Mi­crobeads re­veal how lar­vae move, eat

Honolulu Star-Advertiser - - NEWS - By James Gor­man

It was one of those lovely nights when the moon­light on Mon­terey Bay makes you won­der: What would hap­pen if I put some mi­crobeads in with the starfish lar­vae?

At least that’s what you won­der if you are Manu Prakash, who runs a lab­o­ra­tory at Stan­ford Uni­ver­sity and is in­trigued by the way life is shaped by the laws of physics.

He was ac­tu­ally in a lab that night, with the bay just out­side. He and his col­leagues had col­lected the starfish lar­vae from the bay with other in­ver­te­brates that they were study­ing. ———

The lar­vae were from a species called the bat star, and they pro­pel them­selves, like many other small in­ver­te­brates, by the beat­ing of many, many hair­like cilia.

“They look like alien star­ships,” Prakash said.

He put the beads in the sea­wa­ter with the lar­vae un­der a mi­cro­scope to watch the tur­bu­lence they pro­duce as they swim. The beads, smaller than red blood cells, fol­low even small swirls of wa­ter and re­flect light, so the lines of wa­ter flow are vis­i­ble.

What he saw en­tranced him. Un­der the mi­cro­scope, cilia on the sur­face of a larva look “al­most like an or­na­ment — a line that goes around the edge of the an­i­mal,” Prakash said.

If they all beat to­gether, the larva moves as fast as it can. But if some patches of cilia beat against the pre­vail­ing mo­tion, they cre­ate vor­texes, swirling ed­dies that the re­searchers found bring al­gae close to the sur­face of the larva and, even­tu­ally, to its mouth. The larva varies its speed by the num­ber of vor­texes it cre­ates. It may make as few as two, in which case it swims along at a good clip and eats lit­tle, or as many as six, slow­ing down to munch the daisies, or al­gae. Af­ter a year of study, Prakash and his col­leagues re­cently pro­duced de­tailed math­e­mat­i­cal de­scrip­tions of how this all works.

The vor­texes also pull in par­ti­cles of a cer­tain size, so that the tiny an­i­mal gets the food it wants. This kind of fil­ter­ing is very dif­fer­ent from the sieves and nets that hu­mans use to sep­a­rate out par­ti­cles of a cer­tain size.

It is used by not just starfish lar­vae, but count­less bil­lions of other mi­cro­scopic in­ver­te­brates that fil­ter food from the oceans. Yet the re­search was never in­tended to ex­plain a bi­o­log­i­cal phe­nom­e­non, Prakash said, be­gin­ning only “with a very pure ques­tion of shape and beauty and form.”

The starfish larva varies its speed by the num­ber of vor­texes it cre­ates.

Newspapers in English

Newspapers from USA

© PressReader. All rights reserved.