In order to characterize the determinants of life span in C. elegans an accurate estimate of wild type life span is required as a baseline. However, estimates of the life span of N2 hermaphrodites under ostensibly identical conditions (monoxenic plate culture, 20 C) is highly variable, varying from 11.4 to 19.9 days (50% survival or mean life span)(1). Recent reports have given estimates of N2 hermaphrodite mean life span (same conditions) ranging from 11.8 days (2) to 20 days (3). In order to establish whether this reflects strain differences or environmental variation we measured the life spans of six N2 lines from different locations under identical conditions. These were the male and hermaphrodite stocks distributed by the CGC (here denoted CGCM an CGCH, respectively); the Riddle lab male and hermaphrodite stocks which should be identical to their CGC equivalents (denoted DRM and DRH); JW, an N2 strain obtained by Don Riddle from the LMB, Cambridge in the mid-1970s
; and BA, the Ward lab N2, which originated from the LMB in the mid-1970s
. In two or more trails using 50-60 animals each we observed the following strain variation in mean life span, measured from L4): CGCM, 17.3+0.3 (SEM) days; DRM, 17.4+0.6: CGCH, 16.0+0.3; DRH, 15.5+0.4 days; JW, 12.7+0.4 days; and BA, 14.0+0.7 days (see figure). Thus, CGC and DR male strains are distinct from CGC and DR hermaphrodite strains with respect to hermaphrodite life span. A similar pattern of variation was seen in male life spans, although the life spans of CGCM/DRM and CGCH/DRH males were not distinguishable. Which is the real wild type life span? Clearly , the established convention that N2 is wild type by definition, cannot answer this question. However, F1 progeny from crosses between JW and BA had a life span (50% survival) of 14.5+0.6 days, compared to 11.7+0.8 and 12.0+0.3 days for JW and BA, respectively (two trials). This suggests that JW and BA are mutant and that complementation is occurring in the F1 progeny resulting in a longer life span relative to the parental strains. This study underscores the importance of using the same strain of N2 as a starting point in aging studies, and as the genetic background in comparing mutations which affect life span. (1) Johnson and Simpson, CRC Handbook on the Biology of Aging 481-495, 1985. (2) Van Voorhies, Nature 360 456-458, 1992. (3) Kenyon et al, Nature 366 461-464, 1993.