I

ick Serious disease of freshwater fishes, caused by the ciliate protozoan Ichthyophthirius multifiliis.

icterus Yellowing of the skin and other organs because of bile pigments in the blood.

ideal free distribution The distribution of individuals among resource patches of different quality that equalizes the net rate of gain of each individual. Assumes that organisms are free to move and have ideal knowledge about patch quality.

idiosoma Posterior of the two basic parts of the body of a mite or tick, bearing the legs and most internal organs.

IgE Immunoglobulin E; specific class of antibodies involved in allergic reactions; individuals who suffer from allergies have elevated levels of these antibodies.

igneous Most of the molten mass of the earth, igneous material cooled to form the earth's crust.

igneous rocks Crystalline minerals solidified from molten magma from deep in the earth's interior; basalt, rhyolite, andesite, lava, and granite are examples.

iliac ilia = flank, loin.

imago The adult and sexually mature insect.

imagochrysalis Quiescent stage between the nymph and adult in the life cycle of a chigger mite.

imbibition The process of taking up water physically.

imitation An act that occurs when an animal immediately copies the actions of another animal while they are in each other's presence.

immediate hypersensitivity Biological manifestation of an antigen-antibody reaction in which the maximal response is reached in a few minutes or hours. Intradermal injection of the antigen produces local swelling and redness with heavy infiltration of polymorphonuclear leukocytes. Intravenous injection may produce anaphylactic shock and death.

immune cross reaction Binding of an antibody or cell receptor site with an antigen other than the one that would provide an exact "fit"; that is, an antigen-antibody reaction in which the antigen is not the same one that stimulated the production of that antibody.

immunity State in which a host is more or less resistant to an infective agent; preferably used in reference to resistance arising from tissues that are capable of recognizing and protecting the animal against "nonself."

immunization The process of making one immune. The induction of protective immunity by administration of either (1) a vaccine or toxoid (active immunization) or (2) preformed antibodies (passive immunization).

immunogenic Refers to any substance that is antigenic; that is, stimulates production of antibody or cell-mediated immunity.

immunoglobulin Any one of five classes of proteins in blood serum that function as antibodies; abbreviated IgM, IgG, IgA, IgD, and IgE.

immunoglobulin Any of a group of plasma proteins, produced by plasma cells, that participates in the immune response by combining with the antigen that stimulated its production. Antibody.

immunological Pertaining to the immune response, in which a protein antibody is synthesized by an organism to counteract some pathogenic factor.

immunology The study of the immune system. This study reveals the many phenomena that are responsible for both acquired and innate immunity. It also includes the use of antibody-antigen reactions in other laboratory work (serology and immunochemistry).

imperfect flower Unisexual flower; either staminate or pistillate.

imperfect stage The asexual phase in a fungus life cycle characterized by the production of asexual spores.

impermeable Having the property of restricting the passage of substances.

implantation im = into; plantare = to set. Attachment of the blastocyst to the endometrium.

imprinting A process that occurs when an animal learns to make a particular response to only one type of animal or object. The sensory modes used for establishing such a connection can be visual, auditory, olfactory, or some combination of these, depending upon the animal.

inbreeding depression In a small population, an accumulation of harmful genetic traits (through random mutations and natural selection) that lowers viability and reproductive success of enough individuals to affect the whole population.

inbreeding The tendency among members of a population to mate preferentially with close relatives.

incidence In epidemiology, the number of new cases of a disease per unit time; that is, a rate measurement. Contrast with prevalence.

incidental parasite Accidental parasite.

incisive Cut into.

inclusive fitness The sum of an individual's direct and indirect fitness. See direct and indirect fitness.

incomplete dominance Referring to the phenotypic expression for a given trait demonstrating a blending of the genetic messages from the allele partners controlling that trait; no dominant allelic partner.

incomplete dominance An interaction between alleles in which both alleles are expressed more or less equally, and the phenotype of the heterozygote is different from either homozygote.

incomplete dominance See intermediate inheritance.

incomplete flower Lacking one or more of the four floral parts (sepals, petals, stamens, pistil).

incomplete linkage Two genes that are carried on the same chromosome but are far enough apart that crossing-over between them occurs.109

incomplete protein Protein that lacks the full complement of essential amino acids in the correct proportions.

incus The middle of a chain of three bones of the mammalian middle ear.

indehiscent Denoting mature fruit that do not split open to release their seed.

indehiscent fruit Dry fruit that does not split open on maturity.

independent assortment The random alignment of homologous chromosomes in meiosis.

independent data points A reference to the fact that each of the data points collected to use in a statistical test of a hypothesis must be independent of every other data point.

independent variables The variables that define the treatment conditions in an experiment; literally, the variables that we manipulate to test their effects on behavior.

indeterminate cleavage A type of embryonic development in which the fate of the blastomeres is not determined very early as to tissues or organs, for example, in echinoderms and vertebrates; regulative cleavage.

indeterminate Pertaining to a stem that produces unrestricted vegetative growth; the stem does not terminate in flowering.

indigenous Pertains to organisms that are native to a particular region; not introduced.

indirect development In arthropods, refers to development in which larva or nymph hatches from an egg and is distinctly different in body form from the adult; that is, development with metamorphosis.

indirect fitness A measure of the potential for an individual to contribute copies of the genes it possesses to future generations through its influence on the reproduction of nondescendant relatives. Only the portion of the nondescendant kins' reproduction due to helping by the relative is included in the measure of its inclusive fitness.

indirect flight Insect flight accomplished by flight muscles acting on the body wall. Changes in shape of the thorax cause wing movements. A single nerve impulse results in many cycles of the wings; also called asynchronous flight. See direct (synchronous) flight.

individual distance The fixed minimal distance an animal keeps between itself and other members of its species.

Indo-west Pacific region The tropical Indian and west and central Pacific oceans.

indoleacetic acid (IAA) The naturally occurring auxin.

induced fit The precise fit between an enzyme and its substrate.

induced ovulators Species in which copulation is necessary to effect ovulation.

inducible enzyme An enzyme present only when induced by some particular substrate.

induction Reasoning from the particular to the general, that is, deriving a general statement (hypothesis) based on individual observations. In embryology, the alteration of cell fates as the result of interaction with neighboring cells.

inductor In embryology, a tissue or organ that causes the differentiation of another tissue or organ.

indusium A thin membrane that covers the sori of many ferns; the membrane often breaks at the time of spore maturation.

industrial fishery A fishery in which the catch is used for purposes other than direct human consumption.

industrial revolution Advances in science and technology that have given us power to understand and change our world.

industrial sewage Wastewater from industries. Compare domestic sewage.

industrial timber Trees used for lumber, plywood, veneer, particleboard, chipboard, and paper; also called roundwood.

inertial confinement A nuclear fusion process in which a small pellet of nuclear fuel is bombarded with extremely high-intensity laser light.

infauna Animals that burrow in the substrate. Compare epifauna.

inferior ovary Ovary lies below the attachment of the sepals, petals, and stamens; an epigynous flower.

inferior Below a point of reference (e.g., the mouth is inferior to the nose in humans).

infiltration The process of water percolation into the soil and pores and hollows of permeable rocks.

inflammation The complicated physiological process in mobilization of body defenses against foreign substances and infectious agents and repair of damage from such agents.

inflammatory response A complex series of interactions between fragments of damaged cells, surrounding tissues, circulating blood cells, and specific antibodies; typical of infections.

inflorescence A flower cluster with a definite arrangement

informal economy Small-scale family businesses in temporary locations outside the control of normal regulatory agencies.

information In communication, a measure of the uncertainty of the behavioral response of an individual. In learning, refers to the fact that for successful classical conditioning to occur there must be some intuitive knowledge of the relationship between the CS and US.

infra- Below.

infraciliature All cilia, basal bodies, and their associated fibrils in a ciliate protozoan.

infrapopulation All individuals of a single parasite species in one host.

infrared That portion of the sun's total range of radiation having wavelengths immediately longer than the longest of the visible spectrum (red); between approximately 750 nm and1 m in length.

infundibulum Stalk of the neurohypophysis linking the pituitary to the diencephalon.

infusoriform larva Ciliated larva produced by an infusorigen within a dicyemid mesozoan.

infusorigen Mass of reproductive cells within a rhombogen.

ingroup Taxon being studied in a cladistic analysis of evolutionary history.

inhibition In the context of modern classical conditioning, the learning of negative relationships between the CS and US.

ink sac A gland found in some cephalopods that secretes a dark fluid

used to discourage predators.

innate A characteristic based partly or wholly on genetic or epigenetic constitution.

innate releasing mechanism (IRM) A neural process, triggered by the sign stimulus, which preprograms an animal for receiving the sign stimulus and mediates specific behavioral responses.

inner ear A paired, sound-sensitive organ in vertebrates.

inorganic molecules (compounds) Pertaining to compounds that are not hydrocarbons or their derivatives. Compounds other than organic compounds.

insecta See Hexapoda.

insecticide A chemical that kills insects.

insectivore An insectivorous animal or plant. Any mammal of the order Insectivora, comprising the moles, shrews, and Old World hedgehogs.

insectivorous plants Plants which actively or passively capture insects as an adaptation to acquire nitrogen. Examples include the venus flytrap, sundew, and pitcher plant.

insects Arthropods with three pairs of legs and one pair of antennae. Few are marine, an exception being the water strider.

insertion mutant A type of mutation in which an extra base pair is inserted and shifts the sequence out of phase by one pair; also called a frame shift.

insertion A mutation resulting from the addition of a small segment of DNA.

insight learning The use of cognitive or mental processes to associate experiences and solve problems.

insolation Incoming solar radiation.

instar Stage in the life of an insect or other arthropod between molts.

instinct Stereotyped, predictable, genetically programmed behavior. Learning may or may not be involved.

instrumental conditioning Trial-and-error learning. The reinforcement of certain behaviors in animals leads to an animal repeating the behavior.

instrumental value Value or worth of objects that satisfy the needs and wants of moral agents. Objects that can be used as a means to some desirable end.

intangible resources Abstract commodities, such as open space, beauty, serenity, genius, information, diversity, and satisfaction.

integral protein Protein that spans or penetrates the lipid bilayer of cell membranes.

integrated pest management (IPM) IPM is an ecologically based pest-control strategy that relies on natural mortality factors, such as natural enemies, weather, cultural control methods, and carefully applied doses of pesticides.

integument An external covering or enveloping layer(e.g., the skin).

integument Outermost layers of an ovule that typically develop into the seed coat.

integumentary exchange The exchange of gases through the integument. Also cutaneous exchange.

integuments The two outer layers of an ovule that enclose the nucellus tissue within.

intelligence A collection of mental capacities including imagination, problem-solving ability, memory, the ability to use information gained from past experiences, perceptiveness, and behavioral flexibility. The processes by which animals obtain information about their environment, retain it and use the information to make decisions during the course of their behavioral activities.

intensity Number of parasites in an infected host (infrapopulation). Mean intensity is the average number of parasites per infected host.

intention movement The preparatory movements that an animal makes prior to a complete behavior pattern, as with wing movements before taking flight.

inter- Between.

intercalary meristem A type of meristem present at the base of the blade and/or sheath of many monocots.

intercalated disk Membranous boundary between adjacent cardiac muscle cells.

intercellular Occurring between body cells.

interdemic selection The selection of entire breeding populations as the basic units.

interfascicular cambium The layer of cambium that develops between vascular bundles and connects with the fascicular cambium to form the vascular cambium of woody tissues.

interference A form of competition in which organisms defend or otherwise control limited resources; also called contest competition. Contrast with exploitative competition.

interferons Several cytokines encoded by different genes, important in mediation of natural immunity and inflammation.

interkinesis The activities occurring between meiosis I and meiosis II; similar to interphase but without chromosome replication.

interleukin Cytokines produced by white blood cells and mediating their own activities or those of other white blood cells.

interleukin-1 A cytokine produced by macrophages that stimulates T helper lymphocytes.

interleukin-2 A lymphokine produced by T helper lymphocytes that leads to proliferation of T helper cells and other T lymphocytes.

intermediary meiosis Meiosis that occurs neither during gamete formation nor immediately after zygote formation, resulting in both haploid and diploid generations, such as in foraminiferan protozoa.

intermediate filament The chemically heterogeneous group of protein fibers, the specific proteins of which can vary with cell type. One of the three most prominent types of cytoskeletal filaments.

intermediate host A host in which some development of a symbiont occurs, but in which maturation and sexual reproduction do not take place.

intermediate inheritance. Neither of alternate alleles of a gene are completely dominant, and heterozygote shows a condition intermediate between or different from homozygotes for each allele.

intermediate layer Of the three main layers of the ocean, the one below the surface, or mixed, layer. It includes the main thermocline.

intermediate lobe The area in the pituitary gland between the anterior and posterior lobes.

intermittent parasite Temporary parasite.

intermittent reinforcement Schedules of reinforcement that involve providing rewards, not on every trial, but on usually one of four other types of schedules: fixed ratio, fixed interval, variable ratio, or variable interval.

internal costs The expenses, monetary or otherwise, borne by those who use a resource.

internalizing costs Planning so that those who reap the benefits of resource use also bear all the external costs.

International Whaling Commission (IWC) An agency that regulates whaling around the world.

interneuron A neuron located between a sensory neuron and a motor neuron. Interneurons function as integrating centers.

internode Region on a stem between nodes.

internuncial processes Cytoplasmic channels that connect one part of a cell to another, such as those linking the distal cytoplasm to the tegumental cytons in many flatworms.

interobserver reliability A method for checking on the agreement between two or more people watching the same animals behave. This becomes important both as a check on the definitions developed for particular behavior patterns and when we have two or more individuals gathering the data in a particular investigation and we wish to know that they are taking down their records of the data in as nearly similar a manner as possible.

interosseus inter = between; os = bones.

interphase Period between two cell divisions when a cell is carrying on its normal functions. Long period of the cell cycle between one mitosis and the next. Includes G1 phase, S phase, and G2 phase. The replication of DNA occurs during interphase.

interplanting The system of planting two or more crops, either mixed together or in alternating rows, in the same field; protects the soil and makes more efficient use of the land.

intersexual selection Selection on characteristics of one sex (usually males) based on mate choices made by members of the other sex (usually females).

interspecific competition In a community, competition for resources between members of different species.

interstitial Situated in the interstices or spaces between structures such as cells, organs, or grains of sand.

interstitial animal An animal that occupies the spaces (interstices) between sediment particles

interstitial fauna Animals living between sediment particles. Also see meiofauna.

interstitial water The water contained between sediment particles.

intertidal Living in the area between high and low tides and, thus, alternately exposed to the air and to the sea.

intertidal zone The vertical extent of the shoreline between the high and low tide lines.

intine The inner layer of the pollen wall.

intracellular Occurring within a body cell or within body cells.

intracellular digestion Digestion that occurs inside a cell.

intralecithal cleavage Cleavage in which the nuclei undergo several divisions within the yolk mass without concurrent cytokinesis; common in arthropods.

intrasexual selection Selection on characteristics of the sexes based on competition among them (usually males) for access to members of the other sex (usually females).

intraspecific competition In a community, competition for resources among members of the same species.

intrinsic growth rate Exponential growth rate of a population, that is, the difference between the density-independent components of the birth and death rates of a natural population with stable age distribution.

intron An intervening or noncoding segment of a gene; introns separate exons.

introvert A tubular, eversible extension of the head, bearing the mouth at its tip.

invagination An infolding of a layer of tissue to form a sac-like structure.

inversion A turning inward or inside out, as in embryogenesis of sponges; also, reversal in order of genes or reversal of a chromosome segment.

invertebrates Animals without backbones.

involucre Whorl of bracts that subtend a flower or an inflorescence.

involuntary Nervous system Stimulates smooth and cardiac muscle and glands of the body.

involutions Infolding of membranes to increase surface area.

iodinophilous vacuole Vacuole within a protozoan that stains readily with iodine.

ion An atom or group of atoms that is electrically charged.

ionic bond Chemical bond formed when ions of opposite charge attract.

ionize To split a molecule into two or more parts, each part becoming an electrically charged particle.

ionizing radiation High-energy electromagnetic radiation or energetic subatomic particles released by nuclear decay.

ionosphere The lower part of the thermosphere.

ions Electrically-charged atoms that have gained or lost electrons.

iridocyte A fish skin cell that contains reflecting crystals made of guanine.

iridophore A chromatophore with light-reflecting crystals.

irregular symmetry Bilateral symmetry; having only one plane through which the structure (flower) could be cut to result in mirror image halves; zygomorphy.

irrigation The application of water to agricultural crops by transporting it to the crop through canals, pipes, and sprinklers.

irritability The ability of a cell to undergo a change in membrane potential.

irritants Corrosives (strong acids), caustics (alkaline reagents), and other substances that damage biological tissues on contact.

irruptive growth See Malthusian growth.

is composed; primarily calcium pectate and pectic acid.

Ischia Hip.

island arc A curved chain of volcanic islands that form along a trench.

island biogeography The study of rates of colonization and extinction of species on islands or other isolated areas based on size, shape, and distance from other inhabited regions.

island effects Reductions in species diversity caused by reduction in ecosystem area.

island of fertility The region in a desert ecosystem directly beneath a tree or shrub. Leaf fall and accumulation of litter result in nutrient cycling directly around the plant, even though the bare soil between plants may be depleted of nutrients.

isogametes Outwardly similar male and female gametes.

isogamy A condition in which gametes are equal in size.

isohaline Having the same salinity.

isolating mechanisms Any physical or behavioral characteristic that prevents successful exchange of genes between members of different species or populations.

isolecithal Pertaining to a zygote (or ovum) with yolk evenly distributed. Homolecithal.

isomer Organic compounds with the same molecular formula but different structures, functions, and properties.

isopods Small, dorsoventrally flattened crustaceans such as the sea louse.

isoprenes Five-carbon compounds that are the basic unit of terpenes.

isotonic Pertaining to solutions having the same or equal osmotic pressure; isosmotic.

isotope Alternate form of an element with a different number of neutrons but the same number of protons and electrons.

isozyme Different chemical forms of the same enzyme; thought to be important in adaptation to environmental extremes.

iteroparity The production of offspring by an organism in successive bouts. Contrast with semelparity.