Tag Archives: hands

Sea lion whiskers can move like human fingertips: here’s how we found out

Credit: Pixabay.

Humans have amazing fingertips. They are sensitive and can be moved over objects to feel its softness, texture, size and shape. These movements are both complex, and “task-specific”. This means that you adopt different movements depending on what you want to feel about an object. We squeeze or push objects to judge softness, and feel around the edges of objects to judge size and shape. And if you wanted to feel the texture of an object, you would sweep your fingertips over the surface.

Being able to adopt different movement strategies shows that we can precisely control our fingertip movements and draw on our past experiences in order to pay attention to important aspects of an object – the edges of shapes and the surfaces of textures, for example. This means that we have a high level of control over our sensory perception, and we call this active touch sensing.

Touch sensing in mammals

Most mammals do not have as moveable or sensitive fingertips as humans. Instead they have whiskers, which are touch sensitive hairs on their faces, and used to guide locomotion, foraging for food and to explore objects.

Neuroscientists have been studying whiskers for decades, especially in laboratory rats and mice, trying to understand how signals from the whiskers are processed in the brain. But only now are we realising that whiskers are also moved with amazing strategies, just like our fingers.

Rats, mice, and some other mammals, can move their whiskers in a to-and-fro scanning motion called “whisking”. Whisking is one of the fastest movements that mammals can make, occurring up to 25 times per second in mice.

When rats and mice contact objects they also adopt other whisker movements. These include bunching up their whiskers to make more of them touch a surface, making light touches to enable clearer signals against a surface, and slowing down whisker movements so they contact the surface for longer.

But no one knew whether animals could adapt their whisker movements specifically for different tasks.

Such “task-specific” movements would be an exciting discovery as it would indicate a precise level of control over their sensors and perception.

Choosing a candidate species

The first step in answering this important question was to choose a likely candidate species for our investigation.

Pinnipeds, including seals, sea lions and walruses, have whiskers that are particularly thick and long, making them easier to measure than those of smaller mammals such as mice.

They also have some of the most sensitive whiskers of any mammal – they can detect textures and shapes to the same sensitivity as human fingertips, even in cold water when our fingers would go numb.

They are also moveable. We have previously found that California sea lions make the largest and most controlled movements with their whiskers, when compared to harbour seals and Pacific walruses.

Those factors, plus their ability to perform object-discrimination tasks – where they could distinguish between objects based on size and shape – made California sea lions the ideal subject for our investigation on task-specific whisker movements.

Our work with Lo

For our study we used a sea lion, Lo, for the full complement of experiments. Having only one individual is common in marine mammal studies, but it does put pressure on the investigators to collect good quality and highly quantitative data from that one individual.

Lo was trained to complete a texture-discrimination task using only her whiskers.

She had to find a medium-textured, fish-shaped object among other distractor fish. She also completed a size-discrimination task of finding a medium-sized fish amongst other distractors, and a visual task of finding a grey fish amongst other coloured distractors (sea lions use very small whisker movements in visual tasks).

Lo was filmed doing the tasks thousands of times, and her whisker and head positions were tracked in the video footage.

Looking at the data and the video footage it was clear that Lo made task-specific movements with her whiskers. She made sweeping movements over textured surfaces, and felt around the edges of the different sized shapes. These specific movement strategies are also used by humans with our fingertips.

The sea lion, Lo, participating in different tasks for this study.

The ability to switch whisker exploration strategies between tactile tasks enabled Lo to complete the tasks efficiently. Lo found the correct fish in almost all trials and made decisions quickly, in under half a second. Video footage of the other sea lions also showed them employing the same strategies, so we think that this might be common among California sea lions in general.

And now other animals

Seeing the same movement strategies conserved from sea lion whisker movements to human fingertip movements showcases how important these strategies are for improving touch signals across different tasks.

It is likely that other species of Pinniped will be able to make task-specific whisker movements, since they also have sensitive, moveable whiskers. We are investigating this now, along with other species of carnivores, such as otters.

This is the first time that task-specific whisker touch sensing has been documented. It demonstrates that studying whiskers can give us important insights into animal movement control, as well as their perception and cognition.The Conversation

Robyn Grant, Senior Lecturer in Comparative Physiology & Behaviour, Manchester Metropolitan University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Mouse hand and zebrafish fin, both colored with the same protein markers. The two grow using the same blue-print with significant consequences to our understanding of evolutionary biology. Credit: Marie Kmita and Andrew Gehrke

Hands and digits evolved from fish fins, groundbreaking study proves

Mouse hand and zebrafish fin, both colored with the same protein markers. The two grow using the same blue-print with significant consequences to our understanding of evolutionary biology. Credit: Marie Kmita and Andrew Gehrke

Mouse hand and zebrafish fin, both colored with the same protein markers. The two grow using the same blue-print with significant consequences to our understanding of evolutionary biology. Credit: Marie Kmita and Andrew Gehrke

Using CRISPR, a gene editing tool that can work like a scissor to cut genes from the genome, University of Chicago researchers proved our beloved hands are coded by the same genes that make fish fins.

Water to land — different needs, same blueprint

At first glance, there aren’t that many similarities between a human hand and a fish’s fin, apart from both being protruding extremities. If we’re to remove the skin and muscles, we’ll see the human hand is made from bones which grew from cartilage and contain blood vessels — this sort of tissue is called enchondral bone. A fish, such as a zebrafish, has endochondral bones too but these appear only at the base of the fin. From here, the similarities end because the rest of the fin is made of thin rays composed of a different kind of tissue called dermal bone, which doesn’t start out as cartilage and doesn’t contain blood vessels.

There’s reason to believe, however, that all hands, paws, hoofs, wings and afferent digits diverged from the ray-fins of a common aquatic ancestor some 430 million years ago. Only after four-limbed creatures, the tetrapods, first landed on the continents did nature worked its magic — and you can now create just about anything with those wonderful five digits, and especially talented thumb.

So goes the theory, and we have a treasure trove of fossils to prove this is how the transition went. It remained unclear, however, how the terminal ends of fish and tetrapods, such as humans, are related and consequently how digits developed. Are our hands the product of a new evolutionary process or are they merely following the fin genetic lineage? Most scientists hang to the former.

For two decades, evolutionary biologist Neil Shubin and colleagues at the University of Chicago have been studying this transition. Shubin’s work is very familiar to experts in the field and he is among those who first showed that an ancient 370-million-year old fish had limb-like fins. In 1996, he and his colleagues were startled when a group of French researchers found two genes called Hoxa13 and Hoxd13 which when switched off in mice caused the rodents to grow only stubs — no hands, no digits. This was incredibly exciting because life-long experience and study told Shubin that fish must have these gene counterparts nestled somewhere that code the development of fins. He didn’t have the means to manipulate these genes though — not until technology caught up and CRISPR entered the picture.

CRISPR-Cas9 is a unique technology that enables geneticists and medical researchers to edit parts of the genome by cutting out, replacing or adding parts to the DNA sequence. The technology is so powerful that scientists can use it to cut out HIV genes from live animals, and even engineer superhumans, which has caused quite a stir.

Using CRIPR, Shubin’s lab inserted bits of DNA into the Hoxa-13 and Hoxd-13 genes of zebrafish — a model animal often used in genetic research because its embryos are transparent and development can easily be tracked. To monitor what they were doing, the team also used a special technique that adds glowing red molecules to any cell that activates Hoxa13. When this is done on mice, only the cells that go on to grow the wrist glow — cells which eventually turn into the bones that form the hand and digits.

Before the zebrafish experiment, the researchers believed that hands and digits did not evolve from fin rays because the two are made of different bones. But when Andrew R. Gehrke, a graduate student, showed his results, Shubin was dumbstruck — the fin rays glow red and kept glowing until they reached their final location in the fish’s body.

“Here we’re finding that the digits and the fin rays have some sort of equivalence at the level of the cells that make them,” Dr. Shubin told the New York Times. “Honestly, you could have knocked me over with a feather — it ran counter to everything that I was expecting after working on this problem for decades.”

The findings published in Nature essentially mean that hands and fins follow the same development rules. It means that our hands and digits aren’t evolutionary novelties. Instead, they were built from the same hundreds-of-millions-of-years-old blueprint that had been making fins since times immemorable.

“It’s not saying that fin rays and digits are the same thing,” emphasizes Kimberley Cooper from the University of California, San Diego, told The Atlantic. “But there was so much talk about how they are different, and at a fundamental ancient level they’re more similar than we appreciated.”

“It shows us how bodies are built,” says Shubin. “By understanding the biology of fish, we understand the basic architecture of our bodies, and how genes and cells interact to build us, and how we evolve.”