Worm Breeder's Gazette 8(3): 36
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.
Males from several wild isolates of C. elegans exhibit a detectable difference from males of the Bristol N2 strain: when mated with an hermaphrodite of any genotype the males lay down (or conceivably stimulate the hermaphrodite to secrete) a gelatinous acellular blob or plug over the vulva. The plug increases in size with repeated matings, up to about 40 microns in diameter. It remains in place for several days after formation, not being dislodged by egg-laying. Hermaphrodites from a plugging strain of C. elegans from Sara Doniach's compost heap in Palo Alto) were crossed with him-5( e1490) males, and a him-5 strain carrying the plugging trait was recovered as a F2 segregant. The trait behaves as a single autosomal dominant mutation, and was mapped to a locus tightly linked to unc-69 III, designated plg-1 (for 'mating PLuG formation'). The dominant plugging allele has been designated e2001. It is probable that N2 is in fact a mutant, because the plugging trait is seen in other wild isolates and in other species such as C. remanei, and also because e2001 is dominant. The e2001 allele may therefore represent the true wildtype, but since all C. elegans genetics is based on N2, the plugging trait is regarded as a dominant mutation. N2 probably carries at least one other mutation, affecting burrowing behavior, because most wild isolates of C. elegans exhibit a strong burrowing tendency not seen in N2. The genetic basis of the burrowing trait is not known. The fact that N2 may be mutant in some properties is not surprising in view of its long sojourn in the unnatural environment provided by the worm community. N2 may also have lost other abilities; for example, it could be that some N2 sensory receptors are genuinely nonfunctional, rather than functioning as detectors for an unknown stimulus. We call the blob a mating plug by analogy with the plugs formed during copulation in many animal species: insects, rodents and so on. The plugs in these animals act to prevent sperm loss and to block further insemination, but as yet we have no evidence that C. elegans plugs have these functions. The mating efficiency of plg-1;him-5 males appears to be higher than that of him-5 males, but not dramatically so. Also, an N2 male can successfully fertilize a hermaphrodite after it has been plugged. So, the function of the blob is not clear. It is potentially useful to worm breeders as a means of showing that copulation has occurred, even in the absence of successful fertilization. For example, C. remanei males will plug C. elegans even though no progeny are produced.