Vertebrate Functional Morphology Final

Gills Structure

Operculum covers gill

Gill filaments contain vessels (oxygen poor entering the gills, oxygen-rich leaving the gills)

Oxygen is also diffused across lamellae (networks of blood vessels) from oxygen-rich blood leaving the gills into oxygen-poor blood entering the gill

The oxygen-poor vein is positioned along the anterior margin of the gill filaments to ensure maximum exposure to water contacting the gills (the oxygen-rich artery is positioned along the posterior margin of the gill filament)

“Countercurrent exchange” system within lamellae (oxygen rich blood flows in the opposite direction from the oxygen poor blood, diffusing oxygen into the oxygen poor blood through the lamellae)

Gill-based respiration occurs in cartilaginous fishes, ray-finned fishes, and amphibians

• The gills are external in some salamanders (larvae and adults) as well as some tadpoles

• Superficially similar as gills in some invertebrates (e.g., mollusks, insects, crustaceans)

Gills Function

Water is drawn into the buccal cavity by opening the mouth and opening the operculum

• Creates an area of low pressure in the buccal cavity

• Water is funneled out through the gill slits

• As water exits it passes across the gills

Oxygen-poor blood is pumped from the heart to gills

First passes through the gills arch

Redirected into gill filaments

Oxygen diffuses through from the water through membranes into blood

Oxygen is also diffused across lamellae from oxygen-rich blood leaving the gills into oxygen-poor blood entering the gill

“Countercurrent exchange” system within lamellae

Gills Benefits and Drawbacks

Benefits:

• Very efficient by percentage (of O2)

• Pumping operculum, paired with forward motion can consistently move water across gills

• “Breathing at every moment”

• No “backwashing” (not literally inhaling and exhaling), which reduces accumulation of particles, as the gills are constantly being flushed with water

• Energy efficient, as only gill/mouth opening require input of energy (closing is passive during breathing)

• Dynamic in terms of pace (can modulate how much water flows across gills in response to oxygen demand)

Drawbacks:

• Way less O2 in water than air (inefficient by volume)

• Only works in water, as the gill filaments collapse and “drown” one another in air

Lungs Structure

Site of oxygen uptake in mammals, reptiles, birds, some amphibians, some fish

Generally, centrally located in the upper abdomen since air taken in during respiration is transported directly to the lungs

Trachea = the “wind pipe” that directs inhaled air into lungs

Bronchus = paired tubes that guide air into each lung

Bronchioles = small ducts that direct air to alveoli

Alveoli = elastic air sacs surrounded by alveolar-capillary membrane (“Alveolus” —> singular)

Lungs Function

Site of gas exchange

• O2 from inhaled air is transferred into blood stream

• CO2 exhaled (not exchanged due to larger molecule)

Gas exchange through alveolar-capillary membrane surrounding alveoli

Lungs Benefits and Drawbacks

Benefits:

There’s more O2 in air than water, so breathing via lungs is very efficient per volume

Dynamic in terms of pace (can breath shallow or hard in response to oxygen demand)

Drawbacks:

Inherently “rhythmic”

Must breath in then out, then repeat

Results in high energetic demand (both inhale and exhale use energy)

Gas exchange really only occurs during inhale and lungs are empty during part of breathing cycle

This “dead time” introduces some inefficiency

The internal nature of lungs facilitates the accumulation of particles over time (i.e., smoke, dust, etc.) that can lead to health issues

Only works in air because they don’t have enough surface area to extract enough O2 from water

Cutaneous Respiration Structure

Gas exchange occurs across the skin

Most effective if skin is a thin, moist membrane

Reliance on Cutaneous Respiration varies tremendously

Cutaneous Respiration Function

Utilizes a “counter current” system, where oxygen-poor blood mixes travelling from the heart via arteries and towards the heart via veins

• Positioned near the surface of the epidermis across which O2 and CO2 both exchange

Cutaneous Respiration Benefits and Drawbacks

Benefits:

Works in water or air (an advantage over gills and lungs)

Passive process (minimal energy required)

Drawbacks:

A passive process (a fixed rate, can’t simply respire more in response to demand)

Requires a moist environment to be efficient

Generally occurs along all the skin's surface area, but may be concentrated in specific areas such as the mouth and throat (where skin is very thin)

Can be associated with behaviors like expansion of the throat (to maximize surface area against water)

Usually a behavior only necessary in response to low oxygen levels

Eastern Newt

Notophthalmus viridescens

Eggs are laid in stagnant water (small temporary ponds)

Have larval stage with external gills (< 6 months)

• Keeled (flattened) tail

Metamorphose into terrestrial “eft” juvenile phase (2-3 years)

• Lose gills

• Develop lungs

• Also secondarily use cutaneous respiration

• Round tail

Metamorphose again into aquatic adult (up to 12 years)

• Retain lungs (must surface to gulp air)

• Keeled tail

Woodland Salamanders

Plethodon

Eggs are laid on land

Young hatch as small terrestrial adult forms

Develop directly into terrestrial adults

• Lack gills

• Lack lungs

• Exclusively use cutaneous respiration

Materials that are difficult to digest

Bone – the skeletal system

• Very dense, which physically limits absorption of acids and digestive enzymes

Keratin – claws, nails, hair

• Very dense, which physically limits absorption of acids and digestive enzymes

Enamel – teeth

• Very dense, which physically limits absorption of acids and digestive enzymes

Chitin – material in exoskeletons of crustaceans and insects as well as cell walls of fungi

• Complex structures with strong molecular bonds

Cellulose – material in plant cell walls and vegetable fibers

• Complex structures with strong molecular bonds

Materials that are relatively easy to digest

Cartilage – connective tissue in joints as well as soft-tissue structures like ears and noses

• Not dense, easily penetrated by acids and digestive enzymes

Muscle

• Not dense, easily penetrated by acids and digestive enzymes

Material digestion trends

Denser materials are more difficult to digest (although digestible given ample time)

• Blood < muscle < bone < enamel

Higher molecular complexity = more difficult to digest (some being indigestible if lacking the proper enzyme)

• Sugar < starch < fat < cellulose

• More bonds involving O and H → easier

• More bonds involving C (C-C and C=C) → more difficult

C:N ratios in different organisms

Leaves have a C:N ratio of 35-85

Algae: 6-10

Animals: 3-5

Animal waste: 8-24

Fish often consume more algae than insects, even if they get most of their nutrition from insects. Why is this?

Two explanations:

Algae consumption is intentional

• Algae may be an abundant prey item that requires very little energy to eat (non-evasive)

• So fishes opportunistically eat algae but generally need not assimilate any nutrients from it

Algae consumption is inadvertent

• Fishes eat algae while targeting insects

  • E.g. while scraping off rock-clinging insects

• Algae consumption reflects feeding strategy, not preference

• Fishes have a poor ability to digest algae

Strategies for digesting algae/plants

1) Elongated digestive tract

• Increase digestion time and exposure to acids and enzymes

• Often 1.5 to dozens of times longer (depending on animal and diet)

• Herbivores generally have longer digestive tracts than carnivores

2) Specialized enzyme activity

• Target specific molecular compounds

• E.g., cellulase targets cellulose

3) Rely on robust gut bacteria

• Bacteria may use nutrients but reduce otherwise indigestible materials into palatable forms

• E.g., converts undigested fiber into useful chemicals, synthesize some vitamins

4) Physically rupture cells

• Cell walls are mostly made of cellulose

• Tearing the cell wall permits acids and digestive enzymes to enter cell

• E.g., grinding algae in the pharyngeal jaws shears algae cells

• Enhances fishes ability to assimilate nutrients (especially in those that cannot digest cellulose)

• E.g., large ridged teeth in elephants for grinding up plants

5) Send food through digestive system twice

• E.g., rabbits cannot extract enough nutrients from grasses and weeds, and eat their poop to extract additional nutrients

• Effectively an alternative to an elongated digestive tract

6) Compartmentalize the stomach (ruminants – cattle, sheep, deer, antelopes, giraffes, etc.)

• Four chambered stomach (Rumen, Reticulum, Omasum, Abomasum)

7) Selectively eat plants low in cellulose

• E.g., lettuce, kale, spinach

• Cell walls contain more soluble lignin

8) Cook vegetables (breaks down cell walls, enhancing digestion)

Four chambered ruminant stomach

Swallow food…

(1) Rumen: initial breakdown via fermentation

(2) Reticulum: secondary storage for any large items that remain after rumen

Regurgitate food and chew it more, swallow again…

(3) Omasum: absorbs nutrients and water

(4) Abomasum: acids digest food particles, then passes to small intestine

Osmoregulation

The active maintenance of solute concentrations within body fluids

Many cellular functions require or rely upon specific solute concentrations across the membrane

• Ca+ in skeletal/cardiac muscle

• Na+/K- across neural membranes

• NaCl across all cellular membranes

Hypotonic, isotonic, and hypertonic solutions

Types of osmoregulation

Osmoconformers

• Solute concentrations equal to outside conditions (completely passive)

• Mostly found in aquatic invertebrates

Osmoregulators

• Solute concentrations not equal to outside conditions (active regulation)

• All vertebrates

Osmoregulation in fishes

Freshwater

• Body salt concentration ~0.8%

• Environmental salt concentration ~<0.1% (1ppt or lower)

Saltwater

• Body salt concentration ~1.0%

• Environmental salt concentration ~3.5% (35ppt)

Euryhaline (occupy different salinities)

• Body salt concentration ~0.8%

• Environmental salt concentration variable

Osmoregulation in freshwater bony fishes

Live in hypotonic solution

Water diffuses into blood through permeable membranes (i.e. gills/skin)

Solutes diffuse out through permeable membranes to environment

Must actively pump solutes into blood and produce large quantities of dilute urine to maintain homeostasis

Osmoregulation in marine bony fishes

Live in hypertonic solution

Water diffuses out of permeable membranes to environment

Solutes (mostly NaCl) diffuses from environment into blood

Must actively pump solutes into environment and produce highly concentrated urine

Osmoregulation in marine elasmobranchs

Convert nitrogenous waste into urea

Urea and trimethylamine oxide (TMAO) maintained in elevated concentrations in the blood

TMAO stabilizes proteins in presence of urea

Rectal gland near cloaca releases excess salt

Blood is hypertonic to surrounding water

Osmoregulation in freshwater elasmobranchs

Release nitrogenous waste as ammonia like bony fishes

Produce little to no urea

Rectal gland, if present, is small

Blood is hypertonic to surrounding water

Osmoregulation in sarcopterygii

Use urea and TMAO similarly to marine elasmobranchs

Freshwater sarcopterygians store urea as a less toxic form of ammonia and aids water retention during aestivation

Diadromous fishes

Fishes move between ocean and freshwater during their lives

Catadromous: fishes moving from freshwater to ocean to spawn

• Ex. Some eels (American and European eels spawn in the Sargasso Sea)

Anadromous: fishes moving from ocean to freshwater to spawn

• Ex. Salmon (natal homing)

Amphidromous: fishes move between freshwater and saltwater, but not for breeding

• Ex. Gobies

Potadromous fishes

Migration occurs entirely in freshwater

May be following prey responding to temperature changes

Ex. flathead catfish

Oceanadromous species

Migrations occur entirely in saltwater

Follow prey migration patterns

Humans and fish migration

Some catadromous and anadromous fishes may be forced into potadromous or oceanadromous migrations due to human activity (i.e. dams)

Migrations can be vital to survival and reproduction

Terrestrial ecosystems may rely on fish migrations (i.e. PNW forests)

Impact on populations and reliant ecosystems can be mitigated

• Ex. salmon cannon

Dentition in Birds

Some extinct birds had teeth

Modern birds do not have teeth

• Predators and scavengers achieve some of the same functions with other structures

  • The talons are used to subdue and kill prey

  • The tip of the beak is used to tear meat

• Some water birds achieve tooth-like function without teeth

  • Ducks have lamellae – fibrous tissues made of keratin – that run along the edge of their beaks

  • Most ducks feed from the bottom or margin of ponds, lakes, or streams, grazing on vegetation and algae.

  • Lamellae let water drain from the beak, while filtering out any edible items

Categories of Dentition

Homodont – teeth are functionally and anatomically the same

• E.g., sharks, crocodiles, lizards, amphibians, many fishes, very few mammals (armadillos)

Heterodont – teeth are functionally and anatomically different

• E.g., most mammals, many fishes

Early Teeth

Placoderms

• Teeth formed by large bony plates

• Teeth have dentine layer (and bony layer)

Cartilaginous fishes

• Teeth on upper and lower jaws

• Teeth have dentine layer covered with a fluoridated phosphate mineral layer (‘enamel-like’)

• Teeth are continually replaced

Coelacanths

• Teeth on premaxilla, maxilla, and dentary

• Have dentine and enamel layers

• Teeth are continually replaced

Lungfish

• Tooth plates along the inside of the upper and lower jaw

• Have dentine and enamel layers

• Teeth are continually replaced

• Same general tooth arrangement for 360 My!

• Tooth plate

Frog Teeth

Small, conical teeth along the premaxilla and maxilla

No teeth on the dentary (only present on a few species)

Teeth on the vomer (roof of mouth)

Teeth have been lost completely at least 20 times in frogs and is usually associated with reduced jaws

• This trend continues when compared to other amphibians – salamanders and caecilians, which invariably have teeth and comparatively robust jaws

How can frogs manage without teeth?

• They don’t chew their prey and they capture prey with tongue projection

Toothless mammals

Baleen Whales (8 species)

• Have a filter feeding system made of baleen ( = keratin)

• Permits water, but not prey (plankton), from escaping mouth

• Note the similar solution as ducks

Pangolins

• Eat ants, termites, and their larvae

• Use a long sticky tongue to capture prey

• Tongue attaches to sternum and usually longer than the pangolin itself

Anteaters

• Eat ants, termites, and their larvae

• Use a long sticky tongue to capture prey

Homodont Mammals

Dolphins and (non-Baleen) whales

• Simple, conical teeth

  • For grasping prey

Armadillo

• Simple, tapered, interlocking teeth

  • For chewing soft prey (insects, fruit, etc.)

Types of heterodont teeth

Incisors

• Chisel shaped teeth used for cutting through soft material

• Enlarged and grow continuously in rodents

• Upper incisors are absent in cervids (deer) and bovids (cattle)

Canines

• Long, conspicuous, and pointed

• Used to capture, hold, and kill prey

• Not present in rodents, cervids (deer), and bovids (cattle),

• Replaced instead by a wide gap between the incisors and premolars called a diastema

Premolars

• Located between canines and molars

• Used for chewing

Molars

• Principal teeth used in mastication

• Used for crushing and grinding

• Usually larger than premolars

• Are not deciduous (no ‘baby’ version)

Carnassial Teeth

Found in Carnivorans (bears, dogs, cats, raccoons, weasels, etc.)

4th premolar on the top

1st molar on the bottom

Enlarged and positioned for shearing

Sabertoothed Cats

Such as Smilodon, possessed elaborate canine teeth

Probably did not use canines to capture or restrain prey, but may have used them to deliver final bite to neck

Tusks

Enlarged lower canines (hippos, boars) or upper incisors (elephants)

Grow continuously and used for defense or fighting rather than feeding

Crabeater Seal

Specialized, elaborate premolars, hypothesized to act as a sieve for krill

Homodont fish

Piranha

• Predator

• Flattened with a sharp edged, pointed

• Interlocking teeth

• Tear flesh

Muskie

• Predator

• Conical, sharp point (no edge)

• Widely-spaced (non-interlocking)

• Grip flesh

Heterodont fish

Sheepshead

• Omnivore

• Incisors are very human-like

  • Cut through plants (kelp)

• Molars to crush crabs and mollusks

Fish teeth types

Unicuspid

• If conical, for grasping prey

• If flattened, for cutting (plants)

Bicuspid

• Usually for chewing soft items (insect larvae)

Tricuspid

• Usually for scraping algae or biofilm from hard surfaces (rocks or coral)

Fused teeth

• Parrotfishes have teeth that are fused into “beaks”

  • Used to graze coral

• Pufferfishes also have teeth that are fused into “beaks”

  • Used to crush crabs and mollusks

Pharyngeal Jaw Teeth

Can have homodont teeth (usually all conical and curved)

Can have heterodont teeth (including conical, bicuspid, and molariform teeth)

Unique fish dentition

Some fish lack jaws (but have teeth) – agnathans

Some fish lack pharyngeal jaws (and teeth), but have oral jaws (and teeth) – sharks, rays

Some fish lack oral teeth but have pharyngeal jaws (and teeth) – minnows and carps

Some fish lack oral teeth and pharyngeal jaws (and teeth) – sturgeons, paddlefishes