[MARMAM] Publication: Eusociality, menopause and information in matrilineal whales

Hal.Whitehead at Dal.Ca Hal.Whitehead at Dal.Ca
Thu Jan 5 09:40:41 PST 2006


The following very short "Update" has recently been published:

McAuliffe, K and H. Whitehead. 2005.  Eusociality, menopause and 
information in matrilineal whales.  Trends in Ecology and Evolution. 
20:650.

It is available at: 
http://whitelab.biology.dal.ca/hw/McAuliffe_Whitehead_2005.pdf

As it is very short, the text is below.

Katie McAuliffe and Hal Whitehead (hwhitehe at dal.ca)


In their recent article in TREE [1], Foster and Ratnieks
make the interesting proposal that humans should be
considered ‘eusocial’ on the grounds that females spend a
substantial part of their adult life reproductively sterile
and help their close relatives [1]. The authors consider
that menopause, in this sense of the term, is unique
among vertebrates to humans. However, female shortfinned
pilot whales Globicephala macrorhynchus, killer
whales Orcinus orca, and probably a few other species of
cetacean, such as sperm whales Physeter macrocephalus,
have menopause with similar attributes to human females
[2–4]. In all these species, reproduction ceases at
approximately 40 years of age, although females routinely
live on for several more decades. Thus, cetaceans can also
be considered eusocial if the term can be used in the
context of within-individual classes of reproductives and
sterile helpers.

The cetacean species in which menopause is known or
probable all have matrilineal social systems in the sense
that most of the females spend their lives grouped with
their mothers when both are alive [5]. This correlation,
and the presence of menopause in these cetaceans which
(unlike modern humans) have not faced a dramatic recent
change in their living conditions, strongly indicate that
menopause is adaptive, and results from the tradeoff
between continued reproduction and assisting kin. Given
that menopause invariably occurs in these species, the
benefits of assisting kin must outweigh the costs of
reproductive cessation. What is not clear, however, is
how these menopausal grandmothers help. Among menopausal
cetaceans, assistance in foraging is not seen [5],
and at least in killer whales, defence against predators is
rare. Similar to human grandmothers [1], menopausal
cetacean females have experience that might benefit other
members of their matrilines. The value of this information
could explain why females in these species live about a
third of their lives as post-reproductive members of their
social groups.

The informative role of cetacean grandmothers is
consistent with an emerging body of information
indicating cultures in matrilineal cetacean species [6].
Thus, in both cetaceans and humans, the storage and
provision of information might be the primary function
of menopausal females and, thus, the driver of
eusociality [1].

References

1 Foster, K.R. and Ratnieks, F.L.W. (2005) A new social 
vertebrate? Trends Ecol. Evol. 20, 363–364
2 Marsh, H. and Kasuya, T. (1984) Changes in the ovaries of the 
shortfinned pilot whale, Globicephala macrorhynchus, with age and
reproductive activity. Rep. Int. Whal. Commn. 6, 311–335
3 Marsh, H. and Kasuya, T. (1986) Evidence for reproductive 
senescence in female cetaceans. Rep. Int. Whal. Commn. 8, 
57–74
4 Olesiuk, P. et al. (1990) Life history and population dynamics of
resident killer whales (Orcinus orca) in the coastal waters of British
Columbia and Washington State. Rep. Int. Whal. Commn. 12, 
209–243
5 Whitehead, H. and Mann, J. (2000) Female reproductive 
strategies of cetaceans. In Cetacean Societies (Mann, J. et al., 
eds), pp. 219–246,University of Chicago Press
6 Rendell, L. and Whitehead, H. (2001) Culture in whales and 
dolphins. Behav. Brain Sci. 24, 309–324





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