Is it just Shark Week, or did thresher sharks get smarter?

Divers off the coast of Cebu, an island in the Philippines, called Simon Oliver when they noticed sharks exhibiting some strange behavior.

Oliver, an expert on these sharks since he began studying them in 2005, dropped everything to see what all the fuss was about. Apparently they were using their tails to hunt—strange behavior because it was thought that only smart mammals like dolphins and whales practiced tactical use of the tail fin.

Equipped with underwater camera equipment, the Thresher Shark Research and Conservation Project set out to film the new shark activity. They captured footage of 25 hunting events, then went back to the lab to analyze the videos.

The researchers found that the sharks hunt schooling sardines using a four-step procedure. This way, instead of collecting just one fish in their mouth per hunting event, they first stun the fish to eat an average of 3.5 sardines.

Thresher sharks’ tails comprise about 50% of their total length, which is particularly impressive for the 20-foot, 1,000-pound individuals. A sardine lucky enough to survive its initial fear would witness an incredible “tail-slap,” only to die or become stunned shortly after.

First the shark prepares. This preparatory lunge lasts longer than the other three phases, allowing the shark to perform some advanced physics calculations in order to determine tail velocity needed based on mass… Just kidding, they aren’t that smart! The shark then strikes, recovers briefly, and collects its prey.

“This extraordinary story highlights the diversity of shark hunting strategies in an ocean where top predators are forced to adapt to the complex evasion behaviors of their ever declining prey,” said Oliver.

These sharks had been studied previously, but Oliver thinks that lack of food has caused the sharks to hunt near the surface, finally giving humans a glimpse of their unique hunting techniques.

The footage is pretty incredible, and you can check it out here!

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

One way gene expression is altered through epigenetics is called DNA methylation. These are chemical tags that can regulate how genes function. Ed Yong puts it this way in his Discover blog:

These marks, known as methyl groups, are like Post-It notes that dictate how a piece of text should be read, without altering the actual words.

Epigeneticist Andy Feinberg, of John Hopkins, wanted to understand how DNA methylation might be identified in changes in behavior so he teamed up with Gro Amdam, of Arizona State University, a bee behavior expert.

Honeybees make excellent study subjects for this purpose because they are social creatures with very compartmentalized behavior. Female bees are either queens or worker bees, and once the path is chosen, there’s no turning back.

Within the worker bees, however, there are behavior distinctions that are a bit more transient. Workers begin as nurses—tending to the larvae. After two to three weeks, they become foragers, leaving the hive to gather pollen.

The researchers decided to study the chemical tags, DNA methylation, of the two groups—nurses and foragers. “Genes themselves weren’t going to tell us what is responsible for the two types of behavior,” Feinberg says. “But epigenetics—and how it controls genes—could.”

Analyzing the patterns of DNA methylation in the brains of 21 nurses and 21 foragers, the team found 155 regions of DNA that had different tag patterns in the two types of bees. The genes associated with the methylation differences were mostly regulatory genes known to affect the status of other genes.

Then the scientists got tricky. They removed some of the nurses from the hive. When this happens in nature, some of the foragers are able to revert to nursing to fill the gap. Sure enough, the same thing happened in Feinberg’s and Amdam’s experiment—several of the foragers went back to being nurses.

This time, 107 DNA regions showed different tags between the foragers and the reverted nurses, suggesting that the epigenetic marks were not permanent but reversible and connected to the bees’ behavior and the facts of life in the hive.

“It’s like one of those pictures that portray two different images depending on your angle of view,” Amdam says. “The bee genome contains images of both nurses and foragers. The tags on the DNA give the brain its coordinates so that it knows what kind of behavior to project.”

The researchers say they hope their results may begin to shed light on complex behavioral issues in humans, such as learning, memory, stress response and mood disorders, which all involve interactions between genetic and epigenetic components similar to those in the study.

The study is published this week in Nature Neuroscience.

Image: Louise Docker/Wikipedia

According to the journal of Ethology: the International Journal of Behavioural Biology, earthworms use touch to communicate and influence each other’s behavior to travel in the same direction.

This strange behavior, found in the earthworm Eisenia fetida, is the first time any worm has been shown to form active herds.

“Our results modify the current view that earthworms are animals lacking in social behavior,” says Lara Zirbes, lead author of the study and a PhD student at the University of Liege in Gembloux in Belgium.

“We can consider the earthworm behavior as the equivalent of a herd or swarm.”

Originally Zirbes and her colleagues were studying how earthworms interact with other soil microorganisms when they noticed the worms interacting with each other in clusters and compact patches out of the soil.

To test their hypothesis that worms were communicating, they placed 40 earthworms in a central chamber with two identical arms. They then left group alone for 24 hours. After over 30 repeats of the trial, the worms preferred to group in either one chamber or the other.

Additional testing showed that the worms actually used touch, and not pheromone trails (as ants and other social insects do) for their communication.

“To our knowledge this is the first example of collective orientation in animals based on contact between followers,” the researchers wrote in the journal.

“It is also the first one of collective movements of annelids.”

The researchers suspect other earthworm species may have also similar clustering behavior. One reason the Eisenia fetida earthworms gather may be because they secrete fluids with antibacterial properties that potentially deter soil pathogens.  By collecting together they may increase the amount of fluids that cover each of the individuals, according to the researchers.

Creative Commons image by Will Merydith