Worm Breeder's Gazette 14(2): 71 (February 1, 1996)
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.
Division of Biological Sciences, University of Missouri, Columbia, MO 65211
We have examined the behavior of males of several wild type C. elegans strains which deposit a mating plug over the vulva after mating: AB2, RC301, CB4855 (aka 'Mr. Vigorous') and PA-2 (Hodgkin WBG 11-5: 60; 12-2: 82). AB2, isolated by Riddle and Bird (WBG 8-2: 52) in Adelaide, Australia, differs from the other three strains as follows. Among populations of AB2 males maintained for 3-4 days at 20 C in the absence of hermaphrodites mating plugs appear on 22-33% of the animals (three tests, 40-47 animals per test), invariably at the same position on the ventral side of the head. In the presence of hermaphrodites they do not do this. That plugs on hermaphrodites maintained with AB2 males were seen after only one day suggests that mate-less AB2 males grow more motivated and/or less discriminating with the passage of time. The ability of males to make plugs in the absence of hermaphrodites shows that males secrete the plug material themselves (or at least most of it) rather than stimulating the hermaphrodite to do so. To investigate whether the head-plugs are the result of onanistic or homosexual behavior, AB2 males kept in solitary confinement were examined, and no head-plugs were seen (sample size: 58). Although this suggests that AB2 males plug each other, it remains possible that AB2 males do in fact plug their own heads, but only in the presence of other males. Males maintained in the absence of hermaphrodites often congregate into writhing masses where each is probing the other with their copulatory bursa. Possibly only in the ensuing melee do AB2 males plug their own heads. To investigate this possibility single AB2 males were incubated for four days on spot plates with 20 lon-2(e678) males. 44 such AB2 males were examined and none received head-plugs, although in almost all cases clumps of males were observed. In five control sets of 18-20 AB2 males 1-4 males with head-plugs were seen (mean : 2.4/set, or 12.6%: thus, fewer males per plate results in a lower frequency of head-plugs). Given a 12.6% chance that each male will get a plugged head, the probability that none of 44 males gets a plugged head is p = 0.0026 (binomial test). No plugs were seen on the heads of the N2-derived, Lon males either. In a further test, 25 AB2 males were incubated with 25 lon-2(e678)unc-10(e102) males. Head-plugs were seen only on the AB2 males (two trails, two and four plug-headed AB2 males seen). The results indicate that AB2 males are attracted to one another, but not to Bristol males, and plug one anothers heads rather than their own. They also suggest that it is not that AB2 males are unusually attracted to other males, but rather that they in some way resemble hermaphrodites, possibly at the excretory pore, which is located ventrally at the level of the terminal bulb of the pharynx. Thus, it may be that N2 males are similarly attracted to AB2 males. Examination of AB2 males with head-plugs under Nomarski confirmed that the plugs were deposited over the region of the excretory pore. The duct and pore region of the cuticle appeared morphologically normal. An alternative explanation for these results is that AB2 males deposit small quantities of plug material all over each other (and also non-AB2 males), and this provokes onanistic head plugging. AB2 males were occasionally seen with their bursa onanistically applied to their head-plug, possibly in the process of adding material to it. Mating plugs are usually formed in the last stages of copulation (Barker, Anim. Behav. 48: 147-156 1995). This suggests the possibility that AB2 males copulate with each other via the excretory pore, although no sperm cells were observed in the excretory duct of head-plugged males. Alternatively, AB2 males might differ from the plugging strain used in the Barker study (a derivative of Cl2a) in being able to deposit a mating plug without prior copulation. Interestingly, although mating plug formation is dominant in crosses between CB4855 and N2 (Hodgkin et al. WBG 8-3: 36) and also RC301 and N2 (our observations), in crosses between AB2 or PA-2 and N2, plugging is recessive. However, in crosses between AB2 and AB1, a non-plugging strain also from Adelaide, plugging is dominant. This suggests the possibility that the dominance of the plugging trait may serve as a basis for identifying races among wild type C. elegans strains.