A drawing of a lantern shark which emits light from its belly which can be used to camouflage it from creatures below it. Courtesy of Wikimedia Commons.

Most light in the aquatic environment comes directly from the sun, i.e. from above and as anybody who has dived can testify to then this mean that everything moves above you in the water column has a very distinct silhouette against the downwelling sunlight.  This makes it very difficult to remain hidden. Some luminescent shrimps and squids have therefore developed a method of directing their light emissions  downward to act as counter-illumination to hide their silhouettes from predators. However some sharks hunts from above and therefore would also benefit from counter-illumination.  

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Pigs are highly intelligent animals and new research shows that they also have some degree of awareness.Photo courtesy of Photocase.com

Awareness is a difficult thing to study or even to define. Traditional it is defined as the ability to perceive, to feel and to be conscious, but this definition is very difficult to measure. Thus while we can be fairly certain that we ourselves are aware, we can be less certain that our friends are aware but at least they can tell us so. Animals cannot. However, there is one way to assess the self-awareness in animals and human infants. Put them in front of a mirror and looks for signs that they recognise themselves. When human infants are exposed to mirrors age and then fooled to think that a video playback of themselves with a sticker on their head was a mirror, 0% of two year olds, 25% of three year olds and 75% of four year olds reached for the sticker. 

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An ant-acacia Acacia collinsii like the one on which the vegetarian jumping spiders were found. Photo taken by Thomas Hesselberg.

The spider belongs to the group of jumping spiders, which are usually active hunters without a web. They have a good vision and use it stalk prey at a distance before they are within jumping distance. However, this particular jumping spider does not hunt any prey, but spend its life on a plant. Not just some plant though, but an ant-acacia, which is a plant that lives in a close mutualism with an ant. The acacia offers the ants housing in its thorns and food in the form of special fat and protein rich Beltian bodies and in return the ants protects the plant against herbivores and other encroaching plants.

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The small male approaching the much larger female of the golden orb spider, Nephila clavipes. Photo: T. Hesselberg.

A new study explains the observed size difference between females and males (sexual dimorphism) in spiders by referring to gravity. Gravity gives rise to an optimal size above where climbing speed is reduced. Since male spiders are often required to climb to access females located in their webs in the vegetation, large spiders should thus have larger sexual dimorphism. The scientists were able to show that this is true for a wide range of different spiders.

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