A maple seed with the heavy nut at the base and the wing shaped seed at the top. Photo courtesy of Wikimedia Commons (by user Kobako).

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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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Fat Schorsch - advertisement for a german pub (1904)

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Leischmaniasis is transmitted by the sandfly, here seen biting a human finger.

A new study published in Science finds for the first time evidence of sexual reproduction in the protozoan parasites in the genus Leishmania, causing skin ulcers and potentially fatal disease, Leishmaniasis. The American scientists show that mating and subsequent genetic exchange occurs when the parasites are in the sand flies.

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A colony of aphids feeding on a fennel stalk. Wikimedia Commons.

Many animals, especially in aquatic systems, have been shown to react to dead members of their own species by using their presence to assess the predation risk. The more dead individuals they encounter the higher the perceived predation risk. In aphids such a system would also work well since they live in high density colonies on plants and tree, where they feed on the sugar rich liquid. Aphid colonies are often farmed and protected by ants, but nonetheless suffer a very high predation rate from predators such as ladybird beetles, lace wings and parasitic wasps. A team of French scientists from the University of Rennes investigated how aphids respond to death colony members predated by parasitic wasps, which are especially suitable for such studies since the wasps leave the empty corpses intact on the plant.

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Front view of the fruit fly with both antennea (above). Acoustic noise and gravitation cause antenna movements. They are detected by specialized sensory neurones (green, below). Courtesy: MPI Experimental Medicine, Goettingen, Germany)

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Social interaction among hyenas. (Courtesy: Oliver Hoener)

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