Endless Forms

Cutting edge news about discoveries in ecology, evolution and conservation.


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The Trade Routes That Threaten Biodiversity – Video

We all know that human consumption drives habitat destruction, but do we know exactly what areas are hurt by specific industries and trade routes? A recent paper in the scientific journal Nature Ecology & Evolution sheds light on this issue by mapping the degree to which specific international trade routes affect biodiversity in “threat hotspots.” For example, which goods are causing the most problems for Madagascar, and where is the demand from those goods coming from?

To learn how the authors put together these maps, and the reasoning behind some surprises – why do the Brazilian highlands have a higher threat index than the Amazon? – check out this video.

 

 

Moran, D. and Kanemoto, K. 2017. Identifying species threat hotspots from global supply chains. Nature Ecology & Evolutiondoi:10.1038/s41559-016-0023.

 


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How Long Does It Take to Hatch a Dinosaur Egg?

Animals invest tremendous time and effort into their offspring, even before the youngsters take their first breaths. An elephant is typically pregnant for 23 months. Depending on the altitude, black alpine salamanders will gestate for two to three years before giving birth to live young. Sharks stay pregnant for up to 3.5 years. Even the humble velvet worm can carry its offspring for up to 15 months, and komodo dragon eggs take 7 to 8 months to incubate and hatch. All in all, building even a tiny organism is a huge time commitment.

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A very pregnant cat.

And birds? Birds have it relatively easy. Their eggs are ready to hatch after 11-85 days of incubation. Even the immense ostrich needs only 42 days – six weeks – of incubation time for its chicks to emerge and meet the world. This short developmental period is advantageous – rapid development minimizes time spent at especially vulnerable stages, and makes each individual offspring a less risky investment to its parents.

For example, if a predator kills an infant elephant on its first day of life, its mother just wasted two years of her life (and an enormous amount of energy) creating that individual, and won’t be able to have another one for over two more years. On the other hand, if something eats an ostrich chick, much less time has been lost, and a new one can be produced relatively quickly.

Birds are living dinosaurs, so many scientists assumed that bird and dinosaur eggs incubated at similar rates, after adjusting for size and other physical factors . If that were the case, dinosaur eggs would take 45-80 days[*]  to hatch (Carpenter 1999). That was all just an assumption based on extrapolating data, however – until recently, no one had actually tried to measure incubation times of embryonic dinosaurs.

How would you even going about such a study? First, you need some embryonic dinosaurs. While these aren’t incredibly common, they do exist. To be careful, you would probably want samples of dinosaurs covering as broad a size range as possible. You would also need a way to determine daily growth rate of the embryos.

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Embryonic Protoceratops. Photo credit: AMNH / M. Ellison

While all of that may seem like a tall order, it is precisely what a group of scientists from the American Museum of Natural History, Florida State University, and the University of Calgary have done. They acquired fossils of embryonic young from two species spanning a good portion of dinosaur egg size spectrum: Protoceratops, with eggs weighing in at less than half a pound (0.23 kg), and Hypacrosaurus, with eggs that can weigh almost 9 pounds (4 kg). (For reference, an ostrich egg weighs around 3 pounds, or 1.4 kg).

These embryonic specimens had emerging teeth that featured “lines of von Ebner“, which function essentially like the growth rings on a tree. Each line is a record of the daily mineralization of a developing embryo’s teeth. If you count the number of these lines on a dinosaur’s tooth, you have a record of the number of days that tooth had been developing. Teeth don’t erupt at the very start of incubation, so the researchers used information from tooth emergence time in other reptiles to estimate how long the egg had been developing before tooth mineralization began.

The results of Erickson and colleagues’ analyses showed that dinosaur eggs developed at less than half the rate of bird eggs. The smaller Protoceratops egg would take around 40 days to hatch if it developed at the same rate as a bird, but fossil evidence suggests that it took around 83 days. Similarly, the much larger Hypacrosaurus would only need 82 days to hatch at a birdlike rate, but the dental analysis showed that it actually took a whopping 171 days – over five and a half months.

This study has overturned a long-held assumption about one of dinosaur’s most fundamental life history traits: developmental time. So, what does that mean for our understanding of dinosaurs, of how they lived, of what they were? The implications are both broad and deep. With an empirical way to estimate developmental time, scientists will be able to move forward with much more accurate estimates of dinosaur generation times, reproductive investment, lifespans, metabolism, and even nonavian dinosaur extinction.

Today, many of the world’s most endangered animals are those with relatively long generation times, because they require sustained periods of time to recover from population declines. Could the ponderous incubation period required by dinosaurs have put them at a similar disadvantage?  Eggs are incredibly vulnerable objects, and if nonavian dinosaurs required significantly longer periods of time in egg form than avian dinosaurs, that could also help to explain why the latter group survived to the present day, while the others died out at the end of the Cretaceous. Much more research and many more insights and discoveries will likely stem from this work, but for now, we know that dinosaurs had to protect and watch over their eggs for far longer than previously thought.

References

Carpenter, K. 1996. Dinosaur eggs and babies. Cambridge University Press. New York.

Erickson, G. M., Zelenitsky, D. K., Kay, D. I., and Norell, M. A. 2017. Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth how reptilian-grade development. Proceedings of the National Academy of Scientists. 114(3):540-545. doi: 10.1073/pnas.1613716114

[*] If that number seems small, keep in mind that dinosaur egg size wasn’t necessarily proportional to dinosaur body size. There are physiological constraints on how big an egg can be while still diffusing gases between the membranes and shell efficiently. Dinosaurs laid large clutches of small eggs, and the largest eggs known are less than five times the size of an ostrich egg. Even the one hundred ton Titanosaur laid eggs less than two meters in diameter.


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Giraffe Necks: A Tall Tale

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Photo by Anne-Marie Hodge

When the giraffe was first discovered by Europeans, some speculated that it was the result of a cross between a camel and a leopard — hence the Latin name of the northern giraffe: Giraffa camelopardalis. The giraffe is a unique creature in many ways, but the origin of its elongated neck has long served as fodder for many “just-so” stories. Rudyard Kipling used it as a metaphor for self-improvement. Countless biology textbooks use it as the default example for Lamarck’s theory of evolution via inheritance of acquired characteristics. The lengthy neck has provided endless opportunities for comic relief in cartoons and illustrations.

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Photo by Anne-Marie Hodge

Amongst all of speculation as to why any reasonable species would develop such an extreme feature, two hypotheses predominate: 1) Giraffe necks elongated in a co-evolutionary dynamic with Acacia trees, their main food source, as each tried to gain the upper hand in the herbivore-plant war; or 2) long necks are the result of sexual selection, akin to peacock tails, that result in more successful mate acquisition for longer-necked individuals—either because female giraffes think long necks are sexy or because males use them as weapons to compete for mates. It also could have been a combination of both, or long necks could have enhanced capacities for thermoregulation, vigilance for predators . . . or something else. The debate continues.

The giraffe’s neck actually contains the same number of cervical (neck) vertebrae found in nearly all other mammals. What has not been thoroughly explored, however, is the rate at which these vertebrae develop relative to other parts of the giraffe’s body, including its head and overall body mass.

Giraffes are swift, strong, and stunning creatures, but they still look comically disproportionate to many humans. They don’t start out like that, however: giraffes are not born with exceptionally long necks, and their cervicals don’t begin to extend rapidly until later in life. But just how rapidly, relative to the rest of the body? Is there a difference between male and female growth patterns? What can the answers to these questions tell us about the evolutionary roots of the giraffe’s long neck?

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Photo by Anne-Marie Hodge

These questions motivated a group of biologists from the University of Wyoming and the Centre for Veterinary Wildlife Studies at the University of Pretoria to investigate growth patterns of the necks and heads of giraffes (Mitchell et al. 2013). The scientists analyzed numerous morphological measurements in order to determine whether neck growth scaled “allometrically” with head and body growth—ie, whether the neck remained at a consistent size ratio with the rest of the giraffe’s parts, or whether a giraffe goes through an “awkward teen phase” with proportions that are skewed relative to those of adults. The researchers also compared growth patterns between males and females and examined sexual dimorphism (differences in appearance, size, etc between the sexes) to determine whether developmental patterns differ between males and females.

It turns out that there is no significant difference between male and female giraffes in neck growth rate (measured by both neck mass and neck length), but that in both sexes the neck length did increase at a faster rate than body mass. The rates of neck and body growth rates are similar in youngsters, but the necks outpace body mass once puberty hits, elongating out of proportion to the growth of the rest of the body.

In other words, there is now scientific evidence that giraffes go through a gangly teenage stage.

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Young giraffe. Photo by Anne-Marie Hodge

Interestingly, a giraffe’s head actually grows at a slower rate than its overall body mass. Males did end up with slightly heavier heads and necks, due to thicker ossicones and skull bones. The researchers attribute this to basic differences in sex steroid levels, and males have a much longer total growth period during their lives than do females. These factors underlie the slight male:female body size differential found in most mammals.

Giraffe head and neck growth rates and the ratio of neck mass to total body mass both remained similar between the sexes, meaning that they differ a bit in size but not proportion. This low degree of sexual dimorphism in skull and neck proportions has important implications for our understanding of giraffe evolution and biology. If giraffe necks had developed due to pressures from one form of sexual selection, we would expect to find one sex (amongst mammals, it would typically be the males) with profoundly more extreme features. In one form of sexual selection, these extreme features would provide the basis for the other sex (typically the females, sorry guys) to choose a mate from their array of suitors based on display characteristics of some sort. In the other type of sexual selection, male giraffes would use their massive necks to battle for access to mates. The females themselves would exhibit little aesthetic choosiness and would just mate with the males that were the most successful at winning fights.

Many people have probably seen documentary footage of giraffes engaging in dramatic bouts of “necking”, in which they appear to fight by swinging their long necks and heavy heads at each other like weapons. On the surface, this seems like it may indicate sexual selection via male competition, and yet Mitchell et al. point out that studies have shown that large males rarely participate in these activities, and it’s more often immature males with female-like head and neck sizes that do all of the “fighting” in order to establish a dominance hierarchy. Most importantly, the winners of the fights don’t go on to acquire more mates (Pratt & Anderson 1982).

The takeaway message from this study is that although giraffes possess an extremely exaggerated feature, the lack of difference between males and females tells us that it’s unlikely this was due to sexual selection. This makes it much more likely that some form of enhanced resource utilization or physiological efficiency was the mechanism for neck elongation over evolutionary time.

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Photo by Anne-Marie Hodge 

The issue is far from resolved, however. There have been noteworthy criticisms of the main two theories regarding the evolution of giraffe necks. Some studies have suggested that giraffes rarely browse at the full height that their necks can reach (Young & Isbell 1991). Also, in order to “out-reach” other browsers, they would only need a neck that was two meters long, not five meters, and being that high off the ground actually makes it harder to see predators such as lions that slink along the ground (Cameron & Du Toit 2005). Conversely, although Cameron & Du Toit (2007) found that 57% of the forage consumed by giraffes grew below 2 meters, i.e. in the height range of other herbivores, they suggest that the giraffe’s long neck allows it exclusive access leaves in the center of shrubs and bushes by reaching down from above. All of this will require broader and deeper investigation, of course, and in the end it is likely that the selective pressure that have produced such long necks is attributable to more than one precise factor.

Although it is most famous for its long neck, the giraffe exhibits an array of highly specialized features, and Mitchell et al. review a few fun facts about giraffe morphology. For example, relative to total cranial mass, the sinus cavities of giraffes are massive relative to those of other artiodactyls, allowing the development of such an enormous head without a debilitatingly heavy skull. In addition, the cervical vertebrae close to the head are lighter than those lower in the neck, further decreasing the mechanical stress of holding a head that high on a neck that long. The occipital condyles, bony projections that allow the head to rotate on the neck, have such a wide range of motion that the giraffe can actually partially lay the top of its head along its neck while feeding, a sort of reverse flamingo strategy. Fancy, no?

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(Gratuitous photo of me “kissing” a giraffe in Nairobi).

Sources:

Cameron, E.Z. & du Toit, J.T. (2005). Social influences on vigilance behaviour in giraffes, Giraffa camelopardalis. Anim. Behav. 69, 1337–1344.

Mitchell, G., Roberts, D., van Sittert, S. & Skinner, J. D. (2013). Growth patterns and masses of the heads and necks of male and female giraffes. Journal of Zoology. 290, 49–57. doi:10.1111/jzo.12013

Pratt, D.M. & Anderson, V.H. (1982). Population, distribu- tion, and behaviour of giraffe in the Arusha National Park, Tanzania. J. Nat. Hist. 16, 481–489.

Young, T.P. & Isbell, L.A. (1991). Sex differences in giraffe feeding ecology: energetic and social constraints. Ethology 87, 79–89.


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New Species of 2016: The Fab Five

As the year draws to a close, lists and “best of 2016” articles are being written for everything from world leaders to television shows to hamburgers. In the midst of all of the other headlines in 2016, new species were being discovered all over world. Here is a curated list of my five favorite creatures that were first reported in 2016.

1. Flightless scaly-tailed squirrel (Zenkerella insignis)

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This small mammal makes the list for essentially being rediscovered, after only being known to science via fossils and a handful of aging specimens. Previously, no one knew if living flightless scaly-tailed squirrels still walked the earth at all.

Zenkerella insignis began roaming the landscapes and islands of what is now western Africa around 50 million years ago — just 15 million years after dinosaurs went extinct. This scaly-tailed squirrel provides a peek into the past, as  the species has changed very little since then. It is one of only six extant (living) mammal species to boast such a long tenure on our planet.

equatorial-guineaZenkerella insignis‘s rediscovery also serves as a lesson about the value of maintaining museum collections and supporting research expeditions that focus on exploration and discovery. Dr. David Hernandez, a lecturer at the University of West England, came across a Z. insignis specimen that had been languishing in a museum collection for some time, and texted a picture of it to his colleague Dr. Erik Seifert, at the University of Southern California. That text message eventually inspired a new field expedition to search for a surviving population on Bioko Island, off the coast of Equatorial Guinea. Thus, while this is anything but a “new” species, the expedition’s discovery of an island population of “living fossils” was a new and noteworthy revelation.

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Zenkerella insignis specimen (Credit: Steven Heritage)

 

2. New species of basslet named in honor of President Obama (Tosanoides obama)

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Tosanoides obama (Credit: Richard L. Pyle, Bishop Museum)

While this small tropical fish doesn’t have an official common name yet, its Latin name has made it an immediate celebrity: Tosanoides obama was named in honor of U.S. President Barack Obama, in honor of his contributions to marine conservation. This basslet was discovered in Papahānaumokuākea Marine National Monument (PMNM), surrounding the far northwest Hawaiian islands. When Obama expanded PMNM in August 2016, he made it the largest protected wildlife reserve in the world–marine or terrestrial– covering 582,578 square miles (1,508,870 square km). That is approximately twice the size of Texas.

In addition to T. obama, PMNM is home to around 7,000 species, including endangered sea turtles and marine mammals. With the expansion of the park, we can look forward to a wealth of new research from that part of the Pacific.

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Credit: Brian Skerry

 

3. Ruby seadragon (Phyllopteryx dewysea)

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Phyllopteryx dewysea (Credit: Western Australia Museum)

Here there be dragons. The list of known sea dragon species increased by 50% this year, with the discovery of only the third species known to science. The ruby sea dragon (Phyllopteryx dewysea), found off the coast of Western Australia, is the first new sea dragon species to be described in over 150 years.

What is a sea dragon, anyway? It is a highly derived fish, and is closely related to the sea horses. They are not strong swimmers, and tend to “go with the flow,” gliding along in the ocean waves.  Phyllopteryx dewysea is a deeper red color than the other two known species of sea dragon, leading researchers to believe that it may spend its time deeper in the ocean waters than its relatives. Red wavelengths of light are absorbed underwater, making red a better and better camouflage the deeper one dives. This preference for deeper waters could also explain why the species hadn’t been discovered until this year.

4. Peacock spider (Maratus spp.)

Peacock spiders are gorgeous and entertaining little arachnids. This year not one but seven new peacock spider species were described, all in the genus Maratus. These jumping spiders are known for the bright, iridescent patterns that adorn the males. As with peacocks, males use these colorful features as part of elaborate courtship displays, and females are drab in comparison.

My personal favorite from the Peacock Spider Class of 2016 is M. bubo: “Bubo” is genus name for horned owls and eagle-owls, in honor of the colorful pattern on this spider that looks like a tiny owl portrait.

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Maratus bubo (Credit: Jürgen Otto)

See video of peacock spiders dancing

Check out the peacock spider Facebook page

5. Ghost octopus (Latin name TBD)

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In February of 2016, scientists at the National Oceanic and Atmospheric Administration (NOAA) unveiled a surprise character from deep-sea rover footage: a round, pale little octopus that was previously unknown to science. Living at a depth of over 4,000 meters (13,123 feet, or about 2.5 miles), this creature is thought to be not only a new species, but an entirely new genus.

And it’s cute: this cephalopod charmed the world, becoming an internet sensation overnight, frequently being compared to Casper the friendly ghost.

The “ghostopus” is so unique that more analysis must be done before it can be officially described and named. Meanwhile, more exploration of the sea floor around the Hawaiian islands may turn up more individuals, and even more species not yet known to science.


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The Lemur Underground

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From bears slumbering in their dens to frogs sinking into muddy tombs of suspended animation, a wide spectrum of animals use hibernation to survive inhospitable seasons.

We tend to associate hibernating creatures with cold, wintry environments – just a mention of hibernation conjures images of snow-blanketed forests and ice-covered ponds. A group of small tropical primates is breaking the trend, however—recent research has revealed that dwarf lemurs in Madagascar hibernate for up to eight months of the year.

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Madagascar (in red box)

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Cheirogaleus crossleyi

While scientists already knew that that the western fat-tailed dwarf lemur (Cheirogaleus medius) spends seven months of the year hibernating in tree holes (Dausmann et al. 2004), until recently there was no evidence that any other primate species on earth undertakes significant hibernation periods. A recent paper in Nature’s open access journal, Scientific Reports, presents new evidence of hibernation in two other primate species, the Sibree’s dwarf lemur (C. sibreei) and the Crossley’s dwarf lemur (C. crossleyi), both of which occur in east-central Madagascar’s high altitude forests (Blanco et al. 2013). While it may not seem as though primates would need to hibernate on a tropical island, Madagascar’s mountainous regions can indeed experience temperatures that dip below freezing—a significant thermoregulatory challenge for a squirrel-sized primate. Thus, a research group from Duke University Lemur Center decided to see if the overwintering strategies of eastern dwarf lemurs resembled that of the western species.

The researchers managed to trap dwarf lemurs prior to hibernation season, and outfitted each animal with a collar that featured both a radio transmitter and a temperature sensor. The collars allowed the animals to be located after they had retreated to their hibernacula, in addition to tracking fluctuations in body temperature while the lemurs were hibernating.

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Eastern Madagascar

The researchers found that not only do these tropical lemurs hibernate for 3-6 months out of the year, the arboreal creatures actually spend their hibernation underground, despite their lack of adaptations for a fossorial (digging and burrowing) lifestyle. The lemurs nestled 10-40 cm (4-16 inches) beneath a the forest’s floor of secondary roots and humus, no small feat for an animal that appears to be optimized for life in the treetops. Each lemur denned up alone, and they used just one or two hibernacula sites per season.

This underground hibernation habit is intriguing; the other lemur species known to hibernate, C. medius, uses tree hollows exclusively. The researchers suggest that this difference in hibernation sites could be partially due to constraints imposed by soil type: soil in C. medius’ habitat is hard and dry, unlike the soft soils of the eastern forests. Another interesting point about hibernacula choice is that the eastern species use tree hollows, rather than burrows, for their normal resting periods during the non-hibernation season, meaning that hibernation is an event with a very specific site selection pattern, rather than just an extended rest in their usual shelters.

Temperature data from the collars showed that C. sibreei and C. crossleyi tend to keep their body temperatures more stable than C. medius, which may highlight another advantage of subterranean hibernation. Soil provides more resistance to ambient temperature fluctuations than hollow trees, meaning that the eastern species are better insulated during hibernation than their western relative.

A final noteworthy aspect of this study is that C. sibreei and C. crossleyi are basal species (less derived than many other species) within their branch of the lemur phylogeny. This raises the question of whether their hibernation patterns may be an ancestral condition for dwarf lemurs. In the mean time, you never know what could be underfoot in the forest . . .

Sources:

Blanco, M. B., Dausmann, K. H., Ranaivoarisoa, J. F., Yoder, A. D. 2013. Underground hibernation in a primate. Science Reports. 3:1768.

Dausmann, K. H., Glos, J., Ganzhorn, J. U., Heldmaier, G. 2013. Hibernation in a tropical primate. Nature. 429:825-826.

 

 

 


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From Carrion to Carriers: Crows Transmit Infectious Prions

Most of us recall learning the basic rules of protein structure and folding in high school science classes (if not, see neat interactive animations here). Basically, form equals function, and a protein must be correctly folded in order to perform its duties. The critical nature of this process cannot be overstated, and the results of misfolded proteins in the brain—also known as prions—can be gruesome.

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Rabies, “mad cow disease,” foot-and-mouth disease, kuru, chronic wasting disease—all of these ghastly illnesses are caused by prions, which are more technically known as transmissible spongiform encephalopathies (TSEs). Foaming at the mouth, loss of muscle control, hallucinations, hydrophobia . . . the symptoms of prion disorders can lead to truly tragic and painful deaths, all ultimately due to a few misshapen proteins.

Despite the Hollywood-worthy symptoms of prion disorders, the most disturbing part of a TSE is the ‘T’ part: “transmissible.” The specter of such a devastating brain disease being passed from one individual to another seems like something out of a cheap horror novel—and yet it happens every day.

We typically think about TSE infections as resulting from direct contact with an infected animal. However, what if you could become infected simply from exposure to feces left by an exposed yet unsymptomatic vector? A recent PLoS ONE paper describes a study on passive transmission of infectious prions by crows, highlighting a form of prion dissemination that is little-known, yet potentially very important from a disease ecology perspective. What happens when prions can hitch rides on non-symptomatic, aerial hosts?

Crows are notorious scavengers, and feed upon carcasses that may have died from any number of traumas or diseases. It is already known that TSE diseases can be spread by the consumption of flesh: kuru, a lethal form of encephalopathy found amongst the Fore people of Papua New Guinea, is transmitted through ritual cannibalism during funeral rites. Given that prion disorders such as chronic wasting disease and rabies are not uncommon amongst wildlife, there is a realistic possibility that scavengers will be exposed to TSE-infected flesh. The risks to scavengers are obvious, but the hazards extend beyond these animals. Will the prion strains remain infective after the infected food has been digested and excreted? This is a critical question that must be answered if we are to understand the role that scavengers play in transporting pathogens from place to place after feeding on carrion.

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In the recent experiment reported by VerCauteren and colleagues, 20 American crows (Corvus brachyrhynchus) were fed mouse brain material infected with scrapie prions, to simulate feeding upon prion-infected carcasses. Next, the researchers obtained feces samples from the birds, and injected them into lab mice (the CF+ treatment group) to see if the disease remained infectious after passing through the birds’ digestive systems. Another set of mice (the MB+ treatment group) was injected directly with infected mouse brain material—the same substance that had been fed to the crows.

The results were striking. There were a handful of fatalities due to toxicity from uric acid in the bird feces, but all of the mice that survived for at least three days after the inoculations  exhibited neurological dysfunctions characteristic of prion disorders. They also all tested positive for prion infection during their postmortem examinations.

Mice that were injected directly with mouse brain material (the MB+ group) developed neurological symptoms 15 days earlier than those infected through crow fecal material (CF+ group), suggesting that indirect infection may provide a smaller dose, although still enough to be ultimately lethal. Between 83-100% of the crows were estimated to produce feces capable of infecting mammals with the prion disorder.

It is important to keep these results in perspective. This study was designed to provide conservative estimates of post-digestion prion infectivity. The type of scrapie that was used in this study, the RML Chandler strain, is more sensitive to enzymatic activity than many others. This means that more robust strains of prion disorders may be even more infective after ingestion and excretion by birds – an ominous scenario indeed.

The implications of these results are important and fascinating. The takeaway message of this study was that prions can remain lethally infectious after they have been digested and excreted by an avian scavenger. Crows produced infective feces within four hours of feeding, and in that amount of time a crow can travel a nontrivial distance from its initial feeding site.

This kind of transmission by volant scavengers could turn a TSE outbreak from a local, individually transmitted event into a much broader outbreak. Further research on how long prions remain infective in the feces under different environmental conditions will provide additional insights into how avian scavengers may affect the transmission dynamics of these diseases.

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Source:

Prion Remains Infectious after Passage through Digestive System of American Crows (Corvus brachyrhynchos). Vercauteren, K. C., Pilon, J. L., Nash, P. B., Phillips, G. E. , and Fischer, J. W. PLoS ONE. http://dx.doi.org/10.1371/journal.pone.0045774