SEB Bulletin July 2007
Sense And Sensibility - Common Sense Answers To Unique Situations
Several researchers presented work at this year's Annual Main Meeting in Glasgow highlighting how some animals make unusual use of their senses to adapt very effectively to their environment.
The Eyes Have It! How Box Jellyfish Avoid Banging Into Things...
Researchers at Lund University, Sweden, are using box jellyfish (Cubomedusae) as a model system to understand how visual information is processed1 and to understand how the eye has evolved.
Box jellyfish are much more active swimmers than other jellyfish - they exhibit strong directional swimming, are able to perform rapid 180 degree turns, and can deftly move in between objects2. So how do they manage to manoeuvre the obstacle course that is in the sea bed? Given that they possess an impressive 24 eyes one would think they would be well equipped for this challenge! Scientists found that one particular sub-set of eyes performs this job.
Box jellyfish have four morphologically different types of eye. Two of these eye types, called the upper and lower lens eyes, are camera type eyes with spherical fish-like lenses. Scientists measured the role of these camera eyes in obstacle avoidance in two species of box jellyfish - Tripedalia cystophora and Chiropsella bronzie. T. cystophora displayed stronger obstacle avoidance than C. bronzie which correlates well with the differences in their habitats: T. cystophora originates in th Caribbean and lives in between mangrove roots, thus their habitat is filled with relatively small vertical obstacles. C. bronzie hails from northern Australia and their habitat holds, larger obstacles, such as large stones and fallen over trees.
Results showed that obstacle avoidance was visually guided and likely mediated by the lower lens eye, as it was found that the jellyfish did not respond to objects above the surface of the water which are detected by the upper lens eye. Importantly, the strength of response correlated with the intensity contrast between the obstacle and its surroundings. “Contrast is important because without contrast the object cannot be detected by any eye” says lead researcher Dr Anders Garm, “However, there are two kinds of visual contrast; colour contrast and intensity contrast. Obstacle avoidance is governed by intensity contrast which fits with our other data which strongly suggest that the jellyfish are, in fact, colour blind”. Because jellyfish belong to one of the first groups of animals to evolve eyes (the phylum Cnidaria), scientists hope that understanding how their eyes operate will shed light on what eyes were like early in evolutionary time.
Making No Bones About It - Digestion In Burmese Pythons
Burmese pythons don't eat very often, but when they do they like to pig out, ingesting the whole of their prey. There's very little waste as they are able to digest everything apart from hair and feathers. Scientists are investigating how their digestive system copes with this binge eating4.
“Juvenile pythons normally eat every week, while adults can have a meal every month and can even stop feeding for several months under certain circumstances,” explains researcher Dr Jean-Herve Lignot of Louis Pasteur University. “They are therefore physiologically fine tuned to cope with prolonged fasting, re-feeding on large meals, and intense digestion and nutrient absorption”.
Researchers monitored changes in the python gut after feeding. They observed drastic morphological changes, which coincided with a rapid increase in body temperature. Cell replication and death were sparked soon after feeding, as new cells were produced and worn out cells eliminated. In this way the stomach and intestine re-modelled themselves in anticipation of the next fasting and feeding periods.
An exciting development was the discovery of a new cell type in the small intestine of pythons which is responsible for the degradation of bone. Small particles observed in the intestine and colon of pythons within hours of feeding were found to have originated from the prey's skeleton. These particles are degraded in specialised cells, shaped like golf tees, and the components released into the bloodstream. This process is thought to allow pythons to optimise absorption of calcium (a component of bone) from their meals.
Detecting Poisons In Nectar Is An Odour-ous Task For Honeybees.
Though many spring flowers have bright advertisements offering sweet rewards to honeybees, some common flowers have not-so-sweet or even toxic nectars. Why plants would try to poison the honeybees they wish to attract is a scientific mystery. The honeybee, which accounts for the pollination of at least 1/3 of the world's crop plants, may encounter such poisoned nectar in common crop and garden plants, such as rhododendrons5. Can honeybees learn whether nectar contains toxins, and does this influence their ability as pollinators? Scientists are looking at how toxins in nectar affect a honeybee's willingness to eat floral nectar.
Honeybees are very clever and can learn to associate almost any colour, shape, texture or scent with food. The newly-sequenced honeybee genome has revealed that honeybees do not have as many genes for taste receptors as other animals of a similar size, such as flies and mosquitoes. This prompted scientists to think that perhaps honeybees had a reduced need to detect and learn about toxins, despite the fact that some floral nectar contains toxins. Work carried out by Dr Jeri Wright (Newcastle University) and colleagues suggests that honeybees may have the ability to react to toxins, even if they cannot taste them.
Researchers found that both the sugar content and the toxins in nectar affected a honeybee's memory for learned odours. Honeybees learned not to respond to odours associated with toxins within 20 min of eating toxins, and would retain this ability up to 24 hours after eating a toxin. This suggests that honeybees can react to toxins in nectar, but that this ability may mainly be after they have ingested the toxins.
Bats get the munchies too!
Many of us will be familiar with cravings for sweet food after having overindulged in alcohol the night before7. Scientists at the Ben Gurion University of the Negev have found that Egyptian fruit bats also crave particular types of sugar to reduce the effects of ethanol toxicity8.
The concentration of ethanol rises in fleshy fruits, such as figs and dates, as they ripen. Egyptian fruit bats prefer these fruits when they are ripe, however high concentrations of ethanol (around 1%) are toxic to the animals. Intoxicated bats may also be less able to respond to attacks from predators, and to avoid obstacles (much like us humans, some might say!). The sugar molecule, fructose, is known to reduce the toxicity of ethanol9. Therefore, scientists investigated the effect of consuming fructose on ethanol toxicity in Egyptian fruit bats, and whether the fruit bats preferred food containing sucrose after they had consumed ethanol.
It was found that ethanol levels measured in fruit bat breath declined faster after feeding on fructose-containing food, than when the food contained either sucrose or glucose (two other types of sugar). 
Furthermore when the amount of ethanol in food increased the fruit bats preferred food which contained fructose over glucose-containing food. Intriguingly the fruit bats preferred food containing sucrose above either of the other two sugars. Thus, although only fructose reduced ethanol toxicity for Egyptian fruit bats, the bats themselves perceived both fructose and sucrose as being beneficial. “We think that this observation may be due to a matter of taste or flavour”, explains researcher Francisco Sanchez, “The perception of sweetness versus bitterness may vary according the type of sugar and the amount of ethanol consumed. The combination of sucrose and ethanol may just have tasted better than either ethanol and fructose, or ethanol and glucose”.
Gillian Dugan
SEB Press Officer
References
1. http://www.lu.se/o.o.i.s/7248
2. http://www.dnr.sc.gov/marine/pub/seascience/jellyfi.html
3. http://health.howstuffworks.com/eye.htm
4. http://www.le.ac.uk/pa/teach/va/anatomy/case6/frmst6.html
5. http://www.insecta-inspecta.com/bees/honey/index.html
6. http://www.ncl.ac.uk/ion/staff/profile/jeri.wright
7. http://www.bbc.co.uk/science/hottopics/alcohol/
8. http://www.bgu.ac.il/desert_ecology/ecology/CV_pinshow.htm
9. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Carbohydrates.html
