BIOL 3300 Vertebrate Zoology:
Ectotherms - Herpetology
http://www.amphibian.com.au/
How is H2O gained/lost?
• Challenges of each scenario….
– Saltwater herpetofauna
– Terrestrial herpetofauna
– Freshwater herpetofauna
Fresh H2O Flux!
• Amphibian plasma
~250-300 mOsm
• Fresh H2O
~2 mOsm
What is the consequence of this on
water volume?
What about salt content?
Salt H2O Sucks!
• <100 species of amphibians can tolerate
salt water (sea H2O > 1000 mOsm
• Amphibian can elevate plasma and
muscle osmolality to
~500 mOsm
http://kidstvmovies.about.com/od/oceans/ig/Oceans-Photo-Gallery/Marine-Iguana.htm
How?
Amblyrhynchus cristatus
How about marine iguanas?
Figure 6.1 Osmotic challenges of amphibians and reptiles in saltwater, freshwater, and on land. In saltwater, the animal is hyposmotic compared to its environment,
and because its internal ion concentration is less than that of the surrounding environment (internal < external), water moves outward. In freshwater, the animal is
hyperosmotic to its environment, and the greater internal ion concentration (internal > external) causes water to move inward. On land, the animal is a container of
water and ions, but because the animal is not in an aqueous environment, internal fluctuations in ionic balance result from water loss to the relatively drier
environment. The animal actually has much higher ion concentrations (internal > external) than surrounding air, and if ionic concentrations reach high levels, as they do
in some desert reptiles, ion transfer can occur via salt glands, usually in the nasal or lacrimal region.
Figure 6.2 Model depicting how transfer of water occurs in cells based on a freshwater system. Water moves by the process of osmosis across the semipermeable
membrane of the cell. The direction of water movement depends upon ionic gradients. If ion concentrations are higher inside the cell than outside (as in this example),
then water moves in to balance concentration of ions. Semipermeable membranes do not allow all molecules to pass through. Rather, some do and some do not. In
addition, cells have the capability to actively transport molecules across membranes. Amphibians and reptiles use a variety of behavioral and physiological mechanisms
to maintain water and ionic balance because few natural environments are isotonic with their body fluids.
How is H2O gained/lost?
• Observe
Agalychnis annae in
the vivarium…
How are these
animals
gaining/losing
water?
What behaviors or
adaptations are
they exhibiting to
influence rates?
What are the 3 sources of H2O?
• Liquid =
Water in sufficient quantities to form
film, droplets, pools, puddles, etc.
• Preformed
(Molecular) = Water existing as such in foods ingested
• Metabolic =
Water created when H is added to O to
form H2O.
Methods for obtaining H2O?
• Thorny Devil
(Moloch horridus)
http://digimorph.org/specimens/moloch_horridus/whole/
Dew drinkers
http://cmuarch2013.wordpress.com/2009/02/04/tom-wiscombe-lecture-notes/
Figure 6.12 Scale microstructure in the two desert lizards Moloch horridus (Agamidae: A and B) and Phrynosoma cornutum (Phrynosomatinae: C and D). The medial
surface of ventral scale epidermis (&beta1;-layer) is shown at two magnifications for each species, showing the interior bracing support of each scale and the scaledefining interconnections of scale hinges. Hinge joints (hj), deep portions of scale hinges that spread laterally, form a continuously connected surface. The epidermis is
ruptured in B (medial side of &beta1;-layer) showing Oberhäutchen (ob) cover on walls of the scale hinge. The &beta1;-level epidermis in P. cornutum (D) shows surface
pitting on the different levels of the hinge joint.
Figure 6.13 Schematic summary of the mechanism for cutaneous water collecting, transport, and drinking in Moloch horridus (A) and Phrynosoma cornutum (B). Arrows
indicate directional movement of water. C through E are generalized models of the morphology of the water transport system in the two lizards. In C and D, narrow
passageways below each scale expand into scale hinge joints. Water moves through the channels and collects in the scale hinges, which are interconnected (D). The
scale hinge-joint channel system consists of a continuous floor of channels, all directed so that water ultimately flows to the corner of the lizard's mouth. Adapted from
Sherbrooke et al., 2007.
Methods for obtaining H2O?
• Peringuey’s viper
(Bitis peringueyi)
http://www.lonelyplanetimages.com/search/125101?keywords=crawl
Fog drinkers
http://www.flickr.com/photos/hamschtr/3959581417/
Methods for obtaining H2O?
• Desert Tortoise
(Gopherus agassizii)
http://www.rightpet.com/ReptileDetail/desert-tortoise
Puddle drinkers
Up to 17% body
mass of H2O
intake
http://www.basinandrangewatch.org/TortoiseTranslocation.html
Methods for obtaining H2O?
• Great Basin Spadefoot
(Spea intemontana)
Bladder bingers
Urine = 100 mOsm
Plasma = 300 mOsm
Urine = 300 mOsm
Plasma = 500 mOsm
Figure 6.4 Photo of Anaxyrus punctatus (Bufonidae) on glass showing the ventral water absorption patch. (L. J. Vitt and J. P. Caldwell)
Molecular (preformed) H2O!
What is the H2O content of
herpetofauna food?
• Carnivores
Molecular (preformed) H2O!
What is the H2O content of
herpetofauna food?
• Herbivores
>70%
63%
51%
Sauromalus obesus
Metabolic H2O!
What is the chemical (metabolic)
quantity of H2O of herpetofauna
food?
• 1g starch = ~0.5g H2O
• 1g fat = ~1.0 H2O
• 1g protein = ~0.5g H2O
http://www.biolib.cz/en/taxonimage/id24436/?taxonid=177
How is H2O gained/lost?
Wia= Wd + Wf + Wa - We - Ws
How is H2O lost?
Minimizing H2O loss!
• Lipid lotion
Life in Cold Blood
27 minutes 1st episode
Phyllomedusa sauvagii
http://www.youtube.com/watch?v=Ce8a5bFQexA&feature=fvw
Figure 6.8 Phyllomedusa sauvagii (Hylidae) spreads lipids from lipid glands in the skin by a series of stereotyped movements using the feet. Arrows indicate direction of
foot movement. Adapted from Blaylock et al., 1976.
Figure 6.9 Phyllomedusa hypochondrialis (Hylidae), a common frog in semiarid and savanna areas of Brazil, has the ability to reduce water loss considerably more than
other Phyllomedusa species by waxing its skin when active and exposing the maximum amount of its small body (upper). During dry season, these frogs minimize water
loss by minimizing surface area exposed. The frog in the lower panel is just beginning to emerge from a nearly balled-up state. It was found under a dry pile of
vegetation at the peak of the dry season with several others. The skin surface was dry, and it took the frog nearly 10 minutes to come out of an apparent state of
torpor. (J. P. Caldwell and L. J. Vitt)
Minimizing H2O loss!
• Cocooning
Ecdysis… again
and again
(~1 layer/day)
Neobatrachus sp.
http://www.abc.net.au/wa/stories/s1656813.htm
Figure 6.10 The hylid frog Litoria novaehollandiae (Hylidae), encased in its cocoon, emerges after a rainstorm and begins to eat the cocoon. The cocoon consists of
retained layers of shed skin. (S. J. Richards)
What about sirens?
Figure 6.11 Photomicrograph showing 39 layers of stratum corneum forming the cocoon of the South American frog, Lepidobatrachus llanensis (Ceratophryidae). (R.
Ruibal)
Minimizing H2O loss!
• Clustering
http://img468.imageshack.us/img468/7545/sonora3cutff4.jpg
Coleonyx variegatus
Figure 6.14 Rates of evaporative water loss (EWL) are lower for individual geckos (Coleonyx variegatus) when they are aggregated in groups of two or three in retreats
than they are when geckos are alone in retreats. Adapted from Lancaster et al., 2006.
Minimizing H2O loss!
• Regulating urine (H2O, N, ions
[H+, Na+, K+, Cl-, CO3-])
• NH3
• Urea 2 NH3 +2 ATP -> CH4ON2
• Uric acid (K - C5H4O3N4 )
• Feces
Cloaca
Figure 6.3 Diagrammatic representation of the functional kidney in amphibians and reptiles (see text for differences). Solid circles and the heavy line represent the
reduction in osmotic concentration of urine for an amphibian. The line would be lower for a reptile.
Adapted in part from Withers, 1992.
What organs/structures are involved
in water/ion balance… HOW?
– Kidneys
– Bladder
– Skin
– Gills
– Digestive tract
How is H2O maintained?
• Short-term water
balance
• Behaviors can fluctuate
in a diel pattern
• Ex. Canopy frogs
Zetek’s Bromeliad Frog
(Isthmohyla
zeteki)
Figure 6.7 Eleutherodactylus coqui uses different postures to regulate water loss. The chin-down posture with legs underneath the body minimizes water loss. Water
loss is greatest during bouts of calling by males when the greatest amount of skin surface area is exposed. Adapted from Pough et al., 1983.
How is H2O maintained?
• Long-term water
balance
http://rateeveryanimal.com/wp-content/uploads/2011/11/desert-tortoise.jpg
Desert Tortoise
(Gopherus agassizii)
How is H2O maintained?
• Long-term water balance
= Rainfall
How is Salt lost?