Rana tigrina Overview and Habitats

Classification of Rana tigrina

• Phylum: Chordata
• Class: Amphibia
• Order: Anura
• Genus: Rana
• Species: tigrina

Systematic Position of Rana tigrina

• Kingdom: Animalia
• Phylum: Chordata
• Group: Craniata
• Subphylum: Vertebrata
• Division: Gnathostomata
• Super class: Tetrapoda

Habitat and Habits of Rana tigrina

• Found in freshwater ponds, tanks, rivers, ditches, and among green vegetation
• Abundant during the rainy season
• Recognized by their croaking sounds
• Amphibious (live both in water and on land)
• Cold-blooded (poikilothermic) - body temperature varies with environment

Respiration and Protection in Aquatic Environments

• Keeps snout above water surface for air intake through external nostrils
• Eyes and tympanum also positioned above water surface
• Nictitating membrane protects eyes in water

Hibernation and Aestivation

• During winter, lowers body temperature, becomes inactive, digs into the bottom of the pond (approx. 3/4 meter deep) for winter sleep (hibernation)
• Mouth and nostrils remain closed during hibernation, no feeding, greatly reduced physiological activity
• During winter, relies on glycogen stored in the liver for nutrition
• When winter ends, the frog comes out and leads an active life. But after some time during severe summer, with rising temperatures, it goes underground and becomes inactive (aestivation)
• Resumes active life with the commencement of the rainy season (amphibious life)

Defense Mechanisms

• Frog is a friend to agriculturists because it feeds on insects
• Enemies include snakes, cranes, mongooses, and humans
• Camouflage: changes color to match its surroundings, hiding in green vegetation

External Features of Rana hexadactyla

• Cloacal aperture
• Femurs
• Crura
• Web
• Toes
• Antebrachium
• Brachium
• Tympanum
• External Nares
• Eyes
• Upper eyelid
• Nictitating membrane
• Skin: Moist; ventral surface -faint yellow; dorsal surface - green with black spots

Head

• Triangular shape with a large broad mouth bounded by upper and lower jaws
• Snout near the extremity of which are two external nostrils
• Two round eyes - allows for panoramic vision without head movement
• Three eyelids: upper (thick, immovable), lower (small, movable), third (nictitating membrane) - protects eyes

Tympanum and Vocal Sacs

• Round depression behind and slightly downward of each eye covered by a tough grey membrane
• Vocal sacs present in male frogs, absent in females
• Vocal sacs produce croaking sounds, particularly during breeding season

Trunk

• Main part of body with two pairs of legs (forelimbs, hind limbs)
• Forelimbs consist of upper arm, forearm, hand; 4 digits, no thumbs.
• Hind limbs are stronger, longer than forelimbs; thigh, shank, foot; 5 toes connected by web
• Cloacal aperture at posterior end of trunk between hind limbs

Sexual Differences

• Males are larger than females
• Males have more muscular fore limbs
• Vocal sacs are present in males but absent in females
• Copulatory pads thicken and swell during breeding season on the first finger

Food and Prey Capture

• Carnivorous (feeds on insects, fish, worms)
• Sticky, prehensile tongue in buccal cavity
• Tongue is capable of being projected out rapidly and is free and bifid
• Prey is captured, withdrawn into buccal cavity
• Teeth prevents escape of prey

Digestive System

• Alimentary canal extends from mouth to cloaca
• Buccal cavity
• Esophagus
• Stomach: cardiac and pyloric parts; gastric glands secrete gastric juices (HCI and pepsinogen), converts pepsinogen to pepsin to digest protein
• Small intestine: duodenum & ileum
• Large intestine: rectum and cloaca
• Glands: liver and pancreas

Physiology of Digestion

• Enzymes break down large food molecules into absorbable molecules
• Digestion process converts these absorbed molecules into protoplasm, heat and energy → assimilation
• Elimination of undigested food → egestion

Buccal Cavity and Esophagus

• Mouth is bordered by upper jaw with maxillary teeth and lower jaw without teeth
• Prevents food escape from the mouth
• No salivary gland within the buccal cavity, no digestion in buccal cavity
• Esophagus carries food from the mouth to the stomach, no digestion takes place here

Stomach

• Cardiac part secretes gastrin hormone stimulating gastric glands which produce mucous, HCI, and pepsinogen (converted to pepsin)
• Chyme is made from food, which is pulpy from water in gastric juice
• Proteins are broken down to peptones and proteoses
• Carbohydrates and fats are not digested

Duodenum

• As food reaches duodenum, it stimulates the secretion of numerous hormones (secretin, cholecystokinin, enterokinase, and enterogesterone)
• Hormones stimulate the pancreas and gall bladder secretions into the duodenum
• Enterogesterones stop the activity of gastric glands of stomach

Bile in Digestion

• Bile neutralizes acidity of food, making it alkaline, and mixes with food; making it thinner
• Does not contain digestive enzymes
• Bile salts emulsify fats into smaller particles

Pancreatic Juice

• Pancreatic enzymes (trypsinogen, amylase, lipase) break down food
• Trypsinogen is activated by enterokinase within the duodenal mucosa
• Proteins are converted to peptides
• Carbohydrates (starch) are converted to glucose
• Fats are converted to fatty acid and glycerol

Ileum (Small Intestine)

• Intestinal juice (succus entericus) further digests food
• Enzymes (sucrase, maltase, lactase, peptidase, erepsin, and lipase) continue carbohydrate and protein digestion
• Breaks down complex carbohydrates, proteins, and fats into simple absorbable substances
• Nutrients absorbed into blood capillaries (Glucose, fructose, amino acids, fatty acid, glycerol)

Rectum and Absorption

• Rectum absorbs water
• Undigested food is expelled through the cloaca
• Villi increase surface area, facilitating absorption.
• Blood vessels absorb digested nutrients for assimilation (hepatic portal vein)

Assimilation and Egestion

• Digested products are transported and used for building tissues, creating energy, and maintaining temperature.
• Excess nutrients are stored or processed for further use
• Undigested materials are moved into the rectum, then eliminated through the cloaca.