Subscribe free to our newsletters via your

. Earth Science News .

Humidity increases odor perception in terrestrial hermit crabs
by Staff Writers

An adult Coenobita clypeatus hermit crab uses a discarded snail shell for protection: both pairs of antennae are clearly visible. Olfactory receptors are located on the inner pair of antennae, which are bent upwards. The crabs' sense of smell is still underdeveloped in comparison to insect olfaction. Credit: Max Planck Institute for Chemical Ecology/ Krang

Jena, Germany (SPX) Jul 10, 2012 Max Planck scientists have found out that the olfactory system in hermit crabs is still underdeveloped in comparison to that of vinegar flies. While flies have a very sensitive sense of smell and are able to identify various odor molecules in the air, crabs recognize only a few odors, such as the smell of organic acids, amines, aldehydes, or seawater.

Humidity significantly enhanced electrical signals induced in their antennal neurons as well as the corresponding behavioral responses to the odorants. The olfactory sense of vinegar flies, on the other hand, was not influenced by the level of air moisture at all. Exploring the molecular biology of olfaction in land crabs and flies thus allows insights into the evolution of the olfactory sense during the transition from life in water to life on land.

Crabs and flies
Crabs and flies are arthropods. Like many other life forms, they made a transition from water to land life in ancient times. The ancestors of the family of terrestrial hermit crabs (Coenobitidae) probably took this step about 20 million years ago. Today, hermit crabs live their entire lives on land, except for the larval stage.

Odor signals are important cues for the crabs' search for food. In order to detect odor molecules outside the water on land, the sensory organs of arthropods had to adapt to the new, terrestrial environment. How did sensory perception evolve during the transition from sea to land?

"The land hermit crab Coenobita clypeatus is an ideal study object to answer this question," says Bill Hansson, director of the Department of Evolutionary Neuroethology at the Max Planck Institute for Chemical Ecology in Jena, Germany. The animals live in humid regions close to the sea and regularly visit water sources. Females release the larvae into the sea, where they grow into young crabs.

These young crabs look for empty snail shells and live on land. They eat fruits and plants. This way of life suggests that the olfactory sense in crabs is still at an early stage of development.

Voltage and behavior
In a series of experiments, Anna-Sara Krang, who worked on an EU-funded Marie Curie Project, tested 140 odor substances with different chemical properties, such as acids, aldehydes, amines, alcohols, esters, aromatic compounds, and ethers. She measured the excitation in the neurons of the crabs' antennae in response to single substances. The results were so-called "electroantennograms" (EAGs) which measured tiny voltage changes across the cell membranes in the microvolt range.

A striking feature of the subsequently performed bioassays was that the crabs' behavioral responses to odorants were more obvious and much faster at a significantly increased humidity, assumingly due to an enhanced electrical excitability of their antennal neurons.

The EAG showed in fact a reaction at the neurons which was three to ten times stronger if active odors were applied at a higher humidity. In contrast, antennal neurons of vinegar flies did not show any differences and responded evenly and independently of the degree of humidity.

Evolution of olfaction
The analysis of the experiments revealed that hermit crabs responded primarily to water-soluble polar odorants, such as acids, aldehydes and amines, because their effect may be easily enhanced in humid air. These results suggest that crabs have so-called ionotropic receptors in their antennal neurons. Such receptors were found in other crustaceans, such as water fleas (Daphnia pulex) or lobsters (Homarus americanus).

In the water flea genome, no genetic information was actually found for so-called olfactory receptors, which are responsible for the highly sensitive olfactory system in insects, such as vinegar flies. Although the receptor genes which are present in the hermit crab genome have not been elucidated yet, the scientists assume that olfaction in crabs is mediated by the original, evolutionarily older ionotropic receptors.

It is generally believed that the ancestors of many insect species made the transition from the seas to the continents during much earlier geological eras and that insects have adapted their olfactory system to life on land very well. Terrestrial crustaceans, on the other hand, may be able to use their sense of smell on land thanks to a basic molecular "equipment", but their olfaction is still quite underdeveloped in comparison to insects.

Therefore hermit crabs usually stay near the coast: not only because of the short way back to the sea where they reproduce, but also because of their limited sense of smell which does not allow them to orient themselves without any problems in the dry air of the heartlands.


Related Links
Max Planck Institute for Chemical Ecology
Darwin Today At


Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Memory Foam Mattress Review

Yak genome provides new insights into high altitude adaptation
Shenzhen, China (SPX) Jul 10, 2012
An international team, led by Lanzhou University, comprising BGI, the world's largest genomics organization, Institute of Kunming Zoology, Chinese Academy of Sciences as well as the other 12 institutes, has completed the genomic sequence and analyses of a female domestic yak, which provides important insights into understanding mammalian divergence and adaptation at high altitude. This stu ... read more

Japan pushes ASEAN to lift export restrictions

Report faults Fukushima response

Fukushima was 'man-made' disaster: Japanese probe

Aussie patrol boats are 'under pressure'

Naturally adhesive

SMOS satellite measurements improve as ground radars switch off

New technique could reduce number of animals needed to test chemical safety

Physicists find chink in the Batsuit

30% of fish stocks overexploited: UN agency


Top marine scientists warn reefs in rapid decline

Hosepipe bans lifted in Britain after record rains

Argentina court upholds glacier protections against mining

Study: Wrong diet doomed 1912 polar try

Scientists to produce first 3-D models of Arctic sea ice

Canada builds up arctic region defenses


What's cooking? The UK's potential food crisis

US drought hits global grain outlook: FAO

Vertical farm in abandoned pork plant turns waste into food

Russian flood victims pick through damage

Russia mourns flood dead as questions mount

Russian official sacked over slack flood response

Indian floods kill threatened rhinos

War vets threaten Angola elections over unpaid pensions

Mali to form 1,200-strong elite force to protect transition

UN soldier dies as DR Congo rebels take Uganda border post


Seabirds studied for clues to human aging

Hong Kong's land shortage forces bereaved to sea

Diet of early human relative Australopithecus shows surprises

Outside View: 18th-century words for today
