hormones into extracellular space
ii. Exocrine glands secrete material directly
to target organ or outside body.
2. Connective -- tendons/ligaments func. for
support
3. Vascular — circulate blood, gases, wastes
4. Muscle -- ability to contract for movement
function
5. Nervous -- ability to conduct e-
signals for sensory function.
Structural/protective elements......
Components of skeletal tissue:
1. cartilage -- embryonic bone; living cells
that provide flexible support and connections between bones.
2. compact bone -- dense, strong bone serving
as attachment site for muscles.
3. spongy bone -- porous, light-weight,
highly-vascularized; bone marrow is located in the cavities and this is where
blood cells are formed.
Divisions of the skeletal system:
1. appendicular -- the bones of the
appendages (girdles & limbs)
2. axial -- the bones of the central axis
(skull, spinal column, & ribs).
Functions of vertebrate skeleton:
1. support/protection of visceral organs in
body as well as attachment site for muscle tissue.
2. production of cells in blood, including
erythrocytes, leukocytes, platelets.
3. storage site for Ca and P
4. sensory perception -- the bones of the
middle ear that transmit sound.
Specialized bone type — teeth are a
highly-mineralized combo. of bone, enamel, and dentine. Types of root systems:
1. acrodont — fused to top of jaw margin
2. pleurodont — set on shelf on medial side
of jaw
3. thecodont — set in sockets
Body movement is accomplished by
muscles attaching to bones w/ bands of connective tissue called tendons.
Skeletal muscles are arranged in antagonistic pairs such that the contraction
of one muscle to flex a joint can be reversed by the contraction of another
muscle to extend the same joint.
Types of muscle tissue:
1. skeletal muscle -- multinucleate,
striated, voluntary contractions
2. smooth muscle -- mononucleate,
non-striated, involuntary contraction, moves stuff through hollow organs.
3. cardiac muscle -- multinucleate,
semi-striated, involuntary control
Muscle fiber (cell) structure consists of
several subunits called myofibrils each of which has hundreds of bands of
protein chains. One protein type, myosin, attaches to another protein type,
actin, and pulls the two actin chains together, thus shortening the muscle.
The muscle fibers are stimulated by
electrical signals from motor neurons.
Vertebrate muscular systems divided into 2
broad regions:
1. axial — folded blocks originating from the
spinal column, 1° support
(a) epaxial — those articulating dorsal to
the spinal column
(b) hypaxial — those articulating ventral to
the spinal column
2. appendicular — originating from limb
bones, 1° locomotion
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The Unity of Function
Acquisition of nutrients is a
multi-step process:
1. ingestion -- food is brought into the
mouth
2. digestion -- chemical breakdown via
enzymes, acids and mastication (mechanical breakdown of food, typically w/
teeth)
4. absorption -- transport of small molecules
(including water) from digestive cavity into cells or circulatory system.
5. elimination -- indigestible materials are
expelled from the body.
Pathway of food: mouth (mastication,
digestion of starch), to esophagus, to stomach (digestion of protein), to small
intestine (digestion of fats & sugars, absorption), to large intestine
(absorption), rectum, anus.
Accessory digestive organs:
1. salivary glands -- in mouth, secrete
enzyme to digest starch.
2. Gall bladder -- w/in liver, produces bile
salts to digest fats.
3. pancreas -- secretes enzymes to digest
sugars, fats, and proteins.
If the stomach is acidic, why don't we digest
ourselves?
1. cells lining stomach not only produce HCl,
but also mucous to neutralize acid.
2. cells lining stomach are replaced much
more rapidly than other cell types.
3. cells lining stomach have many tight
junctions so that acid doesn't leak out.
What about when acidic contents leave the
stomach?
4. pancreas secretes basic sol'n to
neutralize acid and continue digestion.
All respiratory systems share two
characteristics:
1. a moist respiratory surface to facilitate
gas exchange (gases must be dissolved in liquid in order to enter/exit living
cells).
2. a relatively large surface area in contact
with the environment (to allow for adequate rates of the diffusion of gases).
Pathway of air into the lungs -- From the
nose/mouth, air enters pharynx, to larynx (containing vocal cords), to trachea,
to bronchi, to bronchioles, to alveoli where gas exchange with capillaries
occurs.
A single alveolus and the adjacent capillary
are each only 1 cell layer thick, such that is it easy for O2 to
diffuse across into the blood stream. The bond between O2 and Hb is
weak and reversible, such that when in the tissues, O2 can be
released to the cells for respiration. Some O2 is replaced by CO2,
but most of the CO2 molecules are converted into bicarbonate ions
(-HCO3) for transport to the lungs.
Breathing cycle:
1. Inhalation accomplished by making chest
cavity larger via diaphragm and intercostal muscle contraction.
2. The enlarged cavity generates negative
pressure in lungs which draws air inwards.
3. Exhalation occurs when these muscles
relax, compressing the chest cavity, and forcing air out of the lungs.
Functions of the circulatory system:
1. gas transport & exchange
2. distribution of nutrients from digestive
system to other body areas
3. transport of toxins/wastes to liver
(detoxification) & kidneys (excretion)
4. distribution of hormones from endocrine
glands to target tissue.
5. regulation of body temperature
6. initial wound healing through clot
formation
7. protection from infection via distribution
of antibodies & leukocytes.
Blood elements -- formed elements from bone
marrow
1. erythrocytes (red blood cells), anucleate,
transport gases.
2. leukocytes (white blood cells), nucleate,
protect body from foreign material
3. platelets (fragments of megakaryocytes),
anucleate, cause blood clotting
-- plasma is the fluid bathing the formed
elements that contains proteins (immune, clotting, osmotic function), salts,
hormones, nutrients, and gases.
Flow of blood in mammalian body:
1. blood leaves right ventricle via pulmonary
artery to go to lungs where CO2 can be exchanged for O2
in capillary beds of lungs.
2. blood from lungs enters left atrium via
pulmonary vein (still w/ O2).
3. blood from left atrium enters left
ventricle
4. blood leaves left ventricle via aorta to
go to body where it can exchange O2 for CO2 in capillary
beds.
5. in body, blood goes from aorta to
arteries, to arterioles, to capillaries (gas exchange occurs here), to venules,
to veins to the vena cava and back to heart.
6. blood from body (w/ CO2) enters
right atrium via vena cava (large vein).
7. blood from right atrium enters right
ventricle
What keeps the blood flowing in the same
direction?
1. valves separating atrial & ventricular
chambers prevent backflow when heart contracts.
2. valves in veins that prevent backflow as
blood returns to heart.
3. muscle contraction around veins pushes
blood through valves towards heart.
Evolution of heart structure:
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The Unity of Regulation
The excretory system is effective at
several functions:
1. elimination of digestive waste products.
2. regulation of water content in plasma.
3. regulation of ion balance in plasma (esp.
Na+, K+, Cl-, Ca+2).
4. regulation of pH of blood.
5. retention of nutrients in blood (esp.
sugars and amino acids).
6. secretion of hormones to promote
erythrocyte formation.
Pathway of urine formation in kidney:
1. blood enters the kidney via renal artery which
branches to form a capillary bed called the glomerulus. Water, nutrients, and
waste are filtered from the capillary into part of the nephron called the
Bowman's capsule.
2. The filtrate then passes along the loop of
Henle that is entwined with the capillaries that left the glomerulus. Nutrients
and most of the water are reabsorbed into blood. Also, additional wastes are
actively transported into the nephron tubule.
3. The wastes are then concentrated in the
collecting duct of the nephron which drains to the ureter connecting the kidney
to the bladder. This concentration results in a urine solution that is
hyperosmotic (4x) to the blood in the surrounding capillaries.
4. The bladder is drained by the urethra that
transports the urine out of body.
5. blood containing required concentrations
of water, nutrients, and ions returns to the rest of the circulatory system via
renal vein.
Not all vertebrates use the same structures
within kidney which has two functional units: pronephros & opisthonephros
(= meso- + meta- nephros).
(a) all embryonic forms use pronephros
(b) nonamniotic adults use segmented
opisthonephros
(c) amniotic adults use only metanephric
portion of opisthonephros
Alternate forms of excretion:
1. mammals, chondrichthyes, few amphibians = urea
2. reptiles, birds = uric acid
3. fish, amphibians = ammonia
Other osmoregulatory organs:
1. sweat glands -- secretion of NaCl and H2O
for evaporative cooling
2. liver -- regulation of blood glucose
levels, toxicant removal, and conversion of ammonia to urea (amniotes only).
Excretory systems are closely aligned with reproductive
systems — all vertebrates have separate structures producing stuff, but......
(a) nonmammalian vertebrates all have common
urogenital opening (cloaca)
(b) nonprimate mammals have separate opening
for digestive and urogenital products
(c) female primates w/ separate openings for
digestive, excretory, & gonads.
Mechanisms of sex determination:
1. chromosomal sex — a gene on one
chromosome initiates gonadal development for particular gender.
2. environmental sex determination —
temperature, water potential, or other extrinsic factor influences sex.
The pathway of sperm (mammalian).
1. From the seminiferous tubules in the testis
where they are formed, sperm travel to the epididymis and vas deferens where
they are stored.
2. During sexual arousal, muscles surrounding
the epididymis, (vas deferens, and urethra) contract to eject sperm (from the
penis).
3. The ejaculated semen is actually the sperm
combined with secretions from three other glands along the vas deferens, the
seminal vesicle, (the bulbourethral gland, and the prostate gland). These
secretions provide nutrients for the sperm (and neutralize the acidity of the
female vagina).
The pathway of the egg (mammalian).
1. When mature, the egg is released from a
follicle w/in an ovary that is suspended in the body cavity.
2. The egg is swept into a fallopian tube
where fertilization usually occurs.
(3. If the egg is fertilized, the zygote
passes into the uterus where it implants as an embryo into the endometrium that
will form the placenta. The suitability of the endometrium as an environment to
receive the egg is regulated by hormones from the follicle.)
Modes of reproduction:
1. oviparity — egg-laying
2. viviparity —2 types
: lecithotrophic = retaining a shell-less egg without providing
additional nutrients to developing embryo
: matrotrophic = providing nutrients to embryo via placenta
Anatomy of a nerve cell:
1. cell body -- contains most organelles,
serves as integrating center.
2. axon -- long, thin portion of cell that
transmits AP along length of cell.
3. dendrites -- branched portions of cells
that respond to stimuli and conduct AP to cell body.
4. synapse -- space between adjacent neurons
across which AP is transmitted via use of chemical neurotransmitter.
Nerve cells function to:
1. receive stimuli from environment
(external, internal, other neurons).
2. integrate info. from stimuli and produce
appropriate response.
3. conduct action potential (AP, signal)
along length of cell.
4. transmit AP to neighboring cell.
The nervous system is divided into 2
portions:
1) central nervous system = brain + spinal
cord
2) peripheral nervous system = non-CNS neurons
enervating muscle, glands and sensory organs; the PNS is subdivided into.......
a) sensory division — detecting stimuli
b) motor division — responding to stimuli;
responses fall into 2 categories
i) somatic — voluntary responses (conscious
control)
ii) autonomic — involuntary responses that
stimulate or suppress activity.
Brain structure & function
A. Prosencephalon (forebrain)
1. telencephalon (cerebrum + olfactory bulb)
-- sensory & higher mental function (e.g., intellect, communication, memory).
2. diencephalon (thalamus + hypothalamus +
pituitary) -- homeostasis, endocrine regulation, emotion.
B. Mesencephalon (midbrain) -- filters &
relays sensory info. from all body regions.
C. Rhombencephalon (hindbrain)
1. metencephalon (cerebellum + pons) --
coordination & respiratory rate
2. myelencephalon (medulla oblongata) --
autonomic control of respiration, circulation, swallowing.
The Senses
A. Chemoreception (smell & taste)
1. olfactory receptors in nasal passage,
sensitive to airborne molecules.
2. taste buds on tongue, sensitive to
waterborne molecules.
B. Mechanoreception (movement)
1. specialized nerve endings in skin,
sensitive to vibration.
2. free nerve endings in muscles, sensitive
to stretching (e.g., in bladder,
stomach).
3. hair cells in inner ear, sensitive to
vibration or fluid movement; pathway of sound: auditory canal -> eardrum
-> hammer -> anvil -> stirrup -> oval window -> cochlea ->
hair cells on organ of Corti.
C. Photoreception (wavelengths of light)
1. The pathway of light: cornea - aqueous
humor, iris (the opening of which is the pupil), lens (protein, focuses light),
vitreous humor, retina which is composed of two types of photoreceptive
neurons:
a. rods -- greater #, more sensitive, used
for seeing in low light.
b. cones -- lesser #, sensitive to different
wavelengths of light, used for seeing color.
2. Infrared wavelengths detected by pit organ
in Crotalinae.
D. Thermoreception -- the sense of
temperature change, can accommodate.
E. Pain reception -- regardless of the stimulus,
our sense of pain is relatively unchanged because the nerve cell type is the
same throughout the body.
2 types of endocrine action:
1. water-soluble hormones bind to IMP
receptor on cell surface to trigger rapid responses via secondary messengers
w/in cells (e.g., epinephrine)
2. lipid-soluble hormones pass through cell
membrane and nuclear envelope, then binding to protein receptors that activate
DNA expression (e.g., steroids
like testosterone, estradiol).
Important endocrine glands:
1. hypothalamus (base of brain) secretes
hormones that regulate endocrine function of pituitary gland.
2. pituitary gland (base of brain) secrete
hormones that regulate homeostasis, endocrine function of adrenal glands and
gonads, milk production and secretion in mammary glands. E.g., ADH, prolactin, FSH
3. thyroid & parathyroid (neck region)
secrete hormones that regulate metabolic and developmental rate, and calcium
uptake for bone growth.
4. pancreas (along anterior small intestine)
secretes hormones that regulate blood sugar levels. E.g., insulin, glucagon.
4. adrenal glands (on top of kidneys) secrete
hormones that regulate metabolic rate. E.g., epinephrine.
5. ovaries secrete hormones that regulate
development of 1° and 2° sex characteristics in females. E.g., estradiol, progesterone.
6. testes secrete hormones that regulate
development of 1° and 2° sex characteristics in males. E.g., testosterone.
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Functioning in an Aquatic Realm
1. Gills use countercurrent exchange to
perform a dual function:
a) respiration – blood flows across gill
filaments in direction opposite to water flow such that gas exchange rate is
maximized; pump or ram ventilation of buccal chamber; some fish are obligate
air-breathers thru gut evaginations.
b) regulating ion balance –actively transport
of NH4, Na+, Ca+2 across gill lining depending
on whether organism lives in salt or fresh water.
2. Locomotion:
a) types of lateral undulation –
(i) anguiliform: flexion of more than half a
sinusoidal wavelength
(ii) carangiform: flexion of caudal region of
body
(iii) ostraciiform: flexion of tail fin only
(body is not flexible)
b) overcoming gravity –
(i) positive attack of pectoral fins in water
column during forward motion
(ii) swim bladders may serve dual purpose of
gas exchange & buoyancy
(iii) static lift enabled by low density
lipids
c) overcoming drag in the water –
(i) decrease body length = decreased surface
area for viscous drag
(ii) decrease body surface irregularities =
decreased viscous drag
(iii) decrease % body length that flexes =
decreased inertial drag
(iv) increase aspect ratio = decreased
inertial drag (& burst speed)
3. Sensory perception:
a) photoreception – spherical lens moved
toward/away from retina to focus
b) chemoreception (1° mouth) is relatively
sensitive
c) mechanoreception – specialized lateral
line system of neuromasts provide info about orientation, water current,
motion, pressure.
d) electroreception – modified muscle cells,
electrocytes, synchronously generate net positive unidirectional current (_ 600
v) for orientation, communication, or predation.
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END OF MATERIAL FOR 1ST
EXAMINATION