Midterm II

Question 1

What features distinguish Osteichthyans from other fishes?

Answer 1

• Unique pattern of dermal bones surrounding the jaw and brain case
• Presence of maxilla, premaxilla, and dentary
• Dermal bones form palate
• Dermal head bones attach to pectoral girdle (can form operculum)
• Branchiostegal rays in the floor of the gill chamber (used for suction)
• A gas-containing structure used for buoyancy or respiration (such as a swim bladder or lung)

Question 2

What are the differences between Ray fins and lobe fins?

Answer 2

Ray finned fish ancestors presumably had similar fins to sharks with scapulacoracoid with basal and radial pterygiophores and finally fin rays. Current actinopterygii have lost most of the pterygiophores.
Ancestral Sarcopterygii had monobasal fins made of only bones (no real rays). Modern sarcopterygii (such as the tetrapodomorphs) have an asymmetrical fin skeleton closely resembling the ancestral pattern

Question 3

Describe the basic features of sarcopterygii

Answer 3

Have primitive scale types called cosmine, made of dentine-like material. Have massive tooth plates with enamel for crushing invertebrates. Arose and radiated in devonian

Question 4

What are the living types of sarcopterygii? What is the evolutionary significance of these animals? Which group is the sister group to tetrapods?

Answer 4

Tetrapoda, dipnoi (lung fishes) and actinisita.
The lobe fin’s bone structure is very similar to that of a tetrapod limb (gave way to tetrapod limbs). The locomote using the same opposite movement of front and hind limbs that tetrapods do.
Dipnoi, based on molecular evidence, were found to be the sister group to tetrapods

Question 5

Describe the extant Dipnoi. What is special about the African Lungfish?

Answer 5

Dipnoi are distinguished by the loss of tooth-bearing dermal bones (maxilla, premaxilla, dentary) and fusion of palatoquadrate and chondrocranium. Have an autostylic jaw, tooth plates, choanae (nasal cavity opens to oral cavity) and fused dorsal, caudal, and anal fin.There are three types of lungfish: South American, African, and Australian. All are either facultative or obligate air breathers.
African lungfish live in flood plains where they experience a wet and dry season. During the dry season they estivate: bury into the sand and form a mucous cocoon around themselves, waiting out until the wet season.

Question 6

What characterizes actinistia? Compare and contrast extinct and extant actinistia

Answer 6

Actinistia have lobe fins, a three lobed tail and a conservative morphology.
Miguashaia - Oldest fossil. Devonian.
Dipluris - Jurassic. Has characteristic extra lobe on caudal fin
Holophagus
Rebellatrix - Described in 2012, using fossils from Rockies. Has a very different curved caudal fin, typical of high speed swimmers.
Extant coelocanths are seen very rarely, live in caves, and have a diphycercal (bones extend through the whole length) tail, an unrestricted notochord, are ovoviviparous and lecithotrophic, have a tapetum, cosmine scales, and an electrosensory organ in the snout. They include Latimeria chalumnae, found in 1938 and Latimeria menadoensis, found in 1998.

Question 7

List all the groups of actinopterygians from ancestral to derived, with a brief description of each

Answer 7

Polypterids (bachirs and reed fish) have many miniature dorsal fins, ganoid scales, a ventral lung, and an ancestral fin form.
Paleonisciforms were the early ray finned fishes. They had a single dorsal fin and survived until the Mesozoic.
Acipenseriforms (sturgeons) have no dermal or endochondral bone, have armour-like “scutes” along body, and are suction feeders. Eggs were traditionally used for caviar. Also includes paddlefish, which have a paddle-like Ampullary rostrum.
Lepisosteiforms (garpikes) are lurking predators with a derived crocodilian-like mouth. Their green eggs are toxic and their swim bladders are modified as lungs.
Amiiformes (Bowfins) are the sister group to the teleosts. They are very derived and have cycloid scales, mobile maxilla, Heterocercal tail, and extensive dermal bone.
Teleosts are the most derived and consist of most fish in the world

Question 8

Describe the life cycle of the American eel. What type of life cycle is this?

Answer 8

Eggs are laid in the Sargasso Sea and the leptocephalus larva is born. These drift on the current into rivers where they develop into small glass eels. It is in these rivers where they grow and mature until they eventually become adult silver eels.
This is a catadromous life cycle.

Question 9

What is the function of pharyngeal jaws?

Answer 9

The teeth on pharyngeal jaws allow for further breakdown of plant tissue.
However, they can be used by predators. The moray eel has mobile pharyngeal jaws with sharp teeth for grasping prey to be pulled into the mouth

Question 10

Discuss Elopomorpha

Answer 10

Includes the primitive teleost Tarpon and the Anguilliformes (true eels). Eels have no pelvic girdle or pelvic fins. All eels have the same larval form, the leptocephalus larva.
Pug-nosed eels are typically scavengers but can use jaws to eat their way into the flesh of bottom dwelling fish (also have been shown to eat blood).
Eels live all over the world, especially in deep sea. The deep see eels include the gulpers and swallowers.

Question 11

Discuss trends in jaw mobility within the Actinopterygii, using specific examples.What are the feeding advantages of this adaptation?

Answer 11

Early actinopterygians had amphistylic jaws that snapped shut with the help of a small adductor mandibulae muscle. Later neopterygians such as Amia Calva have a mobile maxilla with teeth on it that swings down, creating suction and stopping prey from escaping. Primitive teleosts such as Tardon would have a mobile maxilla that swings forward, creating a circular opening in the mouth with a fold of skin behind the maxilla to hold food in. More advanced teleosts such as the African cichlid Fish have a protrusible premaxilla (pushed out by maxilla) with folds of skin creating a circular gape for maximum speed and suction

Question 12

Discuss aposematism and mimicry in amphibians.

Answer 12

Aposemitism occurs when organisms have bright colouring to advertise the fact that they are poisonous or taste gross.
It is possible for non-toxic animals to mimic the colouration or pattern of toxic species to avoid predation

Question 13

What are the scientific names of soft rayed and spiny rayed fishes. Distinguish morphologically between “soft rayed” and “spiny rayed” euteleosts. Use as many characteristics as possible.

Answer 13

Spiny rayed fishes - Acanthopterygians. Soft-rayed fishes -
Dorsal fins: spiny rayed fishes have one spiny fin and one soft fin
Pelvic fins: are located more anteriorly in spiny rayed fishes
Cross-sectional shape: spiny rayed fishes are elongated and round, soft rayed fishes are flattened and narrow
Swim bladder: Connected to gut in soft rayed, separate in spiny rayed
Scale type: Soft rayed have cycloid scales, spiny rayed have ctenoid (spiky) scales

Question 14

Discuss locomotion in fishes. Specifically mention thrust and drag

Answer 14

In order to move underwater, the fish must move its body back and forth, with most of the thrust coming from the fish pushing backwards on the water. Two types of drag act on a fish: frictional/viscous drag (caused by friction between body and water) and inertial drag (caused by pressure differences). Viscous drag is worse when there is a higher surface area but lower when there are no scales. Inertial drag is sensitive to the shape of the body. Streamlined shapes produce less inertial drag.

Question 15

Discuss how the aquatic medium shapes the sensory systems of fishes

Answer 15

Underwater the lens of the eye must be spherical to allow for the cloudy light to be focused properly. At great depths, other senses must be finely tuned since there is no light.
Some fishes have phenomenal olfactory senses. Often these fishes are predators who rely on their senses other than sight to find prey?
The lateral line system is used to sense pressure changes in the water around the fish (sensing the movement of animals they may not see).
The inner ear is derived from the lateral line system and plays a big part in sensing the fish’s acceleration and place in space.
A lot of fishes can also detect electrical impulses of other fishes. Some can even create their own electricity (electric “eel”)

Question 16

Mechanoreceptors are the basic receptors in several sensory systems of fishes.
Explain the structure and function of these receptors in each system (lateral line and receptors of the membranous labyrinth).

Answer 16

Hair cells in the neuromasts consist of one large kinocilium and tiny little stereocilia, embedded in the cupular matrix. The cupula deflects the hair cells, triggering nervous signals to quickly be sent, and when the cupula is bent in the opposite direction, there is a reduction in the firing rate of the nervous signals, allowing complex sensory information to be understood.
Each chamber of the inner ear contains an otolith, which is resting on sensitive hair cells. When the otolith moves (which occurs during acceleration and stopping of the fish), the hair cells detect this and send a signal to the brain to prevent confusion. This system also senses static equilibrium.

Question 17

What evidence exists to support the view that the inner ear is derived from the lateral line system?

Answer 17

1. Receptors are identical - hair cells
2. Receptors are derived from same embryonic tissue (neuroectoderm)
3. Endolymphatic duct in sharks connects to surface, remnant of surface origin
4. Ear sinks below surface during embryological development

Question 18

How do fish take advantage of the fact that water is a reasonably good conductor ofelectrical signals? Discuss the processes of electrogenesis, active and passive electroreception, electrolocation and electrocommunication.

Answer 18

Some fishes generate electricity to shock predators and prey. Whereas others generate electricity to communicate. Some predators, such as sharks, can sense the electrical impulses of others.
Electrogenesis - Achieved through modified muscle cells filled with electrocytes stacked in series. These electrolytes can have currents transmitted through them.
Passive electroreception: Detects low frequency electrical signal.
Active Electroreception: Generate a weak EOD which is then detected. Achieved by Ampullary organs and tuberous organs.
Electrolocation: Used in weakly electric fishes for navigation and communication. EOD is detected by tuberous organs and impulses from other fish detected by Ampullary organs.
Electrocommunication: EOD’s can give information about the sex, species and identity of a fish. Female fishes prefer longer EODs, so sexual selection drives that

Question 19

How do cartilaginous and bony fish maintain a constant internal environment in marine and freshwater environments? Are some fish more tolerant of salinity changes?

Answer 19

Freshwater fish - hyperosmotic (tendency to gain water)
Saltwater fish - hyposmotic (tendency to lose water)
Kidney helps regulate water and salt balance by altering glomerular filtration rate and tubular respiration/secretion: freshwater fish secrete dilute urine and saltwater fish excrete lots of sodium.
There are two main types of salinity tolerance: Euryhaline, meaning that the organisms are tolerant to a wide range of salinities (salmon, eels, catfish), and stenohaline, meaning that the organisms have a small range of salinity tolerance (tuna, goldfish).

Question 20

In what form are nitrogenous wastes excreted in various vertebrate groups? Give examples of ammonotely, ureotely and uricotely.

Answer 20

Excreting nitrogenous wastes primarily as ammonia is called ammonotelism, primarily as urea is called ureotelism, and primarily as uric acid is called uricotelism.
Most bony fishes are ammonotelic.
Mammals (including humans) are primarily ureotelic. Urea is synthesized from ammonia and is less toxic.
Reptiles (including birds) are primarily uricotelic. It is a semisolid waste (very little water is lost) and takes more energy than the other two.

Question 21

How are fish gills adapted to extract the maximum amount of oxygen from the water?

Answer 21

There is a steep concentration gradient for the Oxygen exchange, a large surface area with a thin exchange surface, and a one way flow of water. The anti-parallel flow of the blood and water allows for maximum oxygen exchange to occur.

Question 22

Why is it that accessory respiratory structures are best developed in tropical fishes? Describe, with specific examples, the various accessory means of respiration using atmospheric air.

Answer 22

Because there is very little oxygen in warm water.
Gut breathing - the stomach can be used as a site for gas exchange. An air bubble is taken into the body and then absorbed into the walls of the stomach.
The mouth can be used for air breathing, where an air bubble is held between the highly vascularized surfaces on the top and bottom of the mouth (this same process can occur in the pharynx as well).
The interior body wall can be used for gas exchange.
The labyrinth organ can be used for gas exchange.
The mudskipper uses it’s skin and operculum chamber.
Finally, the most important gas exchange structure, the lung.

Question 23

Are lungs a recent product of bony fish evolution? Briefly describe the evolutionary history of lungs.

Answer 23

Lungs are not a recent development in body fishes. They go back all the way to the bichirs and lungfishes, two of the oldest clades of Osteichthyes.
Lungs arose both ventrally and dorsally. It arose dorsally before gars, carp, and perch. In carp and perch it is a hydrostatic swim bladder (physostomous in carp and physoclistous in perch), whereas in gars it is an aerial respiratory organ.
Lungs arose ventrally before bichirs, lungfish, and tetrapods as an aerial respiratory organ. In bichirs it is nonalveolar, contrasting with tetrapods and lungfish. Lungfish have a simple glottis and tetrapods have a guarded one.

Question 24

What selective advantages favoured the fish-tetrapod transition to a terrestrial existence? Discuss the evolution of tetrapods based on fossil evidence of elpistostegid osteolepiforms. Include specific evidence based on the morphology and presumed lifestyle of Panderichthyes and Tiktaalik.

Answer 24

Because there weren’t many predators on land during the Devonian, the selective advantage of life on land was high. The juveniles would have less predators, there was less competition for food, and it allowed for basking onshore.
The elpistostegalians are considered the sister group of tetrapods. Two important organisms in this group are panderichthys and Tiktaalik.
Panderichthys had a dorso-ventrally flattened body, a broad, flat snout, eyes pointing ahead, no dorsal or anal fins, and a tail that is not designed for speed in water. It likely lived in shallow water.
Tiktaalik was a bit more derived. It had an elbow joint, broadly overlapping ribs (for supporting body on land), probably had lungs, but it also had gills as well. Tiktaalik actually had what could be considered a neck (no operculum or suprascapular), which was likely used to snap at prey items that were on land.
Looking at the fossil evidence of the elpistostegalians, you can see the gradual transition from fish to tetrapod. The fins slowly to develop into limbs with elbows and no fin rays. The ribs become more prominent, able to support the animal’s body. The eyes migrate to the top of the head and the body is dorso-ventrally flattened.

Question 25

Discuss the control of buoyancy in chondricthyans and bony fishes. Include anexplanation of how the swim bladder is filled and emptied in physotomes and physoclists.

Answer 25

Chondrichthyans control buoyancy using an oil-filled liver. Osteichthyans often have a swim bladder for buoyancy control, which is filled with air depending on the water around them. There are two types of osteichthyans with swim bladders: Physostomes and Physoclists. Physostomes have their swim bladder attached to the digestive tract via the pneumatic duct. Physostomic swim bladder is empties by burping.
Physoclist’s swim bladder is not attached to anything. This type of swim bladder is emptied by the ovale.
Both types of swim bladder have a gas gland that is used to add air to the bladder. The rete mirabile is a capillary-filled area right by the gas gland. The gland secretes carbonic acid and lactic acid into the blood to lower the pH of the blood and cause gas exchange from the exiting capillary to the entering capillary, resulting in maximum gas exchange from the rete to the gas gland.

Question 26

Describe the anatomy and adaptations of the amphibian integument.

Answer 26

Integumentary is highly permeable to gases and water. Mucus (secreted by small glands near the surface) keeps the skin moist for gas exchange and evaporative cooling. In some species, integument has antibacterial properties.

Question 27

Discuss the distribution, ecology, anatomy and reproductive biology of the Caecilia(Gymnophiona)

Answer 27

Have dermal scales, protrusible tentacles, are carnivorous, are legless and can be burrowing or aquatic. They have very reduced eyes and sometimes no eye socket at all. The skull is very thick and can be used for burrowing.
If they do lay eggs, the female will wrap herself around them and guard them. Some young are dermatotrophic (eat their mothers skin). The eggs inside the mother’s body use up their yolks quite quickly, hatch, and begin to eat her from the inside, snacking on a thick, creamy substance secreted by the walls of the oviduct.

Question 28

Discuss Devonian tetrapods Icthyostega and Acanthostega in terms of their phylogeny, anatomy and probable lifestyle

Answer 28

Acanthostega was primarily acquatic. It had internal, fish-like gills, polydactyly (hand was probably webbed and fin-like), small ribs, non-bendable elbow, weak sacral connection, fin-like hind limbs. It probably also had lungs.
Ichthyostega was primarily aquatic and had internal gills. It had polydactyly and a very robust, paddle-like hind limb. It had a weak tail, strong zygopophyses and thick, overlapping ribs. It likely moved by inching forward because the ribs did not allow for flexing of the trunk.

Question 29

Discuss the origin of digits in the context of adaptations to a shallow water existence. What evo-devo evidence exists for the evolution of the tetrapod limb?

Answer 29

Digits would have been selected for in shallow water because they would enable an organism to take a breath of air or snatch up a prey item from the surface.
Evo-devo work has proven that fin rays in teleosts are determined by the same Hox genes as digits in tetrapods

Question 30

Frogs have highly specialized anatomy adapted for their method of locomotion. Defend this statement with specific examples of these specializations. How are the lifestyle and locomotion connected in anurans? compare the skeletal morphology of the sister group, Triadobatrachus, to modern frogs

Answer 30

Anurans locomote by hopping. This is made simpler by the elongated foot, ankle, and leg. The tibia and fibula are fused, the pelvic/sacral joint is flexible, the sacral vertebrae are fused (urostyle). Fewer vertebrae, short ribs, stout pectoral girdle absorbs the shock of landing. Different types of toads and frogs perform different activities, and their bodies are suited for those. Swimmers have longer fore and hind limbs, walker-jumpers like tree frogs have long forelimbs and long hindlimbs.
Triadobatrachus had short hind limbs and toes, 14 presacral vertebrae, a short ilium with no urostyle, and five toes on the front feet. In contrast to this, anurans have long hind limbs and toes, 5-9 presacral vertebrae, elongated ilium, urostyle, and four toes on front feet.

Question 31

Discuss the reproductive biology of the anura. Include a discussion of vocalization, amplexus,and methods of protection of eggs and young

Answer 31

Anurans can be either explosive breeders or prolonged breeders. Explosive breeders breed in a temporary pond and accomplish mating over a couple of days. Prolonged breeders include species where males set up and defend territories.
Male anurans make advertisement calls - letting the ladies know his size and fitness. By calling, the males are making themselves known to predators both visually and vocally.
Amplexus is a type of grip that the male has on the female, which he can hold for hours or even days while he waits for her to lay her eggs.
Many species lay eggs on overhanging leaves to avoid aquatic predation and so the kids can hatch and just fall into the pond. Male tungara frogs beat their legs in the jelly the female produced to create a foam nest for the tadpoles. Darwin’s frogs hold young in their vocal sac until they are fully grown. Female marsupial frogs form a sac over eggs on their backs. Female surinam toads carry children in pockets on back

Question 32

Discuss the selective advantage of having an aquatic larval stage and the ecology of tadpoles

Answer 32

The aquatic larval stage can take advantage of spring algal blooms in ponds. If they feed on different things there is no competition with adults. Tadpoles come in four varieties:
Surface feeder - Feed on plants and sometimes other tadpoles
Scraper - Have keratinized beak
Filter feeder - Hover in the water, have no keratinized mouth parts.
Holdfast scraper - Use keratinized mouth parts to break bacteria and algae off of surfaces and eat them

Question 33

Distinguish between the “temnospondyls” and the “lepospondyls”

Answer 33

Temnospondyles are a subgroup within batrachomorpha with four fingers, flat, immobile skulls, and two occipital condyles that were present during the time of the dinosaurs. Some were semi-terrestrial and some were aquatic.
Lepospondyls are unknown in origin, thought to have branched off from batrachomorphs. They were generally quite small, with a lizard-like group (microsaurs), a limbless, elongate group (aistopods) and a small, newt-like aquatic group (nectridea).

Question 34

List and describe the shared derived characteristics of the Amphibia

Answer 34

1. Moist skin (kept moist by mucuous glands) used to exchange oxygen and CO2 with the environment. All amphibians have poison glands in their skin.
2. Most amphibians have two bones associated with the inner ear. The columella (derived from hyoid arch) and operculum work together to transmit sound.
3. Papilla amphibiorum- A special sensory area in the wall of the sacculus that is sensitive to frequencies below 1000 Hz (ground vibration). The papilla basilaris detects frequencies ABOVE 1000 Hz
4. Green rods - A distinct type of retinal cell present in all but caecilians which is sensitive to blue light
5. Pedicellate teeth - Most amphibians have teeth with crown and base of dentine and middle area composed of uncalcified dentine.
6. Levator bulbi muscle - Thin sheet in the floor of the orbit causing the eye to bulge out, enlarging the buccal cavity

Question 35

Early anatomists viewed the incomplete septum in the hearts of adult anurans as a primitive or inferior feature. Give evidence that the structure of the ventricle is adaptive, particularly when frogs are underwater and exchanging respiratory gases.

Answer 35

When a frog is diving, blood flow to and from the lungs is restricted (pulmonary artery and vein constrict), which is a natural response to heightened CO2 when diving. Blood going to skin is being oxygenated by exchange of gases at surface (collected by cutaneous veins and brought to heart).
Oxygenated blood from skin can go through ventricle as well.

Question 36

How is water conserved, absorbed, and stored in amphibians?

Answer 36

Amphibian skin is highly permeable to water.
Most amphibians are nocturnal, preventing extreme water loss as a result of heat. They also adjust their posture to limit sun exposure.
The pelvic patch takes up water very efficiently (lots of capillaries).
The bladder is the site where water can be re absorbed after some processing.

Question 37

Discuss the distribution, diversity, and biology of the Caudata (urodela). Include a discussion on paedomorphosis, locomotion, and reproduction in salamanders

Answer 37

They are most diverse in temperate regions, specifically in North America.
They often retain juvenile qualities in later life (paedomorphy). The Mudpuppies are extremely paedomorphic and can retain most juvenile qualities throughout life (lateral line, cartilaginous skeleton, gills). They come in various types ranging from the giant salamander to the (nearly) limbless amphiumidae.
Urodeles choose mates through complex courtship rituals wherein pheremones are released by the male to increase female receptivity. Some salamanders are external fertilizers. They lay their spermatophore on a surface and the female will come and pick it up using her cloaca. The eggs she lays will hatch into larvae with external gills.
Urodeles are able to locomote outside of water because of their well-developed zygopophyses, which strengthen the vertebral column (prevent sagging). Lateral bending advances the limbs. Essentially, salamanders move their bodies back and forth and their limbs move as well.

Question 38

How is the evolution of feeding specializations of plethodontid salamanders related to their respiratory physiology and life history?

Answer 38

The plethodontid salamanders are known for their loss of lungs. The hypobranchial apparatus of other salamanders must be used as part of the respiratory system. Many plethodontids use this leftover hypobranchial apparatus to protrude the tongue to capture prey that are a considerable distance away. This is related to the life history of these salamanders because the larval salamanders filter feed using the hypobranchial apparatus, which creates selective pressures between the larval use of the hypobranchial apparatus and the adult use of it. As a result, bolitoglossine plethodontids often do not have an aquatic larval form.

Question 39

Describe amphibian metamorphosis. Why are metamorphosing anurans more susceptible to predators?

Answer 39

Thyroid hormones play a very important part in amphibian metamorphosis. There are three general parts to anuran larval development: premetamorphosis (size gets bigger, little change in form), prometamophosis (hind legs appear, growth of body continues at a slower rate), and metamorphic climax (forelegs emerge, tail regresses). These events are triggered by thyroxine, which is controlled by TSH (thyroid stimulating hormone), produced in the pituitary gland.
When an anuran is in between tadpole stage and fully grown frog, it cannot properly swim but it also cannot properly hop. This leaves it at the mercy of many predators.

Question 40

What are some of the local and global factors contributing to amphibian population declines?

Answer 40

Local habitat destruction and degradation is a big one. Wetlands are drained to make room for urban environments almost everywhere in the world (even manitoba). Agricultural herbicides can sometimes have a feminizing effect on males. Mining and oil exctraction can point aquatic ecosystems like ponds and lakes.
Global causes include climate change, acid rain, UV-B radiation, and disease (chytrid fungus).