Gasbag

gasbag picture

Background

The genus of gasbags evolved on Scoti to make use of as much daylight as possible. Gasbags have a very light body with a large methane filled cavity to provide buoyancy. The low level prevailing winds across the equator go from winter pole to summer pole and it is thought that early gasbags carried out a migratory existence, alternating between the two summer poles. Initially, the gasbags would spend time during the summer months producing stores (e.g. ethanol) that could be converted to fill the gasbag. At the end of summer these stores are converted to methane and the organism would rise into the airstream to begin the journey to the other pole.

Locomotion

The quantity of methane produced governs whether the destination is reached. If too little reserves were laid down during the summer months then not enough lift could be produced to reach an airstream that would traverse the equatorial ice sheets. If too much was laid down then either the extra weight would similarly prevent sufficient distance being travelled if a small amount of methane was produced, or the gasbag would rise too far into the returning airstream is a large amount was produced. Some adjustment of altitude is possible by the gasbag converting further reserves to generate extra lift or metabolising methane to reduce it. This introduces the problem that there is an end limit to the adjustment possible imposed by the initial size of reserves. To overcome this, a chameleon like characteristic evolved. This allows the gasbag to adjust buoyancy without altering the contents of the gasbag. By making the outside of the gasbag darker, more sunlight is absorbed; the contained gases heat up and expand increasing lift. By making the outside lighter, more sunlight is reflected; the gas cools and lift is reduced. Internal partitions within the gasbag allow different sections of the gas to be warmed and cooled independently. This allows the gasbag to control attitude and orientation in the air, as the warmest parts will be on top. Blood vessels flowing through these partitions can also be used to conduct heat in or out of the core of the bag to speed the rate at which density changes occur. Long tentacles can also be used to steer or propel the gasbag. Rowing, swimming and screw propeller actions have all been observed.

Feeding

The gasbags have long dangling tentacles with which to gather food to the central mouth. By adjusting buoyancy, food can be gathered from the ground or from among the branches of plant life. Other avian creatures can also be attacked. Stings carried on the tentacles can be used to immobilise target creatures.

Predators

Because of their store of methane, gasbags provide valuable energy to predators. The main difficulty is that owing to its gaseous nature it is easily lost during a fight. This is very damaging (frequently fatal) to the gasbag and provides no benefit to the predator. The most dangerous predator is one large enough to entirely consume the gasbag in one mouthful. To avoid this smaller gasbag species have unpalatable surfaces.