JANUARY 2016. TERMAS DEL FLACO, CHILE

Termas del Flaco is a tiny hot springs resort at the end of a long gravel road leading eastward into the Chilean Andes, eighty kilometers southeast of a town called San Fernando.  The road is one-lane and dicey, as it follows the tumbling Tinguiririca River upstream, and remains closed at a police checkpoint until 4 pm each day, at which time outgoing traffic IMG 3586halts and incoming traffic may proceed.  Toward the head of the valley rises Tinguiririca Volcano, a shapely cone.  Around the hot springs are clustered a few simple clapboard hotels and rental cabañas for tourists and Chilean family getaways, a sleek compound for workers on the nearby hydroelectric project, and a derelict seven-story sanatorium that was built in the 1930s, for treating TB patients with salubrious mountain air, but abandoned after the discovery of penicillin, which worked better.  I’ve come here with two evolutionary biologists, John McCutcheon of the University of Montana and Claudio Veloso of the University of Chile.  They are armed and dangerous.

They are armed with butterfly nets, that is, and dangerous to a certain group of insects.  McCutcheon is a tall, lanky fellow who shaves his head bald and wears a blue cap in the antipodes sun.  Veloso is a compact man, slight as a jockey, with a gray stubble beard and a warm, sly smile.  Their mission in the Andes is to collect cicadas—those buzzing motorboats of the sky—for DNA sequencing, in order to explore a subject that’s much, much larger than the genetics of cicadas.  The bugs in question (yes, it’s okay to call cicadas “bugs,” because they’re classified within the order Hemiptera, true bugs) belong to several species within the genus Tettigades, endemic to South America.  Cicadas of that genus, McCutcheon and his lab people have discovered, contain prodigious anomalies of symbiosis: creatures within creatures, with reduced but complementary genomes interacting elaborately.  McCutcheon and one of his postdoc researchers, Piotr Lukasik, with Veloso’s help, and on a grant from the National Geographic Society’s Committee for Research and Exploration, have set themselves to exploring this mystery of boxes within boxes.

Piotr Lukasik is presently on the east side of the Andes, collecting Tettigades native to Argentina.  He will guide this project from the field to the laboratory, under the supervision of his lab boss, McCutcheon.  But the lab boss himself, who happens to be a robust youngish man with a taste for telemark skiing, ultimate Frisbee, and soccer, likes to get out in the field and swing a net with the rest of the gang.  So he and Veloso and I have taken the Chilean side of the mountains, working our way northward from Puerto Montt, beating the bushes (literally) in the low scrub vegetation of the foothills to catch cicadas.

P1000202Trust me, it’s not easy.  First you listen for the characteristic buzz.  Don’t be fooled by grasshoppers or crickets.  Then you skulk forward, net ready, trying to detect which twig of which branch of which bush holds the singing cicada.  When you spot it, you creep closer, then suddenly swoop.  McCutcheon, I’ve noticed, favors a full-bodied move with a forward and then a back stroke, folding the net closed, and sometimes including a leg kick for counter-balance.  Veloso’s style is more furtive and contained, coming up from below.  I walk along behind, like a dim-witted caddy, carrying a nylon cage full of captured and doomed cicadas.  I feel sorry for the little beasts, but I know their lives would be short after mating (like spawned-out salmon) even if they remained free, and that these individuals are giving their bodies for science.

P1000068No one knows exactly how many species of Tettigades may exist in South America, nor the details of their natural history, nor the length of their life cycles (seventeen years? thirteen years? or, probably, somewhat shorter), because few scientists have ever studied them.  McCutcheon got deeply interested in the group back in 2010, when, based on two individual specimens donated by a colleague, he and his lab made an unexpected finding: three different genomes lurk inside each cicada, not counting the cicada’s own.  Several more years passed before McCutcheon grasped the significance—that the insect harbors three different kinds of intracellular bacterial endosymbiont.  This relationship is far more intimate than ours with our famed microbiome, the menagerie of bacteria and other small things that live in our noses, our eyebrows, and our guts.  These three different microbes live not just inside cicadas but inside certain cicada cells, clustered within special organs adapted just for that purpose, from which sanctum they help the cicada and one another make a living.   All three bacteria exist with radically reduced genomes reflecting an obligate interdependence among the four creatures.  Cicadas need such symbiotic partners because they feed only on xylem sap, sucked from the roots of trees during their long, nymphal years underground.  Xylem sap is a lean diet, containing none of the amino acids that an animal needs for growth.  The bacterial endosymbionts process that thin gruel and exude the amino acids to make cicada development possible.  The cicadas in turn provide habitat and everything else necessary for the bacteria to thrive.  None of these four organisms could survive without the other three.  And two of the three bacteria, McCutcheon found, belong to the genus Hodgkinia, which has divided into distinct lineages over the course of its evolution inside the cicadas, sometime within the past 5 million years.

“Cicadas have a history of surprising me,” he says, as we sit waiting for the carabineros checkpoint to open.

IMG 3578The implications of this work on bacterial endosymbionts are vaster than you would expect, casting light on the possible origins of the eukaryotic cell—the kind of cell, with a nucleus and tiny organelles resembling bacteria, of which your body and mine and the bodies of all animals and plants and fungi are composed.  But that’s a tangled subject demanding deeper and broader treatment: the treatment I’m hoping to give it in my book-in-progress on the redrawn Tree of Life.  This little post is only intended to offer a teaser.

After a hard day of swinging their nets through the bushes, collecting cicadas, handling them carefully, pickling the poor critters in ethanol and a preservative called RNAlater, McCutcheon and Veloso walk down to the hot springs for a soak.  I linger in the hotel bar, drinking a couple tequilas and pondering this question: How in the world can I persuade you that cicada genomics is a lens through which to regard a subject so vast as the history of life on Earth?  But the tequila is good, Termas del Flaco is tranquil, and the answer will come.