Learn more about the Herp Course here
Class #1 -What are Herps with Dan Beck, Feb 12 2018
Watch and listen to the 76min lecture portion of the class on this video
Why should we care about herpetofauna (amphibians and reptiles)?
ANF! Spadefoot toads have a bony tubercle on their hind
foot that lets them dig well, and they’ll dig 1 meter deep, finding and
following the water table, and can stay under for maybe up to three years. They
might come out to eat and breed for a week, then go back for a year of burial.
ANF! The toxin in rough-skinned newt (those guys are so
cute) skin is the same as is found in the puffer fish! It binds to sodium
channels, which are critical for nerve function. Garter snakes have evolved
some resistance to this toxin by changing the cell membrane surface so those
channels can’t be affected.
· We’re in the middle of a 6th extinction right now, and humans are the cause. Roughly 1/3 of amphibians are threatened or endangered, and reptiles are close behind. For example, the leopard frog has largely disappeared from Washington State.
· Amphibians and reptiles have provided great benefit to us, scientifically. We’ve learned much through study of their toxins and have developed important medicines using them. For example:
o Blood pressure regulation drugs developed from the venom of pit vipers
o Diabetes treatment drugs developed from the venom of Gila monsters
· They also play a large role in food webs, energy conversion, and other ecological services
· They’re awesome! Ignorance of these animals can lead us to fear, but hopefully knowledge will lead us to respect.
Check out some great resources:
· WDFW's WA herpetology atlas
· Get a field guide!
27 species of Amphibians
14 species of salamander (Order Candata)
13 species of frogs and toads (2 introduced) (Order Anura)
28 species of Reptiles
4 species of turtles (2 introduced) (Order Testudines)
8 species of lizards (1 introduced) (Order Squamata)
12 species of snakes (Order Squamata)
Neat fact!: Tailed frogs are the only amphibians with internal fertilization, and males have external copulatory organs. And they live around here! Look for them up the Twisp River.
(look for more ANF!s below)
Amphibians, reptiles, and mammals are all tetrapods (four legged), limbed vertebrates
The earliest amphibians evolved 360 million years ago, and evolved from fish, transitioning from a round head with eyes on the side to a flat head with eyes on the top, and developing limbs.
Amphibian eggs are dependent on water, but around 340 million years ago there was a major evolutionary break through with the evolution of the amniotic egg. This egg includes food, water, and a space for the collection of wastes, so creatures were no longer dependent on water. After this development, reptiles and mammals evolved and radiated relatively quickly.
So, in this way, reptiles have more in common with mammals than with amphibians, which are in many ways more similar to fish.
ANF!: Crocodiles and birds are closely related, since, of course, birds evolved from dinosaurs.
Amphibians and reptiles are united by ectothermy, which is the mode of temperature regulation where body temperature is determined by a creature’s external environment.
In contrast to endothermy, where body temperature is determined internally through metabolism. Mammals are endotherms.
(there's also poikilothermy (body temperature varies) and homeothermy (constant body temp)).
Endothermic creatures produce more heat in metabolically active tissues (eg. the liver, heart, brain, gastrointestinal organs). Cells have a higher density of mitochondria (powerhouses in the cells that convert sugars to energy), but the membranes of these mitochondria are leaky and heat is given off. This heats the body, but also makes for less efficient energy conversion.
Ectotherms are much more efficient, only needing roughly less than 1/10 of the energy of a comparably sized endotherm.
Ectotherms are more efficient because they:
· Don’t have to regulate their temperature with metabolism, just rely on external heat
· Metabolic rates drop in cooler environments, which increases efficiency. A 10 degree drop in temperature drops metabolic rate 3-fold.
· Don’t need as much food, so don’t have to use the energy to be so active in procuring it
Ectotherms rely on behavioral thermoregulation (modify their body temp by choosing their environment) so habitat selection is important.
Because of the issues of heat loss with increasing surface area to volume ratios (greater mass holds more heat), endotherms are more limited in how small they can get. Ectotherms get much tinier. For example, compare a shrew or a hummingbird (very small) to the tiniest snakes (itty bitty). 80% of lizards and 90% of salamanders weigh 20g or less.
Ectotherms can then put a greater percentage of the energy that they take in towards reproduction.
|Great Basin Spadefoot Toad|
Rattlesnakes need to eat about their body weight per year (more for breeding and growing). This could be maybe 6-12 voles, compared to a weasel which might need to eat 400-600 voles a year. For the quantity of food you need to support 2 weasels you could have 40-60 rattlesnakes. So, reptiles and amphibians convert energy up through the food web at a higher efficiency than mammals and birds.
Amphibians and reptiles have a 3-chambered heart, that either can or can not allow oxygenated and deoxygenated blood to mix, depending on their oxygen demands.
Amphibian means “double life”, which is descriptive of their life history: juveniles (larvae) live in the water, adults tend to live terrestrially (on land). So, these two life stages are able to exploit different habitat niches.
Some amphibians display heterochrony (timing and rate of development is altered) in the form of paedomorphosis (adults remain aquatic and retain larval characteristics. Tiger salamanders often do this, and it may allow them to best exploit unpredictable habitat availability.
Amphibian skin allows water permeation, and the skin can even act as a respiratory organ, which allowed the evolution of lungless salamanders
ANF! Lizards autotomize, which means they can drop their tail off so that it wriggles on the ground and distracts predators
ANF! Reptiles pick up chemicals with their tongues and bring them into their mouths to “smell” with the vomeronasal organ. 2 sides of the tongue can pick up different chemicals, informing directional decisions.
And then we held and touched lots of different snakes and lizards and salamanders, which was super neat!