Worm Breeder's Gazette 10(2): 140

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.

Wild Isolates and Mating Plug Formation

Jonathan Hodgkin

Figure 1

Many natural isolates of C.  elegans differ from the standard 
laboratory strain, N2, in copulatory plug formation: the males from 
these strains deposit a gelatinous blob over the vulva of a mated 
hermaphrodite, but N2 males do not.  Previously (Hodgkin, Doniach & 
Kenyon, WBG 8-3:36) we showed that the plugging trait, as discovered 
in the wild isolate Sta-5 (formerly named Cal-5) behaved as a 
Mendelian dominant, mapping to the locus plg-1 on LGIII.  We suggested 
that N2 had lost the plugging trait at some point during its 
scientific career.  A survey of natural isolates indicates that this 
is not the case; instead, it appears that many natural races are 
nonpluggers.  Male stocks were established from the 24 strains listed 
in the table, and males were tested for plug formation.  All non-
plugging strains were crossed with N2, and F1 heterozygous males 
tested: all were negative.  Thus, if non-plugging represents loss-of-
function, then all these strains carry recessive mutations of the same 
gene, plg-1.  Also, the plugging trait in two of the positive strains, 
AB3 and RC301, was examined genetically, by crossing with N2-derived 
mapping strains.  In both cases the trait behaved as a dominant 
mapping to approximately the same location as plg-1.In almost all of 
these races (or at least the stocks of them presently held in 
Cambridge) males are present at less than 1% of the individuals in a 
growing population, but these males are always potent and male stocks 
are easily established.  The only exceptions are the two Bergerac 
strains, RW7000 and N62, which are well known to produce males that 
mate very poorly.
It is not obvious what advantage or disadvantage is associated with 
plugging.  The trait is stable in culture: both plugging and non-
plugging strains maintain their character over hundreds of generations.

DNA from these strains has been examined using transposon probes.  
As previously reported by others (Katzenberg & Emmons, WBG 7-2:34; 
Riddle et al., WBG 8-2:52), the pattern of Tc1-hybridizing bands in a 
restriction digest can be used to classify the different races.  A Tc3 
probe can also be used, and gives similar results, where tested.  The 
data confirm (with one anomaly) and extend the classification of 
Katzenberg and Emmons, which is therefore used in the table.  The 
anomaly is our strain of 'PA1', which may have mutated into a high-
copy strain, but this is a preliminary result.  Note that for strains 
from the same locale, the plugging status and the racial 
classification are concordant.  Use of other probes, or different 
digests, might however subdivide some of the races.
As other workers have noticed (e.g.  Cassada, WBG 9-3:29), many of 
the different races exhibit slight behavioral and/or morphological 
differences from N2.  It is likely that they could be used as good 
sources of natural variability for experiments in population genetics, 
evolution, and so on.  Also, in view of the general intention to learn 
as much as possible about the biology of C.  elegans, it remains 
desirable to obtain further natural isolates of this species, 
especially from exotic parts of the world.  
I am grateful to Phil Anderson, Randy Cassada, Tabby Doniach, Ed 
Hedgecock, David Hirsh, Carl Johnson, Don Riddle and Dick Russell for 
collecting and providing the strains examined.
[See Figure 1]

Figure 1