Australasian Science — May-June 2017

(C. Jardin) #1

Joeys Neglected When


Mums Mingle
Having a social life comes at a cost for grey kangaroos, with research
published in Behavioral Ecology and Sociobiology finding that joey
survival is lower among mingling mothers.
Lead author Dr Wendy King of The University of Queens-
land’s School of Biological Sciences said young kangaroos that
spent more time with their mothers grew faster and gained more
weight than other joeys of the same age, and were more likely to
survive to adulthood.
“For kangaroo sons, spending time with their mother corre-
lates closely with receiving milk, and so sons are likely to benefit
nutritionally from this extra maternal care,” King said. “Some
daughters, however, associate closely with their mothers even if
the mother no longer provides milk, and must benefit in other
ways.”
King said that grey kangaroo mothers did not defend their
young from aggressive adult females, but mothers could reduce
harassment of their offspring just through their presence. “Juveniles
feeding alone with their mothers do not need to compete with
others for food, and have more time to feed and grow more rapidly,”
King said. “However, mother kangaroos rarely interact with their
young through activities such as playing and grooming, so it is
unlikely juveniles benefit from behavioural development or para-
site removal.”
Co-author A/Prof Anne Goldizen said the findings suggest
there is a cost to being sociable for female kangaroos. “That cost


may relate to young more easily losing their mothers when in a
large group,” she said. “This cost of being social raises the ques-
tion of why kangaroos usually forage in groups.”
The study of 129 kangaroo offspring aged 10–21 months took
place over 6 years at Wilsons Promontory National Park in
Victoria. While previous studies have investigated the links between
mother–offspring relationships and offspring growth and survival
in mammals, none have done so in marsupials. King said the
mother–offspring bond in macropods such as kangaroos appeared
to be quite special.

An international team of astronomers has spotted a massive inactive
galaxy from a time when the universe was only 1.65 billion years old.
Astronomers expect most galaxies from this epoch to be low-
mass minnows, busily forming stars. However, team leader
Prof Karl Glazebrook of Swinburne University’s Centre for
Astrophysics and Supercomputing says this galaxy is an inactive
“monster”.
The researchers found that within a short time period this
massive galaxy, known as ZF-COSMOS-20115, formed three times
more stars than the Milky Way during an extreme starburst event.
However, it stopped forming stars only a billion years after the Big
Bang to become a “red and dead” galaxy – common in our universe
today, but not expected to exist at this ancient epoch.
The galaxy is also small and extremely dense, with 300 billion
stars crammed into a region of space about the same size as the
distance from the Sun to the nearby Orion Nebula.
Astrophysicists are still debating just how galaxies stop
forming stars. Until recently, models suggested that dead galaxies
such as this should only exist from around three billion years after
the Big Bang. “This discovery sets a new record for the earliest
massive red galaxy,” Glazebrook said. “It is an incredibly rare find
that poses a new challenge to galaxy evolution models to
accommodate the existence of such galaxies much earlier in the
universe.”

The research, published in Nature, took deep spectra at near-
infrared wavelengths to seek out the definitive features signifying
the presence of old stars and a lack of active star formation. “By
collecting enough light to measure this galaxy’s spectrum, we
decipher the cosmic narrative of what stars and elements are present
in these galaxies and construct a timeline of when they formed their
stars,” said co-author Prof Vy Tran of Texas A&M University.
“This huge galaxy formed like a firecracker in less than 100
million years, right at the start of cosmic history,” Glazebrook
adds. “It quickly made a monstrous object, then just as suddenly it
quenched and turned itself off. As to how it did this, we can only
speculate. This fast life and death so early in the universe is not
predicted by our modern galaxy-formation theories.”
Co-author Dr Corentin Schreiber of Leiden University
speculates that these early firecrackers are obscured behind a veil
of dust, and that future observations using sub-millimetre wave
telescopes will spot them. “Sub-millimetre waves are emitted by
the hot dust which blocks other light, and will tell us when these
firecrackers exploded and how big a role they played in
developing the primordial universe,” Schreiber said.
With the launch of the James Webb Space Telescope in 2018,
astronomers will be able to build up large samples of these dead
galaxies due to its high sensitivity, large mirror, and the
advantage of no atmosphere in space.

MAY/JUNE 2017 | | 13

The Monster Galaxy that Grew Up Too Fast


michaklootwijk/Adobe
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