Worm Breeder's Gazette 14(5): 64 (February 1, 1997)
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.
MRC Laboratory of Molecular Biology, Cambridge CB2 2QH, England
Previously (WBG 12(2): 82) I reported that males from a wild isolate of
C. elegans, CB4855 (collected from Stanford, California) exhibit
substantially higher male fertility than males from the standard
laboratory wild strain, Bristol N2. These observations have been
confirmed and extended, as illustrated in the figure below (Hodgkin &
Doniach, 1997 (in press)). CB4855 (Sta) males achieve higher rates of
per diem paternity, and remain fertile for subtantially longer: N2
(Bri) males do not sire progeny for more than four days of adulthood at
20 degrees C, whereas Sta males can continue to sire progeny for nine
days or more.
In order to examine the basis of the difference between the
strains, six congenic lines were constructed, consisting of regions of
the Sta genome crossed onto a Bri background. One line was constructed
for each of the five autosomal cluster regions, and a sixth line was
constructed for the region around lon-2 on the X chromosome. Males
from these strains were tested for the ability to sire progeny for more
than four days. Three of the congenic lines exhibited little
difference in endurance from N2, but the LGIII line showed some
improvement, and the LGIV and LGX lines were significantly better,
though both were inferior to CB4855. Crosses between the LGIV line and
N2 produced males which also showed some superiority, indicating
dominance of the Sta trait mapping to this chromosome. Further crosses
have been carried out in the hope of localizing the factor(s)
responsible on LGIV, but so far these have yielded inconsistent results.
Both CB4855 and the derived LGX line exhibit a clumping phenotype
similar to the Bor (bordering) trait originally described by Cassada
(WBG 9(3): 29) in the Freiburg wild isolate, RC301, so it is possible
that this may be responsible for the improved performance of the LGX
congenic.
Many wild isolates, including CB4855, are noticeably smaller in
body size than N2. At late L4 stage, Sta hermaphrodites are
significantly shorter than Bri hermaphrodites, by about 8%. Crosses
between Bri and Sta strains, and derived congenics, indicate that small
size is determined by dominant or semi-dominant factors. Length
measurements were carried out on the Bri/Sta congenic lines, and the
congenic lines for LGV and LGX regions were found to be significantly
shorter than N2. Further mapping of the factor(s) responsible has not
yet been attempted.
Figure:
Average progeny sired per day by N2 (Bri) or CB4855 (Sta) males.
Five individual males from each strain, picked at late L4 stage, were
permitted to mate ad libitum with fem-1(hc17) young adult females.
The males were transferred to plates with fresh females at daily
intervals, until they became incapable of siring further progeny.
Total progeny sired on each day were counted.