Thermotaxis

The directed movement of an organism in response to a temperature gradient. Movement may be towards either a higher or lower temperature.

Male sexual development

The establishment of the sex of a male organism by physical and physiological differentiation through sex-specific developmental pathways leading to a fully fertile male of the species.

Sensory perception

The series of events required for an organism to receive a sensory stimulus, convert it to a molecular signal, and recognize and characterize the signal. This is a neurological process.

Hormesis

The process whereby a low exposure to a toxin or stressor produces a generally positive response in the animal that is the opposite effect produced in response to a higher exposure. This can be observed in cases where C. elegans is exposed to short doses of temperature stress during development. Under such limited exposures, animals exhibit a longer life span than animals reared at room temperature. However, extended exposure to thermal stress results in severely shortened lifespans.

Development

Development is the process of temporal and spatial control of gene expression that gives rise to a fully functional adult form of the organism. Studies of development in C. elegans have traced every cell from birth to final differentiated state in the developing nematode. These studies have elucidated cellular, genetic, and molecular mechanisms that control the division, growth, differentiation and morphogenesis of cells giving rise to tissues and organs in the nematode body. While most terminally differentiated cells can be traced by lineage back to a founder cell, there still remains a few cells types in the nematode with stochastic identity, relying on signals from the environment for their final identity.

Larval development

During post-embryonic development the temporal and spatial regulation of cellular and molecular mechanisms continue past embryogenesis to give rise to a fully functional adult. Post-embryonic development in C. elegans involves progression of the animal through four larval stages. Post-embryonic development involves further limited somatic cell division and cell death to bring the final total to 959 somatic nuclei in the hermaphrodite and 1031 in the male. Other remarkable processes during this period include cell migrations, neuronal rewiring, and adoption of final cell fates. Under conditions of stress, e.g., starvation, reproductive development ceases and the animal switch to a physiologically distinct developmental program to produce the dauer larva.

Signal transduction

Signal transduction begins with a stimulating event, such as a ligand binding to a receptor on the surface of the cell, and is followed by intracellular signaling steps that eventually trigger a response. In many cases the end response is modification of the regulation of gene transcription, but could also be the regulation of a metabolic process.

Adaptation

Adaptation occurs when a stimulus that once elicited a particular response, now elicits the opposite reaction. In C. elegans, this behavior has been shown through chemotaxis studies where extended exposure to an odor in the absence of food will result in a suppression of the chemotaxis response. In addition, by coupling an attractive stimulus to a starvation environment, the once attractive chemical is responded to as a repellent. However, these adaptations can be restored by brief exposure to the stimulus in the presence of food.

Response to toxicity

Exposure to a toxic substance can activate any number of processes that result in a change in state or activity of the organism. As a soil dwelling organism, C. elegans has evolved defenses against damaging substances in the soil environment and as such has proved to be an ideal organism for studying biological responses to toxins. These responses can occur at an organism level, such as invoking an avoidance behavior, or on a cellular level, such as activation of a cellular stress response. Cellular defenses have been shown to be invoked in response to reactive oxygen species, heavy metals, and toxin-induced unfolded proteins.

Response to pathogens

C. elegans is susceptible to disease or death brought on by a number of different microbial or fungal pathogens. While some of these pathogens, e.g., Drechmeria conispora and Microbacterium nematophilum are more specific to nematodes, other pathogens, e.g., Pseudomonas aeruginosa, Salmonella enterica, etc., are also pathogenic to humans. Genetic studies of C. elegans response to these pathogens have shown the nematode to employ three main mechanisms to defend against pathogen attack. First, as a behavioral response, C. elegans has been shown to use olfactory cues to distinguish different bacteria and respond with avoidance to those that are deemed harmful. Second, C. elegans has evolved physical barriers to infection that include a cuticle of collagen and chitin that protects the worm from its environment. This cuticle is also replaced at each larval molt, decreasing the worm's exposure to harmful bacteria that may be hitching a ride. In addition, C. elegans has evolved a pharyngeal grinder capable of pulverizing bacteria, keeping live bacteria from entering the gut. Third, C. elegans nematodes have inducible innate immune responses that are analogous to stress response pathways present in other organisms, for example, the PMK-1/P38 MAPK signaling pathway induced in response to Salmonella enterica.