Freezing the Winter Away

An edited reposting of an article from January 8, 2014.

During this frigid winter we can be thankful for our home heating, our layers of warm clothing, and most of all, our bodies’ abilities to generate heat. But it is times like these that make me wonder about our friends that live outside year-round… especially those that don’t generate most of their own body heat. How do they survive these periods of intense cold? There are several species of North American frogs that have an unusual trick up their sleeve: They freeze nearly solid and still live to see the next spring.

This picture of a wood frog is by Ontley at Wikimedia Commons.

Frogs are ectothermic, meaning they take on the temperature of their surroundings rather than generate their own body heat. This introduces some intriguing questions about how these species even exist in northern climates that experience freezing temperatures every year. When various North American frog species (including wood frogs, spring peepers, western chorus frogs, and a few gray tree frog species) take on freezing winter temperatures, they actually allow their bodies to freeze nearly solid. For most species, this would be a deadly approach: a frozen circulatory system would halt the delivery of oxygen to cells, which require oxygen to generate the energy they need to do just about everything a cell does. Furthermore, jagged ice crystal edges could rupture the cells they are inside. Dead cells lead to dead organs, which in turn lead to dead animals. These freezing frogs have found the secrets to freezing without killing their cells.

The first secret of the freezing frogs is to spend the winter snuggled in the leaf litter below the snow. This environment insulates and protects the frogs from the deadly wind chills we have been facing for the last several days.

The second secret of the freezing frogs is a creative use of colligative properties. Colligative properties are properties of solutions that depend on the ratio of the number of liquid molecules to the number of molecules of stuff dissolved in that liquid. One of those properties is called freezing point depression: The temperature at which a liquid will freeze can be lowered by adding particles to it. (This is why salt is spread on roads in the winter). A critical component of the freezing frog strategy is for the liver to produce massive amounts of glucose in response to the start of freezing. This glucose is pumped throughout the body, which lowers the freezing point of all of the organs.

A third secret of the freezing frogs is the use of ice nucleating agents: proteins that actually encourage freezing. This may seem counterintuitive, but remember that ice crystals inside cells can cause them physical damage. By having a high concentration of ice nucleating agents in the fluid between the cells, this ensures that ice first forms in the spaces surrounding the cells. When ice forms, the ice crystals are made of only water molecules, which draws water out of the solution and leaves behind a higher concentration of other stuff (like glucose) in between the cells. The high concentration of glucose between the cells draws water out of the cells and into that space. This additional water also freezes. In the end, the cells are chock-full of particles, lowering their freezing temperature, and are surrounded by ice, which insulates the cells. Thus, this process of ice formation around the cells prevents ice from forming inside the cells.

A fourth secret of the freezing frogs is a metabolic shift. Most animal cells rely on oxygen to produce the energy they need to support their demands. But cells have ways of producing energy without oxygen too. These ways are not very efficient, but are useful when there is not enough oxygen available to meet demand (such as when a seal dives or a cheetah reaches burst speed). When freezing frogs start to freeze and oxygen delivery to the cells slows and eventually stops, their cells shift from an oxygen-reliant system of energy creation to an oxygen-independent system of energy creation. Additionally, freezing organs do less and don’t require as much energy anyway, so they can continue functioning at low levels for a long time if the freezing spell is prolonged.

When the environment warms up (as forecasters promise will happen), the body temperatures of these frogs raise and body fluids slowly become liquid again. The heart starts to beat again within hours of the start of thawing and oxygen can again be delivered around the body. The delivery of oxygen-carrying blood helps the rest of the organs return to their normal functions.

There are still many secrets of these freezing frogs left to uncover. Maybe you’ll be the one to do it… once we thaw out a bit.

Want to know more? Check these out:

1. Storey, K.B. (2004). Strategies for exploration of freeze responsive gene expression: advances in vertebrate freeze tolerance Cryobiology, 48, 134-145 DOI: 10.1016/j.cryobiol.2003.10.008

2. Layne, J.R., & Lee, R.E. (1995). Adaptations of frogs to survive freezing Climate Research, 5, 53-59 DOI: 10.3354/cr005053

Why Reptiles Won't Wear Fur

A reposting of an article from September 19, 2012.

Have you ever seen a furry lizard? A fuzzy snake? A wooly turtle? Me neither. That's because a reptile in a permanent fur coat would whither like Superman with a pocket full of kryptonite. But why? Other animals are so content in their soft, luxurious layers... Why can't reptiles be?

"I wouldn't be caught dead in that fur coat you're wearing". Photo by Naypong at freedigitalphotos.net.

Animals exchange heat with their environments in four major ways: conduction, convection, radiation and evaporation:

• Conduction is when heat moves from a hotter area to a colder area across a still surface. If you stand barefoot on a cold sidewalk, the heat in your feet is going to transfer to the cooler surface of the sidewalk by conduction and you will get cooler (which is nice in the hot summer, but uncomfortable when the weather starts to get chilly). Conduction can happen when the body is in contact with a solid (like a sidewalk), a liquid (like a bath), or a gas (like the air around you).
• Convection is essentially conduction with movement, and this movement makes the transfer of heat even faster. If you are standing inside and it is 70ºF in the building, you will likely be fairly comfortable. But if you are outside on a windy 70º day, even though the environment is the same temperature, you will get colder faster.
• We are all familiar with the warming effects of the sun's radiation, but in reality, all objects give off electromagnetic radiation. Radiation within the visible spectrum we perceive as colored light, but most radiation is outside our visible range.
• Evaporation happens when water (like sweat or moist breath) converts from a liquid state to a gaseous state, taking heat away from the body. Animals are always in contact with something (like surfaces, air, or water), so conduction is always occurring.

The speed at which an animal's body heats or cools depends on the temperature difference between the animal's body and its environment. That is, in a very cold environment, an animal will cool quickly and in a very hot environment, an animal will heat up quickly, whereas in an environment that is close to the animal's body temperature, the animal will heat or cool very slowly. To put this in mathematical terms, let's call the animal's body temperature Tb and the environmental temperature Te. The bigger (Tb-Te), the faster the animal will cool. And the bigger (Te-Tb), the faster the animal will heat up. This difference between Tb and Te (in either direction) is called the driving force of heat exchange.

Imagine this circle is an animal's body, Tb is the animal's body temperature and
Te is the environmental temperature. The bigger (Tb-Te), the faster the
animal will lose heat and cool down.

This works the other way around, too.
The bigger (Te-Tb), the faster the animal will heat up.

What happens if you put fur on that animal? Now you can imagine this animal as having two separate layers, a body (with the temperature Tb) and an insulation layer (with the temperature Ti). Now for heat to be exchanged, it has to be conducted twice, once between the environment and the insulation, and again between the insulation and the animal's body. Ti is always going to be some intermediate temperature between Tb and Te and so the driving force of heat exchange will be much lower and the animal will heat up or cool down much more slowly. The thicker this insulation layer, the more stable Ti becomes and heat exchange happens even more slowly. Also, because insulation prevents movement at the body's surface, insulation layers eliminate any heat exchange at the body's surface (but not the surface of the insulation layer) by convection. (By the way, this logic also holds true if the animal has feathers or blubber or even a winter coat).


This inside circle represents an animal's body and the outside circle shows its insulation
layer. Tb is the animal's body temperature, Te is the environmental temperature and Ti is
the insulation temperature. Ti is always between Tb and Te, so the driving force of
heat exchange is reduced and the animal's body temperature does not change quickly
at all, even if the environmental temperature is extreme.

Most animals that have fur are mammals, as are most animals with blubber layers (like seals and whales) and animals that wear coats (like people and Paris Hilton purse dogs) and most animals with feathers are birds. What do these insulated mammals and birds have in common? They are endotherms. They generate most of their own body heat. This means that by slowing the exchange of heat between the animal's body and environment, the animal is provided with more time to generate heat and the insulation then helps to preserve this heat.

But reptiles (as well as amphibians and fish) are ectotherms. They get almost all of their heat from their environments. They maintain their body temperatures behaviorally, by choosing what environment to hang out in and what position to put their body in. If they are cold, they go bask in the sun to absorb radiation heat or lay on a warmed rock to absorb conducted heat. If they are hot, they lay on a cool rock in the shade to lose heat by conduction or soak in a cool stream to lose heat by convection. To maintain a relatively constant body temperature, they are constantly moving between warm and cool areas to adjust their body temperature one direction or another.

Many ectotherms rely on their ability to adjust their body temperatures quickly, and this ability depends on creating large driving forces of heat exchange. If an ectothermic reptile were to have an insulation layer, like fur, it would reduce its ability to adjust its body temperature by conduction and convection. It would lose its heat slowly and not be able to replace it fast enough. In the end, it would become too cold. It may seem paradoxical, but a lizard in a fur coat would likely die of cold-related physical issues (if not embarrassment).

Interestingly enough, just because lizards don't have fur doesn't mean they couldn't have hair. In fact, some of them do have hair, but not how you may think. Hair, fur, feathers, and scales are all made up in large part by keratin proteins. Many gecko species are well known for their wide, sticky toes that help them climb smooth, vertical surfaces (like walls). Their secret? Ultra-thin keratin hairs growing out of the geckos' feet provide a chemical adhesive force to keep the animal secured to the wall surface. So reptiles may not have a need for fur, but some of them have an innovative use for hair.

Want to know more about hairy geckos?

Autumn K, Liang YA, Hsieh ST, Zesch W, Chan WP, Kenny TW, Fearing R, & Full RJ (2000). Adhesive force of a single gecko foot-hair. Nature, 405 (6787), 681-5 PMID: 10864324

Where the Wild Things Are: Amazing Animal Watching Vacations

A modified repost of an original article from May, 2012.

School is winding down, the weather is beautiful and it is time to start thinking about summer vacation! Do you love watching and learning about animals? Then consider one (or more) of these animal watching vacations:


Go to a zoo:

Get a great view of a Siberian tiger at the Toronto Zoo.
Photo by Ber Zophus at Wikimedia.

Zoos allow you to explore the world in a single day: Meandering paths lead you past animals from across the globe. Lions, and tigers and bears, Oh my! But don’t forget the primates, reptiles, birds, and sea mammals. No matter what your animal fancy, you can likely see it at the zoo. Walk through the zoo reading the posted information on each species. Or sit at your favorite exhibit and focus on a single animal. Participate in an educational activity like touching and feeding animals with their keepers, a course, or even a sleepover. And while you are there, learn about how the zoo contributes to animal well-being: Many zoos provide research opportunities to study animal behavior and health (such as the friendship study in crested macaques), support captive breeding programs to restore threatened wild populations, rehabilitate injured or abandoned wild animals, and support habitat conservation.

If you have a local zoo, see what it has to offer. And if you like to travel, consider the San Diego Zoo, the Smithsonian National Zoological Park in Washington, DC, the Singapore Zoo, the National Zoological Gardens of South Africa, or the Toronto Zoo. All of these zoos are well-respected institutions that promote animal conservation and have fantastic educational programs.

Learn more about some of these zoos here.


Go to an aquarium:

Interact with dolphins at the National Aquarium.
Photo by the National Aquarium at Wikimedia.

Aquaria are places of wonder and tranquility. Learn about teleost fish, sharks, rays, crustaceans, octopuses, jellyfish, coral, and many more species that inhabit our oceans, lakes, and rivers. Relax while watching the graceful movements of sea animals and marvel at the agility of apex predators at feeding time. Learn about the many aquatic habitats our planet supports and the amazing diversity of the animals that live in them. Like zoos, aquaria provide research opportunities (such as the individual recognition study in octopuses), support conservation, and have fun educational programs and activities.

If you get a chance, you may want to check out the National Aquarium in Baltimore, the Georgia Aquarium, the Monterey Bay Aquarium, the Aquarium of Western Australia (AQWA) in Perth or L’Oceanogràfic in Valencia, Spain.

Learn more about some of these aquariums here and here.



Take a wildlife tour:

See breathtaking animals in their natural habitat
from the security of your guide's vehicle.
Photo by Brian Snelson at Wikimedia.

If you want to see wild animals in their natural habitats, experienced guides can help you find animals that are often elusive while keeping you safe and preserving animal habitats. Guides can give detailed information about the animals you encounter and can often tell thrilling tales of their own personal experiences. Some even provide lunch.

Maybe your dream has always been to go on an African safari. Consider the Safari Serengeti trip in Tanzania by Overseas Adventure Travel, where you can see animals like Thomson’s gazelles, buffalo, and elephants. Or participate in a North American safari in Yellowstone National Park with Wolf & Bear Safaris by the Yellowstone Safari Company. If a Northwoods flavor suits you, check out Northwoods Outfitters Moose Wildlife Safari in Maine. Or take a Hawaiian vacation and go whale watching with Ultimate Whale Watch in Maui. For a scientific marine vacation, go on an Educational Shark Encounter trip with Fish Finder Adventures based in Ocean City, Maryland. Whatever your dream animal watching trip, a guide can help you bring it to life.


Go somewhere wild on your own:

Kayak by thousands of birds in the Everglades
(but don't forget your anti-bird-poop-hat).
Photo by Matt Magolan.

If you are an independently minded and experienced adventurer, the world is awaiting. And if you want to increase your chances of observing spectacular wild animals in nature, you should go somewhere that has a lot of spectacular wild animals… like Manuel Antonio Park in Costa Rica, where you can see four monkey species, two iguana species, two sloth species, coatis, toucans, vultures, parakeets, and hundreds of other species on a single hike. Or kayak in the Everglades National Park in Florida, where you can see crocodiles, dolphins, manatees and over 350 species of birds. Or SCUBA or snorkel the coral reefs of the Cayman Islands and feel like part of the community of coral, sponges, tropical fish, rays, sharks, and sea turtles.

Learn more about some of these trips here.


We share this world with countless amazing animals. Find your own way to experience, learn about and appreciate them. I’ll go into more detail on these vacations and others in future posts, so comment below and let us know what animal watching vacations you have done and what you are interested in doing in the future.

But for now, I will be going on my own vacation. Don't worry, there will be new The Scorpion and the Frog articles about animals in July!

Can You Feel the Love Tonight? (A Guest Post)

A reposting of an article by Maggie Nannenhorn from March 14, 2016.

If you’re like me, you never truly realize how quiet winter is until all the sounds of spring come back in a chorus of celebration. Between the birds, crickets, and frogs, you can really hear the love in the air. So you can hear the love, but can you feel the love?

Wood frogs are known for their chorus of calls that sound like a duck laughing. Seriously, tell a duck a good knock-knock joke and that is what a male wood frog sounds like when trying to attract a mate. He makes the call by expanding his two vocal sacs, membranes of skin underneath the neck, forming a bubble-like appearance. When a female surfaces, drawn to the call, the male frog clasps onto her, causing her to lay her eggs. The male frog then externally fertilizes the eggs. This form of mating is termed amplexus. The use of the call in the reproduction ritual is well studied. However, it is possible the small ripple formed in the water from the expanding vocal sack is relaying information that influences the mating behavior of these frogs.

Male wood frog resting on the water surface. Image by Maggie Nannenhorn.

Male wood frog calling with vocal sac expanded.
Notice the ripple it creates in the water. Image by Maggie Nannenhorn.

In 2010, Gerlinde Höbel and Robb Kolodziej from the University of Wisconsin-Milwaukee conducted an experiment that explored the use of water surface waves in wood frog reproductive behavior. They hypothesized male wood frogs use ripples in the water to find female wood frogs to mate with, while female wood frogs use ripples in the water as indicators of harassing males.

Video of a wood frog calling by Maggie Nannenhorn.

Wood frogs have a very short mating period: only 1 to 3 days per year! This study occurred on April 1st - 2nd, which corresponded with the wood frogs’ natural mating period. The first component of the study was the observation of a pond containing more than 500 wood frogs in amplexus. Amplexus was determined by the presence of males clasping on to the backs of female frogs in the water. They learned males approach surface waves on the water and clasp onto the frog that caused the ripple. However, females move away from surface waves on the water and dive downward.

After preliminary observations, they developed an experiment to cause rippling of the water. The first experiment tested the effect of stimulation (dipping a wooden probe into the water) near male wood frogs. The males tested were randomly assigned to either a control group or an experimental group. The 34 males in the control group were simply observed, and the direction and pattern of movement was recorded. For the experimental group, a long wooden probe was dipped in and out of the water 25 cm away from a male frog for 10 seconds. The resulting ripple was meant to mimic a ripple caused by a female frog moving in the water. Based on the hypothesis, the male wood frogs should approach the ripple hoping to find a female to mate with. Of the 60 males in the experimental group, half were stimulated from the right and half were stimulated from the left. A circle diagram (depicted below) was used to map the direction the males moved.

Video of a wood frog approaching ripples by Gerlinde Höbel.

This figure shows: a) the control group and b) the experimental group.
A circle diagram representing the reproductively driven movement direction
of wood frogs (Lithobates sylvaticus) in a laboratory pool as a result of
stimulated surface waves on both the left and right sides.
Figure from: Höbel, G., & Kolodziej, R. C. (2013). Behaviour, 150(5), 471-483.

The females are difficult to observe in the field since they prefer to stay beneath the surface. So, the researchers set up a tank to test 4 breeding pairs of wood frogs. They tested the females both while in amplexus and while alone. They dipped wooden probes into the water to stimulate the females on both the left and the right side in turn. Their positions and directions were also recorded using a circle diagram.

So, what did they find? It turns out, their predictions were correct! The males would approach the ripple caused by the probing. This is likely because the ripple may indicate a competing male they want to drive away or a female they want to mate with. The females moved away from the ripples by either swimming away or diving underneath the water surface. This may reduce the amount of harassment they receive from males. If a female becomes the center of attention for too many males, she may drown from the weight of them all attempting to grab her. Besides, if a male is fit, he will likely be able to catch up to her and successfully mate with her despite her swimming away.

The mating calls and movement of the wood frogs affect the surface waves, and these waves are used to make sexual behavior choices. This spring, the chorus of love will still ring out through the reeds, and I encourage you to take a moment to stop and listen. When you’re stopped, take a moment to notice the waves of love bringing these wood frogs together. Hopefully this spring, we will all be feeling the love.



Reference:

Höbel, G., & Kolodziej, R. (2013). Wood frogs (Lithobates sylvaticus) use water surface waves in their reproductive behaviour Behaviour, 1-13 DOI: 10.1163/1568539X-00003062

Need a Hand? Just Grow it Back! How Salamanders Regenerate Limbs (A Guest Post)

By Maranda Cardiel

(A reposting of an original article posted on February 29, 2016)

How cool would it be if you could regenerate your own body parts? Just imagine: you are chopping up some carrots for dinner, but whoops! You accidentally cut off your thumb! No worries, it’ll grow back in a few weeks, good as new and fully functional. No need to take a trip to the hospital and pay all of those annoying medical costs.

That all sounds pretty nifty, but that can’t actually happen, right? Tissue regeneration on that large of a scale is something you can only find in science fiction. …Or so you may think. Nature has actually found a way to regenerate full limbs and other body parts after they have been completely amputated. However, among animals with spines, this unique ability is only found in salamanders. But how does it work, and why can’t we do it too?

A cartoon illustrating examples of the three different methods of tissue regeneration in animals. A.) An
adult hydra being cut into two pieces and regenerating into two separate hydras. B.) Part of a human
liver being cut off and the remaining liver regenerating via cell division. C.) A salamander’s arm being
amputated and undergoing epimorphosis to regenerate an entire new arm.
Source: Maranda Cardiel

There are actually three ways that animals can regenerate tissues. Some animals, such as hydras, can use the tissues they already have to regenerate themselves after being cut in two, resulting in two separate hydras. Mammals, including humans, have the ability to regenerate their livers by having the liver cells divide into more liver cells. This is how liver transplants work – a portion of liver from a live donor will grow into a fully-functioning liver in the recipient. The third method is called epimorphosis, which is the ability to change existing cells of specific types so that they can re-grow as different cell types, and this is what salamanders are able to do.

When the limb of a salamander is cut off, only the outermost layer of skin moves to cover the wound. This single layer forms a special skin cap known as the epithelial cap, and the nerves at the amputation site shrink back from the wound. Then the cells beneath the cap dedifferentiate, losing their specific characteristics so all of the different types of cells become the same and detach from each other.

A cartoon illustrating the process of a salamander regenerating its arm. A.) The limb is amputated.
B.) The outermost layer of the skin begins to cover the wound. C.) This single layer of skin creates
an epithelial cap and the blastema forms underneath it. D.) The cells of the blastema begin to
differentiate into bone, nerves, etc. E.) The cells continue to divide and differentiate until the limb is
fully formed. Source: Maranda Cardiel

Now the amputated limb has a mass of indistinguishable cells under the cap, and this mass is called the regeneration blastema. A blastema is simply a clump of cells that is able to grow into an organ or body part. Over the course of several weeks, this blastema divides into more cells and the cells begin to differentiate - or turn into multiple types - again, forming different cell types such as bone, muscle, cartilage, nerves, and skin. Eventually, the salamander will have a brand new limb.

The salamander’s body can even tell what body part it’s supposed to re-grow; if it’s amputated at the wrist it will grow a new hand, and if its entire hind leg is amputated it will grow a new hind leg. And it’s not only limbs that salamanders can regenerate – they can even grow back their tails, retinas, spinal cords, and parts of their hearts and brains!

As you can see, the process of epimorphosis is much more complicated than simply having a single cell type divide a lot. It also requires certain chemicals and patterns of immune signaling to work properly. But why can’t people do this too? One of the reasons is because when our tissues are damaged, all of our skin grows to cover and heal the wound, which forms scars. In salamanders, only the outermost layer of skin does this, which prevents the scarring that would stop tissue regeneration. The salamander’s immune system is also regulated differently than our own, which allows them to regenerate whole body parts.

Unfortunately we are not salamanders, so when you cut off your finger it’s not going to grow back. But researchers are continuing to study salamanders and their astounding regenerative abilities in the hopes of finding a way to apply it to people. Who knows, maybe someday we’ll be able to grow back our own limbs too.


Sources:

Gilbert, Scott F. Developmental Biology 6th Edition. Ncbi.nlm.nih.gov. National Center for Biotechnology Information, 2000.

Godwin, J., Pinto, A., & Rosenthal, N. (2013). Macrophages are required for adult salamander limb regeneration Proceedings of the National Academy of Sciences, 110 (23), 9415-9420 DOI: 10.1073/pnas.1300290110

The Best Dads in the Animal Kingdom

Paternal care is not nearly as common in the animal kingdom as maternal care, and for good biological reason. In most species, females produce fewer, larger, and costlier eggs than males do sperm. Therefore, it is usually beneficial to females to maximize the possible success of each one, sometimes by gestating them inside their own bodies (as mammals do), or incubating the eggs until they are ready to hatch (as birds do), or by providing prolonged protection, food and training until they are ready to take on the world for themselves. Males, on the other hand, are usually benefitted more by spending their time trying to mate with as many females as possible and avoiding the costs of parenting. But for some species, these costs and benefits of parenting are such that it pays for males to be good dads. Here are some of the best dads in the animal kingdom:

1. The Endurance Prize goes to the emperor penguin: Emperor penguins breed on the sea ice of Antarctica, the coldest place on Earth. After Mom lays her egg, her nutritional reserves are so depleted that she must return to the ocean (which can be over 100 miles away) to feed. This leaves the responsibility of keeping the egg warm through the freezing Antarctic winter to Dad. Dad goes months without feeding to balance the egg on his feet in subzero weather (-30 degrees Fahrenheit, on average) with freezing winds up to 120 mph, often forced to huddle together with other dads for warmth until their chicks hatch. If he moves too suddenly or the egg becomes exposed to the freezing temperatures, the chick will die. Even though he hasn’t eaten for months and has lost about 40% of his body weight, Dad provides the newly hatched chick with sustenance: a milky-type substance produced by a gland in his throat until Mom returns to the family with a belly-full of fish.

An Emperor penguin dad feeds his chick after a brutal winter without
eating a single bite himself. Photo by Mtpaley at Wikimedia Commons.

2. The Provider Prize goes to the water bug: Water bugs (also known as toe-biters) are huge, predatory, aquatic insects that can reach sizes up to 4 inches in length! They have a strong beak and a painful bite and they have been known to eat small fish, frogs and even birds! In order to grow into a large predatory insect, one must hatch from a large egg. Water bug eggs are so large that they require more oxygen for development than they can naturally absorb through the water. This requires a parent to help supply them with oxygen. However, Mom spends so much of her energy producing these humongous eggs that she doesn’t have enough energy reserves to then care for them. This leaves all of the parental duties up to Dad. In these species, Mom lays her eggs on Dad’s back in between matings. Once the full clutch of up to 150 eggs are glued to Dad’s back, he dances around and does underwater pushups to keep the water circulating and periodically takes them on a field trip to the surface for air (which has more oxygen that water does) until they hatch.

A water bug dad carries his eggs. Photo by Marshal Hedin at Wikimedia Commons.

3. The Protector Prize goes to the Darwin’s frog: Darwin’s frogs are small South American frogs that look a bit like a bloated leaf. When they mate, Mom lays her eggs in the leaf litter, which Dad fertilizes and then guards for a few weeks until the developing embryos begin to move. At that point, he “swallows” the eggs into a pouch near his throat called a vocal sac, where they hatch. He carries the tadpoles in his vocal sac until they have fully developed into frogs, at which point he “vomits” them up and they hop away to start their new lives. It’s pretty gross. Watch:

4. The Pregnancy Prize goes to the seahorse: Male seahorses have fewer (and thus more precious) sperm than males of other species and they are the only males that take on the full responsibility of pregnancy, carrying up to 2,000 babies at a time! Although they don’t have a mammalian womb and placenta, they do have an enclosed abdominal pouch specifically for the purpose of incubating the babies. Mom deposits her eggs in Dad’s brood pouch. He fertilizes them and incubates them in his expanding belly for 10-45 days (depending on the species). During this time, his body undergoes a number of hormonal and physiological changes and Mom never even makes an ice cream run for him or rubs his (non-existent) aching feet. When the babies are ready to emerge as fully developed little seahorses, seahorse dads even experience contractions as they give birth!

The best dad and grandpa in the world.
Photo by Sarah Jane Alger.

5. The Multi-Generational Prize goes to humans: Many human dads are not only good fathers, but also good grandfathers. Grandparenting is extremely rare in the animal kingdom (the first documented case of grandparenting in non-humans was as recent as 2008) and human males excel at it. They provide care, advice, lessons and resources to increase the success of their offspring and grand-offspring… It’s amazing other species haven’t picked up on this amazing secret yet!

Think You're Stressed Out? At Least You're Not THIS Guy!

It's a stressful time for many of us, and you may feel like life is eating you alive, but at least you're not this poor snake who is having the worst day of his life:

And for some hilarious commentary, check this out.

The Princess IS the Frog (A Guest Post)

By Hayley Trzinski

Image by Hayley Trzinski

The Princess and the Frog is a very fun and imaginative children’s story… but not when pesticides are involved. Have you ever wondered how dangerous pesticides can be? Well, pesticides can harm more than just pests and weeds, and in the case of frogs, many pesticides and herbicides are causing problems. Atrazine, a chemical commonly used as an herbicide, can cause reproduction in male African clawed frogs to be impossible. In some cases, atrazine is even turning some male frogs into females!

Tyrone Hayes, a biology professor at the University of California, Berkeley, and his research team looked at the effects of atrazine on African clawed frogs. The hypothesis of the researchers was to determine if exposure to atrazine would feminize or stop reproductive ability of male frogs. Tyrone Hayes and his team raised some frogs in atrazine dissolved in a weak ethanol solution and some in only a weak ethanol solution for a control group. Even though the ethanol solutions did not contain enough ethanol to impact the frogs, it is important to put the control group frogs in ethanol as well so both the treatment and control groups are equal in that way. Fertility in the frogs was later determined by looking at the number of developed embryos produced from atrazine-treated males and females, and from normal males and females.

Atrazine is an endocrine disruptor, meaning that it contains chemicals that can change the hormone systems in animals. Some endocrine disruptors block hormone receptors, causing the hormones needed for reproduction to stop working. Atrazine works as an endocrine disruptor by increasing the production and activity of aromatase, a chemical that turns testosterone into estrogen. This decreases the amount of testosterone and increases the amount of estrogen in the male frogs.

Tyrone Hayes and his team saw that aromatase was found in normal females and in atrazine-treated males, but not in normal males. The aromatase production caused a decrease in testosterone and an increase in estrogen in the atrazine-treated males. Subsequently, the atrazine-treated males' calls became less masculine, their sperm died, and they started forming characteristics such as female sex organs.

In the long run, atrazine could affect whole frog populations by skewing the sex ratio, meaning that there will be many more of one sex of frog than the other, making it hard to keep a healthy frog population. The main way that atrazine could skew the sex ratio of frogs is by changing their behavior. This starts by male frogs not being able to mate or by their fertility decreasing. Tyrone Hayes found that the behavior of male frogs treated with atrazine was different than the behavior of male frogs not treated with atrazine. Non-treated males out-competed atrazine-treated males for females and only two atrazine-treated males obtained correct mating posture. Also, non-treated males had much higher testosterone levels when around females than atrazine-treated males. This behavior change in male frogs affected by atrazine could cause fewer of those males to act like males, and more of them to act like females or to not reproduce at all.

Atrazine can skew the sex ratios of frog populations in other ways, too. African clawed frogs have the opposite type of sex determining chromosomes as humans. While human males have one Y and one X sex chromosome and human females have two X sex chromosomes, normal male African clawed frogs have two Z chromosomes and female African clawed frogs have one Z chromosome and one W chromosome. The sex ratio becomes skewed, in part, because even though some of the newly transitioned female frogs can successfully breed, they still have male genetics. When these newly transitioned female frogs mate with natural male frogs, all of the offspring will be males. This is because two frogs that both have original sex cells that are both Z’s create offspring that must inherit two Z chromosomes, making all of the babies male. This is dangerous for populations of frogs, because only one sex of frogs being created could lead to extinction of these creatures.

Although you may like the idea of crops being pest and weed free, there are many negative side effects to the dangerous pesticide chemicals, including changing the reproduction of frogs and even fish, reptiles, birds, and mammals, sometimes including humans. Even though the effects of these pesticides are pretty interesting, I don’t know about you, but I would rather read a story where frogs turn into princes instead of princesses.

Sources

Hayes, T., Khoury, V., Narayan, A., Nazir, M., Park, A., Brown, T., Adame, L., Chan, E., Buchholz, D., Stueve, T., & Gallipeau, S. (2010). Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis) Proceedings of the National Academy of Sciences, 107 (10), 4612-4617 DOI: 10.1073/pnas.0909519107

Mnif, W., Hassine, A., Bouaziz, A., Bartegi, A., Thomas, O., & Roig, B. (2011). Effect of Endocrine Disruptor Pesticides: A Review International Journal of Environmental Research and Public Health, 8 (12), 2265-2303 DOI: 10.3390/ijerph8062265

Can You Feel the Love Tonight? (A Guest Post)

By Maggie Nannenhorn

If you’re like me, you never truly realize how quiet winter is until all the sounds of spring come back in a chorus of celebration. Between the birds, crickets, and frogs, you can really hear the love in the air. So you can hear the love, but can you feel the love?

Wood frogs are known for their chorus of calls that sound like a duck laughing. Seriously, tell a duck a good knock-knock joke and that is what a male wood frog sounds like when trying to attract a mate. He makes the call by expanding his two vocal sacs, membranes of skin underneath the neck, forming a bubble-like appearance. When a female surfaces, drawn to the call, the male frog clasps onto her, causing her to lay her eggs. The male frog then externally fertilizes the eggs. This form of mating is termed amplexus. The use of the call in the reproduction ritual is well studied. However, it is possible the small ripple formed in the water from the expanding vocal sack is relaying information that influences the mating behavior of these frogs.

Male wood frog resting on the water surface. Image by Maggie Nannenhorn.

Male wood frog calling with vocal sac expanded.
Notice the ripple it creates in the water. Image by Maggie Nannenhorn.

In 2010, Gerlinde Höbel and Robb Kolodziej from the University of Wisconsin-Milwaukee conducted an experiment that explored the use of water surface waves in wood frog reproductive behavior. They hypothesized male wood frogs use ripples in the water to find female wood frogs to mate with, while female wood frogs use ripples in the water as indicators of harassing males.

Video of a wood frog calling by Maggie Nannenhorn.

Wood frogs have a very short mating period: only 1 to 3 days per year! This study occurred on April 1st - 2nd, which corresponded with the wood frogs’ natural mating period. The first component of the study was the observation of a pond containing more than 500 wood frogs in amplexus. Amplexus was determined by the presence of males clasping on to the backs of female frogs in the water. They learned males approach surface waves on the water and clasp onto the frog that caused the ripple. However, females move away from surface waves on the water and dive downward.

After preliminary observations, they developed an experiment to cause rippling of the water. The first experiment tested the effect of stimulation (dipping a wooden probe into the water) near male wood frogs. The males tested were randomly assigned to either a control group or an experimental group. The 34 males in the control group were simply observed, and the direction and pattern of movement was recorded. For the experimental group, a long wooden probe was dipped in and out of the water 25 cm away from a male frog for 10 seconds. The resulting ripple was meant to mimic a ripple caused by a female frog moving in the water. Based on the hypothesis, the male wood frogs should approach the ripple hoping to find a female to mate with. Of the 60 males in the experimental group, half were stimulated from the right and half were stimulated from the left. A circle diagram (depicted below) was used to map the direction the males moved.

Video of a wood frog approaching ripples by Gerlinde Höbel.

This figure shows: a) the control group and b) the experimental group.
A circle diagram representing the reproductively driven movement direction
of wood frogs (Lithobates sylvaticus) in a laboratory pool as a result of
stimulated surface waves on both the left and right sides.
Figure from: Höbel, G., & Kolodziej, R. C. (2013). Behaviour, 150(5), 471-483.

The females are difficult to observe in the field since they prefer to stay beneath the surface. So, the researchers set up a tank to test 4 breeding pairs of wood frogs. They tested the females both while in amplexus and while alone. They dipped wooden probes into the water to stimulate the females on both the left and the right side in turn. Their positions and directions were also recorded using a circle diagram.

So, what did they find? It turns out, their predictions were correct! The males would approach the ripple caused by the probing. This is likely because the ripple may indicate a competing male they want to drive away or a female they want to mate with. The females moved away from the ripples by either swimming away or diving underneath the water surface. This may reduce the amount of harassment they receive from males. If a female becomes the center of attention for too many males, she may drown from the weight of them all attempting to grab her. Besides, if a male is fit, he will likely be able to catch up to her and successfully mate with her despite her swimming away.

The mating calls and movement of the wood frogs affect the surface waves, and these waves are used to make sexual behavior choices. This spring, the chorus of love will still ring out through the reeds, and I encourage you to take a moment to stop and listen. When you’re stopped, take a moment to notice the waves of love bringing these wood frogs together. Hopefully this spring, we will all be feeling the love.



Reference:

Höbel, G., & Kolodziej, R. (2013). Wood frogs (Lithobates sylvaticus) use water surface waves in their reproductive behaviour Behaviour, 1-13 DOI: 10.1163/1568539X-00003062

Need a Hand? Just Grow it Back! How Salamanders Regenerate Limbs (A Guest Post)

By Maranda Cardiel

How cool would it be if you could regenerate your own body parts? Just imagine: you are chopping up some carrots for dinner, but whoops! You accidentally cut off your thumb! No worries, it’ll grow back in a few weeks, good as new and fully functional. No need to take a trip to the hospital and pay all of those annoying medical costs.

That all sounds pretty nifty, but that can’t actually happen, right? Tissue regeneration on that large of a scale is something you can only find in science fiction. …Or so you may think. Nature has actually found a way to regenerate full limbs and other body parts after they have been completely amputated. However, among animals with spines, this unique ability is only found in salamanders. But how does it work, and why can’t we do it too?

A cartoon illustrating examples of the three different methods of tissue regeneration in animals. A.) An adult hydra being cut into two pieces and regenerating into two separate hydras. B.) Part of a human liver being cut off and the remaining liver regenerating via cell division. C.) A salamander’s arm being amputated and undergoing epimorphosis to regenerate an entire new arm.
Source: Maranda Cardiel

There are actually three ways that animals can regenerate tissues. Some animals, such as hydras, can use the tissues they already have to regenerate themselves after being cut in two, resulting in two separate hydras. Mammals, including humans, have the ability to regenerate their livers by having the liver cells divide into more liver cells. This is how liver transplants work – a portion of liver from a live donor will grow into a fully-functioning liver in the recipient. The third method is called epimorphosis, which is the ability to change existing cells of specific types so that they can re-grow as different cell types, and this is what salamanders are able to do.

When the limb of a salamander is cut off, only the outermost layer of skin moves to cover the wound. This single layer forms a special skin cap known as the epithelial cap, and the nerves at the amputation site shrink back from the wound. Then the cells beneath the cap dedifferentiate, losing their specific characteristics so all of the different types of cells become the same and detach from each other.

A cartoon illustrating the process of a salamander regenerating its arm. A.) The limb is amputated. B.) The outermost layer of the skin begins to cover the wound. C.) This single layer of skin creates an epithelial cap and the blastema forms underneath it. D.) The cells of the blastema begin to differentiate into bone, nerves, etc. E.) The cells continue to divide and differentiate until the limb is fully formed. Source: Maranda Cardiel

Now the amputated limb has a mass of indistinguishable cells under the cap, and this mass is called the regeneration blastema. A blastema is simply a clump of cells that is able to grow into an organ or body part. Over the course of several weeks, this blastema divides into more cells and the cells begin to differentiate - or turn into multiple types - again, forming different cell types such as bone, muscle, cartilage, nerves, and skin. Eventually, the salamander will have a brand new limb.

The salamander’s body can even tell what body part it’s supposed to re-grow; if it’s amputated at the wrist it will grow a new hand, and if its entire hind leg is amputated it will grow a new hind leg. And it’s not only limbs that salamanders can regenerate – they can even grow back their tails, retinas, spinal cords, and parts of their hearts and brains!

As you can see, the process of epimorphosis is much more complicated than simply having a single cell type divide a lot. It also requires certain chemicals and patterns of immune signaling to work properly. But why can’t people do this too? One of the reasons is because when our tissues are damaged, all of our skin grows to cover and heal the wound, which forms scars. In salamanders, only the outermost layer of skin does this, which prevents the scarring that would stop tissue regeneration. The salamander’s immune system is also regulated differently than our own, which allows them to regenerate whole body parts.

Unfortunately we are not salamanders, so when you cut off your finger it’s not going to grow back. But researchers are continuing to study salamanders and their astounding regenerative abilities in the hopes of finding a way to apply it to people. Who knows, maybe someday we’ll be able to grow back our own limbs too.


Sources:

Gilbert, Scott F. Developmental Biology 6th Edition. Ncbi.nlm.nih.gov. National Center for Biotechnology Information, 2000.

Godwin, J., Pinto, A., & Rosenthal, N. (2013). Macrophages are required for adult salamander limb regeneration Proceedings of the National Academy of Sciences, 110 (23), 9415-9420 DOI: 10.1073/pnas.1300290110

Caught in My Web: Funky "New" Species

Image by Luc Viatour at Wikimedia.

Given the rate of extinction of creatures great and small, you may be surprised to learn that we discover about 18,000 new species every year! For this edition of Caught in My Web, we explore some of these new-to-us species.

1. Jessica Schmerler explains how animals are classified and named and has a fun slideshow of 2014's top 10 interesting animals at Scientific American.

2. Jane Lee at National Geographic talks about a newly discovered deep sea anglerfish with big teeth, spikes on its snout and a crazy-looking lure on the top of its head!

3. Justine Alford at IFLScience! shows us a newly discovered species of peacock spider.

The male dons a blue mask is is about as cuddly as a spider gets. Check out his dance here:

4. Stephanie Pappas at livescience shows us an adorable newly discovered jelly-bean sized masked frog.

5. Against conventional wisdom, a newly discovered species of frogs gives birth to live young! Dr. Dolittle at ScienceBlogs tells us all about it.

Freezing the Winter Away

The clutches of the Polar Vortex are finally releasing its grasp on us and we can be thankful for our home heating, our layers of warm clothing, and most of all, our bodies’ abilities to generate heat. But it is times like these that make me wonder about our friends that live outside year-round… especially those that don’t generate most of their own body heat. How do they survive these periods of intense cold? There are several species of North American frogs that have an unusual trick up their sleeve: They freeze nearly solid and still live to see the next spring.

This picture of a wood frog is by Ontley at Wikimedia Commons.

Frogs are ectothermic, meaning they take on the temperature of their surroundings rather than generate their own body heat. This introduces some intriguing questions about how these species even exist in northern climates that experience freezing temperatures every year. When various North American frog species (including wood frogs, spring peepers, western chorus frogs, and a few gray tree frog species) take on freezing winter temperatures, they actually allow their bodies to freeze nearly solid. For most species, this would be a deadly approach: a frozen circulatory system would halt the delivery of oxygen to cells, which require oxygen to generate the energy they need to do just about everything a cell does. Furthermore, jagged ice crystal edges could rupture the cells they are inside. Dead cells lead to dead organs, which in turn lead to dead animals. These freezing frogs have found the secrets to freezing without killing their cells.

The first secret of the freezing frogs is to spend the winter snuggled in the leaf litter below the snow. This environment insulates and protects the frogs from the deadly wind chills we have been facing for the last several days.

The second secret of the freezing frogs is a creative use of colligative properties. Colligative properties are properties of solutions that depend on the ratio of the number of liquid molecules to the number of molecules of stuff dissolved in that liquid. One of those properties is called freezing point depression: The temperature at which a liquid will freeze can be lowered by adding particles to it. (This is why salt is spread on roads in the winter). A critical component of the freezing frog strategy is for the liver to produce massive amounts of glucose in response to the start of freezing. This glucose is pumped throughout the body, which lowers the freezing point of all of the organs.

A third secret of the freezing frogs is the use of ice nucleating agents: proteins that actually encourage freezing. This may seem counterintuitive, but remember that ice crystals inside cells can cause them physical damage. By having a high concentration of ice nucleating agents in the fluid between the cells, this ensures that ice first forms in the spaces surrounding the cells. When ice forms, the ice crystals are made of only water molecules, which draws water out of the solution and leaves behind a higher concentration of other stuff (like glucose) in between the cells. The high concentration of glucose between the cells draws water out of the cells and into that space. This additional water also freezes. In the end, the cells are chock-full of particles, lowering their freezing temperature, and are surrounded by ice, which insulates the cells. Thus, this process of ice formation around the cells prevents ice from forming inside the cells.

A fourth secret of the freezing frogs is a metabolic shift. Most animal cells rely on oxygen to produce the energy they need to support their demands. But cells have ways of producing energy without oxygen too. These ways are not very efficient, but are useful when there is not enough oxygen available to meet demand (such as when a seal dives or a cheetah reaches burst speed). When freezing frogs start to freeze and oxygen delivery to the cells slows and eventually stops, their cells shift from an oxygen-reliant system of energy creation to an oxygen-independent system of energy creation. Additionally, freezing organs do less and don’t require as much energy anyway, so they can continue functioning at low levels for a long time if the freezing spell is prolonged.

When the environment warms up (as forecasters promise will happen), the body temperatures of these frogs raise and body fluids slowly become liquid again. The heart starts to beat again within hours of the start of thawing and oxygen can again be delivered around the body. The delivery of oxygen-carrying blood helps the rest of the organs return to their normal functions.

There are still many secrets of these freezing frogs left to uncover. Maybe you’ll be the one to do it… once we thaw out a bit.

Want to know more? Check these out:

1. Storey, K.B. (2004). Strategies for exploration of freeze responsive gene expression: advances in vertebrate freeze tolerance Cryobiology, 48, 134-145 DOI: 10.1016/j.cryobiol.2003.10.008

2. Layne, J.R., & Lee, R.E. (1995). Adaptations of frogs to survive freezing Climate Research, 5, 53-59 DOI: 10.3354/cr005053