My Science School

The Mu Koh lanta national park in Southern Thailand had a rather unusual appeal to make to the public. The park authorities requested the public to donate cone-shaped shells they may have to the hermit crabs that have boomed in the last few months in the park. The population of the crustaceans, which protect themselves by wearing and living inside the discarded shells of other animals such as sea snails, has exploded on some islands in the Mu Koh Lanta national park Marine biologists believe the lack of visitors to the park in the backdrop of the COVID-19 pandemic could be a contributing factor. They feel that low number of tourists means fewer activities in the coastal areas, which could have led to the high survival rates of the hermit crabs.

As tens of thousands of hermit crabs thrive on the island, there is a serious shortage for shells. Some hermit crabs, having outgrown their previous homes, have moved into pieces of rubbish such as plastic cans, bottles, or caps. While going without a shell make them extremely vulnerable to their predators, living inside plastic homes is not safe either. The hermit crabs that climb into plastic bottles find the surface too slippery to get traction. Therefore, they cannot climb out of them. A 2020 study found that around 570,000 hermit crabs die annually from getting caught in plastic debris on two tropical islands in the South Pacific.

Plastic debris, in fact, creates a cascade of death for hermit crabs, because when a hermit crab dies, it releases chemical signal to other crabs conveying that its shell is available for occupation. This lures other crabs into the plastic container. One after the other hermit crabs get into the bottle or plastic can thinking they will get their next home, when in reality, it’s their last home.

Have you heard of the vacancy chain?

Hermit crabs begin their lives in larval forms on the seafloor. The larvae eventually metamorphose into small crabs, at which time they must search for their own shells. Hermit crabs are not true crabs - they do not grow their own shells, instead they have hard exoskeleton in the front and soft body in the back, which they protect using the discarded shells of other animals. As the hermit crab grows in size, it must find a larger shell and abandon the previous one.

These social animals display a fascinating behaviour when they are out to look for a new shell. At least 20 individual hermit crabs line up in size order - biggest to smallest - to see if a new shell turns up and who fits into it best. Their curled tail with a hook enables their bodies to fit inside these borrowed shells. Once a member fits into a new shell, it will eject itself from its former calcified castle and the next smallest will take this hand-me-down home, while leaving its older one for another and so on - the aim is that everyone walks away with a new shell that is a better fit than their old one! Scientists call this the vacancy chain.

 

Picture Credit : Google

Living organisms thrive in different kinds of habitats, including acquatic environments. An important factor that helps some creatures adapt to changes in the external environment is the regulation of their internal environment - physiological processes. And body temperature plays a crucial role in this adaptation. As you may be aware, warm-blooded animals - such as birds and mammals - are those that maintain a high body temperature, and this temperature does not change with any change in the environment. On the other hand, cold blooded animals - such as fish, amphibians, and reptiles - tend to have temperatures that change depending on their surroundings. While warm blooded animals are generally called homeotherms, cold-blooded animals are called poikilotherms. And then there are heterotherms. These are creatures - such as some species of birds and mammals - that generate their own body heat but whose temperatures are also regulated by their environment. They have variations in temperature within different regions of their body, and during different times of the year too. In such cases, the body temperature is usually warmest at the core and much lower in the extremities. For example, the feet of penguins are cold to match their surroundings so that their feet are not stuck to the ice they are on. But their core body temperature is conserved by warning the blood returning from the extremities. Also, during winters, penguins are said to have body temperatures lower than normal, and this helps them conserve energy. Though heterotherms are usually small creatures, a study has shown that the king penguin - a large bird weighing about 10 kg - too exhibits heterothermy.

 

Picture Credit : Google

Most snails, of course, have a coiled anatomy to fit the shape of the shell. Also since there’s only one opening from the shell (with exceptions like keyhole limpets), their intestinal tract has to loop back on itself so the mouth, anus, respiratory organs, and reproductive orifices are all situated pretty close together around that one opening. They’re not immediately adjacent to each other, as you can see, but they’re a lot closer than in most animals.

This looping back of the GI tract is called torsion. It occurs in the embryo or, in marine gastropods with free-swimming larvae, in the larval stage (veliger). It can take as little as a few minutes and results from a muscle on one side of the body being stronger than the corresponding muscle on the other side. In two quick 90-degree bends, the embryo or larva basically folds in half before secreting the shell. It’s followed by coiling, assuming the spiral form within the shell. This allows the shell to enlarge with age without becoming so long it makes locomotion difficult.

Snails and slugs both evolved from ancestors with coiled shells, so slugs show many of the same features. Both of them have a mantle, for example. Like a person’s mantle—a cloak hung over the shoulders to keep warm—a snail’s mantle enfolds its body and secretes the shell. A slug’s mantle, however, looks more like a saddle on its back, since it has no shell to secrete. After undergoing torsion (the more primitive condition), the slug embryo undergoes a degree of detorsion to straighten out again, moving the anus farther posteriorly.

Detorsion is most complete in the nudibranchs or sea slugs, such as Aplysia. Here, the anus is all the way back at the posterior end.

 

Picture Credit : Google

 The one animal I found the most interesting regarding visually seeing the stars is the Dung Beetle!

Yes, would you believe the dung beetle uses the milky way for navigation?

Apparently the dung beetle is actually pretty smart. Other than playing with poop, that is. Some really unfortunate scientists got to spend some quality time with one of the most maligned creatures on the earth. But what they found was nothing short of amazing. They had known for some time that the beetle used the polarized light from the sun for navigation, but what did they do at night? They thought it could be the moon, but what about moonless nights? It turned out that they were using the milky way, which was confirmed by taking them to a planetarium. They found that the beetles used the visual cues of the milky way instead of something like the magnetic field.

They confirmed this in the field by giving the beetles cool hats like what you see here (the control group got transparent hats). The beetles with the opaque hats could not navigate.

 

Credit : Quora

Picture Credit : Google