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.

The Blob From California: A Gene For Mating Plug Formation

J. Hodgkin, T. Doniach, C. Kenyon

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.