Falling with Style: Controlled Gliding in Spiders

Sometimes I read a paper because the methods catch my eye. I can just imagine some scientists sitting around a table with a beer and saying, “I wonder what would happen if we just dropped a bunch of spiders from the tops of trees.” An article published online yesterday did just that.

Barro Colorado Island is a man-made island is located in Gatun Lake, created by filling of the Panama Canal. It is covered in tropical rainforests, and its inhabitants have been studied extensively. It would be a mistake to look at a forest as only ground habitat. The canopy supports a tremendous abundance of life, particularly arthropods. These critters are particularly tasty to predators and must find a way to escape within their decidedly hazardous habitat that is located over 90 feet (30 meters) off the ground. Falling is a bit of a risk. But what if you do fall? You could land in the understory or on the ground which, if it doesn’t kill you, is both unfamiliar and full of predators. To avoid this potentially lethal scenario, many wingless arthropods have developed the ability to orient their bodies (via visual cues, appendages, and other structures) such that they are more likely to fall towards tree trunks.

The genus Selenops is a large and common group of nocturnal spiders. They are easy to find and collect, often hiding under bark or in crevices. The researchers went out into the forests and collected a bunch of these spiders. The spiders were then weighed and photographed. The images were then analyzed for the horizontally projected areas of different segments and appendages. Then these data were put together to give “effective wing loading.” Here’s where we get to the fun part. The spiders were put into individual plastic cups and taken up into the canopy. The cups were held at a known distance from a tree trunk, inverted and tapped to release the spider. Geronimo! These drop tests were filmed at 60 frames per second so that glide index (ratio of horizontal distance from the tree trunk to the total distance traveled) could be calculated. The videos also allowed for the measurement of how the legs were being used to maneuver. The spiders were also scored in terms of their performance, either directly reaching the tree, indirectly or irregularly gliding towards the trunk, or failing completely and landing elsewhere.



Most of the spiders had a successful, directed decent without the aid of draglines or balloons. They fall several meters and then glide to a trunk. During this fall, they were observed to adopt body postures that orient their bodies to descend head first with the forelegs out to the side and slightly forward and the rest of the legs out and back. This foreleg asymmetry was shown to significantly change body heading meaning that they are using their legs to control their glide trajectory. Also, glide index was shown to decrease with increasing body mass. They hypothesize that this negative relationship means that larger spiders must accelerate under gravity to airspeeds where aerodynamic lift becomes significant relative to body weight.

This is an interesting result because other arachnids do not show it. These spiders have developed the ability to control their glide trajectory. This means that they have evolved novel mechanisms of body righting and maneuvering. Gliding spiders….cool.


Stephen P. Yanoviak, Yonatan Munk, & Robert Dudley (2015). Arachnid aloft: directed aerial descent in neotropical canopy spiders J. R. Soc. Interface, 12 : 10.1098/rsif.2015.0534

(image via Toy Story screencap)

Mutualism a.k.a Caterpillars Drugging Ants To Do Their Bidding

From the study - Figure 1. Attendant Workers of
Pristomyrmex punctatus standing on or around
Narathura japonica caterpillars

The manuscript is done! Submitted! Summer interns are finished. Boot up Normal Life Mode, please. Recommence blogging. So many good papers have come out during my hiatus. Where to start…where to start…

If you have read this blog for any amount of time then you will come across my fascination with ant manipulation, particularly zombification. This is why my cursor stopped over a new paper in Current Biology about caterpillars manipulating ants to do their bidding.

Let’s start with mutualism. This is a topic that I have visited in the past, and in ants for that matter. It’s a nice little relationship between species that involves an exchange of goods and/or services. In the natural world, this often means food and protection.

In this study, the researchers chose the Japanese oakblue butterfly (Narathura japonica), a lycaenid belonging to the Theclinae subfamily of butterflies. Many in this group are myrmecophilic, meaning they associate (often mutualistically) with ants in some way. The Japanese oakblue caterpillar has a specialized exocrine gland, the “dorsal nectary organ (DNO),” that is located on the seventh abdominal segment and is flanked by tentacle organs (TO). The DNO secretes sugar- and amino acid-rich honeydew while the TO secretes scents to “talk” to the ants. A “Come on down!” or “Danger, Will Robinson!” type thing. The ants tend to the caterpillars and keep them safe for a nice, sugary food reward. But is that all to the story? Obviously not or this post would end here.

To do this experiment, butterfly eggs and their associated ants (Pristomyrmex punctatus) were collected and reared separately. Then three test situations were set up with 50 ants per treatment:

1. “Experienced” ants – had free access to the caterpillars and their DNO secretions
2. “Inexperienced” ants – no caterpillar access, just some sugar soaked cotton balls
3. “Unrewarded” ants – had access only to caterpillars that had their DNO’s blocked (a little bit of clear nail polish goes a long way)

After 3 days in their test situation, 10 ants from each treatment were moved to Petri dishes that were set on pieces of white paper with a line on it to divide the dishes into 2 halves. After the ants acclimated to their new little plastic arenas, they were observed to see how many times they crossed the center line (“locomotory activity”). Also at the 3 day time point, ants and caterpillars were frozen in liquid nitrogen until their brains could be dissected out, specifically removing the optic lobes. Now, I’ve done some pretty small dissections, but those come nowhere close to ant brain removal! Wow, just wow. Once those itty bitty brains were out, they were processed for liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) for serotonin, dopamine, octopamine, and tyramine. Very simply, that means making an ant-brain-aerosol that is then separated and identified by component.

They found that experienced ants had significantly less locomotory activity than the other two groups. So what does an ant walking, or in this case not walking, across a line even mean? Well, the fact that the ants are staying put signals that they are “standing guard” for the caterpillars. Okay, let’s say that standing means guarding, how do we know that this is really caterpillar-related and not just standing there? Well, first of all, it was only the experienced ants that did this. Second, the researchers observed that the caterpillars often “everted their TOs,” meaning that they turned them outward. This is typically a response the caterpillar makes when it is attacked by a predator – “Raise shields!” Experienced ants responded differently than the other two when they saw this caterpillar behavior in that they responded aggressively. This aggression is a response to the caterpillars’ alarm, one that has the ants defending against the predator. The fact that only experienced ants had these responses suggests that something in the DNO secretions is eliciting these defense behaviors.

So what is it about these secretions? That’s where the LC-MS/MS comes in. Biogenic amines are known function as neurotransmitters, neuromodulators, and/or neurohormones. This means that they can modify behavior in insects. DNO secretions contain biogenic amines. This analysis showed that experienced ant brains had low dopamine levels. Now, that’s important because dopamine has been shown to be involved in both locomotory activity and aggression in well studied organisms like fruit flies. Starting to see some links here, yes? To confirm the linkage, ants from each treatment were given reserpine, a small-molecule inhibitor that depletes dopamine but not serotonin in the brain. This test resulted the same behaviors, but the LC-MS/MS showed increased dopamine and serotonin in the ant brains. So same but different.

There is another aspect to consider: Who loses if the mutualism goes away? The honeydew is not the sole source of nourishment for the ants. They can leave and be still be fine. The caterpillar has much more to lose than the ant (its life via predation). So the caterpillars must be doing something besides sugar-loading their ants.  This is where the caterpillar gets sneaky - finding a way to make their ants to both stick around and defend against predators. As the authors put it, they they insert “manipulative drugs [into the honeydew] that could function to enforce cooperative behavior…from attendant ants.” Put that way, I’m okay calling it “ant mind control.”


Hojo, M., Pierce, N., & Tsuji, K. (2015). Lycaenid Caterpillar Secretions Manipulate Attendant Ant Behavior Current Biology DOI: 10.1016/j.cub.2015.07.016

p.s. The supplementary materials have a nice little video of ants in lined Petri dishes.

(image is Figure 1 from the above paper)

Not So Simple: Social Evolution in Silk-Weaving Ants

Silk weaving ants. That in and of itself is really neat. Then you see this picture of Polyrhachis shattuck...I mean, look at her! How many cool points can one animal rack up? A new study in Behavioral Ecology and Sociobiology takes a look at these arboreal nesting and silk-weaving ants.

Let's begin with sociality. It is one of those subjects in biology that is considered its own discipline. When you think of social animals you probably think of herds of mammals or maybe schools of fish. Sociality reaches its peak in eusociality, a surprisingly complex and truly social organization. These animals live in groups, cooperatively care for juveniles, divide labor, and overlap in generations. Studies of these social systems has shed light onto broader concepts of collective decision making, even leading to advances in our own technology (traffic flow, communications networks, internet searches, etc.). However, as much as we know about the social mechanics, we know very little about the evolution of such systems.

Most eusocial animals are found in the phylum Arthropoda, with the order Hymenoptera being the largest and most well-known, and all ants classified as eusocial species. And ants are the focus of today's chosen study. Ant larvae spin individual protective cocoons of silk and, depending on the species, that silk is either allocated to the colony or sequestered for the larvae’s individual needs. Donated silk is used by the worker caste to weave together leaves into nests. The “lowest grade” of arboreal (a.k.a. tree-dwelling) ants, Dendromyrmex, have larvae that produce silk without any interaction or provocation from the worker ants. In “intermediate grade” ants, Camponotus senex and Polyrhachis ?doddi (re-described as Polyrhachis robsoni (Kohout 2006)), the workers hold larvae at the work site and, with simple ritualized behaviors, the workers collect the silk. In the “highest grade” genus, Oecophylla, the larvae donate their silk supply to the colony. A worker ant will use highly ritualized behaviors - bring the larvae to the work site, straddle a leaf seam, use antennae to tap the head of the larva (telling it to extrudes silk from its salivary glands), use silk to glue together the seam, repeat.

A comparison of ant genera in this way, simple to complex, is thought to represent possible evolutionary steps in nest-weaving behavior. However, molecular sequence data suggests that nest-weaving has evolved independently in each of the four genera in which it occurs. This new study focuses on Polyrhachis ants. This genus offers good within-taxa comparison of multiple life strategies as different species vary in their nesting locations, from intertidal to subterranean to arboreal, the presence of nest construction, and even silk sources.

A total of 37 specimens of ants from all 13 currently recognized (*grr*, an often frustrating term in insect taxonomy) subspecies and five outgroup taxa were used for this study. The researchers isolated total genomic DNA and amplified and sequenced DNA from six fragments using specific primers for each gene region. After they collected the sequences, they analyzed and aligned them using computer programs. In their complicated analysis (they used Bayesian…that always makes my eyes cross) they input the gene level data along with variables of nesting preference (ground = soil, logs, stones vs. arboreal = twigs or leaves in trees) and nest construction (silk weaving vs. no silk vs. other silk). All of this allowed them to construct phylogenies (like an evolutionary family tree) and infer relationships among the species and ancestral states for behavior.

Their results showed robust phylogeny with strong support for the monophyly of the genus Polyrhachis, further supported by the inclusions of nesting preference and nest construction.This is good because it provides a nice, solid ancestral reconstruction for the evolution of the different species and their relationships to each other. It also allows for the comparison of the different nesting strategies within the framework of evolution. The investigation turned up some very interesting results. Simply, their results do not support the stepwise evolution of simple to complex. They found that the production of arboreal silk nests is the ancestral state with at least two transitions to subterranean nesting and the loss of silk weaving as species become more derived. There is also some flexibility and reversal in the behavior. Basically, the ants evolve, abandon and then re-evolve the nest weaving practices. The loss of silk nest weaving seems to occur with the transition from arboreal to terrestrial nesting followed by the re-evolution of silk nest weaving. This suggests a strong but flexible link between nesting preference and nest construction.

To illustrate this evolve-abandon-re-evolve point, the researchers present the example of Hedomyrma, a subgenus within a larger clade of subterranean nesters. This larger clade has already lost both arborality and nest weaving. But there are 2 species of Hedomyrma (Polyrhachis argentosa and Polyrhachis fervens) that have reverted to arborality. The re-evolution of this nesting preference has come with the modification of building nests within the hollow internodes of bamboo sans silk. Another reversal pattern is seen in a third species of Hedomyrma (Polyrhachis turneri), which has larvae that retain all of their silk for their own cocoon-constructing needs. Rather, worker ants steal silk from spiders to build nests on the sides of rocks. So the nest construction characteristic is what has re-evolved, just with a different mechanism. Larval cocoons have been lost in 2 of the arboreal nest-weaving species studied, and the allocation of larval silk to colony rather than individual need is considered a more derived but decoupled characteristic of nest construction.

I think that both the flexibility and the rapid evolution (or re-evolution) of this system is what attracted me to this paper. We know that evolution is a complex concept that we often boil down to from-simple-to-complex, and in many cases it is exactly that. This study almost reads like a sequel, a what-happens-next sort of thing.


Robson, S., Kohout, R., Beckenbach, A., & Moreau, C. (2015). Evolutionary transitions of complex labile traits: Silk weaving and arboreal nesting in Polyrhachis ants Behavioral Ecology and Sociobiology DOI: 10.1007/s00265-014-1857-x


(image of Polyrhachis shattuck, Maliau Basin, Sabah via AntWiki via California Academy of Science Ant Course)

Small Things, Big Problem: Microplastics Uptake in Shore Crabs

Lately I've been gearing up for some nano-particle research, and so I've been doing a lot of reading about very small things. While perusing the literature, I came across a paper published online in Environmental Science and Technology that takes a look at microplastics.

Let’s start with the Great Pacific Garbage Patch, a very good example of this type of marine pollution. This huge collection of marine debris in the North Pacific Ocean is created by an ocean gyre, a stable circular ocean current that draws in debris where it is trapped and builds up. The collected debris is our litter – plastics and other material that are not biodegradable. They can’t escape the gyre, they just collect. And as they sit out there swirling around, they break down into smaller and smaller pieces called microplastics.

Microplastics are defined as those plastic particles less than 5 mm in length, and these small particles are a huge marine pollution problem. They are classified into two groups: (1) primary microplastics that are created at the microscale for use in products like cosmetics and drugs and (2) secondary microplastics that are products of the breakdown of larger items. As a whole, they are persistent and widespread – we’re talking worldwide, the Great Pacific Garbage Patch is just the most well-known aggregation. These microplastics are very abundant, we’re talking 1,000-100,000 particles per cubic meter of seawater! And there is growing evidence of the danger these tiny materials are having on marine life, everything from turtles to sea birds to fish and even zooplankton.

A new study by Watts et al. takes look at the uptake of these microplastics in the shore crab (Carcinus maenas). Previous studies have shown that an important prey species of the shore crab, the common mussel (Mytilus edulis), accumulates microplastics as it filters the water for food (“ventilation”). In laboratory conditions, the direct transfer of microplastics from mussels to crabs has been shown, but then again, it has also been shown that crabs uptake microplastics as they pull water through their gills. So what exactly is going on here? How are these crabs exposed and are they able to clear the microplastics from their bodies?

This is one of those studies where I just love to describe the methods. The first thing the researchers had to do was to assess the ability of the crabs to uptake microplastics (in the form of 8-10 um polystyrene microspheres) through their gills. To do this, they fitted the crabs with masks designed to allow measurements of ventilation. Yep, they put little masks on crabs. Picture that. I love science. Next they assessed the ability of the crab to take up microspheres in their food by exposing mussels and then turning them into “jellified mussel homogenate” to then feed to the crabs. I wonder which undergrad had the lovely job of making gelatin mussel popsicles? To see if the microplastcs were cleared, they let the crabs sit in their tanks and tested the abundance of microspheres in the water during water changes every 2 days for 22 days, sampling periodically. During each stage of the experiment, they measured the abundance of microspheres in the gut and gill tissues, fecal material, and hemolymph (like blood). Using fluorescent microscopy and Coherent Raman scattering microscopy (CRS; a multiphoton microscopy that produces label-free contrast of both the target sample and the surrounding biological matrix), they were able to look at the location of the microplastics within the tissues.

The researchers found that the masked crabs took up 31,000-62,000 microspheres (0.39-7.7% of the initial exposure concentration) into their gills after only 16 hours. But this uptake was not even across the gills, with greater uptake in the posterior gills. The crabs where able to expel some of the spheres, but slowly, still expiring microspheres 21 days after being exposed. Imaging the gills showed the microspheres to be associated with the gill epidermis. The feeding experiment showed all crabs to have microspheres in their foregut and later in their fecal material. The residence time of these microspheres was short, but still took longer to excrete than regular food waste, up to 14 days. Microscopy showed microspheres associated with the internal setae of the foregut lining. But, neither the ventilation experiment nor the feeding experiment showed any microspheres in the hemolymph.

Back to the question of what’s going on here? The shore crabs did take up microplastics in both types of exposure, but residence time is the key. They were able to clear the microplastics they got through dietary means, but they were still trying to clear microplastics they took up during ventilation almost a month later. The authors constructed a model to explain the mechanism of the movement of the microplastics. They found that the crabs tended to exhibit an asymmetry in microplastic uptake in the gills, which they attributed to the pumping mechanism of the scaphognathite being more dominant on one side of the gill chamber. Also, the posterior gills have a larger surface area than the anterior gills so they are more likely to take up microplastics into their lamellae. The crabs were unable to dislodge the tiny particles by normal gill cleaning actions. It is interesting that no microspheres were found in the hemolymph at any of the sampling points in either experiment. That suggests that there is no movement of the particles. It is likely that the particle size they used (10 um) was a little bit too large as it has been shown that sizes of 0.5 um are able to translocate in these crabs. This idea of particle size is something I’ve been seeing with increasing frequency within the nano-particle literature, along with polymer type, shape, and coatings. To that I would add that species is probably also in the mix as gills in crabs and fish are structured differently, and nano-particles have been shown to move in to organs like the liver in fish.

Studies like this are interesting because they show how very small things can become a very large problem affecting multiple tissues of the same organism up to multiple levels of a trophic cascade. I mean, think about it, even we humans could be affected. After all, we consume a lot of crab. How many microplastics are you ingesting when you stop at the crab shack for a quick lunch?


Watts AJ, Lewis C, Goodhead RM, Beckett SJ, Moger J, Tyler CR, & Galloway TS (2014). Uptake and Retention of Microplastics by the Shore Crab Carcinus maenas. Environmental science & technology PMID: 24972075


I know I used some technical terms, if you need some help with crustacean anatomy check out Invertebrate Anatomy OnLine.

(image via UGA Evolution 3000H)

The Charge of the Crazy Ant: Chemical Warfare Between Invading Species

LeBrun, Jones, and Gilbert (2014) Figure 1A

I’ll be the first to admit that I've been a little blog-negligent lately. Even when all of the ice and snow we've gotten here on the East Coast forced me to stay inside I just binge watched shows on Netflix instead. I’m not sure what brought me out of my procrastination funk and compelled me to do a little reading and writing. If you've been following the Facebook page then you've been getting a lot of yummy sciency tidbits, but it’s time for me to get back on the hard science wagon. I think I’ll start off with a great couple of papers about ant chemical warfare.

These papers focus on invasive ants, a big problem in many regions. To really grasp one of the underlying aspects of their warfare strategies, you must first understand the basics of an invasive species. Start by recognizing the difference between a native species and an exotic species. Put simply, a native species occurs naturally (or natively) to a habitat and an exotic species does not. Exotics can come in any biological form, but they are not necessarily a problem to their new habitat (think: earthworms). It’s when an exotic species becomes an invasive species that there is a problem because invasives cause environmental, economic, and/or human health harms. The reason for this is that they did not evolve together with the ecosystem in which they find themselves. There are no checks and balances in place to curb their population growth, things like predators, parasites, and competitors. Their unnaturally large population numbers then become harmful to the native species that suddenly have to deal with and compete against them, dramatically altering the community and habitat.

It is often the case that multiple species invade a region. Throughout the rest of this post I’ll be discussing new papers by Michael Kaspari and Michael Weiser and by LeBrun, Jones, and Gilbert (specifically at the latter) that take a look at just such a case in ants. The red imported fire ant (Solenopsis invicta) first came to the United States from South America around 1930. This species is far more aggressive than your typical American ant, not only in how they like the bite the hell out you (that’s a lot of personal experience talking) but also in their predatory abilities and landscape re-engineering. Now enter the tawny crazy ant (Nylanderia fulva). This new exotic invasive species was transported to the southeastern U.S. in the early 1980s and has begun to spread.. These two species have common source assemblages, their native ranges overlapping in northern Argentina, Paraguay, and southern Brazil. Until the introduction of crazy ants, the fire ant has enjoyed an uninterrupted domination of the native grassland ant assemblages. But now that the crazy ant has arrived on the scene they are displacing the fire ants. Why is this?

Since the fire and crazy ants have overlapping native habitats, they have evolved to compete directly for resources. The tawny crazy ant easily expels the fire ant from any food items it controls, up to 93 percent of the time. Also, tawny crazy ants have often been found living inside fire ant mounts, having usurped the mound and evicted the owners. Fire ants are strong and resilient and so the crazy ants must have a strong competitive advantage.

Now, finally, we get to the meat of the post: chemical warfare. If you've been stung by a fire ant (or ants, plural, as is usually the case) then you know that they pack a wallop! They have an alkaloid venom called Solenopsin that to humans causes a painful, fiery sting, and to other ants acts as a topical insecticide. The crazy ants do not have stingers but instead possess an acidopore (a specialized exocrine gland) on the end of the abdomen that sprays their venom into a mist of formic acid. They will charge into masses of fire ants misting as they go. But the fire ants don’t just stand by idly to be sprayed with venom and die, they fight back. The fire ants “gaster flag,” extruding venom from their stingers and dabbing it onto a nearby attacking ant. Normally this would result in the death of said ant. However, LeBrun and his colleagues have observed what they are calling a “detoxifying behavior” in the attacking tawny crazy ants. In this behavior, an afflicted ant stands on its hind legs, run its front legs through its mandibles, and grooms itself vigorously, periodically reapplying its acidopore to its mandibles (check out the video!).

To test this behavior the researchers conducted a series of experiments to see if there is really a detoxifying component, to see where it is coming from, and to evaluate the species-level specificity of the behavior. For the first they staged antagonistic interactions between the two species, sealing a portion of the crazy ant acidopores, and then observing afflicted individuals for behavior and survivorship. They found that those tawny crazy ants that had had their acidopores sealed had a low survival rate (only 48 percent). However, those with working acidophores had a 98 percent survival rate, supporting the detoxifying hypothesis. The Dufour’s and venom glands (exocrine glands used for communication and defense) both duct to the acidopore in this species. To see where the detoxifying agent was coming from they applied solutions of fire ant venom and tawny crazy ant glandular products to Argentine ants (Linepithema humile), which are morphologically similar to crazy ants but do not have the detoxifying capability. These tests showed the venom gland of the crazy ant to contain the detoxifying agent. When the crazy ant’s formic acid was tested it was found to be the compound responsible for detoxifying fire ant venom.

The production and application of this antidote is a potentially costly endeavor for the crazy ants. Yes, it is the difference between life and death, but when to apply it must be considered. Why use a costly resource if you don’t have to? The authors conducted a series of ant interaction tests where they had crazy ants interact independently with eight Texas ant species including fire ants, observing when the crazy ants chose to apply their detoxifier. They found that after chemical conflict with fire ants, crazy ants detoxified themselves with almost 7 times more frequently than the average response to other ant species. This suggests that this detoxifying behavior is specifically adapted to competition with fire ants, and it is probably a key factor in the displacement of invasive fire ants now underway in the southern United States.


LeBrun, E., Jones, N., & Gilbert, L. (2014). Chemical Warfare Among Invaders: A Detoxification Interaction Facilitates an Ant Invasion Science, 343 (6174), 1014-1017 DOI: 10.1126/science.1245833


Kaspari, M., & Weiser, M. (2014). Meet the New Boss, Same as the Old Boss Science, 343 (6174), 974-975 DOI: 10.1126/science.1251272


U.S. Fish and Wildlife Service's page on Invasive Species
The University of Texas at Austin Fire Ant Project
Texas A&M AgriLife Research Extension page on Tawny Crazy Ants

Pinpointing the Pollen: Honeybees and a Host Jumping Virus

Lately I've been revisiting some of my past topics and continuing the story with new research. Such is the case today. A relatively popular post of mine from 2010 called The Buzz on the Bees described a study from that year by Jerry Bromenshenk et al. investigating Colony Collapse Disorder (CCD). CCD describes the mysterious, sudden and serious die-off seen honeybee (Apis mellifera) colonies across the U.S. It is characterized by sudden colony death with a lack of adult bees in front of the die-outs. Honey stores and recent brood rearing are often evidenced, and sometimes the queen and a small number of survivor bees remain. The 2010 study found CCD colonies to contain an iridescent virus (IIV) (Iridoviridae; a DNA virus) that tracks with the microsporidia, Nosema apis and N. ceranae (specifically the latter), when compared to healthy colonies. This and previous scientific studies, using sensitive genome-based and proteomic methods, have also found small RNA bee viruses. These RNA viruses, alone or in conjunction with other pathogens, have frequently been implicated in CCD.

A new study published a couple of days ago in mBio by Ji Lian Li et al. correspondingly takes a look at the role of viruses in CCD. Evidence from previous studies shows that viruses that cause common infections in honeybees also infect other hymenopteran pollinators. A study published by Singh et al. (2010) even showed these viruses to be present and infective in pollen pellets.

I’ll conjecture that if you ask most people you’ll find that they don’t really think of plants as capable of getting viruses. That is until some disease comes and kills all of the fruit trees in their back yards. But plant viruses are like other viruses, obligate intracellular parasites, and they require a way to transmit from one plant to another. As you may have noticed, plants don’t generally get up and move around. This means that their viruses need a vector. Generally, these vectors are herbivorous insects. These insects are carriers, usually by carrying around infected pollen spreading the virus from one plant to another without themselves getting sick. To date, only a few plant viruses are known to also affect their insect vectors.

Li et al.’s new study takes a closer look at the role of pollen in virus transmission in honeybees. Initially, they carried out a study to screen bees and pollen loads of bee colonies for the presence of frequent and rare viruses. This resulted in the chance detection of a plant virus, tobacco ringspot virus (TRSV). This virus is a type species of the genus Nepovirus within the family Secoviridae, and it is known to infect a wide range of herbaceous crops and woody plants. Like other members of this genus, TRSV has a bipartite genome of positive-sense, single-stranded polyadenylated RNA molecules, RNA-1 and RNA-2, encapsidated in separate virions of similar size. For you non-biologists, this basically means that the virus has two genome segments/virus particles and can be directly translated into the desired viral proteins by the host cell. RNA viruses typically mutate very fast and are really good at working around host defenses (HIV and hepatitis are good examples of RNA viruses).

It is known that honeybees transmit TRSV from infected plants to healthy ones, but its presence in the researchers' screens got them to wondering if this plant virus could cause systemic infection in the exposed honeybees. To answer this, they collected adult worker bees, samples of the pollen being processed by a colony, and the ectoparasitic mite Varroa destructor (great name!) within the hive. They assessed 10 colonies for 1 year, classifying them as strong or weak based on the size of adult populations, amount of sealed brood, and presence of food stores. From their samples they purified virus particles from the adult bees and used them for cDNA library construction, virus-specific primer design, total RNA extraction, conventional RT-PCR, in situ hybridization, cDNA sequencing, and a phylogenetic analysis.

The observations of the colonies revealed an increase in bee deaths starting in the autumn and peaking in the winter. The researchers found both TRSV and IAPV (Israeli acute paralysis virus, common in honeybees) to be absent in colonies classified as strong, but both were found in weak colonies. Weak colonies too were found to have more multiple virus infections. These weak colonies were the ones less likely to survive through the cold winter months. Additionally, TRSV of the same strain was detected in the mites of infected colonies suggesting they obtain it from their bee hosts.

These results are the first evidence that honeybees exposed to virus-contaminated pollen can also be infected and that the infection can be systemic and spread throughout their entire body. Any host jumping is not without its challenges. In order for a virus to jump to a new host it must have the opportunity to come into contact with a perspective host, undergo genetic changes so that it may enter a new type of host cell, and gain the ability to spread horizontally between individuals within the new host populations. It seems that TRSV has been successful in overcoming all of these challenges. Its presence in the mites suggests that they could be a vector for the horizontal transmission between colonies. However, food-borne transmission (via pollen) is the most important route for transmission. Their results suggest that TRSV is neurotropic (affecting the nerves) in the honeybees, potentially causing severe functional impairment of nerves and muscles.

Do these results definitively conclude that TRSV is the cause of CCD? Well, no. But this study does add to a growing body of evidence that implicate parasites and pathogens as the key culprits.


Ji Lian Lia, et al. (2014). Systemic Spread and Propagation of a Plant-Pathogenic Virus in European Honeybees, Apis mellifera mBio, 5 (1) DOI: 10.1128/mBio.00898-13


NY Times article: "Bee Deaths May Stem From Virus, Study Says"

Also, check out these links for more information on Colony Collapse Disorder:
Mid-Atlantic Apiculture Research and Extension Consortium (MAAREC)
United States Department of Agriculture: Agricultural Resource Service
United States Department of Agriculture: National Agricultural Library
The Ohio State University's Agriculture Network Information Center's Bees and Pollination Page


(image via Wikipedia)

Dung Beetles and Ball-Rolling: Star Light, Star Bright

Lately, it seems that poo is a popular topic in science news sections, and the dung beetle seems to be up front and center. I suppose that, if you are a dung beetle, you've solved all sorts of poo-related problems. If you recall the dung beetles and ball-cooling post from November, you will remember that these insects use their dung balls to help cool off their feet on the blazing hot African sands. But what if you are a beetle that works at night? You can chuck out the hot feet problem and worry about a whole new one: navigation. A new paper published in Current Biology suggests how dung beetles may solve this navigation dilemma.

For African ball-rolling dung beetles (Scarabaeus satyrus), the best ball rolling strategy is the straight line. The straighter the path the beetle uses to roll the ball away from the dung pile the less likely it is their ball will be stolen by rival beetles. They spent all that time to pinch and roll the poo together, it is a waste of time and energy if it is stolen. Competition is fierce near the dung heap, so a quick and straight exit strategy is best. Getting that ball to roll straight isn't simply a matter of putting one tarsus in front of another, it usually involves exploiting such celestial features as the sun and the moon to orientate. However, it has been observed that many beetles will still manage to orientate along straight paths on clear moonless nights. So what are they using to help them navigate?

To answer this question, a group of researchers set up some beetles in arenas. I know, it already sounds good. On a starlit night, they placed dung beetles with their dung balls in a flattened, leveled, and enclosed circular arena.They first wanted to know how accurately the dung beetles could orientate along straight paths when they were prevented from seeing any celestial cues at all. So they made little hats for them. No kidding. They made little caps from small pieces of cardboard and attached them to the beetles' heads so that their dorsal field of view was obscured but their ventral eyes were unimpeded. Then they let them roll, filming them from above so that the rolling paths could be reconstructed and measured. The sight impeded beetles had path lengths almost 4 times longer than beetles that could see the moonless night sky. Okay, so maybe the beetles are using landmarks, like trees, to help them. To test this, the researchers made another arena that removed all visual cues (including the observer), enclosing it with a circular black cloth wall. Because they removed all observer cues, like the camera, they had to design the arena such that it could tell them when the beetles were at the edge without the researchers filming or looking. So they made the arena wall with a slightly larger diameter than the floor so that there was a gap large enough to allow the beetles reaching the edge to fall from the floor into a trough below, resulting in an audible thump sound. Since ball rolling speed is relative to path straightness (the straighter your path the faster you get to the edge), they just had to time the thumps. Clever. Under a full moon, starry night the beetles took 21.4 seconds to exit the arena and on a moonless, starry night they took a reduced, but not significantly so, 40.1 seconds. The story changes when you put the little beetle hats back on. With the caps they take a significantly longer 124.5 seconds (note: this is not significantly different than an overcast night at 117.4 seconds).

Figure 2 from Dacke et al. (2013) showing the effect of stars on dung beetle orientation

Now we know that stars are important in getting a dung beetle to roll its ball straight. Good. But we also know that most stars are too dim for tiny beetle eyes to discriminate. It is probably unlikely that the beetles are picking out constellations for their navigating needs. So what orientation information are they extracting from a starry sky? To answer this question, the researchers grabbed their beetle arena and took it to the Johannesburg planetarium, where they could manipulate the sky the beetles were seeing. Again, clever. They performed the experiments under five different conditions: (1) complete starry sky, with more than 4,000 stars and the Milky Way, (2) Milky Way only, (3) dim stars, with the brightest 18 stars excluded, (4) 18 brightest stars only, or (5) total darkness. They found that the beetles took the same amount of time to exit the arena, irrespective of whether they could see the full projection of the starry sky or only the Milky Way. This means that the dung beetles are using the bright band of light produced by the Milky Way. The Milky Way is a bright band because it is made up of stars, and when the Milky Way part of the projection (a diffuse streak of light) is removed you still see a sky where a higher density of stars defines the galaxy's axis. In this case, the beetles were still able to use the star density but it took them somewhat longer to reach the edge of the arena. It is high density of light forming into the streak across the sky that is visible, and therefore usable, to the beetles.

There is all sorts of navigating going on in the animal kingdom. Now, it appears that we've found another one. One that may be more widespread than we yet know. We just need to go looking.

Dacke, M., Baird, E., Byrne, M., Scholtz, C., & Warrant, E. (2013). Dung Beetles Use the Milky Way for Orientation Current Biology DOI: 10.1016/j.cub.2012.12.034

Some press stories on this paper:
National Geographic: "Dung Beetles Navigate Via the Milky Way, First Known in Animal Kingdom"
ScienceNOW: "Dung Beetles Navigate by the Milky Way"
The Naked Scientists: "Dung Beetles Navigate by the Light of the Milky Way"
The New Yorker: "Dung Beetles, Dancing to the Milky Way"
Wired: "Lowly Dung Beetles Are Insect Astronomers"

(dung beetle hat photo credit to Eric Warrant via the NatGeo link above)

Dung Beetles and Ball-Cooling: The Secret of the Poo

You’re a dung beetle. That isn’t an insult, it’s a visualization aid. You are a dung beetle, you live in South Africa, you roll up feces into balls, you push those balls to a storage location, and you use the balls as food or for brooding. Now, as a human visualizing yourself as a dung beetle, consider the environment you are rolling your dung ball across: the sands of the South African desert. Are your feet hot? How do you cool them down?

The authors of a new paper in Current Biology asked just these questions. The hot desert sands of South Africa can exceed temperatures of 60°C (140°F). Even for the resident dung beetle (Scarabaeus lamarcki) that’s hot. It is known that many species will seek refuges to cool down in these hot climes. For example, desert ants will spend up to 75 percent of their foraging time cooling down on elevated thermal refuges (like stalks of grass). It would make sense that dung beetles, which work under similar hot conditions, would seek refuges as they roll their poo-balls across the sand. Returning to your imagined-dung-beetle-state, what do you do to cool off?

The researchers used infrared thermography and behavioral experiments to see how dung beetles use their dung ball as a mobile thermal refuge onto which they climb to cool down. Jochen Smolka and his colleagues set up two sandy, circular, 3 meter diameter arenas in a natural South African habitat. One of the arenas was shaded in the morning to keep the ground temperature cooler. The other arena was exposed to full sunlight. They found that at the cooler ground temperatures, below 50°C, the beetles roll their dung balls straight across the arena without stopping. On the hotter ground, the beetles were observed to occasionally stop, climb up onto their ball and preen their front legs with their mouth-parts. It is likely that this preening covers the legs in regurgitated liquid, cooling them down by evaporative cooling. After the preening, the beetles perform an orientation dance and continue to roll their balls across the arena.

Fig 1. The dung ball as a mobile thermal refuge. (A) With rising soil temperature, beetles climb onto their dung balls more frequently while rolling (B) Temperature of the right front leg (red) and thorax (blue) of a beetle during its first three ball climbs (periods of rolling are grey) (C) Front leg temperature profile averaged over 84 ball climbs from 7 beetles (D) With silicone ‘boots’ on their legs, beetles perform fewer ball climbs. Similarly, beetles climb onto cool balls less often than hot balls

Ground temperature also significantly affected the frequency of this ball climbing behavior. At progressively high temperatures, the beetles climbed up on their balls more often, spending almost 70 percent of their time on top of their balls when the ground temperature went above 60°C.

So why climb balls? Answer: Ball-cooling. Infrared thermography shows that when the beetles roll their dung balls, the surface temperature of the beetles’ front legs increases by as much as 10°C, but when they climb up on their balls that temperature decreases again. That’s quite a bit, but is it really their hot feet that causes the beetles to ball climb? To this, they applied dental silicone to the beetles’ front legs. Pause: Beetle-booties, fun to say and I’m sure fun to see, and reminds me of the awesomeness that is ants on stilts. They found that these beetle-boots doubled the beetles’ ball rolling time, decreasing their ball climbing by 35 percent. This suggests that the ball climbing behavior is related to ground temperature and the heating up of beetle feet. As it turns out, the poo-balls are acting as thermoregulators in three ways:

1. They are portable, elevated platforms that can be used to escape the hot sand.

2. They are heat sinks. The moist dung ball undergoes evaporative cooling, keeping it the much cooler temperature of 31.8°C. This is substantially cooler than the beetle and the sand.

3. They are sand-coolers. Essentially, they are performing another heat sinking duty, sort of a heat vacuum, if you will. The dung ball draws the heat from the sand so it is cooler for the beetles to walk on.

If the poo-balls are actually acting as heat sinks, both during rolling and while the beetle is on it, then warmer balls should be less efficient heat sinks and the beetles should climb on them more often. The researchers tested this by giving beetles cold balls and hot balls. They found that the beetles climbed the hot balls 73 percent more often than the cold balls, supporting the heat sink hypothesis. “Because beetles roll their ball rather than drag it, the ball, preceding the beetle, cools down the sand the beetle is about to step on” by 1.5°C.

Put together, these mechanisms allow dung beetles to operate during a time of day when most arthropods, and other animals for that matter, seek a cool shelter. I guess there are a lot more good things about poo than I ever realized. And it appears that dung beetles have uncovered the secret of the poo.

Smolka, J., Baird, E., Byrne, M., el Jundi, B., Warrant, E., & Dacke, M. (2012). Dung beetles use their dung ball as a mobile thermal refuge Current Biology, 22 (20) DOI: 10.1016/j.cub.2012.08.057


Here are a few news outlets that have picked up the story:
From Wired UK "Study: Dung beetles cool their heels atop balls of poo"
Discovery News' story "Why Dung Beetles Like to Chill on Poop Balls"
LiveScience's "That's Hot! Beetles Dance on Poop Balls to Keep Cool"
The Naked Scientists' report "Beetles use dung balls to keep cool"

Airlifting Ants

Competition. A contest. An opposition. A rivalry for supremacy.

It may occur directly or indirectly between members of the same species or different species. Commonly you will see it over such resources as food, space, or mates. Usually something that is limited. Let’s focus on indirect competition. Here species clash over access but in such a way that one interferes with the other’s ability to utilize the resource. These interference interactions are common in social insects, and that is the topic of today’s post.

A recent article in Biology Letters reports such interference behavior in ants and wasps. Now, you might think indirect competition would be a common avenue of study as the evolutionary and ecological importance of exploitative competition has been well documented. Not so. It was only recently that behaviors such as ant avoidance when wasps catch prey, wasps robbing food from ants, and wasps guarding mutualists against ants has been published. Why even care? Don’t think of this topic as wasp vs. ant (although it is fun to envision such a showdown) but rather from the viewpoint of an invasive species biologist or manager. Understanding interactions between invasive wasps and native ants can inform us as to why a species (invasive or native) thrives or declines after an introduction.

This study takes a look at the social wasp Vespula vulgaris. This wasp is native to temperate regions of the Northern Hemisphere and is a major invasive species in New Zealand, particularly in beech (Nothofagus spp.) forests. Enter the limiting resource: honeydew. Mmmm. These beech forests have healthy populations of scale insects and scale insects produce large amounts of honeydew, which is rich in carbohydrates. The invading V. vulgaris consumes this honeydew as do a variety of native animals including ants (particularly Prolasius advenus). But honeydew isn’t the only resource of contention. Wasps and ants have also been observed scavenging on the same prey.

What peaked the scientists attention was the observation that wasps would pick up worker ants in their mandibles and then drop them some distance away from the food. The researchers hypothesized that this was an example of interference behavior and that by removing the ants the wasps were effectively decreasing the competition and freeing up more of the food for themselves. Sorta like shoving the weaker kid to the back of the cafeteria line. To test this they set up 48 bait stations containing canned tuna fish randomly among the leaf litter and filmed them. They counted and time-averaged the numbers of ants and wasps that visited the traps as well as the number of aggressive wasp-wasp interactions. Then they looked at each interaction between wasp and ants by looking at the film frame by frame, scoring them as one out of 12 behavioral categories. One of these categories included “ant-dropping” where a wasp would pick up an ant in its mandibles, fly backward, and drop it away from the resource.

AIRBORNE from Science News on Vimeo.

They found that when few ants were present the wasps had more conflict among themselves, but if many ants were present it was more likely interference behaviors would predominate. They concluded that the ant-dropping behavior was not predatory as the wasps were never seen leaving the bait station with an ant and not returning, and the removed ants were not injured. They also ruled out a defensive response as most of the ants were not behaving aggressively towards the wasps. The results showed that even though a wasp weighs 212 times more than an ant, that the wasp more often hung back or moved away in the presence of a high abundance of ants. I feel it is important to mention that P. advenus belongs to the Formicidae, so named because of their ability to produce and spray formic acid along with their bite. You can see why the wasps limited their contact with the ants. They typically picked up an ant to remove it from the bait when it was feeding or walking around the food. In fact, ants were successfully moved away from the food 83.9% of the time, 47.3% of which those dropped ants did not return to the food. And if the ant did return the wasp preceded it in 75% of the cases.

As a competitive strategy, this behavior is pretty efficient, at least on an individual level. V. vulgaris lack nest-based food recruitment mechanisms and so individual workers must be independent and opportunistic. In strategies such as this you often find that individuals adopt behaviors that allow them to exploit a resource early and quickly. The results of this study support this. Ant-dropping is a short term advantage to individual wasps that allows them to garner additional food.

Here’s the paper:
Grangier, Julian and Philip J. Lester (2011) A novel interference behaviour: invasive wasps remove ants from resources and drop them from a height Biology Letters: published online 30 March. (DOI: 10.1098/rsbl.2011.0165)

and the link for the above video: http://vimeo.com/21599670

Story links:
http://www.sciencenews.org/view/generic/id/71986/title/Wasps_airlift_annoying_ants
http://news.sciencemag.org/sciencenow/2011/03/watch-out-below-wasps-battle-ant.html
http://www.wired.co.uk/news/archive/2011-03/31/wasps-airlift-ants-away
http://news.nationalgeographic.com/news/2011/04/110406-aliens-wasps-ants-drop-food-new-zealand-animals-science/
http://www.abc.net.au/science/articles/2011/03/30/3176913.htm

(image from kuleuven.be/bio/ento/photo_gallery.htm)

Attack of the Zombie Ant!

A couple of years ago a study was published in The American Naturalist about an interesting fungal parasite known as Ophiocordyceps unilateralis. This fungus infects ants in the tribe Camponotini (carpenter ants) but does not kill them outright. Rather, the ant remains alive for a short time but the fungus is in control. The fungus compels the ant to crawl down from its nest in the high forest canopy down to the small plants of the understory. Then the fungus has the ant crawl onto the underside of a leaf, clamp down its mandibles, and then die. There the ant body will stay while the fungus continues to grow inside of its body, producing a hyphae and stroma (fruiting body) that grows right out of the ant's head. The stroma then releases spores on to the forest floor, spores waiting to infect the next unsuspecting ant passerby. You can see where the nickname "zombie ants" and "zombie fungus" came from. Now, this was not a previously unknown species of fungus but rather an unknown effect of the fungus on ants, a previously unknown part of the life cycle. What is truly amazing is the accuracy to which the fungus directed the ant. The ants always clamped on to the underside of a leaf and almost always on a leaf vein. The chosen leaf was about 25 centimeters above the ground, with 94-95% humidity, and between 20-30 Celsius. The fungus directs the ant to a location with the parameters that it needs to survive and reproduce.

Now a new paper in the journal PLoS ONE describes four new species belonging to the O. unilateralis species complex from the Atlantic rainforest in Brazil. The species are named according to their ant host species (specifically Camponotus rufies, C. balzani, C. melanoticus, and C. novograndadensis). Ultimately, this paper is just recognizing and naming new species. However, it helps to draw attention to the south-eastern region (Zona de Mata) of the State of Minas Gerais in Brazil, one of the most heavily degraded biodiversity hotspot on the planet. A total of 92% of this rainforest is gone, and four new species have just been discovered. How many more are there to find and how many have already been lost?

Want more zombie animals? Check out these:
The nematode-ant relationship in Central America
The emerald cockroach wasp (Ampulex compressa)-cockroach relationship in the Polynesian Islands.
The spider (Plesiometa argyra)-wasp (Hymenoepimecis argyraphaga) relationship in Costa Rica.

The list goes on and on; pill bugs and spiny-headed worms (Plagiorhychun cylin-draceus), grasshoppers (Melanoplus sanguinipes) and the protist (Nosema acridophagus), the fluke (Dicrocoelium dendriticum) and the ant, the wasp (Glyptapanteles) and the caterpillar, the distome (Leucochloridium paradoxum) and the snail, the barnacle (Sacculina carcini) and the crab, etc. Wasps, ants, and caterpillars tend to have a lot of parasite-host stuff going on (there's even a whole group of parasitoid wasps), although admittedly not all that much zombism. It is an ever-so-interesting evolutionary arms race!

Read more about zombie animals here: http://www.newscientist.com/article/mg14018983.500-evolutions-neglected-superstars-there-is-nothing-glamorous-about-fleas-flukes-or-intestinal-worms-so-why-are-they-suddenly-attracting-so-much-attention.html
and here: http://discovermagazine.com/photos/04-zombie-animals-and-the-parasites-that-control-them

The original zombie ant study (online version of the paper contains a video):
Andersen, Sandra B., et al. (2009) The Life of a Dead Ant: The Expression of an Adaptive Extended Phenotype. The American Naturalist: 174(3), 424-433. (DOI: 10.1086/603640)

The new study, and because it is published in PLoS ONE it is free access (yay!):
Evans, Harry C., Simon L. Elliot, and David P. Hughes. (2011) Hidden Diversity Behind the Zombie-Ant Fungus Ophiocordyceps unilateralis: Four New Species Described from Carpenter Ants in Minas Gerais, Brazil. PLoS ONE: 6(3), e17024. (DOI:10.1371/journal.pone.0017024)

Online stories on this paper:
http://blogs.plos.org/everyone/2011/03/02/four-new-species-of-zombie-ant-fungi-another-step-forward-for-open-access-taxonomy/%20
http://www.physorg.com/news/2011-03-species-zombie-ant-fungi-brazilian.html
http://www.sciencedaily.com/releases/2011/03/110302171309.htm

Walking Cactus

"(An) armoured lobopodian with ten pairs of appendages. Trunk region with nine segments, bearing rows of transverse annulations each with some tubercles. Each region possesses a pair of robust and sclerotized spiny appendages with primary articulation. Anterior is extended, probably forming a proboscis. Posterior region bears a protrusion."

That's the description of a new species found in China and described in the journal Nature last week. The species name is Diania cactiformis, the genus name referring to the Chinese province of Yunnan and the species epithet refering to it's cactus shape. Since, it has garnered the nickname the "walking cactus." It belongs to the group Lobopodia, a now extinct group consisting of small, segmented animals dating back to the early Cambrian. The dorsal armored or sclerotized plates are characteristic of this group. This group of organisms resembles velvet worms (Onychophorans) which are terrestrial worms with legs.

The new species was nicknamed the "walking cactus" because of its many appendages and spiny appearance. The specimen dates from around 500 million years ago, is about 6 centimeters (2.4 inches) long, and has the long worm-like body characteristic of lobopodians. What makes this creature unique is its hardened, jointed legs. These joints are important because they provide a link between lobopodians and arthorpods. Sure missing links are always great to find, but in this case what makes this link so significant? Well, the group Arthropoda contains more than 80% of all known living animal species, we're talking all insects, crustaceans, etc. This newly described link gives insight into how this group evolved. For example, the hardened surfaces of the legs of D. cactiformis imply that arthropods developed hardened limbs before hardened bodies, effectively the first step in evolving the body plan from soft-bodied to an articulated exoskeleton.

The Field Museum in Chicago have imagined it to move something like this:



Read more and see pictures in the paper:
Liu, Jianni, et al. (2011) An armoured Cambrian lobopodian from China with arthopod-like appendages. Nature: 470, 526-530. (DOI: 10.1038/nature09704)

And some story links:
http://www.nature.com/news/2011/110223/full/news.2011.121.html
http://www.npr.org/blogs/krulwich/2011/03/01/134138005/cactus-walking-on-20-legs-found-in-china
http://news.nationalgeographic.com/news/2011/02/110223-walking-cactus-worm-new-species-fossils-animals/