Check out this cute, red-pigmented, copepod.
Archive for the 'Arthropods' Category
Tags: Acyrthosiphon, Aphid, Carotenoids, Fungi, Lateral Gene Transfer
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.
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?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.
- 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.
Tags: A-pod, Biomechanics, Robot
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.
Tags: Disney, Mantis Shrimp, Odontodactylus
Disney Nature has a new IMAX documentary out titled, ‘Oceans‘. A quick survey of the reviews of the film indicates that a mantis shrimp, Odontodactylus scyllarus, is a part of the most memorable sequence of the film. Here is a clip of the mantis shrimp’s scene, (available in 1080p on Youtube). Near the beginning there is a really nice shot of the pseudopupil (the facets of the eye looking directly at the observer).
I, however, have a couple criticisms of this sequence. First off, this was almost definitely shot in an aquarium. Secondly, what is it with IMAX movie makers and repeatedly pushing animals towards stomatopod burrows until they lash out? Similarly to the sequence from ‘Deep Sea 3D’ where an octopus is forced to approach the burrow of a Hemisquilla californiensis, the mantis shrimp in this video shows no interest in predating the crab. He just seems to be trying to get the crab away from his hole. Normally, the crab would surely oblige if it wasn’t for the Disney filmmakers repeatedly pushing it back.
I can’t help but be reminded of Disney’s ‘White Wilderness‘ documentary where the filmmakers pushed lemmings off a cliff into the ocean in order to convince people, incorrectly, that lemmings engaged in suicidal behavior. They are quite a viscous bunch over in the Magic Kingdom.
Tags: Migration, Panulirus, Spiny Lobster
Spiny lobsters, Panulirus argus, have an unusual and poorly understood migratory behavior. Every autumn, many of the shallow living lobsters around the Bahamas begin forming traveling queues that aggregate into long chains of marching lobsters. These chains can swell to thousands of individuals as the animals migrate to deeper waters.
Our main man, David Attenborough, breaks it down and somehow manages to make a skittering train of lobsters feel epic:
As mentioned in the video, the migration possibly occurs in order for the lobsters to escape turbulence and turbidity in the shallows resulting from autumn storms that sweep into the Bahamas. The migration has long been observed in tight correlation with these storms. Following the first storm of the year, the spiny lobsters begin amassing at buildup areas and prior to embarking on the mass migration. The cue to begin queueing (hah) is likely the sharp water temperature drop following the first storm. Indeed, in laboratory observations, decreases in water temperature increased queueing among captive spiny lobsters.
The purpose of the lobster queue formation during migration is likely twofold. For one, traveling in a line reduces water drag for the lobsters traveling behind others. To borrow a term from racing, the lobsters are drafting on the wakes of their line-mates. In this manner, the lobsters conserver energy and momentum on their trek. The other reason for forming the migration queues is likely predator defense. Beyond projecting increased size via aggregation, the lobster queues can rearrange into a defensive circle to cover their vulnerable back-sides. You can see an example of the onset of defensive formations in the photo below.
- Kanciruk, P and Herrnkind, W. 1978. Mass migration of spiny lobster, Panulirus argus (Crustacea: Palinuridae): Behavior and environmental correlates. Bulletin of Marine Science, 28(4): 601-623,
I am going to start a running catalogue of the diverse arthropod microfauna of my reef tank. Here is my first attempt to capture one of these tiny animals. This is a sediment-dwelling ostracod, about 250 microns in carapace length.
I know, ugly photo, but this was a first attempt. Can anyone ID it further? The rubble in the tank was aquacultured on the gulf coast of Florida, but this little guy could have hopped on at the fish store.
Tags: Drosophila, Fruit Fly, Phylogenetics
Celebrities 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.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.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.
Check out some of my other posts about phylogenetics:
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