Processes on the abdomen of Daphnia that close the brood chamber.

How commonly a taxon or group of taxons occurs. Usually used without units. More precise terms are distribution, prevalence, and density.

1. Process by which populations undergo modification so as to function better than their immediate ancestors in a given environment. 2. Any developmental, behavioral, anatomical, or physiological characteristic of an organism that improves its chances for survival and propagation in its environment. See also Local adaptation.

Part of the phenotypic variance of quantitative traits, such as body size or age at maturity. The additive genetic variance is proportional to the expected change attributable to selection and is used to calculate the heritability.

One of a series of possible alternative DNA sequences at a given locus.

Gene product of one of several alleles that have the same function but differ in their amino acid sequence and therefore in their physio-chemical properties so that they migrate different distances in an electrophoretic assay. They are used as genetic markers to identify a genotype.

Form of asexual reproduction. Offspring is formed without meiosis and fertilization. Daughters are genetically identical to their mothers.

Occurs when an adaptation in one species reduces the fitness of individuals in another species, thereby selecting in favor of counter-adaptations in the other species. These counter-adaptations, in turn, select in favor of new adaptations in the first species. Arms races are a form of antagonistic coevolution. See also Coevolution.

See Phyllopoda.

Space between the thorax and the dorsal carapace of Cladocera in which the oviduct ends and the eggs develop. It is in direct contact with the exterior medium.

Hard shell of crustaceans.

One of the pair of small appendages of the Daphnia midgut. They are sealed from the gut by a membrane and may participate in the production of digestive fluids.

Order of the Entomostraca. They have a bivalve shell covering the body but not the head, four to six pairs of legs, and two pairs of antennae used for swimming. They mostly inhabit fresh water. See also Entomostraca.

Group of organisms that have arisen from a single female by asexual reproduction and are therefore genetically identical. A clone is often called an iso-female line.

Changes in the genotypes of two or more species that are a direct consequence of the species’ interaction with one another. Coevolution can occur among mutualists and host--parasite pairs, as well as among entire groups of interacting organisms (e.g., pollinator--plant systems).

Aquatic arthropods characterized by the presence of biramous appendages and two sets of antennae. Examples include crabs, lobsters, copepods, barnacles, shrimps, and waterfleas.

Mode of reproduction in which phases of parthenogenetic (asexual) and sexual reproduction alternate. Several asexual generations may follow a sexual generation. Found in Cladocera, Rotifera, and aphids.

Seasonal change in phenotype of many plankton species. For example, some Daphnia species produce spines to protect themselves against predators during the summer season.

Population that is sufficiently isolated so that it can be considered an evolving unit. Deme is more typically used by evolutionary biologists.

Indicates that the intensity of a process depends on the density of a population. When fecundity or individual survival in a population are negatively dependent on density (e.g., parasite-induced host mortality), the process could potentially regulate population density. Transmission of horizontally transmitted parasites is usually host density dependent.

Behavior by which the zooplankton maintains a particular vertical distribution in relation to the stratification of the water (light, temperature, food, predation pressure). See also DVM.

Resting period during unfavorable conditions, e.g., during winter freezing or during draughts.

Special case of depth selection behavior in which the preferred depth changes in a diel (daily) pattern.

A change in response to exposure to some agent attributable to a change in that agent’s concentration. For example, the increase in virulence or infection risk for hosts during exposure to increasing parasite spore doses.

Method to study the movement of charged molecules in solution in an electrical field. The solution is generally held in a porous support medium such as cellulose acetate or a gel made of starch, agar, or polyacrylamide. Electrophoresis is generally used to separate molecules from a mixture based upon differences in net electrical charge and also by size or geometry of the molecules, dependent upon the characteristics of the gel matrix.

Permanent presence of a parasite population in a host population. Compare Epidemic.

Symbionts located within the body of the host. They may be intra- or extracellular.

1. Membranous external walls surrounding the resting eggs (usually sexual eggs) of Cladocera. 2. Resting stage of Cladocera consisting of one or two resting eggs, surrounded by a membranous external wall.

Organism that lives attached to the body surface of another organism. Sometimes regarded as ecto-parasites. In zooplankton, epibionts are often ciliates, algae, bacteria, and fungi.

Sudden, rapid spread or increase in the prevalence or intensity of an infection. Compare Endemic.

Study of infectious diseases and disease-causing agents on the population level in a parasitological context. It seeks to characterize the disease’s patterns of distribution and prevalence and the factors responsible for these patterns. In a more applied context, it also strives to identify and test prevention and treatment measures.

Changes in allele frequencies over time.

Study of epidemiology in replicated experimental populations.

Study of evolutionary change in replicated experimental populations.

Extent to which an individual contributes its genes to future generations in relation to the contribution of other genotypes in the same population at the same time.

Occurrence of two or more genotypes in a population.

Degree to which members of a population differ at certain loci.

Genetic composition of an organism as distinguished from its physical appearance (phenotype).

Phenomenon describing increased growth (or large body size) of certain members of a population. Sometimes parasitized hosts show gigantism compared with nonparasitized conspecifics. In this case, gigantism is often associated with parasite-induced host castration.

The living place of a population, characterized by its physical, chemical, and/or biotic properties.

Wormy parasite. Helminths are not a taxonomic group.

Parasite transmission between infected and susceptible individuals or between disease vectors and susceptibles.

See Infective dose 50%.

Defense that is only expressed in response to a specific stimulus.

1. Number of parasite individuals in an infected host individual. 2. Mean number of parasites within infected members of the host population.

Number of parasite transmission stages (exposure doses) that results in 50% of hosts being infected.

Discrete stages of development in insects and crustaceans, whose growth is accomplished by molting.

Chemical cues released from predators and recognized by the prey. Kairomones from several different predators have been reported to lead to adaptive morphological and life history changes in Daphnia.

Genetic differentiation attributable to selective forces specific to the local environment. Local adaptation is best demonstrated by showing that immigrant genotypes are inferior to resident genotypes. Locally adapted parasites usually show higher levels of damage and have higher levels of transmission stage production in their local hosts.

Parasite that usually does not multiply within its definitive hosts but instead produces transmission stages (eggs and larvae) that pass into the external environment or to vectors. Macroparasites are typically parasitic helminths and arthropods. The key epidemiological measurement is generally the number of parasites per host.

Concept used to describe the transmission dynamics of infectious diseases. Mass action transmission occurs at a rate directly proportional to the number or density of both susceptible individuals and infected individuals in the population.

See Shell gland.

Substance used by invertebrates to (among other functions) encapsulate parasites. See proPO system.

Group of partially isolated populations belonging to the same species. Migration among subpopulations is important for the ecological and evolutionary dynamics of a metapopulation.

Parasite that undergoes direct multiplication within its definitive hosts (e.g., viruses, bacteria, fungi, and protozoa). Microparasites are characterized by small size and short generation times. The key epidemiological variable, by contrast with macroparasites, is whether the individual host is infected.

Place in the genome where a short string of nucleotides, usually two to five bases long, is repeated in tandem. The number of repeats at any given locus is usually highly variable (many alleles) in a population and can be used for DNA fingerprinting.

State of ill-health produced by a disease. Includes aspects of reduced fecundity, lethargy, and other signs of disease.

Infection in which an individual is infected by parasites of more than one species or more than one genotype of the same species.

See Richness.

1. Disease-causing organism. 2. Organism exhibiting an obligatory, detrimental dependence on another organism (its host). Conceptually, parasite and pathogen are the same. Endoparasites live in the host’s interior (They may be intra- or extracellular). Ectoparasites live on the surface of the host.

Development of an organism from an unfertilized egg. See also cyclic parthenogenesis.

Disease-causing microorganism, such as viruses, bacteria, and protozoa. In the context of this book, equivalent to parasite.

Phenotypic variation expressed by a single genotype in different environments.

Behavior that is expressed in the presence of light stimuli.

Order of Entomostraca including a large number of species, most of which live in fresh water. They have flattened or leaf-like legs, often very numerous, which they use for swimming. Also called Branchiopoda.

Changes in the population size through time. Also used to describe change in the demographic structure of the population (sex ratio, age and size structure, etc.).

Group of interbreeding individuals and their offspring. In asexual species, this definition cannot be applied; in this case, a population is a group of phenotypically matching individuals living in the same area.

Measure of population growth. The instantaneous rate of increase of a population or genotype. It is used as a measure of fitness.

Defense reaction of prey triggered by the presence or action of a predator so as to reduce the expected damage of the predator.

An animal that kills its victim, the prey item, and then feeds on it to subsist until the next kill.

In helminth infections, time period from infection until a female starts to produce eggs. It is equivalent to the latent period in microparasitic infections.

Proportion of host individuals infected with a particular parasite. Often expressed as a percentage. A measure of how widespread an infection or disease in a host population is. Sometimes used to indicate the proportion of infected hosts in a sample with any parasite species. In many studies, prevalence is measured only in a certain fraction of hosts. In zooplankton studies, often only adult hosts or adult females are considered. Prevalence is usually underestimated in field samples because new infections may escape detection by the investigator.

Female producing offspring or eggs for the first time.

The proPO activating system plays several functions in invertebrate immunity and is considered one of the most important defense mechanisms. The oxireductase phenoloxidase (PO) is part of a complex system of proteinases, pattern recognition proteins, and proteinase inhibitors that constitute the proPO activating system. It is thought to be part of the invertebrate’s immune response against parasites because the conversion of proPO to active enzyme can be initiated by molecules from invading microorganisms. PO is the final enzyme in the melanization cascade, which is a common response to parasite entry in many invertebrates. During a successful immune reaction, melanin encapsulates the invader and kills it.

Hypothesis that states that the adaptive importance of genetic recombination is to create genetic variation among the offspring, which is important in confrontation with coevolving parasites.

Reduction in host susceptibility to infection.

See Ephippium.

Number of parasite species per host individual or the mean number of parasite species within members of the host population.

Process by which certain phenotypes are favored over other phenotypes. Selection leads to adaptation. Clonal selection is found when clones differ in their lifetime reproductive success and is usually seen in the form of genotype frequency changes.

Allocation of resources into male and female functions. For Daphnia, which reproduce asexually for most of the life cycle and thus produce mostly daughters, sex allocation refers to the extent to which males and resting eggs are produced.

Organ found in Daphnia that may have a role in excretion and/or osmoregulation.

Strategy of parasites and predators to come in contact with their host or prey. It relies on the antagonist being active, while the parasite or the predator is waiting motionless. Many parasite transmission stages can endure long time periods before they are activated by an encounter with the host.

Describes the observation that only a subset of hosts is susceptible to infection. A high specificity refers to the observation that only a few host lines can be infected by a given parasite.

In a parasitological context, transmission stage.

Spores resting in soil or sediments.

Number of spores or sporophorous vesicles of a parasite (e.g., microsporidium, bacterial) in a host individual. It is a measure of parasite infection intensity and may be used to calculate parasite multiplication rate within the host.

Accessible to or liable to infection by a particular parasite.

Organism living together with another organism. This includes mutualists, parasites, and commensals.

Unescapable compromise between one trait and another. In evolutionary biology, it is important because a negative genetic correlation between two traits, both of which affect fitness, limits their response to selection (a fitness-increasing change in one trait is coupled with a fitness-decreasing change in the associated trait).

The process by which a parasite passes from a source of infection to a new host. Horizontal transmission is transmission by direct contact between infected and susceptible individuals or between disease vectors and susceptible individuals. Vertical transmission occurs when a parent conveys an infection to its unborn offspring, as in HIV in humans.

Life stage of a parasite that is able to cause a new infection.

See Diel vertical migration.

Parasite transmission from parent to offspring.

Morbidity and mortality of a host that is caused by parasites and pathogens. More specifically, it is the fitness component of the parasite that is associated with the harm done to the host.

Intracellular bacteria that commonly infect a variety of arthropod species and induce various changes in its hosts’ life history, sex allocation, and sex ratio.

Animal component of small aquatic organisms that mainly drift with water movements. They include protozoans, small crustaceans, and in early summer, the larval stages of many larger organisms.