Amphibians

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NGSS Performance Expectations

MS-LS1-1 Conduct an investigation to provide evidence that living things are made of cells; either one cell or many different numbers and types of cells.

MS-LS1-2 Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.

HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

HS-LS1-5 Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy.

The content and activities in this topic will work towards building an appreciation for the evolutionary and ecological significance of amphibians.

From Fish to Tetrapods

Tetrapods are vertebrate animals with four limbs or feet, a term that is derived from the Greek root words tetra meaning “four” and pod meaning “foot.” Scientists believe the evolutionary adaptation of four limbs likely began in an aquatic environment among a group called the lobe-finned fishes. However, the purpose of the first limbs is unknown. They may have been an adaptation to stalk prey or to prop the body up above the water in shallow areas for aerial respiration.

<p><strong>Fig. 5.2.</strong> (<strong>A</strong>) Red-eyed tree frog (<em>Agalychnis callidryas</em>), an example of an amphibian , Playa Jaco, Costa Rica</p>

Fig. 5.2. (A) Red-eyed tree frog (Agalychnis callidryas), an example of an amphibian , Playa Jaco, Costa Rica

Image courtesy of Carey James Balboa, Wikimedia Commons

<p><strong>Fig. 5.2.</strong> (<strong>B</strong>) Arrau River turtles (<em>Podocnemis expansa</em>), examples of reptiles, Ecuador</p>

Fig. 5.2. (B) Arrau River turtles (Podocnemis expansa), examples of reptiles, Ecuador

Image courtesy of Dirección de Información Turística del Ministerio de Turismo del Ecuador

<p><strong>Fig. 5.2.</strong> (<strong>C</strong>) European bee-eaters (<em>Merops apiaster</em>), examples of birds, Ariège, France</p>

Fig. 5.2. (C) European bee-eaters (Merops apiaster), examples of birds, Ariège, France

Image courtesy of Pierre Dalous, Wikimedia Commons

<p><strong>Fig. 5.2.</strong> (<strong>D</strong>) Black rhinoceroses (<em>Diceros bicornis</em>), examples of mammals, Etosha National Park, Namibia</p>

Fig. 5.2. (D) Black rhinoceroses (Diceros bicornis), examples of mammals, Etosha National Park, Namibia

Image courtesy of Yathin S. Krishnappa, Wikimedia Commons

The tetrapod group includes four classes of vertebrates. The first are the amphibians (Class Amphibia), a group of tetrapods with an aquatic developmental stage and a terrestrial adult stage (Fig. 5.2 A). The reptiles (Class Reptilia) are scaled tetrapods that use lungs to breathe (Fig. 5.2 B). The birds (Class Aves) are tetrapods in which the two front limbs are wings (Fig. 5.2 C). The mammals (Class Mammalia) are warm-blooded and possess hair, among other characteristics (Fig. 5.2 D). It should be noted that scientists now consider birds to be a type of reptile (Fig. 5.3). Even though all tetrapods share a common ancestry, there is great diversity in their morphology and physiology, thus the study of tetrapods has been divided into several disciplines. The study of amphibians and reptiles is known as herpetology. The study of birds is called ornithology. The study of mammals is known as mammalogy.

<p><strong>Fig. 5.3.</strong> Phylogenetic tree of all vertebrate animals</p>

Fig. 5.3. Phylogenetic tree of all vertebrate animals

Image by David Lin, adapted from image by Petter Bøckman, Wikimedia Commons

Organisms within the subphylum Vertebrata, which includes the tetrapods, are an amazingly diverse group, currently living in almost every habitat on Earth. Vertebrates possess an internal skeleton, or endoskeleton, with a backbone made of vertebrae and cartilage. Within the subphylum Vertebrata there are seven classes of organisms and approximately 52,000 species (Fig. 5.3). However, prior to 360 million years ago, the only vertebrates that existed were the fishes, including the jawless fish (Class Agnatha), the sharks and rays (Class Chondrichthyes), and the bony fishes (Class Osteichthyes). Ancient fishes were a very diverse group, but they had been constrained to marine habitats. At that time plants, molluscs, and arthropods dominated terrestrial habitats, though they were primarily centered on coastlines and areas with an abundance of water. Around 390 to 360 million years ago, a significant evolutionary step took place that initiated a radiation of species into terrestrial habitats. The fins of some lobe-finned fishes evolved into the limbs of tetrapods. Figure 5.4 shows two examples of extant lobe-fined fishes.

<p><strong>Fig. 5.4.</strong> (<strong>A</strong>) West Indian ocean coelacanth (<em>Latimeria chalumnae</em>)</p>

Fig. 5.4. (A) West Indian ocean coelacanth (Latimeria chalumnae)

Image courtesy of Sini Merikallio, Flickr

<p><strong>Fig. 5.4.</strong> (<strong>B</strong>) South American lungfish (<em>Lepidosiren paradoxa</em>)</p>

Fig. 5.4. (B) South American lungfish (Lepidosiren paradoxa)

Image courtesy of Alex Giltjes, Wikimedia Commons

Adaptive radiation is a process in which organisms diversify rapidly into many new forms. Adaptive radiations particularly occur when new environmental resources arise, providing new habitats and food sources. When tetrapods first evolved, the land represented a new environment with an abundance of plant and insect food resources that were not being exploited by the relatively large land animals. However, life on land presented a number of challenges for aquatic organisms. In the ocean, an organism’s weight is supported by the water, and some organisms have additional adaptations that help them remain buoyant such as swim bladders in fish. The water’s resistance against the body can make movement and other behaviors like grasping food easier. Air is much less dense than water, so organisms that live on land had to develop structural systems to support their weight and allow for movement. For example, the evolution of jointed limbs allowed tetrapods to walk by transmitting muscle energy against their endo-skeleton to the ground. Another challenge on land is the threat of desiccation, or drying out, from water loss. Land-based organisms developed much thicker skin compared with fish as a way to prevent water loss. Other sensory organs also had to work in air rather than water. The lateral line and electric organs of bony fish no longer worked, so ears, nasal passages, and focusing eyes developed. A common misconception is that lungs developed in early tetrapods. However, lungs that were used for respiration had already developed in some bony fishes from their swim bladders. The lungfish (Fig. 5.5), for example, has lungs and is currently found in Africa, South America, and Australia. Tetrapods did develop pumping mechanisms to bring air in and out of the body cavity.

<p><strong>Fig. 5.5.</strong> (<strong>A</strong>) Armored birchir (<em>Polypterus delhezi</em>) and other birchirs and ropefish are ray-finned fishes with lungs</p>

Fig. 5.5. (A) Armored birchir (Polypterus delhezi) and other birchirs and ropefish are ray-finned fishes with lungs

Image courtesy of ばぶじ～, Wikimedia Commons

<p><strong>Fig. 5.5.</strong> (<strong>B</strong>) Lung inside a dissected spotted African lungfish (<em>Protopterus dolloi</em>)</p>

Fig. 5.5. (B) Lung inside a dissected spotted African lungfish (Protopterus dolloi)

Image courtesy of Mokele, Wikimedia Commons

Marine Tetrapod

Tetrapods evolved from fish ancestors and diversified on dry land or in freshwater habitats. Some of these terrestrial reptiles (including birds) and mammals then independently evolved adaptations that allowed them to survive in ocean conditions. There are no extant marine amphibians. Examples of marine tetrapods include sea turtles, shorebirds, penguins, whales, and seals. Most marine tetrapods retain some connection to dry land. Sea turtles and penguins must return to shore to build nests and lay eggs just as their non-marine ancestors did. All marine tetrapods have to surface for air to breathe. Figure 5.6 shows some examples of marine tetrapods.

<p><strong>Fig. 5.6.</strong> (<strong>A</strong>) Marine iguana (<em>Amblyrhynchus cristatus</em>), Española Island, Galápagos Islands</p>

Fig. 5.6. (A) Marine iguana (Amblyrhynchus cristatus), Española Island, Galápagos Islands

Image courtesy of Benjamint444, Wikimedia Commons

<p><strong>Fig. 5.6.</strong> (<strong>B</strong>) Green sea turtle (<em>Chelonia mydas</em>), Keauhou, Island of Hawai‘i</p>

Fig. 5.6. (B) Green sea turtle (Chelonia mydas), Keauhou, Island of Hawai‘i

Image courtesy of Brocken Inaglory, Wikimedia Commons

<p><strong>Fig. 5.6.</strong> (<strong>C</strong>) Emperor penguin (<em>Aptenodytes forsteri</em>), Gould Bay, Antarctica</p>

Fig. 5.6. (C) Emperor penguin (Aptenodytes forsteri), Gould Bay, Antarctica

Image courtesy of Christopher Michel, Flickr

<p><strong>Fig. 5.6.</strong> (<strong>D</strong>) Polar bear (<em>Ursus maritimus</em>), Svalbard, Norway</p>

Fig. 5.6. (D) Polar bear (Ursus maritimus), Svalbard, Norway

Image courtesy of Andreas Weith, Wikimedia Commons

What is an Amphibian?

Amphibians are a group of tetrapod vertebrate animals with moist, scaleless skin, all sharing a common evolutionary ancestry. Examples of amphibians include frogs, toads, salamanders, and newts (Fig. 5.7). Amphibians are a diverse group of animals that includes almost 7,000 species and that are adapted to live in a wide variety of environments. All amphibians are aquatic animals to some degree. Most amphibian species live in freshwater or moist terrestrial environments but not marine environments. Although there are no marine amphibians alive today, some species of frogs can tolerant brackish water. Some species, like desert toads, have adapted to arid conditions but still require aquatic habitats to breed.

<p><strong>Fig. 5.7.</strong> (<strong>A</strong>) Purple caecilian (<em>Gymnopis multiplicata</em>), El Zota, Costa Rica</p>

Fig. 5.7. (A) Purple caecilian (Gymnopis multiplicata), El Zota, Costa Rica

Image courtesy of Andy Kraemer, Flickr

<p><strong>Fig. 5.7.</strong> (<strong>B</strong>) Central newt (<em>Notophthalmus viridescens louisianensis</em>) in eft stage, Leon County, Florida</p>

Fig. 5.7. (B) Central newt (Notophthalmus viridescens louisianensis) in eft stage, Leon County, Florida

Image courtesy of squamatologist, Flickr

<p><strong>Fig. 5.7.</strong> (<strong>C</strong>) Blue poison dart frog (<em>Dendrobates azureus</em>)</p>

Fig. 5.7. (C) Blue poison dart frog (Dendrobates azureus)

Image courtesy of Michael Gäbler, Wikimedia Commons

Evidence of Common Ancestry and Diversity

<p><strong>Fig. 5.8.</strong> Phylogenetic tree illustrating the evolutionary relationships among the three major amphibian groups</p>

Fig. 5.8. Phylogenetic tree illustrating the evolutionary relationships among the three major amphibian groups

Image courtesy of Zardoya & Meyer 2001 in Proceedings of the National Academy of Sciences of the United States of America (PNAS), 98(13):7380–7388. http://www.pnas.org/content/98/13/7380

Amphibians were the earliest tetrapods to evolve. Modern amphibians can be classified into three major groups: legless caecilians, salamanders, and frogs. The first amphibians evolved from lobe-finned fishes approximately 390 to 360 million years ago (Fig. 5.8). Modern caecilians, salamanders, and frogs all evolved from these basal amphibian ancestors.

Caecilians (pronounced “see-seal-ee-un”) are long, slender, legless amphibians superficially resembling earthworms or snakes (Fig. 5.9). Most caecilians burrow through the soil, but some species thrive in freshwater ecosystems. There are approximately 170 extant species, all occurring in the tropical regions of Central and South America, Southeast Asia and equatorial Africa. They vary in length from 7 centimeters (cm) to 1.5 meters (m).

<p><strong>Fig. 5.9.</strong> (<strong>A</strong>) Purple caecilian (<em>Gymnopis multiplicata</em>)</p>

Fig. 5.9. (A) Purple caecilian (Gymnopis multiplicata)

Image courtesy of Teague O'Mara, Flickr

<p><strong>Fig. 5.9.</strong> (<strong>B</strong>) Yellow-striped caecilian (<em>Ichthyophis kohtaoensis</em>)</p>

Fig. 5.9. (B) Yellow-striped caecilian (Ichthyophis kohtaoensis)

Image courtesy of Kerry Matz, Flickr

<p><strong>Fig. 5.9.</strong> (<strong>C</strong>) Mexican caecilian (<em>Dermophis mexicanus</em>)</p>

Fig. 5.9. (C) Mexican caecilian (Dermophis mexicanus)

Image courtesy of Kerry Matz, Flickr

<p><strong>Fig. 5.9.</strong> (<strong>D</strong>) Head of an Asian caecilian (<em>Ichthyophis</em> sp.)</p>

Fig. 5.9. (D) Head of an Asian caecilian (Ichthyophis sp.)

Image courtesy of Shyamal, Wikimedia Commons

Salamanders are amphibians with elongated, slender bodies and long tails (Fig. 5.10 A). There are approximately 550 extant species of salamanders. One group of salamanders, commonly called the giant salamanders, is the largest of all the amphibians (Fig. 5.10 B). The largest species is the Chinese giant salamander (Andrias davidianus), which can reach up to 1.8 m in length. One familiar group of salamanders is the newt family. Newts are generally smaller than 20 cm but are famously known for their toxic skin secretions and bright colors (Fig. 5.10 C). Sirens are a group of salamanders that lack hind limbs. They have reduced forelimbs giving them an eel-like appearance (Fig. 5.10 D). The sirens are common in slow moving waters of North America.

<p><strong>Fig. 5.10.</strong> (<strong>A</strong>) Ensatina salamander (<em>Ensatina eschscholtzii</em>)</p>

Fig. 5.10. (A) Ensatina salamander (Ensatina eschscholtzii)

Image courtesy of squamatologist, Flickr

<p><strong>Fig. 5.10.</strong> (<strong>B</strong>) Hellbender (<em>Cryptobranchus alleganiensis</em>)</p>

Fig. 5.10. (B) Hellbender (Cryptobranchus alleganiensis)

Image courtesy of John Clare, Flickr

<p><strong>Fig. 5.10.</strong> (<strong>C</strong>) Eastern newt (<em>Notophthalmus viridensis</em>) in “red eft” developmental stage</p>

Fig. 5.10. (C) Eastern newt (Notophthalmus viridensis) in “red eft” developmental stage

Image courtesy of Jason Quinn, Wikimedia Commons

<p><strong>Fig. 5.10.</strong> (<strong>D</strong>) Western lesser siren (<em>Siren intermedia nettingi</em>)</p>

Fig. 5.10. (D) Western lesser siren (Siren intermedia nettingi)

Image courtesy of Andrew Hoffman, Ohio State University

Frogs are arguably the most successful group of amphibians, with approximately 5,000 known species alive today. Frogs are squat, tailless amphibians with short forelimbs and muscular hind limbs (Fig. 5.11). Several families of frogs with leathery skin and short legs are commonly called toads (Fig. 5.11 C). However, this is simply a colloquial term. Frogs have adapted to a wide range of habitats and can sometimes be found in very dense populations.

<p><strong>Fig. 5.11.</strong> (<strong>A</strong>) Italian tree frog (<em>Hyla intermedia</em>)</p>

Fig. 5.11. (A) Italian tree frog (Hyla intermedia)

Image courtesy of Benny Trapp, Wikimedia Commons

<p><strong>Fig. 5.11.</strong> (<strong>B</strong>) Iberian midwife toad (<em>Alytes cisternasii</em>)</p>

Fig. 5.11. (B) Iberian midwife toad (Alytes cisternasii)

Image courtesy of Benny Trapp, Wikimedia Commons

<p><strong>Fig. 5.11.</strong> (<strong>C</strong>) Cane toad (<em>Rhinella marina</em>)</p>

Fig. 5.11. (C) Cane toad (Rhinella marina)

Image courtesy of Sam Fraser-Smith, Flickr

<p><strong>Fig. 5.11.</strong> (<strong>D</strong>) Phantasmal poison frog (<em>Epipedobates tricolor</em>)</p>

Fig. 5.11. (D) Phantasmal poison frog (Epipedobates tricolor)

Image courtesy of H. Krisp, Wikimedia Commons

Weird Science

Amphibians in Decline

Structure and Function

<p><strong>Fig. 5.12.</strong> (<strong>A</strong>) Skeleton of an angler or monkfish (<em>Lophius piscatorius</em>), a bony fish, Museum of Toulouse</p>

Fig. 5.12. (A) Skeleton of an angler or monkfish (Lophius piscatorius), a bony fish, Museum of Toulouse

Image courtesy of Didier Descouens, Wikimedia Commons

<p><strong>Fig. 5.12.</strong> (<strong>B</strong>) Skeleton of a salamander</p>

Fig. 5.12. (B) Skeleton of a salamander

Image courtesy of cmh4529, Flickr

<p><strong>Fig. 5.12.</strong> (<strong>C</strong>) Skeleton of a bullfrog</p>

Fig. 5.12. (C) Skeleton of a bullfrog

Image courtesy of Ryan Somna, Flickr

<p><strong>Fig. 5.13.</strong> Frog anatomy. Organs labeled by number: (1) Right atrium, (2) Liver, (3) Aorta, (4) Egg mass, (5) Colon, (6) Left atrium, (7) Ventricle, (8) Stomach, (9) Left lung, (10) Spleen, (11) Small intestine, and (12) Cloaca</p>

Fig. 5.13. Frog anatomy. Organs labeled by number: (1) Right atrium, (2) Liver, (3) Aorta, (4) Egg mass, (5) Colon, (6) Left atrium, (7) Ventricle, (8) Stomach, (9) Left lung, (10) Spleen, (11) Small intestine, and (12) Cloaca

Image courtesy of Jonathan McIntosh, Wikimedia Commons

Amphibians have some major changes in body structures compared with their most recent ancestors, the fish. One of the most striking is the change in skeletal structure with muscular limbs. All tetrapods have hard bony skeletons (Fig. 5.12). Sturdy skeletons are necessary to support the body weight of animals out of water. Fishes have musclar heart organs with two chambers that pump out and take in blood. Amphibians have a three-chambered heart (Fig. 5.13).

Activity

Identifying Amphibians

Use a simple dichotomous key to correctly identify amphibian major groups.

Adaptations

Amphibians and reptiles are sometimes called “cold-blooded” animals. The term cold-blooded does not mean that their body is always cold, rather that is ectothermic. Ectothermic means that organisms maintain their body temperature by absorbing heat from their environment. By contrast, endothermic organisms maintain a relatively constant temperature in their bodies. Birds and mammals are examples of endothermic or “warm-blooded” animals. Maintaining an appropriate body temperature is important for metabolism, locomotion, and many cellular processes. Ectothermic organisms will often move to new locations to increase or decrease their temperature if necessary. Some amphibians and reptiles will find a location in the sun and absorb sunlight to increase their temperature, this process is known as basking. Amphibians in general have relatively moist skin, meaning that evaporative cooling occurs quickly in the air. Amphibians maintain their temperature by moving locations or changing their postures.

All animals require oxygen to survive. Vertebrate animals have respiratory systems, or collections of organs that allow the exchange of oyxgen (O₂) and carbon dioxide (CO₂) gases to and from the surrounding environment. Most fish species use gills to extract dissolved oxygen from water. The first true lungs evolved in a group of fishes called lungfishes (Fig 5.5). Lungs are balloon-like internal organs that can be filled with gases for respiration. Most amphibians have lungs in their adult life stages. However, the largest group of salamanders (family Plethodontidae) is the lungless salamanders. The species in this group “lost” their lungs secondarily over the course of evolution, although the cause for this remains unclear. Biologists use the term secondary loss to describe traits that have reverted back to an ancestral condition or appear to be more similar to earlier ancestral traits than recent traits. For example, “lungless” plethodontid salamanders lack lungs just like most lungless fishes, even though they evolved from ancestors with lungs (e.g. lobe-finned fishes). Similarly, snakes evolved from lizards with legs. It can be said that snakes lost their legs secondarily through evolution. To read more about lungfishes, see the introduction to lobe-finned fishes and this article, From Water to Land.

Another adaptation in amphibians is their skin. Amphibians generally have soft moist skin without scales. There are some exceptions. Toads have dry and warty skin. Skin acts as a preventive barrier against changes in the external environment and can prevent cuts and microbial infections. The skin of amphibians is unique because it can be used for gas exchange and respiration. In fact, some species have lost lung organs over time. In addition to respiration, the skin has two types of glands present in juveniles and adults: mucous and poison glands. Mucous glands secrete a protective coating over the skin. Some amphibian species have evolved poisonous secretions that serve as protection against predators. Poisonous amphibians are typically brightly colored (Fig. 5.14).

<p><strong>Fig. 5.14.</strong> (<strong>A</strong>) Red-bellied newt (<em>Taricha rivularis</em>), northern California</p>

Fig. 5.14. (A) Red-bellied newt (Taricha rivularis), northern California

Image courtesy of John Clare, Flickr

<p><strong>Fig. 5.14.</strong> (<strong>B</strong>) The dyeing dart frog (<em>Dendrobates tinctorius</em>) is one of over 170 species in the “poison dart frog” family native to Central and South America.</p>

Fig. 5.14. (B) The dyeing dart frog (Dendrobates tinctorius) is one of over 170 species in the “poison dart frog” family native to Central and South America.

Image courtesy of Brian Gratwicke, Smithsonian Conservation Biology Institute

Energy Acquisition

Almost all amphibians are predatory. Juvenile frogs, which eat mainly bacteria and algae, are the exception. Amphibians have several interesting adaptations that they use to capture prey. Most amphibians capture prey by biting and grasping (Fig. 5.15). Teeth structure is diverse depending on the prey type and serves to hold the prey or to break it down. The tongue of most amphibians is used to swallow and help guide the food to the esophagus. Frogs and most salamanders use their sticky projectile tongues to capture prey. Their diet mainly consists of insects but some larger species feed on birds, lizards, and even small mammals. Some salamanders and frogs also use a form of suction feeding in which they capture prey by opening their mouth and mouth cavity at the same time, sucking the prey into the mouth.

<p><strong>Fig. 5.15.</strong> (<strong>A</strong>) Allegheny Mountain dusky salamander (<em>Desmognathus ochrophaeus</em>), eating an earthworm, Allegany County, New York</p>

Fig. 5.15. (A) Allegheny Mountain dusky salamander (Desmognathus ochrophaeus), eating an earthworm, Allegany County, New York

Image courtesy of Dave Huth, Flickr

<p><strong>Fig. 5.15.</strong> (<strong>B</strong>) Frog eating another frog, Siem Reap, Cambodia</p>

Fig. 5.15. (B) Frog eating another frog, Siem Reap, Cambodia

Image courtesy of Bjørn Christian Tørrissen, Wikimedia Commons

Growth, Development & Reproduction

Almost all amphibians produce offspring through sexual reproduction. Recall that sexual reproduction is the joining of male and female gametes (sperm and eggs, respectively). For more information about sextual reproduction, please read the Growth, Development, and Reproduction topic in Aquatic Plants and Algae.

<p><strong>Fig. 5.16.</strong> The male wood frog (<em>Lithobates sylvaticus</em>) clasps a female and deposits sperm as the female lays eggs.</p>

Fig. 5.16. The male wood frog (Lithobates sylvaticus) clasps a female and deposits sperm as the female lays eggs.

Image courtesy of Richard Bonnett, Flickr

In caecilians and salamanders, fertilization of the female’s eggs occurs internally. A male will deposit sperm into the female cloaca. The cloaca is a posterior opening that serves as an opening for the reproductive, intestinal, and urinary tracts in amphibians, reptiles, and birds. In frogs, fertilization occurs externally. The male clasps onto the female and deposits sperm as the female lays eggs (Fig. 5.16).

Amphibian eggs are highly vulnerable to water loss, and they are typically laid in aquatic habitats or very moist sites. Some frogs that live in drier habitats form bubble nests to keep their eggs moist following fertilization (Fig. 5.17).

<p><strong>Fig. 5.17.</strong> (<strong>A</strong>) The túngara frogs (<em>Engystomops pustulosus</em>) of Central America generate floating foam or bubble nests around their egg masses.</p>

Fig. 5.17. (A) The túngara frogs (Engystomops pustulosus) of Central America generate floating foam or bubble nests around their egg masses.

Image courtesy of Geoff Gallice, Flickr

<p><strong>Fig. 5.17.</strong> (<strong>B</strong>) Many amphibian species such as the northern red-legged frog (<em>Rana aurora</em>) attach egg masses to submerged freshwater plants in marshes, streams and temporary vernal pools.</p>

Fig. 5.17. (B) Many amphibian species such as the northern red-legged frog (Rana aurora) attach egg masses to submerged freshwater plants in marshes, streams and temporary vernal pools.

Image courtesy of John Clare, Flickr

<p><strong>Fig. 5.17.</strong> (<strong>C</strong>) All poison dart frog species carry newly-hatched tadpoles on their backs. Adults deposit the tadpoles into small streams and water pools for further development.</p>

Fig. 5.17. (C) All poison dart frog species carry newly-hatched tadpoles on their backs. Adults deposit the tadpoles into small streams and water pools for further development.