Dingoes have gotten bigger over the last 80 years, and pesticides might
be to blame

Date:
August 3, 2020
Source:
University of New South Wales
Summary:
The average size of a dingo is increasing, but only in areas where
poison-baits are used.



FULL STORY ========================================================================== Dingoes have gotten around 6-9 per cent bigger over the past 80 years,
new research from UNSW and the University of Sydney shows -- but the
growth is only happening in areas where poison baiting is used.


==========================================================================
The findings, published in the Biological Journal of the Linnean Society
over the weekend, compared the sizes of dingoes that lived in three
baited regions (Kalgoorlie, Pilbara and pastoral South Australia), with
those from an unbaited region that stretched from Northern Territory to
South Australia.

The scientists measured the skull size -- which is a marker of animal
size - - of nearly 600 dingo specimens originating from the sites.

"Skulls from the baited regions grew by about four millimetres since
poison baiting was introduced," says Michael Letnic, lead author of the
paper and professor in conservation biology and ecosystem restoration
at UNSW Science.

"This equates to roughly a kilogram in body mass." While both male
and female dingoes grew, female dingoes had the biggest growth spurt:
their skulls increased by 4.5 millimetres, which is almost 9 per cent
body mass. Male skulls grew by 3.6 millimetres, or 6 per cent body mass.



==========================================================================
The question is: why are dingoes in poison-baited areas growing?
"The most likely theory is that dingoes who survive baiting campaigns
have less competition for food," says co-author Associate Professor
Mathew Crowther from the University of Sydney.

He explains that dingoes' primary prey, kangaroos, have been shown to
increase in numbers when dingo populations are suppressed.

"With more food in abundance, dingoes' physical growth is less
restricted." The pesticide sodium fluoroacetate -- known as 1080
(pronounced 'ten eighty') - - is commonly used across Australia to
control dingo and other pest populations.



==========================================================================
A flavourless white powder, 1080 is usually stuck into meat baits and left
in dingo hotspots, often via helicopter drops. Baiting was rolled out in Kalgoorlie, Pilbara and pastoral South Australia over the 1960s and 70s.

Dingoes from the unbaited region -- which included Indigenous-owned
lands and conservation reserves -- saw no change in body size.

A predictable cycle This is not the first time a pesticide has been
linked to changes in animal bodies.

"Our interventions have consequences -- and they're actually quite
predictable consequences," says Prof. Letnic.

"Whatever pressures we put on animal populations -- be it pesticides
or not - - there will be side effects." Scientists usually observe
these impacts in invertebrate pests: for example, some insects -- like cockroaches -- are becoming more resistant to the insecticides used
on them.

However, this study is one of the first to show that vertebrates, like
dingoes, also change from pesticide use.

"Poison baiting campaigns could be favouring the survival of larger
dingoes," says A/Prof. Crowther. "Smaller dingoes need less poison for
a lethal dose, so are more likely to be killed by baiting. This leaves
the larger dingoes to survive and breed." As a result of their growing
size, the 1080 dose required to kill a dingo in the baited regions has increased since the toxin was introduced.

"The reaction to this finding may be to add more poison to the baits,
or to find a new poison," says Prof. Letnic. "But, eventually, the cycle
will start again." Looking for an explanation The exact mechanisms at
play are still unclear -- but a greater abundance of food post-baiting and dingoes adapting to the poison are likely the most influential factors.

Other factors that could have potentially led to the dingoes' growth,
like climate change or interbreeding with dogs, seem unlikely.

"We only tested dingoes in areas that have very low dog hybridisation
rates, making it highly unlikely that dog genetics are contributing
to the size growth," says Prof. Letnic. Most dingo-dog hybridisation,
he explains, occurs on the east coast of Australia.

The researchers also suggest that -- if anything -- a warming climate
would decrease dingoes' body size, as cooler conditions favour larger
animals.

Further studies that use a broader sample of dingoes from across Australia could help better understand the cause of the dingo body change.

In the meantime, the researchers hope to explore other ecological impacts
of 1080 baiting.

"Baiting is changing dingoes, so it could be changing other animal populations," says Prof. Letnic.

"Animals respond to human interventions, whether directly or
indirectly. The changes could well be adaptive, and we must think
about that."

========================================================================== Story Source: Materials provided by University_of_New_South_Wales. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. M Letnic, M S Crowther. Pesticide use is linked to increased body
size in
a large mammalian carnivore. Biological Journal of the Linnean
Society, 2020; DOI: 10.1093/biolinnean/blaa084 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200803105230.htm

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