[
Worm Breeder's Gazette,
2002]
N2 males live ~20% longer than hermaphrodites when maintained in isolation to prevent deleterious interactions with other worms (1). We have found that this is also true of 9/12 other C. elegans wild isolates tested. Increased male lifespan is therefore typical of C. elegans as a species, and not unique to N2. Why might this male longevity bias have evolved? One possibility is that it is a consequence of protandrous hermaphroditism, which is likely to lead to a skew in the male reproductive probability distribution to later ages. The evolutionary theory of aging suggests that this would result in the evolution of greater longevity in males. To test this idea, we measured the lifespans of both sexes of four dioecious and three more hermaphroditic terrestrial nematode species. However, males proved to be significantly longer-lived than hermaphrodites/females in all other nematode species tested, bar one. This disproved our hypothesis, and suggested that a male longevity bias is typical of free-living nematodes. The exception was C. briggsae, since hermaphrodites were significantly longer-lived than males in the three isolates tested, G16, HK104 and VT847. This could be an evolutionary consequence of the fact that following mating in this species, oocytes are preferentially fertilised by X-bearing sperm, so that outcross progeny are initially mainly hermaphrodites (2). Given that the frequency of males among progeny of selfing hermaphrodites is comparable to that in C. elegans (3), it seems likely that C. briggsae males are exceptionally rare in the wild. Potentially, this rarity results in reduced selection against deleterious mutations with male-specific effects, and the evolution of reduced male longevity. Interestingly, lifespans of males of dioecious species as a whole were greater than those of males of hermaphroditic species (p < 0.001); females were not longer-lived overall than hermaphrodites. Thus, the rarity of males in hermaphroditic species may lead to the evolution of reduced male lifespan.