Vertebrate Zoology Exam 2

Chondrichthyes Synapomorphies

• Tesserate prismatic calcified cartilage in endoskeleton

  • Globular or stellate deposits of crystalline calcium in the superficial layers of the cartilage matrix

• Placoid scales

  • Composed of a vascular (supplied with blood) inner core of pulp, a middle layer of dentine and a hard enamel-like outer layer of vitrodentine

• Pelvic claspers

  • Present in males, used for internal fertilization

Holocephali

• Ratfishes and Chimeras

• Swim by gently flapping pectoral fins

• Synapomorphies:

  • Gill openings covered by soft tissues

  • Teeth in the form of toothplates that are slowly replaced

  • First dorsal spine erectile

  • Clasping organ on head of males (tentaculum)

• 3 families, around 30 species, mostly deepwater marine

Elasmobranchii

• Sharks, skates, rays

• Synapomorphy:

  • Gill openings separate and uncovered

Ancient vs. Modern Sharks

• Snout characters

  • Ancestral condition

    • Short, rounded snout

    • Long jaws

    • Located at front of head (terminal)

  • Modern condition

    • Long pointy snout

    • Short jaws

    • Located underneath head (subterminal)

  • Significance - long jaws are structurally weaker than short jaws; results in less powerful bites

• Jaws

  • Upper and lower components

    • Palatoquadrate (upper)

    • Meckel’s cartilage (lower)

  • Hyomandibula supports the palatoquadrate

• Jaw suspension

  • Ancestral condition:

    • Amphistylic - palatoquadrate is fixed to the braincase in front and back

  • Modern condition:

    • Hyostylic - palatoquadrate is not fixed to braincase; entirely supported by hyomandibula.

    • Result – protrusible upper jaw

• Teeth

  • Ancient condition - cladodont teeth

    • Smooth-edged

    • Multi-cusped

    • Large central blade

    • Best suited for grasping prey and swallowing whole

  • Modern condition - serrated teeth

    • Serrated edges

    • Single-cusped

    • Enables gouging pieces from prey too large to be swallowed and slicing through tough skin

Neoselachii Characteristics

• Characteristics:

  • Underslung or ventral mouth

  • Polyphodont dentition – can undergo serial tooth replacement

    • Ancient sharks – spiral replacement

  • Ampullae of Lorenzini - electroreception for detection of prey, possibly for navigation

    • Jelly-filled canals

Galeomorphi

• Sharks with an anal fin

• Hexacanthiformes

  • Sixgills, sevengills, and frilled sharks

• Heterodontiformes

  • Bullhead and horned sharks

• Lamniformes

  • Sand, tiger, goblin, thresher, basking, mackerel, mako, and great white sharks

• Orectolobiformes

  • Carpet, blind, nurse, zebra, whale, and wobbegong sharks

• Carcharhiniformes

  • Cat, hound, leopard, soupfin, tiger, gray, blue, lemon, and hammerhead sharks

Squalomorphi

• Sharks without an anal fin

• Pristiophoriformes

  • Sawsharks

• Squaliformes

  • Spiny dogfish, bramble, and sleeper sharks

• Squatiniformes

  • Angel sharks

Batoidea

• Skates and rays

• Synapomorphies:

  • Dorsoventrally-flattened bottom dwellers large pectoral fins; dorsal fins reduced to absent; caudal fin reduced

  • Large dorsal spiracle

  • External gill openings are on the ventral side of the body; water (for breathing) is taken through the large spiracle on the dorsal side

  • Teeth usually flattened and united to form a pavement for crushing mollusks; also feed on crustaceans, and occasionally, fish

• Rajiformes

  • Sawfishes, guitarfishes, rays, and skates

General biology of elasmobranchs

Large bodied

Feeding

• Many sharks, but not the rays and skates, are specialized as piscivorous predators

  • In these sharks, the lower teeth are usually spiky, the upper teeth blade-like

• A few filter feeders (megamouth, whale shark, basking shark, manta ray)

• The rays and skates are usually hard shelled invertebrate feeders: teeth from multiple rows form pavement

Habitat

• Marine (5% found in freshwater, as casual visitors or lifelong residents)

  • Bull sharks in Lake Nicaragua

  • Amazon stingray

Sensory abilities

• Have relatively large brains

• Very good olfactory capabilities

• Good vision (particularly night vision), hearing

• Electroreception

  • Location of prey, in near range

  • Possibly for orientation in migration

• Physiology

  • Resting metabolic rate 1/3-1/2 that of bony fish of comparable size

  • Active metabolic rate of dogfish only 3X resting, vs. 10X for bony fish

  • Lamnidae (e.g., great whites) have regional endothermy - able to warm their muscles, stomach, viscera, brain and eyes to a temperature above that of the ambient sea water; rete mirable

  • Slow growth, late age at maturity, long lifespan (spiny dogfish mature at 35 years off of British Columbia)

Reproduction

• Internal fertilization

• Low fecundity

• Direct development, development slow

• Three reproductive modes

  • Ancestrally, oviparity (lay eggs) (30%-40% of extant spp)

  • Young retained in uterus, nourished by yolk sac: ovoviviparity (when yolk sac is depleted, mother gives birth) (in some, oophagy (young eats unfertilized eggs in the uterus) or embryophagy (young eat other young in the uterus) - a.k.a. intrauterine cannibalism)

  • Viviparity (mother gives birth to live sharks and feeds them) - maternal nourishment via placenta or uterine milk (secretion in wall of uterus)

• These features make the elasmobranchs very susceptible to over-fishing, because the populations have low values for r_max (intrinsic rate of natural increase)

Osteicthyes Synapomorphies

• Original dermal bone jaws are covered with marginal mouth bones that have rooted teeth

  • Upper jaw = maxilla, premaxilla

  • Lower jaw = dentary

• Bony operculum – gill cover

• Branchiostegal rays – fanlike series of dermal bones that form the floor of the gill chamber and aid in rapid expansion of the mouth for suction feeding and respiration

• Lung or swim bladder

Sarcopterygii vs. Actinopterygii

• Fins

  • In ancestral osteichthyans, individual rays are associated with a bone

    • Result: each individual fin ray can move independently (fine movement in the water)

  • Actinopterygii lost many of the bones

    • Better for propulsion; paddles; not fine movements

  • Sarcopterygii elaborated and gained many bones

    • Not good for propulsion; good at rotating (like a ball and socket joint)

  • Tetrapodomorph Sarcopterygii

    • Further elaborate ball and socket joint

    • Bones shorter and heavier, better for crawling and terrestrial locomotion

• Skull

  • Actinopterygians: reduced the dermal bones in skull; greater mobility of premaxilla and maxilla (important for feeding and respiration)

  • Sarcopterygians: retained dermal bones in skull; little to no upper jaw mobility

Polypteriformes

• Bichirs and reedfish

• Breathe atmospheric air

• Ancient lineage

Acipenseriformes

• Sturgeons and Paddlefishes

• Ancient lineage

• Larger upper lobe in caudal fin, generating lift

  • Large pectoral fins stabilize

Neopterygii

First appeared 345 mya

Most extensive radiation was 80-65 mya

Leedsicthys: probably the only actinopterygian ever mistaken for a stegosaur; around 100 ft in length; supposedly the largest actinopterygian of all time

Lepisosteiformes

• Gars

• Now restricted to North America, but once Pangean in distribution

• Specialized fish eaters; covered with heavy bony scales (ganoid scales; ganoine covering gives the scales an enamel-like cover

Amiiformes

• Amiidae

• Now restricted to eastern North America

• Retain several primitive characters:

  • Spiral valve intestine

  • Ganoine covering scales

  • Solid jaws

  • Large, lung-like gas bladder (can breath air similar to gar and survive in low oxygen environments)

  • Gular plate to help crush prey (effective predators on fish and crayfish)

Teleostei Synapomorphies

• Stiffened tail (uroneural bones)

  • Homocercal tail (internally asymmetrical (slightly) and externally symmetrical)

    • Stiffer, provides greater thrust

  • Earlier fishes were heterocercal (internally and externally asymmetrical)

• Mobile Premaxilla

  • Maxilla and premaxilla move down and forward

    • Great for suction feeding

• Mobile pharyngeal jaws

  • E.g. moray eels (can protrude pharyngeal jaws to grasp prey)

• Lost basal fin bones (greater rigidity)

Osteoglossomorpha

• Live in backwater areas in South America, Africa, Asia, some in North America

• Have an elaborated bone on the floor of their mouth

Elopomorpha

• Eels, tarpons, bonefish

• Synapomorphy:

  • All elopomorphs share a specialized larval stage call a leptocephalus larva

    • Only a few cells thick

    • No GI tract

    • Absorb nutrients directly from the seawater

    • Teeth present → serve as a calcium reservoir to later form the skeleton

Otocephala

• Herrings, sardines, anchovies, minnows, suckers, catfishes, loaches, characins

• Otophysi

  • Have a special connection between their “ears” and their swim bladder that gives them enhanced hearing

    • Herrings, shad, sardines = otophysic connection

    • Minnows, suckers, catfishes, characins = Weberian apparatus

      • Series of bones connecting swim bladder to hearing organs

Euteleostei

• Characteristics:

  • Large, toothed maxilla

  • Adipose fin (an additional, often small and fatty fin between dorsal and caudal fins without separate skeletal support)

  • Tubercles develop on breeding males (nuptial tubercles) - pattern timing and location of tubercles often diagnostic

• Ca. 24,000 species

Neoteleostei

• Retractor dorsalis muscle: greatly enhanced pharyngeal jaw mobility

• Superorder Acanthopterygii (Acanthomorpha)

  • True spiny-rayed fishes

  • Monophyletic group, but relationships uncertain

  • Ca. 14,000 species

  • Percomorpha

    • Very diverse group

What made teleosts so successful?

Caudal fin locomotory complex

• Homocercal caudal fin designed for thrust

  • Two advantages

    • Increased efficiency in horizontal swimming because all thrust is horizontal

    • Increased versatility because paired fins are now free to evolve other locomotory functions

  • Results in pectorals moving up the body and pelvics moving forward; both providing greater maneuverability

Feeding mechanisms

• Greater jaw mobility (esp. upper jaw) opened up new trophic possibilities; allowed for specialization of mouth parts, which lead exploitation of specialized food resources

• Most significant evolutionary change begins with freeing posterior end of maxillary bone from bones in the cheek

Mobile pharyngeal jaws

• Retractor dorsalis in Neoteleosts

How did derived vertebrate jaws evolve?

• Palatoquadrate cartilage evolves to form part of suspensorium, palatine bone, and part of quadrate. In primitive tetrapods, it forms part of the roof of the mouth (palate); in mammals, part of it forms the incus (one of the three inner ear bones)

• Mandibular cartilage in derived fishes forms the articular. In mammals, part of it becomes the malleus (another inner ear bone)

• In teleosts

  • A ball and socket joint developed between head of maxilla and palatine bone

  • In highly evolved teleosts, anterior end of premaxilla develops an ascending process that extends upward and backward to overlap the snout

  • Exclusion of maxilla in the gape

  • In addition, bony connection between premaxilla and snout in lower teleosts is replaced with a more flexible cartilaginous and connective tissue hinge

Categories of fish feeding

• Hit and run

  • Used by mostly fast-swimming open water fishes

  • Rim of jaws used for biting and grasping; requires a firm jaw construction and large, powerful muscles to shut jaws quickly and firmly

• Filter feeders

  • Open their mouths and hold them open while swimming

• Gape and suck

  • Depends on ability to create sufficient negative pressure to suck-in individual food items

  • Effectiveness of this method depend on:

    • Degree to which the mouth cavity can be expanded

    • Suddenness with which the mouth cavity can be expanded

Sarcopterygii Synapomorphy

• Monobasal fin

  • Compare a shark fin, with three supports attached to the limb girdle (tribasic fin) to a lungfish fin, which is attached to the pectoral girdle and supported along its length by a single row of bones

    • Gives more rotation: ball-and-socket joint

Actinistia

• Coelacanths

  • Thought extinct since Cretaceous (ca. 65 mya)

  • Two species were discovered in the 1900s

Dipnoi

• Synapomorphy:

  • Separate pulmonary circulation

• Very little change in over 400 my of evolution

• Their "lung" is a modified swim bladder, absorbs oxygen and removes wastes.

  • Respiration using the lungs is critical for survival - lungfish can drown if they can’t breathe air

    • Obligate air breathers

• African and S. Am. lungfish survive dry season by estivation

  • Burrow into the mud and seal themselves within a mucous-lined burrow

  • Fossilized lungfish burrows found in Permian age rocks, with the lungfish still inside; older (empty) burrows are known from the Carboniferous and Devonian.

Osteolepiformes

• Extinct group of lobe-finned fish

• Synapomorphy

  • Labryinthodont teeth - teeth in cross-section that show complex infoldings

  • Loss of postaxial elements in fins

Panderichthyidae

• Extinct group of lobe-finned fish; most are known only from fossil fragments, but there are a few complete specimens

• Have more tetrapod-like characters (synapomorphies):

  • Flattened skull with snout

  • Eyes on top of head

  • No dorsal or anal fin

  • Reduced tail fin

Late Devonian Sarcopterygii Characters:

• Development of free digits

• Increased mobility of limb joints

• Pelvic girdle attaching to spinal column

• Pectoral girdle becoming free from its attachment to the skull

• Vertebrae develop stronger interlinkages (zygapophyses)

Tiktaalik roseae

• Symplesiomorphies w/ more primitive Sarcopterygians

  • Similar body scales, fin rays, lower jaw and palate bones

• Autapomorphies

  • Shortened skull roof, dorsally placed eyes, a modified ear region, a mobile neck, imbricate ribs, a pectoral girdle and fore-fin capable of complex movements and substrate support, and a functional wrist joint

Advantages and Obstacles with Transition to Land

• Advantages to invasion of land

  • New food resources

  • Avoidance of aquatic predators and competitors

  • Oxygen abundant

• Disadvantages (Obstacles)

  • Water becomes limiting factor in distribution (desiccation, respiration, reproduction)

  • Gravity - necessitates new morphological designs

    • Water provides buoyancy and allows for good support even though it is more difficult to move through than air

  • Water has high heat capacity

    • Most aquatic animals, especially marine species do not have problems with the drastic temperature changes that occur on land

Locomotion in the transition to land

• Modified axial skeleton with zygapophyses

• Strengthened shoulder and pelvic girdles

• Loss of skull bones, freeing the shoulder from the skull allowing a flexible neck; shoulder girdle supported by serratus musculature

• Attachment of ilium to sacral rib

• Evolution of paired limbs

  • Proximal limb elements are homologous with bones of rhipidistian (early sarcopterygian ‘fishes’) fins

    • Fins are divided into axial, preaxial and postaxial elements

    • To make a limb from a fin, the axis of the limb has to curve around; need an elongate, laterally directed humerus and femur

    • Some preaxials were incorporated into the arm and wrist, or fused with other bones

    • Some postaxials end up as digits

Respiration in the transition to land

• Air versus water

  • Air has higher O2 content - 20 X more per volume; faster diffusion (500,000 X)

  • Less energy for ventilation; up to 25% of total metabolism for fish, 1-2% for air breathers

  • Air is not hyper- or hypotonic (no salt gain or loss)

  • Air does not remove as much heat

  • Air causes problems with desiccation; structures located deep within body; long passageways moisturize air

• Structural adaptations

  • Absence of internal gills

  • Reduction and loss of operculum

  • Better developed lungs than were present in sarcopterygians

  • Three chambered heart with discrete systemic and pulmonary circulation

  • Three chambered heart with separation of blood in the ventricle

  • Loss of scales to allow for cutaneous respiration

Water balance in the transition to land

• Excretion

  • Urea is the principal nitrogenous waste; Latimeria and the living lungfish can synthesize urea in their livers; lungfish use urea for water retention during estivation

• Dehydration

  • Still a problem for most amphibians, so they have to live near water

Sense organs in the transition to land

• Middle ear

  • Derived from spiracle

  • Hyomandibular (freed from jaw support) modified to columella (stapes); initially the stapes is large and heavy and when it became solely involved in aerial sound transmission is questioned

  • Evolution of otic notch - supports a tympanum

Reproduction in the transition to land

• Usually external fertilization, eggs laid in water (e.g., spermatophore in salamanders)

Stegocephalia

• Digit-bearing vertebrates plus Tetrapoda

• Synapomorphies

  • Loss of several cranial bones

    • Allows the head to remain relatively stable while walking.

  • Loss of the opercular bones that cover the gill chamber in bony fishes.

    • The operculum was no longer needed in early choanates because they had lost the internal gills of their early ancestors.

  • A reduction of the notochord and a rigid spine.

    • Centra are thick and they constrict the notochord. Special articulatory surfaces (zygapophyses) link the neural arches to each other.

  • A shorter notochord that does not extend into the braincase.

    • The notochord of osteolepiforms extended up to the vicinity of the pituitary.

  • Four muscular limbs with discrete digits (fingers and toes).

  • A sacral rib connecting the axial skeleton (the spine) to the pelvic girdle (the hip).

    • This allows the weight of the body of tetrapods to be transmitted to the hind limb

  • The loss of dermal fin rays (the modified scales that support the fins).

    • This simply represents the elimination of a structure that was no longer needed and may even have been harmful on land

Acanthostega

• First complete tetrapod with free digits (eight on each hand)

• Based on recent reports, the limbs and gross morphology of the basal form Acanthostega were unsuitable for overland travel. Instead, Acanthostega probably propelled itself along the bottom with its limbs or held itself motionless in wait for an ambush.

• Retained some “fish-like” characters

  • Internal gills, tail fin, partial connection between skull and pectoral girdle, labyrinthodont teeth, lateral line, ulna shorter than radius

Ichthyostega

• Similar to Acanthostega, but…

  • Stronger limbs; radius and ulna of equal length

  • No gills in adult

  • Reduced number of skull bones

• Retains skull like Panderichthyidae, tail fin, labyrinthodont teeth, lateral line

• First tetrapod capable of life on land

• Important characters

  • Pectoral girdle no longer attached to skull

  • Pelvic girdle is attached to vertebrae

  • Seven toes on hindlimb

  • Reduced number of bones in skull

Theories of why fishes moved onto dry land

• Old theory – fish were living in habitats that dried up; survivors were the ones that crawled to new ponds

  • Natural selection for limbs

  • But a problem with this scenario is that the Devonian is no longer viewed as having been seasonally dry

  • Plus, early tetrapod limbs couldn’t support the animal on land

• New theory – Acanthostega and other early tetrapods had fully formed limbs, but never left the water

  • Limbs were useful “after the fact” for moving onto land, but originally had a different function

  • Analogous living species:

    • Frogfishes use their modified pectoral fins for support and to move themselves around on the bottom. Frogfish can even “gallop” in short bursts.

Properties of water

• Water is much more dense and viscous than air

• Sound travels faster in water than air

• Water has a much higher heat capacity than air

• Water contains less O₂ per unit volume than air

  • Solubility decreases as temperature increases

    • Warm water has less O₂ than cold water

  • Solubility decreases as salt concentration increases

    • Salt water has less O₂ than freshwater

Gill arch physiology

• Each gill arch bears a number of gill filaments (holobranchs), each of which is made up of two halves (hemibranchs)

  • Fine subdivisions on hemibranch are gill lamellae (major respiratory portion of gills)

    • Total surface area of the gill lamellae averages about 5 cm² per gram of body weight

      • Increased surface area → increased gas exchange

• Deoxygenated blood reaches the gills by way of the afferent branchial arteries.

• Oxygenated blood from the gills passes into the efferent branchial arteries and into the body

• Blood flows through the lamellae in the opposite direction of water flow across the lamellae (counter-current)

  • Blood with higher O2 content meets water with highest O2 content so that O2 diffuses into the blood along the entire length of the lamellae

  • The effect is an extremely efficient interchange of O2 and CO2 between water and blood

    • O₂ enters blood, CO₂ and protons leave blood

Respiration in Agnathans

• Non-feeding mode

  • Intake is through the nostril (hagfishes)

  • Ventilation pump = velum

  • 1-16 gill sacs with countercurrent setup

• When the hagfish is buried inside prey, water comes in and out through the gill opening behind the last gill pouch

• Lampreys expand and contract the branchial area, causing water to flow in/out; practical when head buried in prey

Respiration in elasmobranchs

• Water intake is through mouth and spiracle

• Ventilation can be either ram (mouth) or pump (mouth and spiracle)

• ≥ 5 individual gill slits (vs single operculum)

• Structure

  • Gill septum supports gill filaments

Respiration in teleosts

• Ventilation ram (mandatory in tunas) and/or pump (buccal, opercular cavity pumps)

• Structure

  • Surface area of gills is correlated to activity levels

Oxygen uptake and release

• The tendency of blood to take up and release oxygen is described with an oxygen dissociation curve

• The amount of oxygen taken up by hemoglobin (Hb) increases with oxygen tension (partial pressure)

  • The half-saturation point (P50) is defined as the oxygen tension at which blood is half-saturated.

  • The dissociation curve is typically sigmoid in shape; this is because of tetrameric molecular structure

• Change in pH influences affinity of Hb for oxygen

  • Blood pH drops where there is higher carbon dioxide (areas of metabolic activity)

  • Conformation of Hb changes, and reduces its affinity for oxygen (lower half-saturation point). This is called the Bohr Effect; occurs in all animal hemoglobins

  • In some fishes, there is an additional effect: low pH lowers the oxygen capacity of Hb (reduction of asymptotic saturation). This is called the Root Effect

  • As a result, Hb unloads oxygen in tissues where there is metabolic activity (where there is lactic acid production)

  • Diversity among fishes in dissociation curves and Bohr effect

    • Relative to Hb in an active fish such as mackerel, the oxygen capacity of Hb in a fish living in lower oxygen waters (toadfish) is lower and the Bohr effect is lower; the toadfish is less active and there isn’t as much oxygen unloading at peripheral tissues

Elimination of CO₂

• In metabolizing tissues

  • Carbon dioxide hydration produces protons (CO2 + H2O => HCO3 + H+)

    • This creates an acidic environment, which facilitates unloading of oxygen from hemoglobin

  • There is Hb uptake of some CO2

  • Hb also binds protons, thereby providing some buffering

  • Most carbon dioxide is transported to the gills in the form of dissolved plasma bicarbonate; this is created in the red blood cells but then diffuses out of the cell.

• At the gills

  • The hydration runs backwards as CO2 leaves gills quickly (because the environment is low in it, the molecule simply runs down gradient)

  • There is a rise in pH, and uptake of oxygen by Hb

  • The point here is to emphasize the linkages between CO2 and O2 exchange, and the roles of blood cells and plasma.

Gas bladder

• Gas filled sac located between the alimentary canal and the kidneys

  • Filled with CO2, O2, and N2

  • Functions primarily in hydrostatic balance, respiration; secondarily in sound production and sound reception

  • When used in respiration, gas bladder is compartmentalized and highly vascularized

Types of gas bladders

• Physostomous - retain connection between the esophagus and gas bladder through a pneumatic duct

• Physoclistous - lose connection

Structures associated with Physoclistous fishes

• Antroventral secretory region

  • Gas gland - secretes lactic acid, lowers blood pH, and reduces solubility of dissolved gasses

    • A change of 1 pH unit releases 50% of O₂ bound to hemoglobin; raises partial pressure of blood O₂ by the Bohr and Root Effects

  • Rete mirabile - countercurrent exchange system for gas; composed of a looping bundle of arterial and venous capillaries

• Posterodorsal resorption region

  • Oval - thin, highly vascularized area in the swim bladder; circular muscles contract and close the oval, preventing gas outflow; longitudinal muscles contract and expose the oval, permitting gas escape

How did early freshwater vertebrates osmoregulate?

Glomerular kidney

Kidneys in freshwater fishes

• Glomerulus: a typical kidney of a freshwater fish has tens of thousands of large glomeruli. Large amounts of water pass through them. Provides a filtrate that can be modified selectively by the kidney tubule

• Neck Region: lined with cilia; ciliary action aids movement of materials into tubule. Important in the low-pressure filtration systems of fishes

• First Proximal Segment (PCT I): location of reabsorption of many macromolecules (e.g., glucose, proteins); also excretion of organic acids

• Second Proximal Segment (PCT II): largest region of tubule; has high metabolic activity (i.e., active transport mechanisms that are responsible for reabsorption of many salts, e.g., Mg2+, SO4-, Ca2+, P, Na+, Cl-, and HCO3)

• Intermediate Segment: highly ciliated portion that assists in moving fluids through the tubule. In freshwater fish it is important to move the fluid through the length of the tubule as fast as possible to minimize reabsorption of water

• Distal Segment (DCT): participates in active reabsorption of Na+ and some Cl-

• Longitudinal Collecting Duct (CT): reabsorbs monovalent ions, again mostly Na+ and some Cl

Chloride cells

• Special cells in the gills and oral membranes to absorb ions by active transport mechanisms

  • Absorbs acid phosphate, bromine, calcium, chloride, lithium, sodium, sulfate ions, etc.

Kidneys in marine fishes

• Glomerulus: glomeruli in marine teleosts are small, poorly vascularized, and blood pressure is low. May be lost (aglomerular)

• Neck Region: may be lost altogether, especially in aglomerular species

• First Proximal Segment (PCT I): location of reabsorption of many macromolecules (e.g., glucose, proteins); also excretion of organic acids

• Second Proximal Segment (PCT II): instead of active reabsorption of salts, as in freshwater teleosts, this is the site of active secretion of salts (e.g., Mg2+, SO4-, Ca2+, P, Na+, Cl- , and HCO3). Also responsible for active secretion of nitrogenous wastes (urea, creatine, creatinine)

• Intermediate Segment: absent in marine fish; because the need here is to slow the movement of fluid to maximize the amount water passively diffusing back into the blood

• Distal Segment (DS): participates in some reabsorption of Na+ and Cl- 

• Longitudinal Collecting Duct (CT): some reabsorption of Na+ and some Cl-

Osmoregulation in marine elasmobranchs

• Marine elasmobranchs osmoregulate in a very different way from teleosts

• Evolved a specialized segment of the nephron that reabsorbs urea and returns it to the blood

  • Influx of urea and TMAO (trimethylamine oxide) raises the osmotic pressure of the blood to a level just above that of seawater so that water flows into the body of the shark (similar to freshwater fish)

• Have numerous well-developed glomeruli and excrete large amounts of dilute urine

• Evolved a specialized segment of the nephron that reabsorbs urea and returns it to the blood

• Have numerous well-developed glomeruli and excrete large amounts of dilute urine

• Rectal gland - an organ with chloride cells, for excreting monovalent ions

• This type of osmoregulation is a physiologically much less costly system than the marine teleost approach of salt excretion

Thermoregulation terms

• Terms associated with the environment

  • Poikilothermy: A condition in which an organism’s body temperature relies on and varies with the temperature of the environment

  • Homeothermy: A condition in which an organism maintains a constant internal body temperature

  • Problem: the body temperatures of most fishes will change with their environment, but the ambient external temperature is often quite stable due to the thermal stability of water

• Terms associated with the source of an animal’s body heat

  • Ectothermy: A condition in which an organism does not generate its own body heat but must use an external source of heat to warm itself

    • Advantage: low metabolic costs

    • Disadvantage: cannot live or function well in extreme thermal environments, especially the cold

  • Endothermy: A condition in which an organism is capable of generating its own body heat and maintaining a constant body temperature

    • Advantage: biochemical reactions become more efficient, fish can utilize wider thermal ranges

    • Disadvantage: high metabolic costs

Thermoregulation mechanisms

• Regional Endothermy: different temperatures in different parts of an animal’s body

  • Rete mirabile near large swimming muscles (often found in tunas and some sharks)

    • Fine counter current network of veins and capillaries that exchange both oxygen and heat

  • Rete mirable on the liver

    • Functions in maintaining increased gut temperatures (aids in digestive efficiency; also found in tunas and sharks)

  • Warm parts of the central nervous system (especially brain and eyes). Allows fish to use deeper, colder, more biological productive habitats without a decrease in brain and visual function.

    • Modify the circulatory system by having retes near the eyes and brain (better vision at cold temperatures)

• Thermogenic tissues - special heat-producing tissues

  • Billfish have specialized eye muscles without contractile filaments that produce heat without muscle contractions when stimulated by nerves.

Batrachomorphs vs. Reptilomorphs

• Batrachomorphs (“similar to a frog”)

  • Skull roof attached to braincase via the exoccipitals

  • Loss of skull kinesis

  • Only four fingers in hand

• Reptilomorphs (“similar to a reptile”)

  • Skull roof attached to braincase via the basioccipital

  • Increased skull kinesis

Temnospondylii

• Temnospondyls are a very large and widespread extinct clade of stegocephalians.

• Known from the Lower Carboniferous (ca. 340 mya) to the Lower Cretaceous (ca. 120 mya)

• Found on all continents from Greenland to Antarctica.

• More than twelve families are known, with about 90 genera.

• Display a great diversity of forms, resembling large salamanders, crocodiles or gavials, with brevirostral (short-snouted) to longirostral (longsnouted) skulls.

• Their size ranges from about 20 cm to 3 m in length

Lissamphibia Lineages

Anura (Salienta)

Caudata (Urodela)

Gymnophiona (Apoda)

Anura (Salienta) synapomorphies/characters

• Frogs and toads have a body that is highly modified from the basic amphibian design:

  • Body is specialized for jumping (and/or swimming)

  • Body & vertebral column stiff and inflexible

  • Hind legs greatly elongated with additional limb segment derived from tarsal bones

  • Pelvis and vertebral column fused, stiffened, elongated

  • Loss of tail

Frogs vs. Toads

• Not natural groupings; rather distinction is based on morphological and life history characters

• Frogs

  • Relatively longer hindlimbs for longer jumps

  • Aquatic to semi-aquatic

  • Well developed webbing on feet

  • Relatively smooth skin

• Toads

  • More stout body with shorter hindlimbs

  • Less aquatic; webbing reduced or absent

  • Skins exhibit a rougher texture

Anuran feeding

• Aquatic frogs use suction feeding

• Terrestrial frogs typically flip out their tongue

Anuran larvae and metamorphosis

• “Tadpoles” have short rounded body, laterally compressed tail, lack legs

  • Internal gills

  • Lateral line

  • Unique hard beak or denticles on mouth parts

• Most tadpoles feed on algae, either by filter feeding or scraping algae off rocks

  • Stream-dwelling tadpoles have sucker-like mouths and muscular tails

• Body forms and mouth structures of tadpoles reflect differences in habitat and diet 

• Some species of frogs have predatory tadpoles

• Tadpole metamorphosis involves:

  • Degeneration and resorption of tail

  • Growth of limbs (bone, muscle, skin, etc.)

  • Reorganization of mouth, head

  • Calcification of skeleton

  • Formation of dermal glands

  • Loss of gills, operculum

  • Development of lungs

  • Changes to eye musculature and retinal pigments

  • Growth of portions of brain (cerebellum, etc.)

  • Alterations to kidneys, pancreas, intestines

• During metamorphosis, tadpoles are more vulnerable to predators

  • Metamorphosis is very rapid (often just a few days)

Caudata (Urodela) generalities

• Salamanders have retained the most generalized body plan

  • Body is somewhat to very elongated, with 4 limbs splayed out to sides

  • Walking gait probably very similar to that of the earliest tetrapods

• Salamanders often live in burrows, crevices, or under debris

  • Often results in reduction in size of limbs (which get in way) and elongation of body

  • Some sirenians have lost their hind limbs

Caudata (Urodela) Reproduction

• Salamander larva are aquatic

• Larval stage has similar elongated body, but…

  • Broad tail fin for swimming

  • External gills (in many)

  • Lateral line, lack of eyelids

• Some salamanders are paedomorphic = retain larval characteristics (including fully aquatic lifestyle) throughout their life (e.g. mudpuppies, Necturus)

• Many Plethodontid salamanders have direct development: young hatch from eggs (laid in moist places on land) in miniature adult form

Caudata (Urodela) Feeding

• Aquatic larvae and adults typically use buccal expansion for suction feeding

• Terrestrial forms typically protrude their sticky tongue to pick up prey

• Plethodontid (lungless) salamanders can project their tongue to capture prey more than half their body length away

  • Involves hyobranchial apparatus which therefore can’t be used for buccal pumping (breathing)

Gymnophiona (Apoda) Generalities

• Caecilians; tropical and subtropical; limb-less worm-like shape for burrowing

• Caecilians are amphibians that resemble large earthworms in shape, but are a different color (yellow or even purple)

• Their mouths, however, are large, and they are predacious upon various small fish or invertebrates. They tend to burrow in both the wild and in captivity.

• Most caecilians are fossorial and remain underground throughout most of their lives while other forms are aquatic

Gymnophiona (Apoda) Synapomorphies

• Limbless and completely lack pectoral and pelvic girdles.

• Eyes completely or partially covered by bone or flesh.

• A tentacle is present on either side of a caecilian’s head between the eye and the nares. These tentacles are apparently significant in receiving chemosensory cues.

• Eversible male copulatory organ (phallodeum) that is partially formed by the cloacal wall and by which internal fertilization is accomplished.

• An absence of ear drums or inner ear cavities.

• Annuli (rings) are found throughout the body of most caecilians.

• Caecilians are the only amphibians with scales.

  • These dermal scales are located within the annuli and require very close inspection and the use of a good microscope to notice.

Gymnophiona Reproduction

• Oviparous species are either direct developing (no aquatic larval stage) or have limbless larvae with external gills and tail fin

• Viviparity evolved several times within caecilians

• After the developing embryos use up the last of their yolk they still require nourishment while inside their mother’s oviduct. The embryos begin feeding upon a substance labeled uterine milk which is secreted by the oviducts.

• The embryos are equipped with tiny uterine teeth that may be used to scrape away and consume the oviduct secretion. The teeth are then lost before or shortly after birth.

Lissamphibia Synapomorphies

• Moist, permeable skin and substantial cutaneous gas exchange

• Pedicellate, bicuspid teeth

• Operculum-columella complex

• Papilla amphibiorum

• Green rods

  • Except in Caecilians, which were secondarily lost

• Levator bulbi muscle

  • Causes the eyes to bulge outward

Lissamphibia hearing

• Stapes (columella) and operculum are sound-conducting structures

  • Stapes is only in tetrapods

  • Operculum is connected via opercular muscle to the suprascapula

    • Caecilians lack opercular muscles (no shoulder girdle)

  • Papilla Amphibiorum sound conduction:

    • From ground through leg through suprascapular through opercularis muscle through operculum to papilla amphibiorum

  • Papilla basilaris sound conduction:

    • Tympanum to stapes to papilla basilaris

  • There are two sensory patches in the inner ear: the papilla basilaris is found in other tetrapods and the papilla amphibiorum is unique to living amphibians

    • These two sensory patches allow them to hear sounds both >1000 Hz (basilaris) and <1000 Hz (amphibiorum)

    • Sound can conduct through the legs to the papilla amphibiorum, allowing them to hear vibrations from the ground

Lissamphibia reproduction

• External fertilization – females lays eggs that males then fertilize

  • A few salamanders have external fertilization

  • Most frogs use amplexus (male grasps female until she lays her eggs)

• Internal fertilization in salamanders accomplished via spermatophores (sperm packet) that males produce

  • Spermatophores may be inserted by males or placed on ground, after which female picks them up

• Viviparity

  • Common in caecilians; possibly up to 75% of species; appears to have evolved several times

    • Embryos obtain nourishment by scraping nutrients off lining of oviduct

    • Caecilian embryos are large (up to 3 - 2 mother’s body length) at birth

  • Rare in salamanders and frogs; involves production of few, large young

    • Requires internal fertilization, but little is known about how it works in these species

• Oviparity

  • Most common breeding method for both salamanders and frogs

  • Eggs are laid in water for most species, but numerous exceptions occur

    • Direct development may avoid competition or predators in the aquatic environment

  • Eggs are vulnerable and survivorship low, so fecundity must be high to compensate

Lissamphibia Parental Care

• Egg guarding

  • Various salamanders, caecilians and frogs guard eggs (esp. terrestrial eggs)

  • Some frogs build nests to protect their eggs. Nests may be made of foam or scooped out pools that fill with seepage or rainwater

• Egg transport

  • Surinam toad (Pipa pipa) eggs are pushed into thickened skin on female’s back with complex aquatic mating dance 

• Egg transport & brooding

  • Hemiphractus tree frogs – these frogs care for the developing eggs by carrying them on their back in a shallow basin or in pouches modified from the skin. The developing embryos hatch as froglets in some species or as tadpoles in others

  • Rhinoderma – the males carry the tadpoles in their vocal sacs, and development is completed as froglets.

• Tadpole transport & care

  • Dendrobatid (dart-poison) frogs lay eggs in bromeliads or on the ground. In some species, females lay infertile eggs as food for the tadpoles

    • When eggs hatch, either male or female (depending on species) picks up tadpoles which stick onto back and carries them around to new locations

Hyoid Coupling

• Emerged in primitive Actinopterygians

• Lower jaw depression is initiated by contractions of epaxial and hypaxial muscles

  • Contraction of epaxial muscles causes head to rotate upward relative to bodies axis

  • Contraction of hypaxial muscles (especially those on the cleithrum) causes a backward and downward rotation of the pectoral girdle

• Anteriorly, the cleithra are attached to the hyoid apparatus by the sternohyoideus muscle

  • This muscle also contracts so that the backward and downwards movement is transmitted to the hyoid

• Because the hyoid lies between and is attached to the lower jaw, the downwards and backwards pull on the hyoid apparatus is transmitted to the lower jaw

Opercular Coupling

• Emerged in bowfins and teleosts

• Opening of mouth initiated by contraction of the levator operculi muscle

  • Causes the opercle to swing up and backward

  • Because the sub- and inter- opercle are attached, this up-and-backwards movement is transmitted ventrally throughout all elements of the opercular apparatus

  • The interopercle pulls back on lower jaw by means of a strong ligament

• Advantage

  • Necessary pre-adaptation for those fish that feed by nipping at rocks and coral, pick-up small prey, bite-off and crush coral (e.g., surgeonfishes, parrotfishes, wrasses, triggerfishes, etc.) 

  • Derived teleosts possess both gape-and-suck feeding and the opercular coupling mechanism

What muscle closes the mouth and where does it attach?

Adductor Mandibulae

Originates on the suspensorium and inserts along the length of the primordial ligament