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.