Current Biology Vol 16 No 24
R1014
cairostris (Cuvier’s beaked whale)
and Mesoplodon densirostris
(Blainville’s beaked whale).
The authors find that both
of these species undertake
long, deep dives to capture
deep- water prey. Diving is highly
regular with most deep foraging
dives being followed by an
extended period of shallow dives
and slow travel and resting near
the surface. All foraging dives of
both species are considerably
longer than the estimated
aerobic dive limits, suggesting
that the whales return to the
surface with an oxygen debt.
“We propose that the shallow
dives and the long periods in
between foraging dives are
needed to repay the oxygen
debt before the next deep dive”,
the authors report.
Another consistent feature
of the dive profiles, the authors
find, is the slow ascent from
the deep foraging dives, which
remains a puzzle. The long
ascents, which are acoustically
inactive but involve active
swimming, appear to divert
substantial time away from
foraging, suggesting that the
animals are constrained by
some physiological requirement
or behavioural need that
prevents them from optimizing
foraging performance.
The depths now found at
which these whales forage may
also throw light on the effects
of naval sonar activities. Mass
strandings of whales associated
with sonar activity have revealed
animals with gas and fat emboli
in their bodies.
The researchers consider
whether sonar may disrupt the
ascent after deep dives and
that “the observed pathologies
may follow from a behavioural
response that has adverse
physiological consequences”.
They argue that regardless
of the precise reason for whale
strandings, “it is a pressing
issue to develop effective
mitigation protocols to reduce
the accidental exposure to
sonar”.
Mysteries: Tagging experiments have revealed the extreme depths and durations
of dives by two little-known species of small-beaked whales but many questions
remain. (Photo: courtesy of Nick Tregenza.)
Quick guide
Social-insect
fungus farming
Duur K. Aanen
1
and
Jacobus J. Boomsma
2
Which social insects rear
their own food? Growing
fungi for food has evolved
twice in social insects: once
in new- world ants about 50
million years ago; and once in
old-world termites between 24
and 34 million years ago [1,2].
The termites domesticated a
single fungal lineage — the
extant basidiomycete genus
Termitomyces — whereas the
ants are associated with a larger
diversity of fungal lineages
(all basidiomycetes). The ants
and termites forage for plant
material to provision their fungus
gardens. Their crops convert this
carbon- rich plant material into
nitrogen-rich fungal biomass to
provide the farming insects with
most of their food (Figure 1).
No secondary reversals to the
ancestral life style are known
in either group, which suggests
that the transitions to farming
were as drastically innovative
and irreversible as when humans
made this step about 10,000
years ago.
Why is insect fungus
farming interesting? The two
independently evolved agricultural
systems are impressive
examples of mutualistic
symbiosis — reciprocally
beneficial relationships between
different species. Some of the
insect societies that evolved
fungus farming are pinnacles of
social evolution. Cooperation and
social evolution within families is
now fairly well understood from
kin selection theory [3], but we are
only beginning to understand the
direct and indirect evolutionary
benefits of cooperation between
unrelated individuals of different
species [4].
What factors stop such
cooperative efforts from being
corrupted by cheating mutants