Molting spider crab

All arthropods need to molt. Here is a time lapse video of how a spider crab does it.

When a crab is ready to molt it rapidly takes up water, causing pressure to build in its body cavities. The rigid outer exoskeleton breaks open and the crab is able to push itself out from inside its molt. The new exoskeleton is softer, so it is undamaged by the increase in body volume, but it will eventually harden over time. Recently molted, soft-shell blue crabs are commonly steamed and eaten whole in my neck of the woods.

Disney murders a crab

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.

All aboard the lobster train

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.

Panulirus argus migratory train. The lobsters at the front of this train were perturbed by the divers, causing them loop back into the train, creating a lobster vortex. Adapted from Kanciruk and Herrnking, 1978.

References:

• 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,

Arthropod on arthropod violence

How does a swarm of army ants take down a heavily armored fresh water crab? Let’s find out…

That’s gotta be a pretty terrible way to go.

Red in mandible and pincer…

Arthropod Roundup: Callinectes in the UK, horny females, artificial arthropod hair, and genetic mosquito control

Brief blurbs about recent arthropod news and research:

• The blue crab, Callinectes sapidus, has been found in England for the second time ever. These ill-tempered, but delicious, swimming crabs are native to North America; where they represent a major marine fishery despite serious conservation concerns. Previously, blue crabs have turned up in Japan and the Mediterranean. It is conventionally thought that these crabs were brought in as larvae in ship ballast water and have since gained a foothold in their new homes. It is possible that this blue crab in Cornwall also came over from America in ballast water, or it could have been carried on ocean currents up from the Mediterranean population. It is unclear weather this is an isolated individual or a representative of a new invasive population.
• You will be disappointed to learn that the horny females I referred to in the title are dung beetles. One usually associates the growth of horns and antlers with males who use them to battle for dominance in a social hierarchy or for their pick of the choicest females. However, female dung beetles, Onthophagus sagittarius, are known to have much more impressive horns than their male counterparts. A new study suggests that these horns are used by the females to compete over reproductive resources (i.e. poop). Size matched females with larger horns were found to achieve greater reproductive fitness, making horn size a positively selected female secondary sex characteristic in these beetles. (Via 80Beats)
  
  

  Horned Onthophagus sagittarius females square off. Photo: Sean Stankowski

• New research reports the development of synthetic superhydrophobic materials inspired by tiny, water repellent hairs in insects. These hairs are found on the legs of water walkers and the backs of Stenocarid beetles, which use the hairs to channel water droplets to their mouth.
• The genomes of the malaria mosquito, Anopheles gambiae, and the yellow fever mosquito, Aedes aegypti, were published in 2002 and 2006, respectively. These sequencing efforts appear to be bearing a lot of fruit as of late; as several genetic approaches to controlling the spread of mosquito vectored diseases have been proposed. These include; increasing the immunity of mosquitoes to the dengue fever virus, weakening mosquitoes by preventing waste secretion, and preventing female mosquitoes from developing functioning flight structures. Some of these ideas are pretty far from real-world application unfortunately, and the buzz surrounding them seems to be the result of overly-excitable university PR departments.

Arthropod Roundup: Crabzilla, altruistic ants, and neuronal recordings from Drosophila in flight.

Quick notes about recent Arthropod news and research:

• The National Sealife Centre in Birmingham, England is hosting a special guest, on loan from Japan. Meet ‘Crabzilla’, a not-quite full grown Japanese spider crab, Macrocheira kaempferi. Crabzilla has an impressive leg-span of about 10 ft, but members of this species can reach over 13 ft. By length, they are the largest know arthropods on the planet. You can read more about Crabzilla’s visit to the UK at the Daily Mail.
• New research on the ant species, Temnothorax unifasciatus, found compelling evidence of altruistic behavior. Altruism is commonly observed in social insects, as single individuals often sacrifice their energies or lives for the good of the colonial super-organism. In the present study, the researchers showed that ants infected with a deadly and contagious fungus would often leave the colony and die in seclusion. This prevents transmission of the disease to other members of the closely interacting colony. Read more at the BBC.
• Finally, researchers have developed new techniques for recording electrical signals from fruit fly neurons while the animals are in tethered flight. Fruit flies, Drosophila melanogaster are the go-to arthropod model organisms, and a plethora of molecular and physiological tools are available for studying any aspect of their biology. This new neuronal recording technique was applied to look at the activity of visual pathways in the brain during flight. The researchers found that the stimulus response time of the Drosophila visual system nearly doubles when the animal is in flight. This allows the flies to change direction rapidly mid-flight in order to avoid obstacles. This work was published in Nature Neuroscience. Read more at Science Daily.

  A tethered fruit fly in flight with a pink electrode in its brain. Photo by Gaby Maimon and Michael Dickinson.

Sea drifters

The BBC has an audio slideshow of some plankton micro-photography. Plankton is not a taxonomic classification, but rather a bulk term for any pelagic aquatic organism that is typically not capable of out-swimming its currents. (I was recently in a prolonged argument with the owner of salt water aquarium store about this. I could not convince the person that a plankton was not a single type of organism.) Damn near every phylum I can think of has some planktonic species or life stages. You can be plankton if you can’t out-swim the current you are in.

In the BBC video you can see several planktonic crustaceans including adult copepods and euphausiids, as well as the larval stages of crabs. A neat feature to notice in the crab larvae are the long spines protruding from their backs. This is an anti-predation adaptation seen in many crustaceans, making the larvae more difficult to swallow. There is a great diversity of spine length and configuration in different species of larval crustaceans.

Some spiny larval crustaceans.

Photos: Peter Parks, Steven G. Morgan, Rudolph Scheltema, artour_a, Kim Taylor and Jane Burton.

The Chesapeake Bay’s declining bumper crab

As a Baltimore resident, it was only a matter of time before I talked about our most popular and ill-tempered local crustacean. The blue crab, Callinectes sapidus (savory beautiful swimmer), is a Portunid (swimming) crab found along the Western Atlantic coast, from Nova Scotia to Argentina. They have also been introduced to the Pacific coast of Central America, Europe, and Asia. They have a complex, migratory life-cycle that takes them between estuaries and the open ocean. Blue crabs are harvested for food in the US and play an integral part in coastal economies, especially within the Chesapeake Bay where they are somewhat of a cultural icon.

Unfortunately, the population and harvest of C. sapidus has been in sharp decline since the early 1990s due to over-fishing, development, and agricultural runoff. Pollution in the bay unbalances the ecosystem, resulting in harmful microorganism blooms, and stresses the crabs, making them more susceptible to bacterial and viral infections. Due to the economic impact of declining harvests, a variety of regulations and research directives have been employed in order to rejuvenate the blue crab population.

Samurai Crabs: Transmogrified Japanese warriors, the product of artificial selection, or pareidolia?

I’m going to share with you two stories about the Samurai Crab, Heikea japonica; one is a ancient Japanese legend, and the other is a modern piece of scientific folklore. First, the historical background of the Japanese myth…

April of 1185 was the end of the line for the Heike Empire in Japan. Their rival clan, the Genji, swept across the southern Inland Sea of Japan and annihilated the final, desperate armada of the Heike at the battle of Dan-no-ura. The defeated Heike child-emperor and his samurai, refusing to surrender, committed suicide by throwing themselves from their boats to drown.

The battle of Dan-no-ura represented a massive cultural and political shift in Japanese history. It was the end of the imperial Age of Courtiers, and the beginning of the Feudal Era of Japan, lasting from 1185 to 1868. During this time, the majority of Japan was ruled by a powerful military dictator, the shogun, and his samurai warriors. Naturally, such geopolitical upheaval has strongly ingrained itself in the culture of Japan, and folklore stemming from the battle of Dan-no-ura survives today.

Popular legend alleges that, following the battle Dan-no-ura, the souls of drowning Heike samurai warriors were transformed into crabs. These crabs are distinguished by having the faces of the fallen samurai on their backs. To this day the Heike crabs roam the depths of the oceans around Japan, searching for the lost heirlooms of their empire.

The ghost of the Heike general Taira no Tomomori (bottom left) at the bottom of the ocean with the anchor he used to drown himself following defeat at Dan-no-ura. He is joined by Heike crabs bearing the faces and souls of his comrades. By artist Utagawa Kuniyoshi, 17th century. Click to embiggen.

Samurai crab, H. japonica and stylized Kabuki samurai face (inset). Click to embiggen.

Deep-sea crustaceans on film and near-bottom ampipod swarms

The BBC is presenting an article and series of films from a recent University of Aberdeen research expedition. The films are shot between 5.5 kilometers and 10 kilometers in depth and feature snailfish, decapod shrimp, isopods, and amphipods as they scavenge on a bait bag. The videos are narrated by Dr. Alan Jamieson, and he shares some neat insights about deep sea life.

I am personally surprised at the ridiculous swarms of amphipods in the 9 km and 10 km videos. I did not think deep sea life was that dense except around vents and seeps. They don’t say how long the bait bag was there before the film starts, and it could have been down there for hours attracting every amphipod in a 100 m radius. However, a quick check of the literature reveals that these near-bottom deep-sea amphipod swarms have been observed near vents as well as in open abyssal plains. Pelagic swarming is not typically a characteristic attributed to deep sea crustaceans and its ecological significance is unknown.

A swarm of undescribed paradaliscid amphipods, photographed from the submersible Alvin near a deep sea vent in the East Pacific Rise (Dover et al., 1992).

References:
Dover, C.L.V. et al., 1992. Deep-sea amphipod swarms. Nature, 358(6381), 25-26.