Baleen plates hang like fringed curtains from the upper jaw of a humpback whale. Photo by Duncan Murrell
Baleen whales are among the largest creatures on the planet. To learn more about how their unusual feeding structure helps sustain the mammals’ enormous size, two Guelph biologists needed to get a close-up — really close-up — view.
Prof. Doug Fudge, Integrative Biology, and Lawrence Szewciw, who completed a zoology master’s degree in 2009, worked with Guelph physicist Diane de Kerckhove to study the keratin-based feeding filter in baleen whales. Unlike toothed whales such as dolphins, baleen whales use comb-like plates in their upper jaw to strain fish and crustaceans from huge gulps of seawater.
In a paper published online in Proceedings of the Royal Society B, the U of G scientists show how calcium helps stiffen the keratin that makes up baleen. They’ve also helped to solve the puzzle of how whales immersed continuously in seawater can stiffen keratin that normally requires air-drying to harden into nail, hair, horn and other structures in land animals.
Szewciw is lead author. Another co-author is Geoff Grime at the University of Surrey Ion Beam Centre in the United Kingdom, where de Kerckhove analyzed fingernail-sized samples of the substance.
Keratin proteins are arranged inside baleen cells as intermediate filaments. Hanging like a curtain from the animal’s upper jaw, baleen plates are frayed along their ends into tapered bristles that sieve prey from the water. Baleen whales — including the blue whale, the largest animal on Earth — typically eat fish and shrimp-like crustaceans called krill.
Szewciw’s extensive mechanical tests in the lab showed that calcium salts like the ones found in bone lend reinforcement to baleen. And Sei whale baleen showed more calcification than that of two other species they studied. That makes sense, says Fudge. Unlike the minke and humpback, the sei whale feeds on millimetre-long plankton such as copepods. It needs fine but tough baleen bristles able to stand up to whale-sized forces.
“Calcification allows the bristles to be thin without compromising their ability to stand up to the water flowing past them,” says Fudge. Remove calcium from sei baleen, he adds, and the material loses about half of its stiffness.
To look at the calcium salts within baleen cells, he and Szewciw used light microscopes and electron microscopes. But they needed more sensitive equipment to get a detailed picture of the ratio of calcium and other elements. That’s when they turned to de Kerckhove.
She uses instruments to bombard samples with streams of protons to measure trace elements. This year, de Kerckhove is completing installation of a high-resolution proton microprobe in the MacNaughton Building that will be the only one of its kind in Canada. But when she started working with Fudge three years ago, she still needed to travel to Surrey’s ion beam facility. Using PIXE (proton-induced X-ray emission) analysis, she mapped the locations of calcium, phosphorus and sulphur in the material and determined relative amounts of each element.
In all three whale species, these elements are distributed in characteristic ways. “This is the first time calcification has been shown in different areas of the baleen plate,” says Szewciw.
Adds de Kerckhove: “It’s fascinating how nature has found the best and optimal way of using these mineral resources.”