Mantis shrimp, small but powerful


This 29 May 2019 video says about itself:

Mantis Shrimp Packs a Punch | Predator in Paradise

“Armed with the most sophisticated vision and fastest strike of any predator on Earth, the [peacock] mantis shrimp is an unsuspect[ed] threat.

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Land crab visits Bermuda petrel chick


This video from Bermuda says about itself:

Land Crab Pays Visit To Cahow ChickBermuda petrel parents visit their chick – May 29, 2019

Watch a land crab slowly creep into the Bermuda Petrel nesting burrow and make its way around the sleeping chick. The crab doesn’t stay for long; it scuttles away as soon as the large nestling is awakened.

The CahowCam is a collaboration between the Cornell Lab of Ornithology and the Nonsuch Expeditions. You can watch the cam live at http://allaboutbirds.org/cahow.

120 million crabs on Christmas Island


This video from Christmas Island says about itself:

120 Million Crabs Spawning On One Beach | Trials Of Life | BBC Earth

In this classic clip, David Attenborough witnesses millions of crabs coming together for their annual spawning.

Strange dinosaur age crab discovery


This video says about itself:

Researchers discovered a ‘platypus of the sea.’ It’s cute — but it’s extinct

On April 24 [2019], scientists announced the discovery of “Callichimaera perplexa”, a new species of crab that lived 95 million years ago.

From Yale University in the USA:

Meet Callichimaera perplexa, the platypus of crabs

April 24, 2019

The crab family just got a bunch of new cousins — including a 95-million-year-old chimera species that will force scientists to rethink the definition of a crab.

An international team of researchers led by Yale paleontologist Javier Luque announced the discovery of hundreds of exceptionally well-preserved specimens from Colombia and the United States that date back to the mid-Cretaceous period of 90-95 million years ago. The cache includes hundreds of tiny comma shrimp fossils, several true shrimp, and an entirely new branch of the evolutionary tree for crabs.

The most intriguing discovery, according to the researchers, is Callichimaera perplexa, the earliest example of a swimming arthropod with paddle-like legs since the extinction of sea scorpions more than 250 million years ago. The name derives from a chimera, a mythological creature that has body features from more than one animal. Callichimaera’s full name translates into “perplexing beautiful chimera.”

Luque noted that Callichimaera’s “unusual and cute” appearance, including its small size — about the size of a quarter — large compound eyes with no sockets, bent claws, leg-like mouth parts, exposed tail, and long body are features typical of pelagic crab larvae. This suggests that several of the larval traits seen in this “perplexing chimera” might have been retained and amplified in miniaturized adults via changes in the timing and rates of development. This is a process called “heterochrony,” which may lead to the evolution of novel body plans.

“Callichimaera perplexa is so unique and strange that it can be considered the platypus of the crab world,” said Luque. “It hints at how novel forms evolve and become so disparate through time. Usually we think of crabs as big animals with broad carapaces, strong claws, small eyes in long eyestalks, and a small tail tucked under the body. Well, Callichimaera defies all of these ‘crabby’ features and forces a re-think of our definition of what makes a crab a crab.”

A study about the discovery appears in the April 24 online edition of the journal Science Advances.

“It is very exciting that today we keep finding completely new branches in the tree of life from a distant past, especially from regions like the tropics, which despite being hotspots of diversity today, are places we know the least about in terms of their past diversity,” Luque said.

How hermit crabs get new shells


This 25 February 2019 video says about itself:

Hermit crabs are drawn to smell of flesh torn from their kin | Science News

Within three minutes on a beach at Osa Peninsula, Costa Rica, land hermit crabs (Coenobita compressus) crowd a tube containing flesh bits of their own kind. Researchers say the smell signals that an empty shell may be available for the taking.

By Yao-Hua Law, 8:00am, February 25, 2019:

Hermit crabs are drawn to the smell of their own dead

Competition for abandoned shells turns into a lively gathering

The death of a millionaire with no heir draws an opportunistic crowd. So, too, does the demise of a land-dwelling hermit crab. Researchers working in Costa Rica found that the curious crabs are drawn to the smell of flesh torn from one of their own.

Dartmouth College biologist Mark Laidre, along with undergraduate student Leah Valdes, set out 20 plastic tubes on a beach, each holding bits of hermit crab flesh. Within five minutes, almost 50 hermit crabs (Coenobita compressus) swarmed around each sample, the pair reports online February 10 in Ecology and Evolution. “It’s almost like they were celebrating a funeral,” Laidre says.

The reality, however, is more macabre. That scent of flesh is a signal that a fellow land hermit crab has been eaten, and that its empty shell is available for the taking, Laidre says. The crabs “are all in an incredible frenzy to try to move into that leftover shell.”

None of the roughly 850 known hermit crab species, most of which live in the sea and some on land, can grow their own shells. Instead, the crabs occupy shells originally left behind by dead snails. A hermit crab grows to the size of its shell, but to grow further, the creature must find and occupy a larger shell.

For the roughly 20 or so species of land hermit crabs, finding a suitable shell can be especially challenging. Big shells with lots of extra room to grow may be too heavy in the short term for a hermit crab to tote around on land without the buoyancy of water to help lighten the load, and lighter shells may be too small.

Land hermit crabs can remodel their shells, making them bigger, Laidre reported in 2012. The animals use corrosive secretions and scraping to widen a shell’s opening, remove the internal spiral and reduce wall thickness. Remodeling can double the available space while trimming one-third the weight. But remodeling is taxing and slow. It’s much faster to take over an already remodeled shell of another land hermit crab, alive or dead. Hence the strong attraction of land hermit crabs toward smells that suggest another is dead, Laidre says.

The researchers also found that land hermit crabs approached bits of snail flesh, though the scent appears to be far less alluring than that of their own species. Sea hermit crabs, however, didn’t find the smell of another hermit crab’s corpse more attractive than those of snails.

That makes sense to Laidre. For sea hermit crabs, upsizing to bigger and heavier shells is relatively easy, thanks to water’s buoyancy that helps the crabs support a shell that’s a little too big at first. That, combined with the fact that there are also many more empty shells in the sea than on land, means that sea hermit crabs face less competition when looking for a home, he says.

By highlighting that shell availability is limited for land hermit crabs, the study makes an important point for conservation, says ecologist Chia-Hsuan Hsu, who studies hermit crabs at National Taiwan University in Taipei and wasn’t involved in the research. “We can tell the public: ‘Don’t take shells from the beach’, ” he says.

Sand fiddler crabs’ burrows, new research


This video from the USA says about itself:

The Atlantic Sand Fiddler Crab (Uca pugilator) performing a very entertaining claw waving display. They do this to attract mates and establish their territory.

Filmed at Little Neck Bay, Bayside, New York on 6/17/2010.

From ScienceDaily:

Sand fiddler crabs have home advantage in competition for breeding burrows

February 6, 2019

Sand fiddler crabs that reside in a burrow usually prevail if challenged by another, intruding crab, provided their claw pinching strength is similar to that of the competing crab, a study suggests.

The features of sand fiddler crabs that determine the outcomes of competition between intruders and residents of breeding burrows are identified in a paper published in the Springer journal Behavioral Ecology and Sociobiology. Dr Denson McLain and colleagues at Georgia Southern University, USA, found that when a resident sand fiddler crab was challenged by an intruder, it took refuge inside its burrow, forcing the intruder into a prolonged fight that was twice as long as other contests. These lengthy contests require the intruding crab to display stamina alongside pinching strength, while the resident crab only needs strength. The mismatch provides the resident crab with a competitive advantage, according to the new study.

Dr McLain, corresponding author of the study said: “Strength and stamina have long been associated with victory in contests between males for breeding territories. However, territory owners may utilize features of their territories to gain an advantage over rivals who possess greater fighting ability. We found that greater claw pinching force leads to victory for burrow owners but that among intruders it only leads to an additional requirement for victory, the display of stamina.”

The researchers observed contests between resident and intruder sand fiddler crabs competing for breeding burrows on a beach in Florida. They analysed competitions between 159 pairs of crabs and measured their claw pinching strength, stamina (measured by the number of pinches delivered at a high level of force), and resilience (the ability to return to former strength and stamina after being pinched). Despite being stronger, intruder crabs only won around 40% of contests.

Dr McLain said: “An intruder crab can only win if it pinches with a high force and also has the energy to endure a long, physically taxing contest. The difficulty of evicting another crab from a burrow may be the reason why residents guard burrow entrances very diligently and why they are quick to retreat when challenged by a strong intruder.”

The researchers explained that when the resident crab retreats into the burrow, the intruder cannot fully open his claw, rendering any advantage in strength held by the intruder ineffective. The intruder may enlarge the burrow tunnel to enable greater access to the retreated resident, but this approach also requires stamina.

The authors found that resilience did not play a role in contest outcome. However, higher resilience enabled intruders who lost contests to challenge more residents, which increased their odds of winning a burrow. Being resilient was also found to be favourable for resident crabs, as it enabled them to engage in multiple contests in short periods of time.