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.

The Turn and the Screw

J. Sulston et al

Figure 1

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.
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 
Normal Mating 
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Horvitz and Sulston, unpublished observations).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.
Some of the cells involved in the various stages of mating have been 
identified mainly by laser ablation experiments as 
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]

Figure 1