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
Additional file 1: Mean ovary weights (g per kg of estimated body mass)
for non-pregnant, non-ovulating female false killer whales. Mean weight of
both ovaries in grams per kilogram of estimated body mass as a function of
age in a sample of non-pregnant, non-ovulating female false killer whales
from Japan (n = 55). We found no evidence for a trend in mean ovary
weight with age, though the power to detect any trends was low due to
the small sample size.
Additional file 2: Thickness of mammary gland in false killer whales in
relation to age and reproductive status. Thickness of mammary gland in
false killer whales from South Africa in relation to age and reproductive
status. Open circles are used to represent animals that were not lactating
(NL) and closed circles animals for those that were lactating (L). We fitted
a linear regression model to mammary gland thickness with age and
reproductive class (lactating, non-lactating) as explanatory variables. The
dashed horizontal line is the fitted mean mammary gland thickness in
non-lactating animals, and the solid line is the fitted mean thickness for
lactating animals. The grey bands around each fitted mean are the 95%
confidence intervals for the estimate. The figure shows that there is some
evidence for greater mammary gland thickness in lactating animals but
there was no evidence for a change with age in either.
Additional file 3: The number of corpora lutea that represent pregnancies
(CLP) and ovulation (CLO) as a function of age in false killer whales.
There were only 13 individuals in each age group (total n = 26) from the
combined dataset from Japan and South Africa so it is not possible to say
anything conclusive about the trend in the corpora lutea of pregnancy and
ovulation as function of age.
Additional file 4: Life table for Pseudorca crassidens. The life table for the
combined dataset for specimens from Japan and South Africa with 1 year
wide age classes, based on the modelled age frequency distribution. x is
the upper limit of the age interval, e.g., 7-8 years of age appears as 8. f is
the age frequency, the number of animals of each age class in the original
data, F denotes the total number of animals at least x years of age, fp
denotes the fitted values from the model for the number of animals in
each age class, Fp denotes the total number of animals aged x or older,
based on fp, l is the survivorship of animals of aged x, d is the frequency of
mortality of animals aged x, px is the age-specific survival rate, q is
the age-specific mortality rate, Lx is the number of individual-years lived
between the ages of x and x + 1, ex is the age-specific life expectancy,
the number of years an individual aged x is expected to still live, Pr is the
number of confirmed postreproductive animals.
Additional file 5: Fitted data from smooth regression models for
age-specific fecundity. Age-specific fecundity data had to be smoothed
to generate values for each single-year age class in the survival dataset to
generate the life table and carry out further analyses. It was not clear what
value should be used for the degrees of freedom, in other words how
smooth the plots should be, so we generated curves under 10 different
scenarios for the degrees of freedom; a: df=2.1, b: df=2.9, c: df=3.7, d: df=4.5,
e: df=5.3, f: df=6.1, g: df=6.9, h: df=7.7, i: df=8.5, j: df=8.9. The plot on the left
shows the curves for the combined dataset and the plots on the right
show the curves for the separate datasets.
Additional file 6: Dataset of fitted values of age-specific fecundity
under 10 different smoothing scenarios for the fecundity data from Japan.
Additional file 7: Dataset of fitted values of age-specific fecundity under
10 different smoothing scenarios for the fecundity data from South Africa.
Additional file 8: Dataset of fitted values of age-specific fecundity
under 10 different smoothing scenarios for the fecundity data from the
combined data from the two populations.
Additional file 9: The estimated PrR and the distribution of PrR under the
null hypothesis of no PRLS for false killer whales from Japan and South
Africa. The distribution of postreproductive representation, PrR, under the
null hypothesis of no postreproductive life span, PRLS, is shown with a
black line in each plot, with the 99% confidence interval shaded grey, and
the estimated PrR marked with a red dashed line. Each plot represents the
calculation of PrR using smoothed fecundity with ten different values for
the degrees of freedom in the model (i.e,. the smoothness); a: df=2.1, b:
df=2.9, c: df=3.7, d: df=4.5, e: df=5.3, f: df=6.1, g: df=6.9, h: df=7.7, i: df=8.5,