4 Things About Frogs

4 Things About Frogs

Skin

Frogs are skin breathers, not just using the nostrils/mouth, as the lungs alone do not provide sufficient oxygen. They have thin, vascular, moist skin with a high surface area to volume ratio; where semi-permeable membranes permit cutaneous gas exchange - particles diffuse across through pores and into the blood.

Since 100% of their oxygen intake is through the skin underwater, they can stay submerged without surfacing for air for long periods. However, this is why they are so susceptible to pollution or pesticide runoff - causing hormone disturbance and potential death. In response, handle with gloves or clean, moistened hands to avoid skin irritation or hydration difficulties due to dirt or natural oils drying their skin out.

Some frogs have glands behind the head that release a wax-like substance, which gets rubbed over the body by the legs like lotion to maintain moisture against the sun and wind.

Mobility

Frogs have elongated, lanky hindlimbs with strong elastic tendons that provide power for jumping and swimming. The most dramatic form of mobility resides in tree frog species (even though not all live in trees, living near clean water sources for skin moisture). They are usually smaller than other frog types, and lots weigh less than an ounce, boosting climbing agility.

Their extensive interdigital webbing doesn't just function as flippers for swimming, but they spread out to provide air resistance for gliding jumps between trees, almost like a squirrel suit. Landings get supported with enlarged, adhesive toe pads/discs for balancing assistance on tree leaves, branches or bark, where feet skin also secrete mucous to keep them grippy.

Otherwise, the best jumper is the south african sharp-nosed frog - jumping over 80x their body length with hindlimbs ~3x the length of the head, thorax and abdomen combined.

Eyes

Frog eyes protrude atop the head with little obstruction for a wide vision field (useful because they have no neck for rotation) - alongside elevation that helps them sit just above water level. The eyes have an upper, lower and nictating membrane layer; which is semi-transparent to see clearer when underwater, protects against foreign particles, keeps the eyes moistened and can even cover the eye colour to blend into surroundings.

They have one of the best night visions of the animal kingdom - over owls, cats and dogs - as the rod cells (sensitive to low-light conditions) are so sharp. Even in pitch-black darkness, they most prominently see in blue and green tones to interpret objects, except their vision is distorted up close, plus for stationary entities.

Their photoreceptor sensitivity levels could be overwhelming initially, as they can detect single little light photons. Just a 60-watt light bulb emits ~10^20 per second (they can get seizures).

Tree frogs have the biggest eyes of any vertebrate proportionate to size, which infers the energy instilled into sight to see past obscurities in trees. They condense their vision by focusing the eye lens like a camera zoom, concentrating light onto the retina. The red-eyed variant can even use said colour for aposematism, possibly deterring some predators despite not being poisonous or venomous.

Chytrid

Chytrid fungi infections induce the chytridiomycosis disease, deriving nutrients from amphibian hosts, often being severely detrimental and fatal in wild ecosystems. Global amphibian populations have declined substantially because of chytrid alone, most prevalently affecting aquatics such as the titicaca water frog.

The most severe circumstance resides in substantial epidermal deterioration, exploiting frog dependency on their skin, leading to immunosuppression. Compromised homeostasis function hinders ectothermic thermoregulation, ventilation, hydration, circulation and osmoregulation. Shedding/sloughing is the most common innate immune mechanism against chytrid, physically removing dead cells and microbes with significantly increased frequencies and smaller skin pieces.

The epidermal and dermal skin layers consist of chemical barrier endocrine glands, secreting substances such as mucous containing defensive enzymes and anti-fungal + anti-bacterial metabolites. In addition, a secondary defence of abundant T (Thymus) and B (Bone marrow) lymphocytes aid disease prevention via methods of 'phagocytosis' (ingestion) and immunoglobulin production. Newly metamorphosing frogs seem most vulnerable as the immune system is immature.

Contrarily, the defence mechanisms often get genetically inhibited, preventing adaptive immune response. Lymphocytes are interfered with and destroyed via stimulation of 'apoptosis' (mechanical cell death) and actively suppressed proliferation. Distress-induced cortisol and lower body temperature only further impair immune responses.

Frogs and amphibians do not all respond equally to fungal infection because a multitude of variables influence clinical infection outcome occurrence and severity - being dependent on the host, fungal virulence and environmental determinants. Some will be passive carriers; others will be dangerously more susceptible.