United kingdom Daily news: Is fidelity impossible? Male spiders STILL cheat

Rabu, 25 April 2012

Is fidelity impossible? Male spiders STILL cheat

Is fidelity impossible? Male spiders STILL cheat

Spiders 'pedipalps' snap off - so they only have two chances at mating
Even so, spiders 'shop around' for a second mate
Two-thirds of male spiders are eaten alive by their mates on first mating

By Rob Waugh

PUBLISHED: 11:29 EST, 25 April 2012 | UPDATED: 11:30 EST, 25 April 2012

Male orb web spiders have a difficult choice when it comes to fidelity - their 'pedipalps', used to transfer sperm into the female spider snap off.

The creatures only have two chances to mate in their lives - made even more complex by the fact that females often eat them.

But after one 'go', males still look around for 'hotter talent' - seeking heavier, more fertile females if they've mated with a small one first time round.

A male spider inside the female's web: Even though spiders risk death - and loss of their 'spiderhood' - they still seek out hotter talent where available

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Klaas Welke of the University of Hamburg said, 'Amongst spiders, regardless of age, heavier females are the most fertile.

'Males were more likely to mate twice with the same female if it was early in the day, she was heavy, and if the nearest other females were sub-adult.

'Males kept on searching for a second female if it was late in the day and the first female was light. We found that bigynous males preferred to 'trade up' to heavier females as second mates, but ran the risk of attempting to copulate with already mated females.'

Sex for male orb web spiders (Argiope bruennichi) is a two shot affair since the act of mating destroys their genitalia.

If they survive being eaten during their first encounter with a female, they have two choices â€" to mate again with the same femal or try to find a new partner.

Most, scientists were shocked to find, shopped around - even at the risk of mating with a female who has already been fertilised by another spider.

Males who mate with a large, fertile female are often eaten - but even so, the male spiders 'shop around' for bigger specimens

Monogamous behavior, such as mating for life, is thought to evolve when paternal protection of the female increases fertilization success.

For cannibalistic spiders, monogamy means that the life of the male can be very short indeed.

However this can improve chances of fatherhood: males of the black widow spider can increase the duration of mating, and hence the likelihood of successful fertilization, by allowing themselves to be eaten.
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Two thirds of the monogamous males were eaten after their first mating.

These males, which only managed to mate once, tended to mate with the oldest and heaviest females.

Klaas Welke explained, 'These females are the ones which have the highest fecundity and which are most ready to lay their eggs. While these males do not have a second chance at mating their probability of reproductive success is high.'

Perhaps as with humans, males alte r their behavior to make the best of the situation they find themselves in.