Does Size Matter? Jellyfish Venom Capsule Length Association with Pain

Japanese Sea-Nettle

Since the PLOS San Francisco office is a quick car ride from the Monterey Bay Aquarium, so many of us at PLOS have been captivated by jellyfish movements. They are simply mesmerizing to watch as they travel through the water. … Continue reading »

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The Nose Knows: Oriental Honey Buzzards Use Nose and Eyes to Forage for Sweet Treats

Winnie the…Buzzard? The Oriental honey buzzard Pernis orientalis feeds primarily on honey and bee or wasp larvae. But how do they find their food? In the winter, thousands of Oriental honey buzzards migrate to Taiwan to forage. These migrating honey … Continue reading »

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Flight of the Bats: Exploring Head Shape and Aerodynamics

It’s a bird…it’s a plane…it’s a bat! All three may be soaring through the sky, but their shapes vary greatly, which affects their aerodynamics during flight. Birds typically have streamlined head profiles that strongly contrast with the appendages featured on … Continue reading »

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Earth Day 2015: Celebrating Our Awe Inspiring World

We share Earth with millions of amazing plants and animals. Whether we’re relaxing in a hot spring like a Japanese macaque, or catching a glimpse of a rare bird, our exposure to Nature’s diversity enriches our lives and makes us … Continue reading »

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Two Shark Studies Reveal the Old and Slow

Sharks live in the vast, deep, and dark ocean, and studying these large fish in this environment can be difficult. We may have sharks ‘tweeting’ their location, but we still know relatively little about them. Sharks have been on the planet for over 400 million years and today, there are over 400 species of sharks, but how long do they live, and how do they move? Two recent studies published in in PLOS ONE have addressed some of these basic questions for two very different species of sharks:  great whites and megamouths.

The authors of the first study looked at the lifespan of the great white shark. Normally, a shark’s age is estimated by counting growth bands in their vertebrae (image 1), not unlike counting rings inside a tree trunk. But unfortunately, these bands can be difficult to Great white vertdifferentiate in great whites, so the researchers dated the radiocarbon that they found in them. You might wonder where this carbon-14 (14C) came from, but believe it or not, radiocarbon was deposited in their vertebrae when thermonuclear bombs were detonated in the northwestern Atlantic Ocean during the ‘50s and ’60s. These bands therefore provide age information. Based on the ages of the sharks in the study, the researchers suggest that great whites may live much longer than previously thought. Some male great whites may even live to be over 70 years old, and this may qualify them as one of the longest-living shark species. While these new estimates are impressive, they may also help scientists understand how threats to these long-living sharks may impact the shark population.

A second shark study analyzed the structure of a megamouth shark’s pectoral fin (image 2) to understand and predict their motion through the water. Discovered megamouth finin 1976, the megamouth is one of the rarest sharks in the world, and little is known about how they move through the water. We do know that the megamouth lives deep in the ocean and is a filter feeder, moving at very slow speeds to filter out a meal with its large mouth. But swimming slowly in the water is difficult in a similar way flying slowly in an airplane is difficult. Sharks need speed to control lift and movement.

To better understand the megamouth’s slow movement, the researchers measured the cartilage, skin histology, and skeletal structure of the pectoral fins of one female and one male megamouth shark, caught accidentally and preserved for research. The researchers found that the megamouth’s skin was highly elastic, and its cartilage was made of more ‘segments’ than any other known shark, which may provide added flexibility compared to other species. megamouth jointThe authors also suggest that the joint structure (image 3) of the pectoral fin may allow forward and backward rotation, motions that are largely restricted in most sharks.  The authors suggest that this flexibility and mobility of the pectoral fin may be specialized for controlling body posture and depth at slow swimming speeds. This is in contrast to the fins of fast-swimming sharks that are generally stiff and immobile.

In addition to the difficulties in exploring deep, dark seas, small sample sizes present challenges for many shark studies, including those described here. But whether studying the infamous great white shark or one of the rare megamouths, both contribute to a growing body of knowledge of these elusive fish.

Citations: Hamady LL, Natanson LJ, Skomal GB, Thorrold SR (2014) Vertebral Bomb Radiocarbon Suggests Extreme Longevity in White Sharks. PLoS ONE 9(1): e84006. doi:10.1371/journal.pone.0084006

Tomita T, Tanaka S, Sato K, Nakaya K (2014) Pectoral Fin of the Megamouth Shark: Skeletal and Muscular Systems, Skin Histology, and Functional Morphology. PLoS ONE 9(1): e86205. doi:10.1371/journal.pone.0086205

Images1: doi:10.1371/journal.pone.0084006.g001

Image 2: doi:10.1371/journal.pone.0086205.g003

Image 3: doi:10.1371/journal.pone.0086205.g004

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Rainforest Fungi Find Home in Sloth Hair

Bradypus_variegatusMost of us have seen a cute sloth video or two on the Internet. Their squished faces, long claws, and scruffy fur make these slow-moving mammals irresistible, but our furry friends aren’t just amusing Internet sensations. Like most inhabitants of the rainforest, little is known about the role sloths play in the rainforest ecosystem.

Three-toed sloths live most of their lives in the trees of Central and South American rainforests. Rainforests are some of the most biodiverse ecosystems in the world and home to a wide variety of organisms, some of which can be found in rather unusual places.

Due to their vast biodiversity, rainforests have been the source for a wide variety of new medicines, and researchers of this PLOS ONE study sought to uncover whether sloth hair may also contain potential new sources of drugs that could one day treat vector-borne diseases, cancer, or bacterial infections. Why look in sloth fur? It turns out that sloths carry a wide variety of micro- and macro-organisms in their fur, which consists of two layers: an inner layer of fine, soft hair close to the skin, and a long outer layer of coarse hair with “cracks” across it where microbes make their homes. The most well-known inhabitant of sloth fur is green algae. In some cases, the green algae makes the sloth actually appear green, providing a rainforest camouflage.

In the study, seventy-four separate fungi were obtained from the surface of coarse outer hair that were clipped from the lower back of nine living three-toed sloths in Soberanía National Park, Panama, and were cultivated and tested for bioactivity in the lab.

Researchers found a broad range of in vitro activities of the fungi against bugs that cause malaria and Chagas disease, as well as against a specific type of human breast cancer cells. In addition, 20 fungal extracts were active in vitro against at least one bacterial strain. The results may provide for the first time an indication of the biodiversity and bioactivity of microorganisms in sloth hair.

Since sloths are moving around in one of the most diverse ecosystems in the world, it’s possible that they may pick up “hitchhikers,” so the researchers can’t be sure how these fungi came to live on the sloth fur. They may even have a symbiotic relationship with the green algae. However the fungi ended up in the fur, the authors suggest their presence in the ecosystem provides support for the role biodiversity plays both in the rainforest and potentially our daily lives.

Citation: Higginbotham S, Wong WR, Linington RG, Spadafora C, Iturrado L, et al. (2014) Sloth Hair as a Novel Source of Fungi with Potent Anti-Parasitic, Anti-Cancer and Anti-Bacterial Bioactivity. PLoS ONE 9(1): e84549. doi:10.1371/journal.pone.0084549

Image: Bradypus variegates by Christian Mehlführer

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Trapped in a Fig: The Perils and Payoffs of Pollination

Fresh figs

Pollinating insects are an industrious bunch, working tirelessly as they flit from blossom to blossom. But for insects like the short-lived, fig-pollinating wasp, the job of bringing fruit to fruition can be a dangerous business. According to a recent PLOS ONE study, some wasps can get trapped and die in the fig during pollination, when they enter to deposit their eggs. The researchers find that wasps of a certain size may take this risk into account when deciding which figs to approach.

Choosing which fig to pollinate is not like shopping at the supermarket, where items are placed in convenient, easy-to-reach places. Though the fig tree can produce fruit all year around?much like the availability of items in a supermarket?its flower is wrapped inside the fruit and only accessible via a small slit. Only pollinators of a certain size can enter these openings, and as the fruit ages, it may become increasingly difficult to get in and out.

In the study, the researchers sought to determine whether the fruit’s age had any correlation with successful entry, and whether the wasp’s size correlated with successful entry. To do this, they first selected fig trees whose fruit were just mature enough to attract pollinators. Then they selected and collected groups of fig-pollinating wasps and placed them in a sealed enclosure with the figs. After one day, they counted how many wasps were still alive and how many had died. They also checked to see how many wasps had successfully entered figs and how many had gotten stuck. Using the same selection process, the researchers ran an additional experiment using fig fruit of various ages.

Sid Mosdell

While not every wasp attempted to enter a fig during the experiment, those that did make the attempt met with various challenges based on their size and the age of the fruit. The researchers found that wasps attempting to enter older figs tended to take longer to reach the flower than wasps that tried  with younger figs. Their findings also indicated that the proportion of wasps that got trapped in the opening increased with fig age. In other words, the older the fruit was, the more likely a wasp would get stuck. The proportion of wasps that reached the flower decreased with fig age.

After measuring the size of the wasps’ heads, the researchers noted that wasps who couldn’t penetrate the fruit tended to have wider heads than other wasps. Wasps who made the attempt but got stuck and those that made it to the flower tended to have narrower heads than others.

The researchers hypothesize that the relationship between fig fruit age, wasp size, and successful entry indicates that a particular partnership has formed between this fruit and its pollinator. The small opening in the fruit may act as a sort of filter or barrier to encourage wasps to pollinate younger, more fertile fruit. Attempts to enter older fig fruit may reduce the number of wasp offspring and may even lead to death!

The next time you bite into a fig bar or wish for figgy pudding, take a moment to appreciate the intricate relationship between the wasp and this fruit. To learn more about this research, buzz over to the full study.

 

Citation: Liu C, Yang D-R, Compton SG, Peng Y-Q (2013) Larger Fig Wasps Are More Careful About Which Figs to Enter – With Good Reason. PLoS ONE 8(9): e74117. doi:10.1371/journal.pone.0074117

Image: Fresh figs by David Blaikie.

Image: Common Wasp by Sid Mosdell.

Plant Roots May Lie Beneath Namibian Fairy Circles

fairy3Circles of barren land, ranging from one to several feet in diameter, appear and disappear spontaneously in Namibian grasslands. The origins of these ‘fairy circles’ remain obscure, and have been attributed to causes ranging from the fantastic (the poisonous breath of a subterranean dragon) to those backed by more evidence, such as the work of a soil termite. A recent PLOS ONE paper suggests another possibility: Patterns that emerge during normal plant growth. Author Michael Cramer elaborates on the results of this study:

How did you become interested in studying the Namibian fairy circles, and are similar circles seen elsewhere?

It would be hard not to be intrigued by these mysterious barren circles on the edge of the spectacular Namibian sand sea! These circles are also reminiscent of soil mounds in other places, for example mima mounds in the US, “heuweltjies” in South Africa and “campos de murundus” in South America that have primarily been ascribed to faunal activity. Like fairy circles, these mounds may, however, represent a distinct product of patterns formed by vegetation. My co-author, Nichole Barger, became intrigued by both these phenomena while I was on sabbatical in her lab.

Many other scientific ideas have been proposed to explain the occurrence of these circles. What’s missing from these explanations? 

Any explanation of fairy circles has to provide a plausible mechanism for regular spacing of these relatively large circles in the landscape. The most common explanation to date has been that termites cause the circles. While it is undoubtedly true that ants, termites and other fauna do occur in the circles and may play a role in maintenance of the circles, we suggest that inter-plant competition is the primary cause that drives circle formation. This places plant competition in focus as a possible mechanism for determining the shape, size and distribution of the circles.

What made you think the patterns could be formed by plant growth patterns themselves?

We stood on the shoulders of giants! Previous studies have alluded to vegetation patterning as a possible cause.  Other researchers have also produced computer models to predict fairy circle occurrence and found plant growth may play a role.  More generally, understanding of spatial patterns formed by plants and the realization that this emergent phenomenon is common in arid landscapes has increased recently. Several groups have produced mathematical models that explain the production of vegetation patterns (gaps, bands and spots) and show that increasing aridity can result in transition from one pattern to another.

fairy2How did you analyze the fairy circles?

We adopted two approaches. We used Google Earth to obtain images of sites across Namibia, analyzed these to determine circle morphological characteristics, and  then combined the images with environmental data to predict the distribution of fairy circles. We performed ground surveys to measure circle morphology and collect soil samples. Soils were sampled at various depths and regular intervals inside and outside the circles and analyzed for water and nutrient contents.

What did you find?

We found that we could predict, with 95% accuracy, the distribution of fairy circles based on just three variables. Rainfall strongly determined their distribution, and differences in rainfall from year to year may thus explain why circles dynamically appear and disappear in this landscape.  The patterns of moisture depletion across the circles are also consistent with plant roots foraging for water in the circle-soil. The size and density of the circles is inversely related to resource availability, indicating that bigger circles occur in drier areas and where soil nitrogen is lower.

Do the data in this study strengthen previous results or disprove any older explanations for the circles?

Our results corroborate previous results and extend them, but we have interpreted the results in a novel manner. Since our study was correlative, i.e: we correlated the occurrence of fairy circles with certain environmental conditions, it does not disprove existing hypotheses. Direct experiments that result in fairy circles being created or closing up are perhaps the only way  to prove or disprove any of these ideas.

fairy1Do these results have implications for other ecosystems? For example, could similar ecological conditions cause fairy circles to form in other grasslands around the world?

Circular grass rings do occur in many contexts. For example, Stipagrostis ciliata in the Negev and Muhlenbergia torreyi (ring muhly) in the US (e.g. New Mexico, Utah) form rings. The distinction is that these are much smaller (ca. < 1 – 2 m diameter) and less regularly spaced than fairy circles. Nevertheless, their origins may have some commonalities with fairy circles. The special circumstance that results in the spectacular Namibian fairy circles may be the fact that the soils are very sandy and homogenous.

More generally, the fairy circles represent an example of how patterns formed by growing plants can create heterogenous spaces in otherwise homogenous grassland. Differences in soil moisture or composition across the span of a fairy circle can provide habitat for both grasses and fauna that would otherwise not thrive in this arid environment.

 

Citation: Cramer MD, Barger NN (2013) Are Namibian “Fairy Circles” the Consequence of Self-Organizing Spatial Vegetation Patterning? PLoS ONE 8(8): e70876. doi:10.1371/journal.pone.0070876

Images: fairy circles by Vernon Swanepoel (top); images below from 10.1371/journal.pone.0070876