Stick insect chastity belts.

The last male stick insect to mate a female is the most successful at fathering the offspring. This is true of many species of insect. In fact some male damsel flies scoop out the previous males sperm before leaving their own. A good strategy is to mate with the female and then guard her against any more matings by sitting on top of her. This is called mate guarding and is also pretty handy because it saves cab fares. One species of stick insect has taken this to ridiculous extremes. Rather than spend the rest of the Summer guarding his female, the male dies whilst copulating and becomes a corpse chastity belt. No other males can mate with the female and all the offspring are his.

Beetles and beer bottles.

A species of beetle is on the verge of extinction in Australia because of beer bottles thrown out of car windows. Male beetles like big female beetles because big female beetles have lots of eggs inside them. The bigger the females that a male mates with, the more offspring he will have. Unfortunately for the continuity of this species of beetle, males are so enthusiastic about the size of females that they often fail to realise that what they mating with is an empty beer bottle whilst females go unnoticed.

Cichlid fish.

Cichlids live in African lakes. Males set up territories which they defend against other males, whilst they also try to attract as many females to lay eggs in their nest. This sounds very straightforward, but there is in fact a male polymorphism (more than one type of male). Some males are very small and when dissected most of their body cavity is taken up by giant testis.(It takes 'testis' to be a small male!) How do these males fertilise female eggs when they are too small to hold territories? Well these males are called 'sneak' males. They wait until the moment that the big male and a female release their sex cells and rush in and release their sperm too. Not only do they father some of the offspring, but they do not expend energy and time looking after their offspring because the big male does this. 6th formers take note: this is an example of disruptive selection.

Pigeons

Like many species, pigeons have been artificially selected to produce a wide array of forms. Some have been selected to fly faster to win races and some have been selected to look beautiful to the pigeon fancier. Pigeons are interesting because not only has their physical appearance been changed so that they are wattled, fantailed and even permed, but some have had their behaviour changed. Tipplers when released from their pigeon loft fly upwards. I have seen these birds fly so high that they disappear into the clouds. Obviously they cannot gain the critical momentum needed to escape the earth's atmosphere, so eventually they return exhausted to the loft. Tumblers are even more bizarre. These birds fly around and every so often they do a somersault in the air. Some birds do more somersaults than others. It turns out that somersaults are caused by epilectic fits and that what pigeon fanciers have been doing is artificially selecting for epilepsy. Of course over doing the selection will end in the fancier's tears when their best bird meets abruptly with the ground, or worst still, the neighbour's new greenhouse.

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