September 2007

The Nation Reviewed

Ticked off

By Ashley Hay
Illustration by Jeff Fisher.
Illustration by Jeff Fisher.

The unlikely combination of a small seaside village in Crete and an Adelaide-born Kylie Minogue look-alike would not have suggested, to the casual observer, news from the frontiers of science. But in the northern summer Dr Catherine Hill of Purdue University, Indiana, announced to the Third International Meeting on Molecular and Population Biology of Mosquitoes, held at Kolymbari’s Orthodox Academy, that sequencing of the world’s first tick genome had been completed.

Clocking in at 2x109 base pairs (each pair forms a double helix of DNA), it’s two-thirds the size of the human genome. To finish sequencing a genome, Hill says later, is one of the few “woo-hoo moments” one gets in science. Not that the project is anywhere near over: in many ways, its real work can now begin.

Hill, 35, completed her PhD on diseases endured by lice - as opposed to diseases transmitted by them - in 1998 at the University of Adelaide. She then switched blood-sucking parasites to work with ticks as part of a post-doctoral position with a pharmaceutical company in the US. But she’s democratic in her attention to vampiric spongers: she works with mosquitoes too, and left that role to work in the laboratory behind the sequencing of the world’s first mosquito genome, just as that project got underway. It was, she says, an “addictive scenario. I saw what the release of that genomic information did for the mosquito community, and the way it revolutionised everything by giving us a better understanding of mosquitoes’ biology.”

All of which got her thinking about other parasites. If mosquitoes are “the world’s number-one vector in terms of human disease and mortality”, then ticks come in second. And, given that these two creatures last shared an ancestor about 500 million years ago (ticks are more closely related to spiders, scorpions and horseshoe crabs), “the tick genome would let us study a whole other branch of the evolutionary tree, and the only other group of blood-fed vectors apart from the mosquitoes. We’d look for some similarities between the two, but we’d also expect to find some big differences.”

When the US National Institute of Allergy and Infectious Diseases called for sequencing projects in 2004, Hill saw an opportunity for a tick genome to fill “a gaping hole in our knowledge”. She and her collaborators submitted their proposal that March, were funded in April and began work in May - “much faster than usual,” she says, “although actual sequencing didn’t start until 2005. We had to grow our ticks, get their DNA; we’d spent a lot of time thinking about which species to use.” Their choice, Ixodes scapularis, is the most important tick in the US, responsible for the transmission of Lyme disease, human babesiosis (a malaria-like infection) and human anaplasmosis (a form of cattle fever).

In Hill’s terms, sequencing a genome is “like taking a completed jigsaw puzzle, breaking it into its pieces and trying to remake it, or” - she pauses - “it’s more than that. It’s like taking a book, chopping it into words and bits of sentences, and trying to put them back together again. Parts of it are easy to work out and parts of it aren’t.” The end of sequencing means that all the pieces of the jigsaw, or all the book’s phrases, have been turned face-up to show what they are and perhaps how sections of them might fit together. Then the assembly and annotation, the decoding of what sits where and what each gene might do, can begin. “Once all the pieces of the genome have been sequenced, we start looking for genes that are interesting or genes that we already know from other genomes - from humans or fruit flies or mosquitoes - and that kind of investigation can go on forever.”

Things both expected and unexpected appear. Ticks stay attached to their hosts much longer than do mosquitoes, so the researchers expected to find mechanisms that let them achieve this undetected - and they did. On the unexpected side was “just how messy this genome would be, and how much of it would be made of repeated material: around 70% is moderately or highly repetitive. It must provide some kind of structural benefit or perform some regulatory function. In nature things aren’t designed to have anything extraneous, so why would you replicate all that DNA if it didn’t confer some kind of advantage?”

Fruit flies have given their genome what Hill calls “a bit of a spring-clean, throwing out everything they don’t need - and they’re recent arrivals on the evolutionary tree. But then, plants like wheat, corn and maize that are thought to have evolved more recently have bigger genomes. And we know that another tick, Rhipicephalus microplus, has an even bigger genome again - around three times the size of Ixodes scapularis, and twice the size of the human genome - and it’s evolved more recently too. These things are following a trend towards genetic obesity, but we don’t know what regulates the size of genomes or why so many ticks have such big ones.” Hill looks out to the horizon. “If there was such a thing as a genome genie,” she says, “Rhipicephalus would definitely be on my wish list.”

It was Francis S Collins, the leader of the first publicly funded human sequencing project, who talked about “human snobbery” and genome size. “Early on,” Hill explains, “people assumed that bigger, more complicated organisms would have more genes and more DNA. The first multi-cellular organism sequenced, a roundworm, had a tiny genome, so that seemed to bear out the theory; but it turned out to have about 18,000 genes. Then we started seeing that in insects. Fruit flies and mosquitoes have around 15,000 genes each; humans have only 30,000. Now scientists are getting better at not making those assumptions, and we’re starting to understand that there’s much more to genomes than just genes.”

Back on the evolutionary tree, there’s evidence that hard ticks - the ticks of most concern in terms of public health and veterinary issues - evolved in the piece of Gondwanaland that became Australia. “We think this because of the funny lineage of the main Australian tick, Ixodes holocyclus,” says Hill. “It’s a wacky little thing, and nasty too. It injects toxins during its blood-feeding which can cause paralysis or kill small animals. Sequencing Ixodes holocyclus to compare to the American tick would be great, because the more genomes you can align in a group, the more you can understand about how new species form and evolve.”

In the meantime, all that information about Ixodes scapularis will go out into the world so that, as Hill puts it, “the community can ask their favourite questions: Does ticks’ saliva have any possible vaccine candidates? What genes are involved in their resistance to insecticides? Like female mosquitoes, female ticks need to feed on blood to reproduce and this can quadruple their body size. How do they get rid of the water and ions and only use what they need?”

That’s the thing about science: any answer only generates more questions. “People think that if we sequence an organism’s genome, we can unravel its mysteries,” says Hill. “They don’t understand that it’s really only the beginning. There are no easy answers; only very slow unravelling and very small steps. In the end, this project has the same importance as all genome projects: it gives us a much better understanding of biology.” An assembly of the genome will be publicly released in a month, although a second, improved version could take several years to appear.

Hill’s eyes light up when discussing the tiny animals. “You know,” she says, “ticks are really cool. They don’t have antennae like mosquitoes; their smell receptors are on their feet. So they crawl up blades of grass and move their legs around like they’re doing a Mexican wave at the cricket. They’re trying to smell ammonia and CO2, trying to detect interruptions to heat or light, which would tell them a host is nearby.”

And her personal favourite? Catherine Hill looks out across the clear, calm water of the Aegean Sea. “Well,” she says at last, “they’re all kind of cute ... I like them all; but I like my mosquitoes too. I wouldn’t want to favour one over the others.”

Ashley Hay

Ashley Hay won last year’s Bragg UNSW Prize for Science Writing. Her last novel, The Railwayman’s Wife, won the Foundation for Australian Literary Studies’ Colin Roderick Award and the People’s Choice category in the NSW Premier’s Literary Awards. Her new novel, A Hundred Small Lessons, will be published this April. She lives in Brisbane.

There is nowhere quite like The Monthly. We are told that we live in a time of diminished attention spans; a time where the 24-hour-news-cycle has produced a collective desire for hot takes and brief summaries of the news and ideas that effect us. But we don’t believe it. The need for considered, reflective, long-form journalism has never been greater, and for almost 20 years, that’s what The Monthly has offered, from some of our finest writers.

That kind of quality writing costs money, and requires the support of our readers. Your subscription to The Monthly allows us to be the home for the best, most considered, most substantial perspectives on the state of the world. It’s Australia’s only current affairs magazine, an indispensable home for cultural commentary, criticism and reviews, and home to personal and reflective essays that celebrate and elevate our humanity.

The Monthly doesn’t just comment on our culture, our society and our politics: it shapes it. And your subscription makes you part of that.

Select your digital subscription

Month selector

From the front page

Illustration by Jeff Fisher

Letter from Dunkley

As a byelection draws the nation’s focus to the scrappy suburb of the author’s childhood, a visit reveals the damage wrought by the housing crisis

Kim Williams seen through window with arms half-raised

The interesting Mr Williams

At a time when the ABC faces more pressure than ever before, is its new chair the right person for the job?

Andrew Tate in dark sunglasses flanked by two men, attending his trial in Bucharest, Romania, July 2023

The Tate race

Online misogyny touted by the likes of Andrew Tate (awaiting trial for human trafficking and rape) is radicalising Australian schoolboys

Exterior of the Department of Treasury, Canberra

Tax to grind

Tax reform should not be centred on what we want, but on who we want to be

In This Issue

Open all hours

Beyond left & right in industrial relations

It's Bennelong time

On the campaign trail with Maxine McKew

Illustration by Jeff Fisher.

The other end of town

Words: Shane Maloney | Illustration: Chris Grosz

HMAS Melbourne & HMAS Voyager


More in The Nation Reviewed

Illustration by Jeff Fisher

Letter from Dunkley

As a byelection draws the nation’s focus to the scrappy suburb of the author’s childhood, a visit reveals the damage wrought by the housing crisis

Illustration by Jeff Fisher

Lines in the sand

By failing to take Indigenous knowledge seriously, a scientific paper speculating on the origin of WA desert ‘fairy circles’ misses the mark

Illustration by Jeff Fisher

Serving time (after time)

Australian citizens are being held in supervised facilities after they have served their prison sentence, amounting to indefinite detention

Illustration by Jeff Fisher

Might as well face it

Lively discussions take place around the country every week on ethical non-monogamy, love addiction and how much sex is too much


Online latest

Osamah Sami with members of his local mosque

In ‘House of Gods’, Sydney’s Muslim community gets to be complicated

Plus, Barnaby Joyce shines in ‘Nemesis’, Emma Seligman and Rachel Sennott deliver ‘Bottoms’, and Chloë Sevigny and Molly Ringwald step up for ‘Feud: Capote vs. The Swans’.

International Film Festival Rotterdam highlights

Films from Iran, Ukraine and Bundaberg were deserving winners at this year’s festival

Two women on a train smile and shake hands

‘Expats’ drills down on Hong Kong’s class divide

Plus, Netflix swallows Trent Dalton, Deborah Mailman remains in ‘Total Control’ and ‘Vanderpump Rules’ returns for another season

Image of a man playing music using electronics and the kora (West African harp)

Three overlooked albums of spiritual jazz from 2023

Recent releases by kora player John Haycock, trumpeter Matthew Halsall and 14-piece jazz ensemble Ancient Infinity Orchestra feel like a refuge from reality