Mate Searching inCaenorhabditis elegans: A Genetic Model for Sex Drive in a Simple Invertebrate

Abstract

Much of animal behavior is regulated to accomplish goals necessary for survival and reproduction. Little is known about the underlying motivational or drive states that are postulated to mediate such goal-directed behaviors. Here, we describe a mate-searching behavior of the Caenorhabditis elegans male that resembles the motivated behaviors of vertebrates. Adult C. elegans males, if isolated from mating partners, will leave the area of a food source and wander about their environment in an apparent search for a mate. When mating partners are present on the food source, males do not wander but remain with them. This behavior is sexually dimorphic for C. elegans and two additional male/hermaphrodite species studied; for these species, hermaphrodites leave food significantly slower than males. In contrast, for three male-female species examined, both males and females left food, in two cases with similar frequency, suggesting coordinate evolution of behavioral dimorphism with hermaphroditism. We use a quantitative behavioral assay to show that C. elegans male mate searching is regulated by signals from hermaphrodites and by physiological signals indicating nutritional and reproductive status. We identify genes in the serotonin, insulin, and sex determination pathways that affect the rate of mate searching. These genes may contribute to physiological and reproductive regulatory mechanisms. Our results establish C. elegans as a model genetic animal with a simple nervous system in which neural pathways leading to a motivated behavior may be genetically dissected.

TMC-1 attenuates C. elegans development and sexual behaviour in a chemically defined food environment

“…Taken together, these data demonstrate that TMC-1 has a developmental effect, (and to a lesser extent, an acute effect) on repressing both appetitive (mating drive) and consumatory (spicule insertion) sexual behaviours on CeMM. Mutations in insulin and serotonin pathway genes have been shown to perturb development and mating, in a bacterial food source 35,49 , whereas our results showed that the tmc-1 mutation displayed an opposite effect, which accelerates larval development and male mating on CeMM.…”

FMRFamide-Like Neuropeptides and Mechanosensory Touch Receptor Neurons Regulate Male Sexual Turning Behavior inCaenorhabditis elegans

“…First, a long-range pheromone acts to attract males (Chasnov et al, 2007). Next, a short-range and short-lived hermaphrodite signal triggers male searching behavior (Lipton et al, 2004). A distinct, diffusible hermaphrodite cue influences male locomotion (Simon and Sternberg, 2002).…”

Generation and modulation of chemosensory behaviors in C. elegans

“…Similarly, although a major regulator of worm behavior and development is levels of the constitutively produced dauer pheromone [8][9][10][107][108][109], the neurons that respond to pheromone are also not yet defined. Presumably, males and hermaphrodites also produce signals to attract or repel each other, but these cues and the relevant sensory neurons are unknown [3,4]. As "...behavior is messy" (with apologies to [110]), the development of technologies for imaging neuronal activity in single neuron types in vivo in response to an applied stimulus [111][112][113][114][115] may allow for more precise functional mapping of chemicals to sensory neuron types.…”

“…For the sake of brevity, I will concentrate solely on these behaviors in the hermaphrodite. I refer the reader to several excellent publications and references therein addressing C. elegans male chemosensory behaviors [1][2][3][4][5][6].…”