BACKGROUND : A substantial period of life after reproduction ends, known as postreproductive lifespan (PRLS), is
at odds with classical life history theory and its causes and mechanisms have puzzled evolutionary biologists for
decades. Prolonged PRLS has been confirmed in only two non-human mammals, both odontocete cetaceans in the
family Delphinidae. We investigate the evidence for PRLS in a third species, the false killer whale, Pseudorca crassidens,
using a quantitative measure of PRLS and morphological evidence from reproductive tissues.
RESULTS : We examined specimens from false killer whales from combined strandings (South Africa, 1981) and harvest
(Japan 1979-80) and found morphological evidence of changes in the activity of the ovaries in relation to age. Ovulation
had ceased in 50% of whales over 45 years, and all whales over 55 years old had ovaries classified as postreproductive.
We also calculated a measure of PRLS, known as postreproductive representation (PrR) as an indication of the effect of
inter-population demographic variability. PrR for the combined sample was 0.14, whereas the mean of the simulated
distribution for PrR under the null hypothesis of no PRLS was 0.02. The 99th percentile of the simulated distribution
was 0.08 and no simulated value exceeded 0.13. These results suggest that PrR was convincingly different from the
measures simulated under the null hypothesis.
CONCLUSIONS : We found morphological and statistical evidence for PRLS in South African and Japanese pods of false
killer whales, suggesting that this species is the third non-human mammal in which this phenomenon has been
demonstrated in wild populations. Nonetheless, our estimate for PrR in false killer whales (0.14) is lower than the single
values available for the short-finned pilot whale (0.28) and the killer whale (0.22) and is more similar to working Asian