BH sparrows adapt to lead pollution
Saturday, 22nd September, 2018
By Craig Brealey
The humble sparrow is so common that most of us barely look at them twice.
But scientists have and their research has led to an amazing discovery - the spoggies of Broken Hill, by natural selection, have adapted to lead pollution.
This study of the house sparrows’ genes is the first evidence of animals adapting to lead contamination in heavily polluted areas of Australia.
Professor Simon Griffith from Macquarie University in Sydney is part of the team that has studied the birds for the past five years.
They began by taking blood samples from sparrows in eastern Australia to see how they had adapted to the climate since being introduced to this country from England and Germany in the mid 19th century.
But Prof. Griffith, who has worked at the Fowlers Gap research station for the past 15 years, had another idea - what had happened to the sparrows in two of the most isolated and longest-established mining cities in the land - Broken Hill and Mount Isa?
“It struck me that in these two cities you have mining and well-documented issues with lead pollution,” he told the BDT yesterday when the study’s findings were publicly released.
“Having these samples gave us the opportunity to explore whether the birds had been naturally selected.
“Sparrows are good for that. All the populations in these towns are isolated genetically because they don’t travel very well through the outback and the desert.”
Once settled, a sparrow will range no further than a kilometre from its nest, he said. “They’re a sedentary bird.”
The sparrow was first spotted in this city in 1899. “There was a newspaper article at the time about their being seen and how they weren’t here six months ago,” said Prof. Griffith.
“They would have come up from Adelaide, spreading from town to town, and it probably took them 30 or 40 years to get to Broken Hill.
“Because they have been really isolated they are different to the sparrows in Wilcannia and Cobar so we know they haven’t come from the north or the east or the rest of New South Wales.
“The frequency of their genes in this town is not affected by other sparrows hopping in from other towns.
“They live intimately with people. You see them in your garden, at cafes, feeding in the gutter, rooting around in the dust for seeds. They live with us so they can tell us something about the contamination in the environment we share.
“It’s a little bit like the canary in the coal mine.”
The researchers found that the genes of the sparrows in Broken Hill and Mt Isa were different to those in other towns, which suggested that they had evolved to cope with the uptake of lead and zinc.
“The message is, there are organisms within our environment that are being affected by pollution and it raises the issue about how we are being affected by the same exposure.”
The researchers caught the birds in nets, measured and weighed them, took a blood sample, fixed an ID tag to a leg and set them free.
It was decided to catch them in the streets in different parts of the city so that a true reading of the lead pollution could be obtained; none were trapped on mine sites.
“This is just the first part of the study,” said Prof. Griffith.
“We would now like to measure the level of lead and we might expect to find how it has affected the sparrows’ behaviour, lifespan, physiology.”
But not all of the sparrows had genes that had adapted to lead and Prof. Griffith said it would be interesting to see what that meant for those that had.
“They should be fitter and live longer,” he said.
The study found 12 genetic variants in the birds from the mining cities.
The presence of these “outlier” genes suggests the sparrows in Broken Hill and Mt Isa had adapted to avoid the uptake of lead into the body and to counter its negative impact on neural and bone development.
This had reduced the amount of lead absorbed and prevented it accumulating in the organs.