Thermoreception: “Is it hot in here, or is it just me?”

Previously I mentioned I have been running some behavioral experiments concerning thermotaxis, the orienting towards or away from a thermal stimulus. Maintaining a normal body temperature is important for any animal, especially those that do not produce their own body heat. We call these animals (such as birds or turtles or crabs!) “poikilothermic”, meaning their body temperatures changes with their environment.

As background research for my experiments, I have been reading a lot about different types of thermoreception (basically, ‘temperature sensing’) and temperature preference. Here are some interesting examples:

Fiddler Crabs

(Silbiger & Munguia 2008)

The semiterrestrial fiddler crab Uca pugilator demonstrates some interesting behavioral changes in response to temperature. First, at ~30 degrees Celsius the crab walks twice as fast as it does at 25 degrees Celsius. Also, there is evidence at the crab’s carapace color changes in relation to temperature—in colder temperatures, the crab is darker, and in lighter temperatures, the crab is lighter and more speckled. This color change is particularly interesting because other research has shown that the enlarged cheliped (claw) of the male fiddler crab is largely involved in thermoreception and thermoregulation (Windsor, Crowe & Bishop, 2005); however, the color change happens in both male and female crabs. Hmm? There must be more to this story… read on to see how it develops!

 

Locusts

Like the fiddler crab, locusts show a propensity to be more active in temperatures on the warmer side of their normal range. They also show the ability to regulate their internal body temperature by moving to areas in their preferred range. A tethered flight experiment demonstrated that locusts make thermal avoidance maneuvers mid-flight via bilaterally located thermal sensors. Thats a pretty rapid reaction time!

 

Pit Vipers

Pit Organs have thousands of nerve endings that can sense temperature changes of less than a thousandth of a degree. Picture from Physics Today, September 2006.

I am not a big fan of snakes (not as pets, not at the zoo, definitely not in the wild), but from a biologist’s perspective—they’re insanely cool! Pit vipers have super sensitive thermoreceptors in their face, called pit organs. The pit organ is thought to be involved in thermal regulation, and is vital to the hunting process of these snakes. The thermal membrane of the pit organ is suspected to contain thousands of sensory neurons, which can react to changes in temperature less than 0.001°C. This hypersensitivity allows the animal to sense its surroundings and its prey even in dark conditions. I find this resolution in perception of temperature contrasts to be absolutely remarkable, especially since humans have to consult each other to decide its “jacket weather” or not! Here’s a great article on pit organs, and another one.

 

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