Worm Breeder's Gazette 12(2): 82 (January 1, 1992)
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.
In the course of investigating relative male mating efficiencies, it was observed that males from the Stanford strain (CB4855, alias Sta-5 or Cal-5 )are able to sire substantially more offspring than standard Bristol (N2) males. The strain CB5855 was originally established by Tabitha Doniach in 1983, from a population living in a compost heap in Palo Alto. Lifetime virility assays were carried out for individual males by providing them with the company of six fresh young adult females daily, until successful mating ceased to occur. Total progeny from all the females were counted. In previous assays (e.g. Genetics 103: 43-64), mating partners were usually uncoordinated hermaphrodites, but the current assay (using fem-1 ( hc17ts )females raised under non-permissive conditions) is more convenient and probably a more stringent test of male prowess. In this assay, Bristol males sire no more than 2500 to 3000 progeny and become exhausted after four to five days, but Stanford males remain fertile for longer and can sire at least twice as many progeny. The current record holder, christened 'Mr. Vigorous', sired a grand total of 9469 offspring over a period of twelve days. He died six days later and has been preserved in a small block of agar, in recognition of his services to science.
The comparison of mating efficiencies was prompted by the fact that Stanford males are 'pluggers', laying down a gelatinous copulatory plug over the vulva during mating, whereas Bristol males are 'non-pluggers', and might be less fertile in consequence. The plugging trait is largely or wholly determined by the dominant allele plg-1 ( e2001 )on LGIII (see WBG 8-3: 36, etc.). However, congenic strains in which the plg-1 region from CB4855 has been crossed onto an N2 background do not show dramatically higher male fertility than normal N2 males, so plg-1 alone is not responsible for the difference in mating efficiency.
A further series of hybrid strains have been examined to investigate the basis of the high virility. In preliminary experiments, individuals have been assayed by a 'one night stand' assay, in which single young adult males were provided with six females for twelve hours. This assay obviously entails counting many fewer progeny, and the difference between Stanford and Bristol males is less conspicuous, although still apparent. F1 hybrid males were generated by crossing Stanford hermaphrodites with Bristol males, or vice versa. Both types of hybrid appear to be of high virility, indicating that the trait is caused by one or more autosomal dominant factors. The observation also suggests that the X chromosome does not greatly affect mating efficiency, although Stanford and Bristol strains differ in the clumping or 'bordering' trait, which appears to be sex-linked (as shown for the strain RC301 by Randy Cassada, WBG 9-3: 29).
Five additional congenic strains have been constructed, containing each of the autosomal clusters from CB4855 separately crossed onto an N2 background. None of these seems to be as virile as the parental CB4855 ,in these preliminary assays. Therefore, the high virility may be a multifactorial trait or may map to a non-cluster region. Experiments to define the basis of the difference are continuing, but indolently, awaiting the development of an assay that does not involve counting thousands and thousands of worms. Direct voyeuristic examination has not yet revealed any notable features in the technique of Stanford males.