Fish That Fake Orgasms The mating game     B IRDS CAN ACT LIKE lovelorn teenagers. At around one year old, barnacle geese ( Branta leucopsis ) begin going on dates, sampling several potential mates by engaging in so-called ''trial liaisons'', which may last from a few days to several weeks. They will keep dating until they settle on a final mate for life at around the age of two or three. Both males and females that find their final partner early in life also raise a family sooner than those that play the field.1   Animals look for compatible mates just as people do. Pinyon jays ( Gymnorhinus cyanocephalus ) that find a partner similar in weight, age and bill length produce more offspring, whereas similarly sized barnacle geese ( Branta leucopsis ) reproduce better than pairs compromising a large and small individual. Great tits (Parus major) look for partners that have a similar desire in exploring the environment. Two fast explorers, and two slow explorers, produce more offspring than a pair of birds comprising a slow and fast explorer, whereas willow ptarmigan (Lagopus lagopus ) are more reproductively successful when they pair up with another bird of a similar social standing.

2   Animals also divorce each other just as readily as people do. Oyster-catchers (Haematopus ostralegus) are a monogamous species where the same male and female birds come together each year to raise a chick. But each year, just under 8 per cent of oystercatcher couples split up. In the majority of these cases, the females instigate the divorce, deserting partners who have not been particularly successful at breeding in the past for a betterquality of life with another bird nearby. Some females walk out on males who routinely knock eggs off their cliff perches, or fail to bring home enough food. And while some divorcees remain on the shelf, most go on to have much greater reproductive success over their lifetime than they would have done had they remained in their dead-end relationship. Divorce rates in birds range from o per cent in the utterly faithful wandering albatross ( Diomedea exulans ) to 99 per cent in the rather more fickle greater flamingo (Phoenicopterus ruber roseus ).3   Around 3 per cent of all bird species practise polyandrous breeding, where three or more adults will live together in a nest and bring up young.

Up to five adults have been known to share a nest this way. The practice is especially common in raptors such as eagles and falcons, and in over half such species, the nest is shared by unrelated birds.4   Male and female Eurasian oystercatchers ( Haematopus ostralegus ) particularly like to indulge in threesomes, but - like many three-way relationships - sometimes all the individuals get along, and sometimes they do not. When the birds, which are common on mud flats, form a threesome, it always comprises one male and two females. But the threesomes occur in two forms, aggressive and cooperative. In an aggressive threesome, each female will defend her own nest, while the male oystercatcher defends a territory that includes the nests of both females. The females lay eggs about two weeks apart, and proceed to attack each other frequently throughout the day. The male also has a favourite partner, contributing most of his parental care to eggs laid first by one mate, and often leaving the second nest unguarded.

However, in a cooperative threesome, the two females share one nest, and both females will lay eggs together, laying each clutch about oneday apart. The females also attempt to mate with each other frequently during the day, only slightly less often than they do with the male. The females also sit together and preen their feathers together. What''s more the male has no favourite, and all three birds defend the nest together.5 The blue-footed booby ( Sula nebouxii ), a sea bird that usually nests on cliffs and rocky outcrops, continually points its beak towards the sky as part of its courtship display. The behaviour is thought to have evolved from the same movements the bird uses when it intends to take to the sky.6   A female penduline tit ( Remiz pendulinus ) attempts to conceal her eggs from her mate until she has laid the entire brood. The reason for the deception is that the female wants to ensure all her eggs are in place before she promptly abandons them to be cared for by the unsuspecting male.

7   For some animals, sex can literally be a life-changing experience. When a male seed beetle ( Acanthoscelides obtectus ) has sex with a female, it inseminates her with chemicals that either make herdie younger, or live longer. During mating, males of this species transfer different peptides and proteins to females. These can have beneficial effects, as some of the compounds appear to increase the number of eggs laid by a female, and females that have been mated tend to live longer than females that have not. They can also have a detrimental impact and be toxic to the female. However, males that tend to reproduce late on in life will inject females with more beneficial compounds, in essence extending her lifespan, than males that tend to reproduce early in life. By doing so, late-breeding males ensure that females will live longer, and hence be around to bear them more offspring, maximising the number of times their genes are passed down the generations.8   A similar thing also happens to bumblebees, except female bees ( Bombus terrestris ) that have been inseminated with sperm by multiple males die younger, being less likely to survive hibernation, than those that have successfully mated with only one male.

It is not clear why, but it could be that multiple inseminations of sperm sap more energy from the queen bee, or that chemicals within the sperm of each male, which are designed to corrupt the sperm of a rival in the bee equivalent of a sperm war, may also physically harm the female.9   The most attractive male field crickets ( Teleogryllus commodus ) die young, the price they pay for putting so much effort into making chirping calls designed to attract potential mates.10   A male flour beetle ( Tribolium castaneum ) can mate and impregnate a female he has never met. No other animal is known to have sex by proxy in this way. Flour beetles lead promiscuous lives, and multiple males often mate with each female. The first male willmate and deposit sperm in the female, then a second male will arrive and use its spiny genitalia to scrape out his competitor''s sperm, before mating itself. But that does not mean he has won the competition. Much of the sperm of the first male survives this ordeal, and is carried unwittingly by the second male on its genitalia.

If this second male mates again within a short period he can inadvertently inseminate a female with sperm that is not his own; and the first male gets to impregnate a female it has never met. One in eight females are fertilised by proxy in this way.11   Virgin male butterflies make better lovers than butterflies more experienced in the bedroom arts. Butterflies that copulate for the first time raise a greater number of young than those that have had multiple sexual partners, possibly because they haven''t depleted their reserves of sperm.12   Male butterflies also use a series of anti-aphrodisiacs to ensure that a female they have mated with does not go on to have sex with another male. Males of the butterfly species Danaus gilippus cover females in a pheromone-laden dust that contains chemicals that both inhibit her ability to fly, and stick like glue to her antennae, making it more difficult for her to identify other potential male partners. Male Heliconius erato butterflies also transfer a pheromone to the female, which she then disseminates from special storage organs called ''stink clubs'' making her highly distasteful to other males. A similar trick is also used by the green-veined white butterfly (Pieris napi) and its relative P.

rapae.   Other males are more obliging. When male arctiid moths (Utetheisa ornatrix) mate they transfer chemical compounds to thefemale, which she bequeaths to her offspring, rendering them distasteful and thus protected against predators.13   More than 90 per cent of the sperm produced by male butterflies and moths is non-fertile. Male Lepidoptera produce two types of sperm: normal, fertilising ''eupyrene'' sperm, and a much larger number of non-fertile, anucleate ''apyrene'' sperm. It is not known exactly what function the non-fertile sperm serve. They might play a role in activating the fertile sperm, or help the active sperm transport themselves through a female''s reproductive tract. Alternatively they might provide a source of nutrients either for the fertile sperm, the female or the developing zygotes produced after fertilisation.

Most likely is that apyrene sperm play a role in sperm competition, either by displacing or inactivating rival males'' sperm, or by remaining in the females'' reproductive tract, delaying her ability to mate again.14   Females of many spider species, such as African golden orb web spiders ( Nephila madagascariensis ), have not one but two genital.