Archive for the 'Hexapods' Category

It’s a trap!

Yesterday, I was poking around a small bush of white flowers looking for insects to photograph. I noticed this butterfly hanging from the bottom of a flower, rather than sitting on top:

What are you doing under there?

I panned around to underneath the flower and found out why:

Unlucky butterfly.

The butterfly had been snared by an ambush bug (Phymatinae), which is a subgroup of assassin bugs (Reduviidae). I think the above animal is a nymph belonging to the genus Phymata. These bugs hang out underneath flower petals until unweary pollinators visit. They then lunge out and snare their prey with their enlarged raptorial appendages, piercing the exoskeleton with a syringe like rostrum.

Here is an adult of the same, or a similar, species. About one of every three flowers in this bush had an ambush bug laying in wait below.

Phymata sp

'Come a bit closer my pretties.'

If any insect-gurus can identify this exact species, it would be much appreciated.

Aphid adornment: Lateral gene transfer from fungi to aphids.

Carotenoids are integral components of animal biochemistry. These organic compounds, characterized by long hydrocarbon chains and loops, are used in photoreception, antioxidation, the immune system, and for ornamental coloration. There are over 800 known carotenoid compounds found in nature. They absorb varying wavelengths of blue and green light, causing tissue containing large quantities of carotenoids to appear green, yellow, orange, or red. This absorptive property is what makes carotenoids crucial for vision and coloration in animals.

However, there is a snag. Animals cannot produce their own carotenoids. Their genomes lack the enzymes necessary to synthesize carotenoids from smaller hydrocarbons, and therefore they must ingest carotenoids from organisms that can. Certain bacteria, archea, plants, and fungi are all capable of producing specific carotenoids. By adding these organisms to their diet, animals can fulfill their carotenoid needs.

One animal that takes advantage of carotenoid coloration is the pea aphid, Acyrthosiphon pisum. There are two primary color morphs of this aphid species, green and red (see below). The green aphid morph has large quantities of greenish-yellow carotenoids: alpha-, beta-, and gamma-carotene. The red aphid has decreased amounts of those carotenoids, and instead has gobs of the red carotenoid, torulene.

Color morphs of the pea aphid, A. pisum, and the carotenoids predominately responsible for the color variation. Adapted from Moran and Jarvik, 2010.

This polymorphism is of great ecological significance for the aphid. Parasitoid wasps prefer to lay their eggs in green aphids, and carnivorous ladybugs prefer to eat red aphids. If there is a spike in wasp parasitism, the red morphs become more predominant. If there is a spike in ladybug predation, then the green morphs become more common. By maintaining the genetic diversity of both color morphs in an aphid population, that population can guard against being wiped out by a temporal increase in parasites or predators.

However, this polymorphic color variation seen in aphids presents an interesting question. Where are the aphids getting their carotenoids? The plant phloem sap that aphids suck out of leaves is low in carotenoids, and the carotenoids produced by aphid host plants do not match those found in the aphids. In addition, the endosymbiotic bacteria within the aphids cannot be the source of the carotenoids, as there are no carotenoid biosynthesis genes in their genomes.

However, researchers were surprised to discover that the aphid’s red-green color polymorphism is inherited in a classic Mendelian autosomal manner (remember your Punnett squares, kids?), with the red allele dominant to the green allele. This indicates that the genes responsible for carotenoid-based colorations in these aphids are located within their own genomes! A search of the newly published pea aphid genome revealed the presence of several carotenoid synthases, cyclases, and desaturases. This suite of carotenoid biosynthesis genes is capable of producing the colored carotenoids necessary for the red and green aphid color morphs. A mutation in one allele of these genes prevents the production of the red carotenoid, torulene, resulting in the green aphid color morph.

These are the first carotenoid biosynthesis genes found in an animal. Indeed, no other known animal genome, including several other insect genomes, contain homologues to these genes: so where did they come from?

Carotenoid synthesis genes from various organisms. Adapted from Moran and Jarvik, 2010.

A gene tree containing the aphid carotenoid genes, as well as similar genes from bacteria, plants, and fungi can bee seen to the left. The aphid genes (blue) are completely nested within fungal carotenoid biosynthesis genes (brown). Therefore, at some point in aphid evolution, the genes for carotenoid biosynthesis were transfered from a fungi directly into the aphids genome. It is likely that a similar event occurred from bacteria (black) to plants (green) as well. The possible mechanisms for such gene transfers, especially between two eukaryotes, are poorly understood at this point.

Earlier, I wrote about a similar case of lateral gene transfer from algae to a sea slug. That was the first known transfer of genes between multicellular organisms. This new example in aphids lends support to the notion that these lateral gene transfers are more common in eukaryotes that once though. It may turn out, as genome sequencing increases at exponential rates, that the eukaryotic tree of life actually resembles (to some extent) the interconnected gene web seen in bacteria.

References:

  • Moran, N., & Jarvik, T. (2010). Lateral Transfer of Genes from Fungi Underlies Carotenoid Production in Aphids Science, 328 (5978), 624-627 DOI: 10.1126/science.1187113

Hat tip to Microecos for tweeting this.

I want my own enormous robotic ant

Unleash the awesome!

A robotic engineer has developed a beautifully designed hexapod robot based on the biomechanics of ants. He calls his remote controlled creation A-pod, and cites the photography of Alexander Wild (of Myrmecos) as an influence on his design.

A-pod is capable of a wide range of motions and body contortions. In addition to walking around, A-pod can grasp and carry objects in its metallic mandibles. The motions are incredibly fluid and I can’t imagine the amount of work that had to go into programming the synchronous movements of all six legs. You can watch videos of A-pod in action here and here, and learn more about the construction of the robo-beastie here.

At this point, A-pod just needs to be programmed to find Sarah Connor, and then it can assist in the inevitable robot uprising.

Is ‘the Drosophila‘ actually Drosophila?

This post was chosen as an Editor's Selection for ResearchBlogging.orgCelebrities commonly change their names on the path to stardom. Elton John began life as Reginald Kenneth Dwight, John Denver as Henry Deutschendorf, Jr, and Bela Lugosi as Be’la Ferenc Dezso Blasko. A name change can make someone more marketable in the fickle entertainment industry. However, once someone makes it big, their name usually stays the same (excepting P-Diddy and Prince, whose constant name changes became marketing strategies in themselves). A celebrity’s name becomes the branding that represents and sells their fame.

What about name changes for scientific celebrities? I’m not talking about people, but rather the components of nature that we observe around ourselves and adorn with nomenclature. There was (unnecessary) public uproar when Pluto was re-designated as a Kuiper Belt planetoid. Neil deGrasse Tyson even got hate mail from children when the American Museum of Natural History updated its displays accordingly. The change was the result of a non-unanimous scientific consensus attempting to better define the bodies of the solar system, but many people had become attached to the idea of PLANET Pluto and reacted negatively to the news.

Now a new conundrum is brewing within scientific circles as biologists try to decide what to do when the nomenclature describing a celebrity organism no longer jives with scientific observation. Nature News asks, ‘What’s in a name?’. Well, when the name is Drosophila melanogaster, there’s 100 years of glorious scientific discoveries in a name.

Photo by mr.checker

D. melanogaster, the common fruit fly, was a major workhorse behind the early 20th century genetic revolution. Researchers like Thomas Hunt Morgan harnessed the fly’s fast reproductive cycle and simple care requirements to elucidate the fundamentals of heredity. Since then, the powerful D. melanogaster model has exploded to become a principle contributer to research in genetics, neurology, development, biomechanics, and evolution. Found in almost any biology department around the world, this animal is of tremendous historical and contemporary importance to science; a true celebrity.

However, there is one slight problem; Drosophila melanogaster is probably not Drosophila melanogaster.

The issue here is the status of the genus, Drosophila. This genus, as it is currently recognized, contains 1,450 species of fruit flies. A genus, or any level of taxonomic organization, is supposed to be monophyletic, that is; composed only of species that are evolutionarily closer to one another than they are to the members of any other genus. However, with Drosophila, this has been shown through extensive molecular and morphological analysis not to be the case.

Fruit Fly supertree. Adapted from Van der Linde and Houle, 2008

Look at the phylogenetic tree to the left (for an overview of phylogenetics, read this post). Each node on the tree represents a group of species of the same genus. Notice, however, that the 1,450 species of the Drosophila genus are split up into six different clades, interspersed with other genera. This is called paraphyly, and it points out an error in the taxonomic nomenclature. All the species of a given genus should be grouped together, in a monophyletic relationship. Ultimately, this means that there is going to have to be some reorganization of the genus. Some members of Drosophila are going to be ousted and given new names.

The obvious solution to preserve the celebrated D. melanogaster species name would seem to be leaving its clade (marked with a red arrow) as genus Drosophila and renaming the others. However, there are two problems with this. First of all, restructuring the genus in the manner would push out, and require the renaming, of 1,100 species of fruit flies. Furthermore, the type species Drosophila funebris (marked with an orange arrow), the animal from which the Drosophila genus was originally described in 1787, lies in a different clade than D. melanogaster. A recent petition to re-designate the genus type species as D. melanogaster was voted down by the International Commission on Zoological Nomenclature.

As it looks at the moment, D. melanogaster is probably on its way to becoming Sophophora melanogaster. This has generated shock and disbelief from biologists; citing possible research impediments should the name change go through. In addition, they surely have a sentimental attachment to the name of their favorite laboratory arthropod. When biologists say ‘Drosophila‘, they mean Drosophila melanogaster. This celebrated animal has a strong claim to being the most important and powerful research tool biologists have in their arsenal. However, even D. melanogaster, like Pluto, may need to bend in name to the powers of parsimonious taxonomic nomenclature.
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Read more about the Drosophila name fight here and here at Nature News, or here at Catalogue of Organisms

Check out some of my other posts about phylogenetics:

References:

    Kim Van der Linde, & David Houle (2008). A supertree analysis and literature review of the genus Drosophila and closely related genera (Diptera, Drosophilidae)Insect Syst. Evol., 39, 241-267

Giant Japanese hornet anatomy rundown

Vespa mandarinia. Photo by netman (Flickr)

The Asian giant hornet, Vespa mandarinia, is one of the largest Hymenopterans; behind only tarantula hawks (Pepsinae) I believe. They are ravenous predators of other insects (watch a honey bee hive massacre here) and can even be extremely agressive to humans, especially if a nest is disturbed. These hornets are fairly intimidating beasties to be sure, and I wouldn’t want to handle a live one. Check out this great video where someone describes the interesting features of a dead giant hornet that he found while walking in Japan.

Yikes, that stinger looks like it can do some serious damage. I wonder if there is any truth to the claims that their venom can melt flesh and kill a non-allergenic person?

Dew covered insects

Miroslaw Swietek takes amazing photos of dew covered insects in the early-morning woods. The insects remain mostly immobile during the night and collect water droplets all over their bodies. Take a look at his beautiful photos here and here.

Water droplet covered dragon fly. Photo: Miroslaw Swietek

Via i09.

Negative feedback signal in a superorganism

It has long been understood that worker honey bees, Apis mellifera, coordinate foraging for nectar using a system for dances. The best understood of these dances is the ‘waggle dance’. The waggle dance is preformed by a worker who has recently returned to the hive from a lucrative nectar source. The bee gives off an olfactory cue that tells her hive-mates to pay attention. The worker then begins to move in a rough figure-eight, vibrating her abdomen at high frequencies between the loops. The angle and duration of the vibration convey the direction and distance to a promising nectar source.

Check out this video about the waggle dance:

Honey bees also preform a tremble dance that lets workers know that a nectar-laden forager needs to be offloaded, and another dance, originally though of as a ‘begging dance’. This dance is preformed by workers that approach waggle dancers and either butt heads or climb on top of the waggler before delivering a brief 380 Hz abdominal vibration. It was originally thought that this dance was a way of begging for nectar from a laden dancer. However, research has shown that this dance does not precipitate nectar exchange.

New research has shown that the begging dance is in reality a ‘stop dance’, that tells a waggler to stop sending others to a perilous location. The research, published in Current Biology, showed that the stop dance is caused by predator and conspecific attacks on foragers. Workers returning from this dangerous location seek out waggle dancers that are sending others into danger. The stop dance decreases waggle dancing and recruitment to that location.

This stop dance is especially interesting when considered within the superorganism concept of eusocial insects. In this view, the entire colony functions as a single organism; with different colony classes acting as different cell types, and individuals analogous to single cellular units. Previously, only positive recruitment signals had been modeled at the superorganism level. Now, the stop dance adds the first example of a negative feedback signal in a superorganism. The collective interplay of waggle and stop dancing by many members of a hive therefore results in a self-organizing labor allocation system similar to those that exist at the cellular level.

References:

    Nieh, J. (2010). A Negative Feedback Signal That Is Triggered by Peril Curbs Honey Bee Recruitment Current Biology, 20 (4), 310-315 DOI: 10.1016/j.cub.2009.12.060

Fruit fly sperm race

Check out this awesome video of fluorescent labeled fruit fly sperm racing through the reproductive tract of a female Drosophila melanogaster. The sperm from one male are labeled with a green marker and sperm from another male are labeled with a much fainter red marker. Read more about the high stakes world of sperm competition at Not Exactly Rocket Science, which recently moved to Discover Blogs.

This video is from recent research published in Science.

Beware the water tigers

T. marmoratus Adult

The sunburst diving beetle, Thermonectus marmoratus, is an adept predator. As adults, these Dytiscid beetles are strong swimmers and prey on a variety of aquatic animals by tearing them to shreds with their powerful mandibles. They also spend some time out of water and can fly from one water supply to another. When it is time to reproduce, female diving beetles enter the water and lay eggs on the stems of aquatic plants and macroalgae. When the eggs hatch, the larvae (known commonly as water tigers) enter the water column and begin their rein of terror.

In the lab, these morphologically distinct diving beetle larvae are typically fed tadpoles or mosquito larvae. In the wild, however, they probably eat anything unlucky enough to get too close. When hunting, these beetle larvae either swim around actively or hang, with their tail touching the surface, just below the water line. When they spot a prey animal, they swim over and strike the target with their powerful mandibles (Watch a video of a predation event below). Unlike the adults, larval diving beetles gradually suck the fluids from their prey, resulting in an unfortunately slow demise.

The predatory nature of sunburst diving beetle larvae is highly dependent on their visual system; and boy is it a bizarre one. While the adults have typical arthropod compound eyes, the larvae see the world through stemmata. Stemmata, which are commonly seen in larval insects, are simple lens eyes that rely on superficially similar optical principles to vertebrate eyes. On each side of the head, the larvae have six stemmata as well as a lens-less eye patch (see below). Within each of these eyes there are two distinct retinas, one on top of another. In total, this means that these T. marmoratus larvae have fourteen eyes and twenty-eight distinct retinas!

Front and side views of the head of a T. marmoratus larva. E, eye; EP, eye patch; M, mandible. Adapted from Mandapaka et al., 2006 and Maksimovic et al., 2009.

This larval visual system has a befuddling number of bizarre optical properties. The retinas are sensitive to a broad range of wavelengths, including UV, and the photoreceptor architecture is suggestive of polarization detection. In addition, some of the lenses seem to have novel bifocal and chromatic aberration-correcting properties. Despite the research into all of these strange visual adaptations, the ecological significance of most of the eyes on this animal is completely unknown.

The best understood eyes in the diving beetle larva are E1 and E2. They are forward-looking and primarily used for predation. However, when you look at the main retina in these eyes, you surprisingly find that it is only composed of a thin horizontal band, two photoreceptors tall. Imagine trying to view the world in a thin strip, two pixels high! So, how is the diving beetle larva using these eyes to zero in on prey? Well, it turns out that these sort of strip eyes are not completely novel in nature. Jumping spiders, some copepods, and a pelagic snail all have strip retinas. In order to see the world, they scan their narrow retinas rapidly back and forth, as in the image below. Diving beetles, on the other hand, have absolutely no musculature to move their eyes or retinas. So how do they see?

Look again at the predation video from above. Notice that once the diving beetle larva spots the mosquito larva, it begins bobbing its entire head up and down. The diving beetle larva is scanning the mosquito with the strip retina in its main eyes. As it gets closer, the scanning movement actually becomes more pronounced, since the target takes up more of the field of view. This technique allows the diving beetle larva to accurately hone in on its prey without sacrificing limited head-space for a full retina or eye muscles.

The closer you examine arthropods, the weirder they seem to get. Who would have though that this small aquatic predator would have such a complex and fascinating visual system? In order to discover the most exciting aspects of living things, you need to look. That’s where science starts; with someone peering through the confounding subterfuge of nature, hoping to widen our glimpse of the gear-works within.

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The research discussed in this post is being carried out at Buschbeck lab at the U. of Cincinnati.

References:

  • Mandapaka K, Morgan RC, & Buschbeck EK (2006). Twenty-eight retinas but only twelve eyes: an anatomical analysis of the larval visual system of the diving beetle Thermonectus marmoratus (Coleoptera: Dytiscidae). The Journal of comparative neurology, 497 (2), 166-81 PMID: 16705677
  • Buschbeck EK, Sbita SJ, & Morgan RC (2007). Scanning behavior by larvae of the predacious diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae) enlarges visual field prior to prey capture. Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology, 193 (9), 973-82 PMID: 17639412

Arthropoda ID (#1)

For a while I’ve wanted to start up a weekly arthropod identification challenge, and I now think my readership is high enough to give it a try.

The idea is: Once a week I’ll post a photo or video of an arthropod that I’m planning to talk about. When someone figures out what it is, I’ll follow up with a post about the animal’s biology.

Let’s start with an easy one:

If you think you know who this little beastie is, leave a comment. Family name or specific common name will probably be acceptable if the exact species is unclear from the photo. Good luck.

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Correct family name by zombieroach.
Answer: Sunburst Diving Beetle, Thermonectus marmoratus (highlight)
Photo from Mandapaka et al., 2006.

I foolishly underestimated you guys. From now on I’m gonna require at least the correct genus.


I have moved.
Arthropoda can now be found here.

Michael Bok is a graduate student studying the visual system of mantis shrimp.

Flickr Photos