Archive for the ‘zoology’ Category

Tastes are a privilege. The oral sensations not only satisfy foodies, but also on a primal level, protect animals from toxic substances. Yet cetaceans—whales and dolphins—may lack this crucial ability, according to a new study. Mutations in a cetacean ancestor obliterated their basic machinery for four of the five primary tastes, making them the first group of mammals to have lost the majority of this sensory system.

The five primary tastes are sweet, bitter, umami (savory), sour, and salty. These flavors are recognized by taste receptors—proteins that coat neurons embedded in the tongue. For the most part, taste receptor genes present across all vertebrates.

Except, it seems, cetaceans. Researchers uncovered a massive loss of taste receptors in these animals by screening the genomes of 15 species. The investigation spanned the two major lineages of cetaceans: Krill-loving baleen whales—such as bowheads and minkes—were surveyed along with those with teeth, like bottlenose dolphins and sperm whales.

The taste genes weren’t gone per se, but were irreparably damaged by mutations, the team reports online this month in Genome Biology and Evolution. Genes encode proteins, which in turn execute certain functions in cells. Certain errors in the code can derail protein production—at which point the gene becomes a “pseudogene” or a lingering shell of a trait forgotten. Identical pseudogene corpses were discovered across the different cetacean species for sweet, bitter, umami, and sour taste receptors. Salty tastes were the only exception.

“The loss of bitter taste is a complete surprise, because natural toxins typically taste bitter,” says zoologist Huabin Zhao of Wuhan University in China who led the study. All whales likely descend from raccoon-esque raoellids, a group of herbivorous land mammals that transitioned to the sea where they became fish eaters. Plants range in flavors—from sugary apples to tart, poisonous rhubarb leaves—and to survive, primitive animals learned the taste cues that signal whether food is delicious or dangerous. Based on the findings, taste dissipated after this common ancestor became fully aquatic—53 million years ago—but before the group split 36 million years ago into toothed and baleen whales.

“Pseudogenes arise when a trait is no longer needed,” says evolutionary biologist Jianzhi Zhang of the University of Michigan, Ann Arbor, who was not involved in the study. “So it still raises the question as to why whales could afford to lose four of the five primary tastes.” The retention of salty taste receptors suggests that they have other vital roles, such as maintaining sodium levels and blood pressure.

But dulled taste perception might be dangerous if noxious substances spill into the water. Orcas have unwittingly migrated into oil spills, while algal toxins created by fertilizer runoff consistently seep into the fish prey of dolphins living off the Florida coast.

“When you have a sense of taste, it dictates whether you swallow or not,” says Danielle Reed, a geneticist at the Monell Chemical Senses Center in Philadelphia, Pennsylvania. She was not involved with the current work, but co-authored a 2012 paper that found the first genetic inklings that umami and sweet taste receptors were missing in cetaceans, albeit in only one species—bottlenose dolphins.

Flavors are typically released by chewing, but cetaceans tend to swallow their food whole. “The message seems clear. If you don’t chew your food and prefer swallowing food whole, then taste really becomes irrelevant,” Reed says.

Thanks to Dr. Rajadhyaksha for bringing this to the attention of the It’s Interesting community.

WHILE KANGAROOS ARE known to munch grass, with the addition of fruit, flowers, sap and bark for tree kangaroos, who knew they favour an occasional bite of meat?

Sam Murray, who captured this curious footage, happened upon this western grey kangaroo (Macropus fuliginosus) tucking into a penguin on the beach at Cape Le Grande national park, located east of Esperance, WA in March 2013.

“We were walking down to the beach in the late evening before sunset, and we noticed a group of five or six kangaroos gathered on the beach. We started towards them and all the others were quick to hop away, but not this smaller one,” Sam says.

“He was really quite focussed on what he was doing. Even when we got to within a metre and a half of him, he wouldn’t stop eating.”

Kangaroos sometime eat meat
Professor Graeme Coulson, a zoologist at the University of Melbourne, explains that “All living macropods appear to be gentle herbivores. They [generally] lack the equipment to capture and kill other animals, or the digestive system to handle a meaty diet.”

While penguins aren’t a typical kangaroo snack, Graeme says that “Australia once had carnivorous macropods. The largest of these was Propleopus oscillans, which stood up to 2 m tall and had teeth that were well adapted to eating meat. This ‘killer kangaroo’ went extinct tens of thousands of years ago.”

While this footage may strike many as peculiar, Professor Tim Flannery, an expert mammalogist, says “This is unusual, I admit, but most herbivores will eat some protein if it’s available. Tree kangaroos will eat birds and even cows will chew on a bone.”

Graeme also recognizes that known herbivores are not all strict vegetarians. “White-tailed deer in the USA have been reported stealing trout from a fishing camp and removing nestlings from nests hidden in prairie grassland. Captive macropods are known to eat a wide range of foods, including chicken and lamb chops. This western grey kangaroo was simply taking advantage of an easy meal,” Graeme says.