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Humidity helps terrestrial hermit crabs smell better

Olfaction in land crabs is still in an early transitional stage between life in water and on land

Max Planck scientists have discovered that the olfactory system in hermit crabs is underdeveloped in comparison to that of vinegar flies. Vinegar flies have a very sensitive sense of smell and are able to identify various odor molecules in the air.  Flies olfactory sense is not influenced by the level of air moisture at all, while humidity significantly enhanced electrical signals induced in hermit crab antennal neurons as well as the corresponding behavioral responses to the odorants.  Furthermore crabs recognize only a few odors, such as the smell of organic acids, amines, aldehydes, or seawater.

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.  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. (Proc. R. Soc. B, June 2012)

“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.

In a series of experiments, Anna-Sara Krång, 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.

The crabs’ behavioral responses to odorants were more obvious and much faster at a significantly increased humidity under the subsequently performed bioassays.  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.

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 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.

Original article:

Anna-Sara Krång, Markus Knaden, Kathrin Steck, Bill S. Hansson: Transition from sea to land: olfactory function and constraints in the terrestrial hermit crab Coenobita clypeatus. Proceedings of the Royal Society B, June 6, 2012, online first. Doi: 10.1098/rspb.2012.0596.

Sizzling summer BBQ Safety

You’re sitting in your backyard, relaxing, as the smoky fragrance of burgers wafts over the fence you’re your neighbors.  Suddenly you get the idea to throw your own BBQ that will have your friends salivating for months to come.  After all summer is all about warm weather, fun times outdoors with friends and what better way to enjoy the short season by inviting your friends for a back yard cook out.  Before you grab your royal tongs and chef’s hat you go through your checklist: plates, cups, cutlery, salad bowls, ice bucket (and beer), napkins, meat, vegetables, and of course you’re Broil King.

Forgetting to buy burger buns or ruining a piece of meat isn’t the only thing you need to worry about.  Grilling can pose a real cancer risk at high temperatures; choosing what you grill and how you do it can keep you safe.  When you grill poultry, seafood or red meat the amino acids from the muscle proteins react with creatine under high heat forming heterocyclic amines (HCAs).  HCAs have been linked to cancers of the colon and stomach.   Furthermore the smoke that rises from burning coals and drips of fat that causes flare-ups deposit polycyclic aromatic hydrocarbons (PAHs) on the outside of the meat.  No fear, there is no need to give up on the barbecued foods this summer.  Here are some tips to keep you and your guest’s safe while still throwing an excellent BBQ.

  • Keep your grill clean to prevent grease fires and flare ups
  • Cook at lower temperatures

If you still want to grill turn the gas down or wait for the charcoal to become low-burning embers.  You can also raise the grilling surface from the heat source to reduce the amount of black char –another carcinogen- that can form on meat.  By flipping the meat every minute and marinating you can decrease HCA formation by up to 96% percent.

  • Don’t overcook your meat!

Of course you want to make sure your meat is thoroughly cooked, you don’t want any guests getting food poisoning.  However, cooking your meat past that point leads to higher levels of HCAs.  A high consumption of well-done meat is linked to two to five times more colon cancer and two to three times higher breast cancer risk.

  • Cook smaller pieces If you still want to eat red meat, make kabobs, they cook quicker and at lower temperatures.
  • Choose leaner meat: less fat should reduce flames and smoke
  • Marinate meat for a minimum of 10 minutes before grilling
  • Precook your meat in the microwave: For meats that require a longer cooking time you can precook for 2 minutes in microwave, drain the juices, and finish on the BBQ; this can decrease HCAs by as much as 90%.
  • Try fish, chicken or veggies

Another way to reduce your cancer risk is to change what you grill.  Fish and chicken both taste great and have lower levels of HCAs than red meat.  The American Institute for Cancer Research recommends limiting red meat to no more than 3Oz. a day.  By far the best choice for grilling is fruits and vegetables because they don’t form HCAs.  By making vegetables, fruits, whole grains and beans the centerpiece of the meal you will be consuming a healthy dose of phytochemicals which has been shown to stimulate enzymes that convert HCAs to inactive forms easily eliminated from the body.

  • Always keep your face away from the open grill and stand upwind if possible

You can lower the risk of exposure to PAHs by exhausted air by limiting your exposure to smoke.  Keep the lid down whenever possible and keep your face away from rising smoke.

Marine Protected Areas Not Effective Against Climate Change

While Marine Protected Areas (MPAs) are an important tool for conservation and protection of reefs they may not be enough to hedge against climate change according to research published in the journal Global Change Biology.

MPAs have been praised for their ability to mitigate stressors like nutrient enrichment, sedimentation, and overfishing.  MPAs offer zones of suppressed physiological stress protecting resilient key source populations and providing a healthy source of recruits to already degraded populations.  The success coral reef MPAs have had for restoring fisheries and trophic structures led to optimism that they would be useful tools for conservation in the face of climate change.

Warming global sea temperatures pose a serious risk to thermally sensitive ecosystems like coral reefs.  High temperatures have been correlated with slow coral growth, increased prevalence of diseases, and mortality from coral bleaching.  Reef-building corals already live near their upper thermal limits so if warming continues at a similar rate most coral taxa would be at risk of exceeding their upper limit in 100 years.

The authors tested whether or not MPAs mitigate temperature-associated coral loss and whether MPA design factors promoted resilience. They compared the effect of temperature on coral cover from 298 tropical MPAs (37 ͦN – 37 ͦS) to adjacent unprotected areas using a 21-year dataset.

The study found that MPAs fail to protect against thermal stress; despite the reduction of various physiological stressors resilience to thermal stress does not increase.  When water temperatures are optimal tropical MPAs lead to an average increase of coral cover of 1-2% per year.  Unfortunately, the benefits of MPAs are only realized after 4-14 years of protection.  This questions the efficacy of creating new MPAs in regions of medium to high susceptibility if warming continues at its current rate.

The authors offer two suggestions to MPA managers hoping to protect reefs against climate change.  First is to focus conservation efforts on protecting reefs with a history of moderate temperature variability because they are more resilient and acclimated to thermal stress.  Second, is to design MPAs on a larger scale.  Managers should design MPAs to be larger than an acceptable percentage of anomaly events so that it is guaranteed to contain unaffected populations within their boundaries.

When faced with the current climate changes crisis the local conservation measure of creating MPAs is not suitable to improve a reef’s resilience to globally increasing thermal levels.  The study suggests that effectively managing coral reef systems will require complementing local measures with global measures aimed at reducing anthropogenic activities responsible for climate change.