Archive for the ‘Uncategorized’ Category
How many feathers does a penguin have? It seems like a straightforward thing to address, but it is also exactly the type of basic natural history question that often gets overlooked. It appears that no one had taken the time to thoroughly calculate the number before. Surprisingly, previous accounts ranged from 11 feathers per square centimeter to 46 feathers per square centimeter, and did not even agree on what types of feathers the penguins have.
Feathers fulfill many functions beyond flight, including thermoregulation, camouflage, display, and waterproofing. Different types of feathers contribute to these functions. Contour feathers are large and stiff-vaned feathers that generally form the outer layer of a bird’s feather coat. Flight feathers are the contour feathers than create the airfoil of the wing. These feathers are large in volant birds, but in penguins the “flight” feathers are reduced to tiny, scale-like structures. Plumules are downy feathers with looser barbs and a soft, cottony texture. These feathers typically lie under the contour feathers and provide an insulating layer. Perhaps the weirdest type of feather is the obscure filoplume. Filoplumes are essentially small, bare feather shafts. They can serve no aerodynamic or insulatory purpose and are instead hypothesized to help birds detect the orientation of their larger feathers. Penguins have long been considered to lack filoplumes, but that turns out not to be the case.
A new study tackled the question of Emperor Penguin feather density, a compelling issue given the ability of these birds to survive extremely cold and windy conditions. The team salvaged Emperor Penguin carcasses from Antarctica and took small square patches of skin from different parts of the body. Within each patch, they counted and mapped out the arrangement of different feather types. Whereas previous scientists had overlooked filoplumes in penguins, the team observed them nestled at the base of larger feathers. In fact, it seems that each contour feather on the body has its own associated filoplume. Overall, the most numerous feathers were the downy plumules, which were four times more abundant than contour feathers and filoplumes. This surfeit of downy insulation makes sense given the harsh environment Emperor Penguins inhabit. It may also play a role in locomotion, as a place to store air to release when speeding towards the surface (see more about Bubbling Penguins here).
So how many feathers does an Emperor Penguin have? It turns out density varies quite a bit around the penguin, from as low 5.8 feathers per square centimeter on the back of one penguin to 13.5 feathers per square centimeter on the front of another. The researchers extrapolated from their samples that the full body would have 144,000 to 180,000 total feathers. Any volunteers to count them individually and confirm?
Reference: Williams CL, Hagelin JC, Kooyman GL. 2015 Hidden keys to survival: the type, density, pattern and functional role of emperor penguin body feathers. Proceedings of the Royal Society B 282: 20152033.
I’ve written an article on color in penguins, highlighting some of the remarkable discoveries my colleagues in the modern penguin world have made about pigments, structural color, and more (plus of course a mention of fossil penguin feathers). The article is in the January/February 2016 issue, and you can check it out here as well:
Today is Penguin Awareness Day. Let’s discuss a feature of which we humans may not be aware, because of our limited visual perception. Our eyes can detect the visible light part of the electromagnetic spectrum, spanning the range from about 700 nanometers (red) to 400 nanometers (violet) wavelength. Many birds, including penguins, see beyond this range into the ultraviolet portion of the spectrum. Birds often have “hidden” markings that they themselves can see, but can only be detected by humans through artificial illumination.
King Penguins are one species that have ultraviolet markings, as scientists have discovered. These large penguins are already stunning birds, with orange patches of color along their necks, ear regions, and the sides of their beaks. Recently, scientists delved deeper to detect ultraviolet patches are also positioned along the lower bill. Both the visible and ultraviolet colors appear to play a role in attracting mates.
How do King Penguins produce ultraviolet colors? The answer is multilayered reflector photonic microstructure. Essentially, the outer layer of the beak contains alternating layers of high refractive index and low refractive index materials. Reflected light from the different layers interacts to bounce back wavelengths in the ultraviolet spectrum. Research by Dr. Birgitta Dresp-Langley and colleagues has revealed that King Penguin beaks have a layer filled with special folded microstructures and intervening filaments
of β-keratin. These markings help indicate maturity, and may also be attractive to other penguins. As a King Penguin grows, the ultraviolet hue of the beak markings increases. Surveys of wild penguins show they are strongest in recently formed male–female pairs. When scientists hid the ultraviolet markings by painting a layer of varnish over a penguin’s beak, those birds had a harder time finding a mate – perhaps the equivalent of the penguin hitting the local watering holes without enough lipstick or cologne!
Dresp, B., P. Jouventin, and K. Langley. 2005. Ultraviolet reflecting photonic microstructures in the King Penguin beak. Biology Letters 1: 310–313.
A recent study suggests penguins may have a poorly developed sense of taste. This is not to be confused with tasting bad – which accounts by sailors forced to survive on penguin meat suggest is also true. Rather, new research suggests penguins lack the ability to detect sweet or savory tastes.
Humans perceive 5 basic categories of taste: sweet, sour, salty, bitter, and umami (which might best be described as savory). However, evidence suggests penguins are limited to just sour and salty. Researchers came to this conclusion after combing through recently assembled genomes from two penguin species. A mutation in the umami taste receptor gene Tas1r1 causes it not to function properly in penguins. Tasr2r genes, responsible for bitter reception, are non-functional in penguins too. Penguins also lack the taste receptor gene Tas1r2, which is associated with sweetness detection. These factors would preclude them from enjoying, say, a Shake Shack burger or a candy apple. Penguins are not alone in lacking the ability to taste sweet – Tas1r2 appears to be absent in all birds, though nectar-loving hummingbirds seem to have repurposed Tas1r1 to detect sweetness.
Are penguins hindered by their diminished sense of taste? Probably not. As the authors note, penguins swallow their food whole, so they might not benefit too much from telling whether or not it tastes good. Truth be told though, I have certainly known a few aquarium penguins who strongly prefer one type of fish to another when it comes to their dinner – so much so that their keepers serve the less desirable portion first while they are still hungry.
There is one aspect of the study that clashes with paleontological evidence. The authors conclude the loss of some tastes may be related to the origin of penguins in Antarctica. However, when one considers the complete penguin family tree including the many extinct species, it is far more likely penguins originated at lower latitudes when climate was much warmer and invaded icy Antarctica late in their history.
One exciting extension of the research is that we now have a reason to test the conclusions in the real world. Perhaps some biologists are now hatching a plan to tempt penguins with sour pickles, salty chips, or sweet pieces of candy to see if they can indeed tell the difference.
Reference: Zhao, H., J. Li, and J Zhang. 2015. Molecular evidence for the loss of three basic tastes in penguins. Current Biology 25 :R141 – R142
Here is a wonderful reconstruction of the fossil penguin we analyzed in our recent penguin brain evolution study, created by artist Santiago Druetta. The fossil species is hunting down an icefish, a type of fish also known from the 34 million year old fossil La Meseta Formation deposits that yielded the fossil penguin skull. In the background swims a modern Chinstrap Penguin, a species named for the party-hat-string-like band of black feathers across its chin. The brains of these penguins are shown in the upper right corner.
But what species is the fossil? Actually, we are not sure. This is because the many extinct species have been named from the La Meseta Formation and each was described by scientists based on limb bones. Because the skull we studied was found in isolation with no traces of the rest of the skeleton, we can’t be sure which species it belongs to with certainty. The skull is roughly the same size as the skull of an Emperor Penguin, but we know that many extinct penguins had small heads relative to their overall body size. Thus, the skull could easily belong to a giant penguin like Anthropornis nordenskjoedli or Palaeeudyptes gunnari.
The situation is even more complex when you consider that we looked at two additional fossil skulls from the La Meseta Formation in the study, and found evidence that each belonged to a different species than the main skull. One has a very different external morphology. The other looks the same on the outside, but had such a different brain shape that we concluded it must belong to a third species. Regardless of the precise species identifications, these skulls have provided excellent new data on early penguin brain structure.
Today, a new research article on fossil penguin brains is available at the Journal of Vertebrate Paleontology. I’m pleased to have been part of this study, led by Dr. Claudia Tambussi and Dr. Federico “Dino” Degrange. We looked at three Eocene fossil skulls from Antarctica, each belonging to a 34 million year old penguin. These fossils were recovered during expeditions by Dr. Tambussi and other scientists to Antarctica. In order to shed some light on the neuroanatomy morphology of the ancient penguins, we used CT scans of the skulls to create virtual endocasts – 3D models of the brain and sensory organs.
Penguins are considered flightless, but when it comes to wing-propelled diving they are essentially practicing underwater flight. The brain morphology reflects this as modern penguins retain an overall “flight-ready” brain. The new Antarctic fossils are important because they provide the oldest penguin endocasts available for study (they are more than ten million years older than the Paraptenodytes antarcticus endocast we studied in 2012). These fossils show that ancient penguin brains had several important differences from modern species.
One of the interesting features in the endocasts from the fossil species was the larger size of the olfactory bulbs. Modern penguins have very small olfactory bulbs compared to their closest relatives, the tubenose Procellariiformes (petrels and allies). This is likely related with their reduced reliance on smell to locate prey compared to sensitive-nosed petrels, which can sniff out stinky slicks of chum from miles away. Penguins tend to rely more on vision to locate prey. The early fossil species had relatively larger olfactory bulbs (though nowhere near as large as petrels), suggesting that reduction of olfactory capabilities was a slow trend in penguin evolution following the loss of flight. Another interesting facet of the endocast data is that it provides more support for the hypothesis that the morphology of the Wulst, a brain structure associated with complex visual function, changed in similar ways in different groups of birds. Researchers like Dr. Stig Walsh have demonstrated that the Wulst is restricted to the front part of the brain surface in early members of many groups of birds, but expands backwards in modern species. Because we see the same pattern in different types of birds (including penguins) over the course of millions of years, it suggests they evolved this feature independently. What advantage this may have conferred remains mysterious because of limits of the technology for studying fossil brains: our endocasts only provide the surface morphology, but cannot “see” the boundaries that would have existed between layers of cells associated with different brain functions because all that remains is the void where the brain was once housed.
Tambussi, C.P., F.J. Degrange and D.T. Ksepka. 2015. Endocranial Anatomy of Antarctic Eocene stem penguins: implications for sensory system evolution in Sphenisciformes (Aves). Journal of Vertebrate Paleontology: e981635.