Worm Breeder's Gazette 7(2): 22
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
In the course of investigating the development of the C. elegans male (Develop. Biol., 78, 542-576 and 577-597 (1980)), we made a few random observations on the contribution to mating behaviour of various parts of the body. Since we are not planning to pursue this any further in the near future, here are the data as they stand. Some of these observations will be found also in Jonathan Hodgkin's paper on male mutants (submitted), but are included here for the sake of a coherent account. Microscopy: Mating can be watched at low resolution on plates under a dissecting microscope, and at high resolution on a standard agar mount under Nomarski optics. The latter method is tedious and uncertain, because the males do not perform well under a cover slip. Therefore, individual males were tested by the following procedure, which combines satisfactory mating with moderate resolution. The male was isolated from hermaphrodites for a few hours after the final moult. It was then placed on an NG plate with a very small lawn of bacteria and a single paralysed hermaphrodite (CB369). The male was chased gently into the lawn with a fine hair, and the plate was transferred to a Zeiss microscope preferably having an opalescent sheet instead of a condenser. Use of a low power objective (e.g., Neofluar 6.3 or 10) allowed the various stages of mating to be scored. Subsequently, the male was returned to its own plate, together with four CB369 hermaphrodites, and wild-type progeny were sought after two or three days. Normal Mating Behaviour: The male seems to locate the hermaphrodite more rapidly than would be expected by chance contact, and indeed preliminary evidence for a weak chemotaxis of males towards hermaphrodites has been obtained ( Horvitz and Sulston, unpublished observations). Upon reaching the hermaphrodite, the male frequently crawls forwards beneath it. This behaviour may explain the tendency of males to crawl through small holes in a mesh (Klass, WBG, 3 (1) 9-10 (1977)). As a result, the male's tail comes into contact with the hermaphrodite; he then backs sharply, curving his tail until the ventral side becomes apposed to the hermaphrodite, and continues backing, sliding along the hermaphrodite's body and turning sharply at its ends. When his tail reaches the vulva, he stops abruptly, sometimes after hunting back and forth, and attempts to insert his spicules. The gubernaculum and spicules are moved to a more transverse position, presumably by the action of the gubernacular erector muscles. As soon as the spicules enter the vulva, the intestino-rectal valve is drawn away from the vas deferens and against the dorsal cord by contraction of the sphincter muscle. The valve dividing the seminal vesicle from the vas deferens opens, and sperm begin to flow into the uterus of the hermaphrodite. The first part of the ejaculate consists only of fluid (presumably secretions from the wall of the vas deferens). A good seal is established between the protruded cloaca of the male and the dilated vulva of the hermaphrodite; the spicules, which remain more or less stationary, probably serve as anchors. After ejaculation, the male falls away and gradually retracts his spicules; there is a short refractory period, and the backing response returns gradually in the course of a few minutes. The male also begins the backing behaviour when his tail encounters other smooth objects, including other males and his own body. Solitary males can often be seen moving endlessly backwards with the tail clasping the head. Functional Analysis: Some of the cells involved in the various stages of mating have been identified mainly by laser ablation experiments as follows: Cephalic companions: The cephalic sensilla of the male differ from those of the hermaphrodite in being open to the outside and in being dually innervated (Ward, et. al., J. Comp. Neurol. 160, 313-338 (1975)) . The additional sensory neurons, known as cephalic companions (CEM's) , are therefore suspected of mediating the sex specific chemotaxis of males towards hermaphrodites. Sensory rays: In order to obtain an animal which lacks functional sensory rays, it is only necessary to prevent the development of the structural cells. In each of three very young L4's, either Rn.ap or Rn.app was ablated in every ray group. The resulting adults did not respond to tail contact with a hermaphrodite; however, they repeatedly turned towards it and passed beneath it, as would be expected if the putative chemotactic sense were still operating. Pre-anal ganglion: Loss of the P10.p-type lineage (see Dev. Biol. 78, 581) results in an animal which can back and turn but is unable to locate the vulva within five to ten minutes, however, such individuals usually yield progeny when allowed prolonged access to hermaphrodites ( perhaps by making use of the postcloacal sensilla). This suggests that the hook and its sensillum are used in vulval location, and indeed after ablation of separate components of this sensillum location is erratic though not usually abolished. Ablation of the three ventral hypodermal cells derived from P10 (P10.paaa, P10.paap and P10.papa) does not affect mating. Loss of the P11.p-type lineage, or of P11.pa, leads to very weak mating behaviour in which the various elements cannot be properly scored. This is probably due mainly to the loss of the motor- and inter-neurons derived from P11.pa. These animals sometimes yield progeny eventually. Muscle: Complete loss of male specific muscle, by ablation of the mesoblast (M) in a young L1, has surprisingly little effect upon initial mating behaviour. Such an animal backs, turns and locates the vulva essentially normally. The spicules, of course, do not move, and the shape of the entire cloaca is abnormal. U: Following ablation of rectal cell U (formerly called E) in a young male, the linker cell of the gonad is not destroyed in the usual way. Furthermore, K.a and K' fail to grow anteriorly, and apparently no functional connection is established between the vas deferens and the cloaca. Such an animal mates normally, except that its sperm remain in the vas deferens or leak into the body cavity. Gonad: Complete ablation of the gonad in a young L1 leads to an adult with entirely normal secondary sexual characteristics and normal mating behaviour. [See Figure 1]