PLOS ONE’s Top 5 Videos of 2015 (So Far)

At the end of 2014, we highlighted some of our favorite research videos from that year. We’re only mid-way through 2015, but we already have a number of popular research videos that we’d like to share. Here are some of … Continue reading »

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Burning the Candle at Both Ends: Intertidal Ant Species Can Work Night and Day

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If you’ve ever experienced rush hour traffic, you know firsthand that most humans base our schedules roughly around the rise and setting of the Sun, during daylight hours. However, the Australian intertidal ant, Polyrhachis sokolova, must instead schedule its busy day of foraging in the mangrove forest according to the rise and fall of the tide. Low tide can occur day or night, and to function effectively in both the brightest and darkest conditions, these ants possess several useful eye structures—not unlike the pupils in our eyes, or night vision goggles—that help them adjust to different light levels so that they can find food.

AntFaceThere are thousands of ant species that can have a variety of habitats, morphologies (shapes), and navigation methods. Australian intertidal ants use vision to identify landmarks like trees, and celestial cues like the angle of starlight to find their way. Low tide, whenever that may be, is the best time for foraging, so these ants need to see in all light levels without the assistance of flashlights or sunhats. Exactly how they manage to adapt to such a wide range of light conditions was investigated and described in a recent PLOS ONE study.

To learn more, researchers made tiny casts of intertidal ants’ eyes using fingernail polish. They flattened the casts and examined them under a microscope. Ants have compound eyes, meaning that their eyes are made of many tiny facets, or eye units, compared to simple eyes like ours that only have one eye unit each. Researchers counted the number of facets in each compound eye and measured each one’s diameter. The eyes were cast at different times—10am and 10pm—to inspect how the eye structures changed in dark versus light conditions. The light sensitivity of the eyes was calculated based on this morphological data.

journal.pone.0076015.g003Intertidal ants’ compound eyes each have around 596 facets and are similar to the eyes of other ant species specifically adapted to darker conditions. Eyes that “see” in the dark tend to have larger lenses and be extremely sensitive to light to get the most out of the little available light. This night vision adaptation would typically limit an ant’s ability to function in daylight because bright light would overload the photoreceptors in these highly sensitive structures, but the researchers found  other mechanisms that protect these ants’ eyes, restricting the amount of light that can enter—like a pupil—by making the openings that allow light to pass smaller. This mechanism helps the ants adapt their night-vision eyes to bright daylight.  This type of pupil is seen in other nocturnal ants but had not been found previously in ants that forage during the day.

Finally, to assist in navigation, the researchers found yet another structure in the ants’ eyes: special light detectors that act like skylights and help determine direction by sensing the angles of light sources in the sky. Therefore, Australian intertidal ants do not have the very best day or night vision, but they instead sacrifice some of their ability to see well in each condition in order to see “adequately” in both.

Citation: Narendra A, Alkaladi A, Raderschall CA, Robson SKA, Ribi WA (2013) Compound Eye Adaptations for Diurnal and Nocturnal Lifestyle in the Intertidal Ant, Polyrhachis sokolova. PLoS ONE 8(10): e76015. doi:10.1371/journal.pone.0076015

Image Credits: Images are from Figures 1, 2, and 3 from the manuscript.

Ant-Mimicking Spider Relies on a “Double-Deception” Strategy to Fool Different Audiences

From snakes that look like they have two heads to color-shifting chameleons, deception is at the heart of many animals’ survival strategies.  Both visual and chemical predator deterrence are well-documented phenomena in the animal world, but new research on ant-mimicking spiders, published in PLOS ONE, may be the first documented case of a species that uses visual deception to elude one group of predators, and chemical deception to escape another.

Ant mimicry, or myrmecomorphy, is a tactic used by numerous spider species, and with good reason, since many predators steer clear of preying on ants due to their aggressive tendencies and often unpleasant taste. Ant-mimicking spiders can have body shapes that closely resemble those of ants, as well as colored patches that look like ant eyes.  Combine these characteristics with behaviors such as waving their front legs in the air to resemble probing ant antennae, and these spiders can successfully convince predators to look elsewhere for their next meal.  The jumping spider Peckhamia picata is one such ant mimic whose visual signals are an effective deterrent for visually focused predators, such as other species of jumping spiders.  The picture below shows a jumping spider on the left and the ant it imitates on the right.

1 Ant mimic and predators

The PLOS ONE study shows that the ant-mimicking spider can also elude predators that rely heavily on chemical signals to identify their prey.  In the current study, the spiders successfully eluded spider-hunting mud-dauber wasps (pictured below), and received significantly less aggression from the ants they mimic than other non-mimicking jumping spiders. The researchers presented wasps with a choice between freshly killed ant-mimicking and non-mimicking spiders. In all of the trials conducted, the wasp probed both types of spiders with their antennae, but every time the wasps chose to sting and capture a spider (seven out of eight times), it chose the non-mimicking spider.The researchers also staged encounters between Camponotus ants and live ant-mimicking and non-mimicking spiders.  After probing them with their antennae, the ants were significantly less likely to bite the ant-mimicking spiders than non-mimicking ones.  These results demonstrate that the jumping spider has a remarkably effective ability to deceive potential predators who focus on chemical cues when selecting prey.

2 wasp

The researchers point out that the spider is not a chemical mimic of the ant species it emulates. Insects rely heavily on hydrocarbons secreted from their cuticles (the hard outer covering of invertebrates) to identify and signal one another. It turns out that ant-mimicking spiders have very low levels of these molecules, only a small fraction of the amount found in non-mimicking spiders and the ants themselves. While further research is required to fully explain the jumping spider’s chemical mechanism for predator evasion, a likely explanation is that the low level of these chemicals does not register as significant to a probing ant or wasp, and the chemical evasion is accomplished in this way.

This study may be the first to describe an animal using a “double-deception” strategy:  visual tricks and a deceptive chemical signature, both intended for different audiences.  The authors hypothesize that this kind of chemical deception is likely widespread among other visual mimics in the animal kingdom.

Related links:

Video of a ramblin’ ant-mimicking jumping spider (great music)

Spiders gather in groups to impersonate ants

Citation: Uma D, Durkee C, Herzner G, Weiss M (2013) Double Deception: Ant-Mimicking Spiders Elude Both Visually- and Chemically-Oriented Predators. PLoS ONE 8(11): e79660. doi:10.1371/journal.pone.0079660

Images:  Images come from Figure 1 of the manuscript

Making the News in May

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Laughter, fungi, pipettes and ants – last month, PLOS ONE papers made headlines with an array of research. Here are some of our May media highlights:

Not all laughter is the same and your brain knows it. In recently published research, scientists studied the effects of three types of laughter (joyous, taunting, and “tickling”) on the human brain. Participants listened to recordings of these laugh and were asked to discern the type and count how many bouts had occurred. The researchers found that the participants could discern joyous and taunting laughter at comparable rates and that it was slightly more difficult to discern laughter in response to tickling. Participants were  able to count the number of taunting laughs more accurately than joyous and tickling laughs. Read more about this study in the Huffington Post UK, TIME, and Los Angeles Times.

There are fungi afoot! New research confirms that the chytrid fungus (Batrachochytrium dendrobatis), which has decimated amphibian populations around the world, can be found in frogs in California. Scientists swabbed 201 South African clawed frogs (Xenopus laevis) in the California Academy of Sciences’ collection, 23 of which were caught in California. Eight specimens tested positive for chytrid, including one frog caught in San Francisco County in 2003. This frog species was once imported to aid in pregnancy testing. To read more, visit the National Geographic, Science News, ABC and the Smithsonian blog, Smart News.

Pipettes are a staple lab equipment, but not without their drawbacks. According to a new PLOS ONE paper, certain methods of dispensing and diluting liquids can introduce errors in experimental data. The researchers of this study compared pipetting, or tip-based transfer, with an acoustic dispensing technique and found that laboratory results depended greatly on the dispensing technique. Learn more about this study by reading the Royal Society of Chemistry’s Chemistry World, Nature’s Methagora blog, and In the Pipeline.

There are plenty of odd couples in nature. For one example, just look at the unlikely partnership of the ant and the pitcher plant. A recent study finds that a particular ant species, Camponotus schmitzi, has formed a mutually beneficial relationship with the carnivorous Nepenthes bicalcarata, a pitcher plant. Scientists observed that the ants provide pitcher plants with nitrogen and preys on other insects, such as mosquitoes, that may otherwise steal nutrients from the plant. In return, the pitcher plant provides a home and a steady source of sustenance. You may find more about this study at Discovery News, The Scientist, and the New York Times.

To find out what other PLOS ONE papers were in the news in May, check out our Media Tracking Project.

Image: Figure 1 from “A Novel Type of Nutritional Ant–Plant Interaction: Ant Partners of Carnivorous Pitcher Plants Prevent Nutrient Export by Dipteran Pitcher Infauna”

Citations:

Wildgruber D, Szameitat DP, Ethofer T, Brück C, Alter K, et al. (2013) Different Types of Laughter Modulate Connectivity within Distinct Parts of the Laughter Perception Network. PLoS ONE 8(5): e63441. doi:10.1371/journal.pone.0063441

Vredenburg VT, Felt SA, Morgan EC, McNally SVG, Wilson S, et al. (2013) Prevalence of Batrachochytrium dendrobatidis in Xenopus Collected in Africa (1871–2000) and in California (2001–2010). PLoS ONE 8(5): e63791. doi:10.1371/journal.pone.0063791

Ekins S, Olechno J, Williams AJ (2013) Dispensing Processes Impact Apparent Biological Activity as Determined by Computational and Statistical Analyses. PLoS ONE 8(5): e62325. doi:10.1371/journal.pone.0062325

Scharmann M, Thornham DG, Grafe TU, Federle W (2013) A Novel Type of Nutritional Ant–Plant Interaction: Ant Partners of Carnivorous Pitcher Plants Prevent Nutrient Export by Dipteran Pitcher Infauna. PLoS ONE 8(5): e63556. doi:10.1371/journal.pone.0063556

No sense of direction? Consider consulting some carp

The ability to navigate using the earth’s magnetic field is a skill that is not unique to humans.  Over the last few decades, scientists have discovered that numerous organisms have an ability to tell which way is north.  And the list is growing.

In one study, “Magnetic Alignment in Carps: Evidence from the Czech Christmas Fish Market,” Hart et al. reported that carp tend to align themselves along a north-south axis.  The authors photographed over 14,000 carp swimming in plastic tubs at pre-Christmas fish markets and found that, on average, the fish positioned themselves facing either the North Pole or the South Pole.

While the authors have not yet proven that carp can sense the geomagnetic field, they did rule out other possible orientation cues, including light, wind, temperature, and water flow. What benefit a common orientation may provide the fish remains unknown.  One possible explanation the authors present is that it may help the fish coordinate their movement when they swim in a school.

Some other organisms also have an ability to detect localized magnetic fields.  In a paper titled “Desert Ants Learn Vibration and Magnetic Landmarks,” Buehlmann et al. demonstrated that ants can sense a strong magnetic field created by two small magnets and use this as a landmark to find their nest.

In the absence of any other landmark (such as a vibrational, visual, or olfactory cue), ants who had been trained to associate the magnetic field with the nest entrance spent a lot more time near the magnetic field than ants who were naive to this landmark.  It is unclear how relevant this experiment is to ants in their natural environment, but the study nevertheless highlights the ants’ ability to sense a magnetic field.

While little is known about how carp align with the earth’s magnetic field or how ants sense a localized magnetic field, more is known about how some tiny organisms, aptly named magnetotactic bacteria, orient with a magnetic field.  These bacteria form straight chains of nano-size magnetic particles within the cells. The magnetic chains are attached to intracellular structures, thus allowing the bacteria to align passively with the earth’s magnetic field, like compass needles.

In a paper published earlier this month, Kalirai et al. showed that some magnetotactic bacteria form anomalous magnetic chains, with some sections of the chain oriented north and others south.  This finding contradicts scientists’ previous understanding that all the magnetic particles in a single chain would have the same alignment.  The study raises many questions: Would bacteria with anomalous magnetic chains have a competitive disadvantage in their natural environment?  Is there a single genetic mutation that leads to the anomalous magnetic chains?

All three of these studies raise intriguing questions, and we look forward to future discoveries from these scientists.

Image: Arrows indicate the orientation of carp swimming in a plastic tub (Hart et al. PLOS ONE 2012)

References:

Hart V, Kušta T, N?mec P, Bláhová V, Ježek M, et al. (2012) Magnetic Alignment in Carps: Evidence from the Czech Christmas Fish Market. PLoS ONE 7(12): e51100. doi:10.1371/journal.pone.0051100

Buehlmann C, Hansson BS, Knaden M (2012) Desert Ants Learn Vibration and Magnetic Landmarks. PLoS ONE 7(3): e33117. doi:10.1371/journal.pone.0033117

Kalirai SS, Bazylinski DA, Hitchcock AP (2013) Anomalous Magnetic Orientations of Magnetosome Chains in a Magnetotactic Bacterium: Magnetovibrio blakemorei Strain MV-1. PLoS ONE 8(1): e53368. doi:10.1371/journal.pone.0053368