Zoology Terms Starting With K

Keratin is a family of fibrous structural proteins that form the hair, feathers, claws, nails, hooves, horns, and outer epidermal layer of vertebrates.

Keratins are classified as intermediate filament proteins and divided into two broad categories: hard keratins, which are sulfur-rich and form rigid structures such as nails, claws, horns, and hair shafts, and soft keratins, which produce more pliable epithelial layers. Alpha-keratins occur in all mammals, while beta-keratins contribute to feathers, scales, claws, and beaks in birds and reptiles. Keratin’s resistance to mechanical damage and enzymatic degradation means that hair and nails persist long after death, and forensic scientists have used keratin isotope ratios from hair to reconstruct an individual’s geographic movements.

A single strand of human hair withstands a tensile force of roughly 60 to 100 grams before breaking, a strength that reflects the tightly coiled alpha-helical structure of its keratin chains. Wool fibers exploit this same coiled architecture to trap air and provide insulation, a property that textile manufacturers have used for thousands of years.

Keystone Predator is a predator whose removal causes a disproportionately large shift in ecosystem structure, species diversity, or trophic interactions relative to the predator's abundance.

Keystone predators suppress dominant prey species, preventing competitive exclusion and maintaining habitat heterogeneity for other organisms. Robert Paine coined the keystone species concept in 1966 after removing ochre sea stars (Pisaster ochraceus) from intertidal plots in Washington State, which caused mussels to monopolize available substrate and reduced local species diversity by roughly 50 percent within one year. Sea otters (Enhydra lutris) in Pacific kelp forests control sea urchin populations; without otters, urchins overgraze kelp holdfasts and convert productive forests into barren rock.

When fur hunters reduced otter populations during the 18th and 19th centuries, kelp forest coverage declined by more than 90 percent in some regions. The 1995 reintroduction of gray wolves (Canis lupus) to Yellowstone National Park triggered a trophic cascade across 2.2 million acres, altering elk grazing behavior and allowing willow and aspen regeneration that subsequently benefited beavers, songbirds, and riparian fish communities.

Kin Selection is a mechanism of natural selection that favors behaviors helping genetic relatives when the indirect fitness benefit outweighs the cost to the actor.

Hamilton’s rule formalizes kin selection with the inequality rB > C, where r is the coefficient of relatedness between actor and recipient, B is the fitness benefit to the recipient, and C is the fitness cost to the actor. When this inequality is satisfied, natural selection can favor the altruistic behavior even if the actor’s direct reproduction is reduced. Worker honeybees (Apis mellifera) in a haplodiploid colony share approximately 75 percent of their genes with full sisters, a higher relatedness than they would share with their own offspring, which helps explain why workers forgo reproduction to raise siblings.

Kin selection differs from reciprocal altruism, which involves unrelated individuals exchanging benefits over time rather than sharing alleles. Ground squirrels (Spermophilus beldingi) give alarm calls more frequently when close female relatives are nearby, a pattern consistent with Hamilton’s rule and documented by Paul Sherman in field studies during the 1970s and 1980s.

Kinetoplastid is a flagellated protozoan distinguished by a kinetoplast, a DNA-rich region within its single large mitochondrion composed of interlocked circular DNA molecules, found in genera such as Trypanosoma and Leishmania.

Kinetoplastids belong to the class Kinetoplastea and include over 600 described species, many of which parasitize animals and plants across tropical regions. The kinetoplast contains a unique concatenated network of circular DNA molecules, comprising up to 25 percent of the total cellular DNA, and this network must be precisely replicated and partitioned at every cell division. Trypanosoma brucei, transmitted by tsetse flies (Glossina spp.) across sub-Saharan Africa, causes African sleeping sickness and threatens approximately 70 million people in endemic areas.

Leishmania species, transmitted by sandflies, cause a spectrum of diseases ranging from self-healing skin lesions to fatal visceral infection affecting the liver and spleen. Most kinetoplastids undergo dramatic morphological changes as they cycle between an invertebrate vector and a vertebrate host, with distinct flagellar pocket arrangements and metabolic profiles at each stage.