BIOL 371: Theme 3 - Animals Life in the Water and on Land

terrestrial animals

relatively few taxa - gastropods, arthropods (insects, arachnids, myriapods, crustaceans), nematodes, annelids, amniote vertebrates, etc

onychophora

the only completely terrestrial animal phylum

desiccation

constant water loss through evaporation (across wet respiratory membrane or surface of skin), water loss in urine and feces, through thermoregulatory methods (sweating, panting)

requires waterproofing of outer layer of body with keratin/wax, minimal exposure of gas-exchange and digestive surfaces to air (internal placement) to gain metabolic water

nitrogenous wastes

toxic ammonia (NH3) produced in every cell of the body by catabolism of amino acids and nucleic acids

uric acid

reptiles, birds, insects, conversion of ammonia - very low water-solubility, semi-solid nitrogenous wastes can be excreted while conserving water

ureotelic

mammals, convert ammonia to less-toxic urea, but must lose water in excretion

loop of Henle

aids in conservation of water in mammals (and some birds), produces concentrated urine (hyperosmotic to blood), the longer the loop the better for water conservation

kangaroo rats

desert-adapted rodents, very long loop of Henle, produces small quantity of highly hyperosmotic urine (22.5% of daily water loss - compare to humans 57.7%), metabolic water very important

insects and desiccation

must deal with small size - favours desiccation due to larger surface area, inevitable evaporative loss from wet respiratory surfaces in trachea, waxy outer layer of cuticle minimizes evaporative water loss from body surface, spiracles permit closing of tracheal system to cut down on evaporative water loss

cryptobiosis

formation of resistant stage (tun) in response to environmental challenges (dehydration, sub-zero temperatures), eg. terrestrial tardigrades - live in water films in damp environments, can survive harsh environments

anhydrobiosis

when slowly desiccated, resistant tun formed - when rehydrated, tardigrade returns to active state, (terrestrial tardigrades - live in water films in damp environments, can survive harsh environments)

rotifer life cycle

live in unreliable, changing environments

unstressed environment (moist) - parthenogenesis (clones), all are female diploid

stressed environment (dry) - sexual reproduction (genetic variability), adult haploid male can reproduce with female’s egg to make a zygote (desiccation resistant)

aestivation

prolonged period of depressed metabolism to avoid seasonal heat and drought

eg. desert-dwelling spadefoot toads - spend most of their adult lives buried deeply, metabolism depressed, only emerge when it rains to breed, some secrete a cocoon during, only nostrils left open, can spend up to 2 yrs buried

disadvantages of breathing air

• CO2 does not diffuse into air as easily as into water

• inevitable evaporative water loss from internal respiratory surface, which must be kept wet

advantages of breathing air

• 21% O2 - much greater than water

• atmospheric O2 diffuses much more rapidly

• bulk flow of air (ventilation) requires less muscular effort (low viscosity and low density)

tracheal system

in insects, delivers air directly to tissues (via interstitial fluid), moist exchange surfaces internal

spiracles permit closing of this system to cut down on evaporative water loss

trachea

form of bulk flow system for air

vertebrate lungs

bulk flow of air to respiratory membrane, moist exchange surfaces internal, requires muscular effort (ventilation)

reproduction in water

anamniotic eggs laid by amphibians (vertebrates) in the water, embryos can exchange gasses, wastes with aquatic environment, adult form can live on land (metamorphosis)

amniotic egg

in vertebrates, provides an aqueous environment for the developing embryo, requires internal fertilization, requires uricotely (to dispose of waste), extraembryonic membranes support developing embryo, shell porous to air, possible to water

enzyme effectiveness

active site changes shape outside of narrow range of temperature and pH, enzyme loses ability to catalyze metabolic reactions, at greater than 45C, proteins denature

why thermoregulation is important

reasons for thermoregulation

enzyme effectiveness, performance depends upon biochemical processes, animals regulate body temperatures for optimal performances

endothermy

the production of sufficient metabolic heat to warm the tissues

metabolic rate changes with temperature in order to maintain a constant body temperature, an energetic cost

ectothermy

insufficient heat from metabolic activities to warm tissues significantly, heat must be exchanged with the environment

metabolic rate changes directly with body temperature, which changes with environmental temperature - a potential liability (loss of performance)

heterothermy

allowing body temperature to vary

homeothermy

tightly regulating body temperature around an unvarying mean

4 ways of heat exchange with the environment

conduction, radiation, convection, evaporation

eg. basking lizard - exposure to all 4, metabolically cheap

conduction

direct heat transfer by contact, air conducts heat poorly, water well, so gill-breathing aquatic organisms tend to be isothermic with the water in which they swim

radiation

transfer of heat as long-wave light, not very effective as a heat sink at biological temperatures, but radiative sources (the sun) very effective for heating up

convection

transfer of heat by a moving medium, air or water flowing over an organism carries heat away or delivers it

evaporation

energy consumed by change from liquid to gas, effective way to carry heat away, eg. sweating

countercurrent heat exchange

cold-climate terrestrial endotherms can conserve heat by using these head exchange structures

warm blood in efferent vessels heats cool blood in afferent vessels

regional heterothermy - different parts of body have different temperatures, but the core is regulated

torpor

reduces energy demands in small endotherms, during periods of low or high environmental temperatures, or resource unavailability, body temperature set point drops, metabolism depressed

hibernation

a seasonal version of torpor, undertaken during seasonal periods of low temperature, extreme, can’t be woken up

heterothermic endothermic insects

eg. bees, flying insects (tend to be furry), generate sufficient heat by the action of the flight muscles to maintain a high constant temperature in the thorax

freeze avoidance

some ectotherms can supercool their ECF - goes below 0C without freezing (mainly marine)

freeze tolerance

some terrestrial ectotherms can allow the bulk of their ECF to freeze for extended periods, high intracellular osmolality depresses freezing point, control of ice nucleation in ECF

air vs. water

• air transmits light more effectively than water

• water conveys chemical signals more effectively than air

• the speed of sound is far greater in water than in air (vibrations)

• being able to sense which way is down matters in air - don’t want to fall, no buoyancy

chemosensors

chemosensory organs, require wet surfaces for adsorption of air-borne chemical particles, eg. insect antennae have minute channels lined with moist adsorptive tissue, terrestrial vertebrates have moist olfactory epithelium and taste buds in oral cavity

hearing

sound does not transmit easily from air to water (ECF), sensing soundwaves by terrestrial animals must take this into account

eg. insects - tympanal organs - air on both sides, nerves (mechanoreceptors) pick up vibrations

hearing in vertebrates

organs for hearing, and for sensing acceleration and which direction is down (vestibular labyrinth) are located in the inner ear, it’s important to be able to tell which way is down on land

hearing in fish

inner ear can pick up vibrations through tissues, hyomandibular bone suspends lower jaw (hyomandibula and stapes are homologous)

hearing in tetrapods

middle ear bones transform large amplitude eardrum vibrations (from air) to low amplitude high force vibrations transmitted to oval window of inner ear - amplifies vibrations so that waves are produced in fluid-filled cochlea

volume

a function of linear dimension cubed

would increase faster than the cross-sectional area

cross-sectional area of limb

a function of linear dimension squared

allometry

differential growth, a characteristic of most animals, different parts of the body grow at different rates with increase in overall size, an evolutionary phenomenon

isometric growth

eg. ants, same proportions of growth

in larger animals, limbs are not thick enough to support efficient locomotion (allometric growth instead)

sprawling limbs

requires less energy to maintain, associated with ectotherms

erect limbs

supports weight more efficiently, associated with endothermy

hard skeletons

skeletons found in aquatic and terrestrial animals, 2 types (exoskeletons and endoskeletons)

provide attachments and leverage for muscles - force transmission, transmit compressive stress to substrate, provide framework for tissues of body, act as mineral bank for physiological requirements (vertebrates) - calcium, phosphate, protection for delicate organs or whole body, eg. turtle shell

endoskeletons

internal, in vertebrates, composed of bone and cartilage

bone

collagenous matrix mineralized by CaPO4 crystals, highly vascularized, matrix architecture supports scattered osteocytes, metabolically active, bears compressive stress well, shear stress not so well

exoskeletons

external

eg. arthropods - consists of chitin (complex polysaccharide), may be impregnated with calcium carbonate, composed of plates (tergae) with joints between them, limb joints mobile, muscles are within the skeleton

tergae

in arthropods exoskeleton, mark segmentation of limbs and body

hydrostatic skeletons

volume of fluid enclosed by 2 layers of muscle (longitudinal and circular), fluid incompressible but pressurized when muscle contracts, muscular container changes shape with contraction of different muscle layers - organ, animal’s whole body

aquatic animals

water supports the body (affects size, stance and skeleton), buoyance - not as much weight to carry, desiccation is a lesser threat, stable and mild temperatures, metabolic waste removed by water, sound transmits well from water to body

challenges of living in aquatic environments

water is dense - takes energy to displace, water is viscous - layer clings to the body, water has low oxygen content (1-2% compared to air 21%) - oxygen levels in water vary greatly with other parameters, water has high thermal conductance (25x that of air)

terrestrial endoskeletons

firmly attached girdles, enclosed ribcages

aquatic endoskeletons

ribcages not enclosed, loosely attached girdles

size

aquatic animals can become much bigger than terrestrial animals

the biggest aquatic animals are air-breathers

salt and water balance

eg. marine tetrapods, birds, and reptiles, excrete excess salt through salt glands associated with upper respiratory tract or eyes, marine mammals can produce highly hyperosmotic urine (long loops of Henle)

heterothermic ectotherms

most aquatic organisms - water is a good heat conductor

aquatic homeothermic endotherms

must insulate with blubber or a waterproof pelage

insulation

fur, feathers, fat

being warm in aquatic environments

insulation, respiratory medium - breathe air (allows higher metabolic rate, air is poor conductor of heat from body), aquatic endotherms utilize counter-current heat exchange - allows outbound blood to heat inbound blood - retains heat by maintaining gradient along length of organ